A.2
Analysis Techniques & Inter-comparisons

A.2

Analysis Techniques & Inter-comparisons
Orals
| Tue, 18 Oct, 15:15–17:57 (CEST)|Lecture Hall, Building H, Wed, 19 Oct, 08:30–12:12 (CEST)|Lecture Hall, Building H
Posters
| Attendance Wed, 19 Oct, 16:15–17:15 (CEST)|Foyer, Building H

Orals: Tue, 18 Oct | Lecture Hall, Building H

15:15–15:27
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GSTM2022-39
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On-site presentation
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Improved alternative GRACE-FO accelerometer transplant product computed at TU Graz 
Torsten Mayer-Guerr, Felix Oehlinger, Andreas Kvas, Sandro Krauss, and Barbara Suesser-Rechberger

The GRACE-FO satellites are equipped with three-axis accelerometers, measuring the non-gravitational forces. After one month in orbit, the GRACE-D accelerometer data degraded and its measurements were replaced by synthetic accelerometer data, the so-called transplant data, officially generated by the Jet Propulsion Laboratory (JPL). For the ITSG-Grace2018 GRACE-FO release, the gravity field recovery is based on an alternative in-house transplant product (Behzadpour et. al. 2021,  https://doi.org/10.1029/2020JB021297). This product is generated by a remove-restore method implementing non-gravitational force models.

In this work, we present a new improved version of TU Graz transplant product. The force modelling includes now a tuned satellite macro model, self-shadowing effects, and thermal radiation forces. For the transplant step, an additional estimate of the thermospheric density along the orbit was introduced to account for the different orientation of the satellites.

How to cite: Mayer-Guerr, T., Oehlinger, F., Kvas, A., Krauss, S., and Suesser-Rechberger, B.: Improved alternative GRACE-FO accelerometer transplant product computed at TU Graz, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-39, https://doi.org/10.5194/gstm2022-39, 2022.

15:27–15:39
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GSTM2022-90
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On-site presentation
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Precise orbit determination and accelerometer data modelling of the GRACE Follow-On mission 
Thomas Papanikolaou

Precise orbit determination is a major objective in satellite geodesy and data analysis of several satellite missions observing Earth or another planet. Satellite gravity missions such as the Gravity Recovery And Climate Experiment (GRACE) Follow-On mission, require high level of orbit precision (cm level) in order to capture the gravity field modelling of static and time-variable components. The mission’s on-board accelerometers form a key instrument for the direct measurement of non-gravitational perturbations. The accelerometry data processing is crucial for accelerometers with reduced performance following the launch into space such as the case of one of the GRACE-FO satellites. The current study focuses on the GRACE-FO accelerometer calibration modelling within a scheme of precise orbit determination. In particular, the estimation of accelerometer calibration parameters includes bias, drift and scale factors in combination with a minimum number of empirical forces of cycle-per-revolution terms and bias accelerations. The consideration of such empirical perturbations aims at capturing periodic mismodelling effects and accelerometer data errors. The applied approach leads to orbital residuals varying within a few mm to cm while the inter-satellite LRI and KBR range-rate data residuals vary within a few μm/sec.

How to cite: Papanikolaou, T.: Precise orbit determination and accelerometer data modelling of the GRACE Follow-On mission, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-90, https://doi.org/10.5194/gstm2022-90, 2022.

15:39–15:51
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GSTM2022-38
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On-site presentation
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New Versions of the AEI-derived LRI1B dataset 
Laura Müller, Vitali Müller, Malte Misfeldt, Henry Wegener, Yihao Yan, Markus Hauk, Pallavi Bekal, Simon Bähre, and Gerhard Heinzel

The inter-satellite distance changes of the GRACE Follow-On spacecraft are measured by the main science instrument, the K-Band Ranging (KBR) system, and by the new Laser Ranging Interferometer (LRI), which exhibits a higher precision. The official ranging data is provided by the Science Data System (SDS) in the so-called KBR1B and LRI1B data products, which are available in the latest version v04. However, the Albert Einstein Institute (AEI) in Hannover is deriving alternative LRI1B data products (v50+v52). These data sets allow us to investigate different processing strategies that might improve the quality of the ranging data.

We will present the most important processing steps for the AEI-derived data products and compare them to the official SDS v04 data. The main differences in the processing regard

  • the deglitching algorithm, which is essential to remove disturbances induced by thruster activations or by single event upsets
  • transformation of LRI time-tags to GPS time using a smooth and at day-bounds continuous correction formed by CLK1B, TIM1B, datation reports and empirical offsets obtained by daily cross-correlating KBR and LRI (only v50)
  • conversion of phase-to-range using a novel formula that was published recently and that can utilize a time-depend laser frequency (scale factor)
  • light-time-correction using alternative formulas that are expected to be more precise
  • tilt-to-length (TTL) coupling correction, which is similar to the antenna offset correction (AOC) in KBR1B but missing in LRI1B v04 so far.

Furthermore, we have implemented a quality flag to indicate special events such as sun-blinding periods or momentum transfer events that might reduce the quality of the ranging data. This allows to down-weight affected segments during gravity field recovery. By comparing LRI1B v04 and AEI-derived LRI1B data, a verification and validation of the official dataset is possible. We will conclude with some examples where the LRI1B data quality can be improved compared to the v04 results.

Our LRI1B datasets are available at:  https://www.aei.mpg.de/grace-fo-ranging-datasets

How to cite: Müller, L., Müller, V., Misfeldt, M., Wegener, H., Yan, Y., Hauk, M., Bekal, P., Bähre, S., and Heinzel, G.: New Versions of the AEI-derived LRI1B dataset, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-38, https://doi.org/10.5194/gstm2022-38, 2022.

15:51–16:03
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GSTM2022-24
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On-site presentation
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Scale Factor Determination for the GRACE-FO LRI and Thermal Coupling in KBR-LRI Residuals 
Malte Misfeldt, Vitali Müller, Laura Müller, Pallavi Bekal, Simon Bähre, and Gerhard Heinzel

The GRACE-FO missions hosts two ranging instruments, namely the prime K-Band Ranging (KBR) and the Laser Ranging Interferometer (LRI) as a technology demonstrator.

The LRI scale factor and a time-tag bias are currently estimated on a daily basis in post-processing through cross-calibrating KBR and LRI range, assuming that the KBR range is accurate enough to estimate these parameters. However, this might not hold, and errors of the KBR might get imprinted onto the LRI measurement. Prominent errors in the inter-satellite ranging data are so-called tone errors, which have a sinusoidal form and appear mainly at 1/rev and 2/rev frequencies. These errors have a significant influence on the estimated scale and time shift.

In this talk, we present a model for the LRI scale factor when GF-1 satellite is in the reference role, i.e., a model for the resonance frequency of the optical reference cavity of GF-1. The model was derived based on four years of flight data. Moreover, we show that the seasonal or beta-angle-related variations in the daily scale and time-shift estimates can be described by a thermal coupling, which produces mainly ranging tone errors proportional to the temperature of specific thermistors. We considered two possible coupling mechanisms, temperature-induced changes to the phase and to the frequency. The dominant coupling term is proportional to the temperature at the zenith-pointing solar array and produces range variations of up to +/- 8 µm at 1/rev frequency in the KBR-LRI residuals. These results can be used to improve the LRI1B data product and have relevance for the development of future LRI-like instruments for upcoming missions.

How to cite: Misfeldt, M., Müller, V., Müller, L., Bekal, P., Bähre, S., and Heinzel, G.: Scale Factor Determination for the GRACE-FO LRI and Thermal Coupling in KBR-LRI Residuals, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-24, https://doi.org/10.5194/gstm2022-24, 2022.

16:03–16:15
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GSTM2022-49
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On-site presentation
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Reprocessing of KBR1B data on GRACE-FO and its advantages 
Yihao Yan, Vitali Müller, Laura Müller, Henry Wegener, and Gerhard Heinzel

The K-Band Ranging system (KBR) is the key payload to measure the inter-satellite distance variations with the accuracy of sub-micrometers in GRACE and its successor GRACE-FO missions. In addition to KBR, GRACE-FO is equipped with a laser interferometer (LRI) with higher precision at the nanometer level. The KBR observations are not only used as the main input data for the gravity field recovery but also play an irreplaceable role in re-scale the biased range measured by LRI. The KBR data processing from Level-1A to Level-1B converts the measured raw phase to the inter-satellite biased range (as well as range rate and range acceleration) mainly by correcting time-tags, fusing the phase for each frequency, correcting ionospheric effects, and low-pass filtering. Furthermore, the light time correction (LTC) and antenna offset correction (AOC) are computed. Although the KBR-LRI range residuals have been recently analyzed with the conclusion that they are mainly limited by time-tag errors at low frequencies, we still attempt to better understand the minor remaining deviations. In this study, we re-process the KBR data from Level-1A to Level-1B in alternative ways by mainly investigating:

1) to use an alternative method to fill gaps that occur sporadically in either the K or Ka channel based on transplanting the phase from the available to the missing channel and linearly interpolating the ionospheric effect. If both channels are missing, we propose to use interpolation ; 

2) to smooth the overlap of time-tags at day boundaries, which can reduce the jumps in bias range at day transitions;

3) to take into account time-varying carrier frequency with intraday variability when converting the phase to range; 

4) to improve the accuracy of LTC in low-frequency areas by using the range rate from KBR measured instead of the range rate from POD and, at high frequencies, reduce the numerical limitations by using analytical equations instead of an iterative equation;

5) to consider the movement of the satellite’s center of mass when computing the AOC.

Although these adaptations to KBR1B data are minor and seem to have no obvious differences in terms of gravity field maps at the current precision level, this study is useful to better understand the relationship between KBR and LRI and for the instrument characterizations in the future more precision missions.

How to cite: Yan, Y., Müller, V., Müller, L., Wegener, H., and Heinzel, G.: Reprocessing of KBR1B data on GRACE-FO and its advantages, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-49, https://doi.org/10.5194/gstm2022-49, 2022.

Coffee break
16:45–16:57
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GSTM2022-53
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On-site presentation
Comparison of GRACE Follow-On Level-2 data from RL06 and RL06.1: Assessing the impact of the new accelerometer transplant data 
Khosro Ghobadi-Far, Susanna Werth, Manoochehr Shirzaei, Bryant Loomis, Martin Horwath, Matthias Oskar Willen, and Thorben Axel Döhne

The GRACE-D accelerometer data shows large bias jumps starting from 21 June 2018. The GRACE Follow-On (GRACE-FO) Science Data System (SDS) centers (CSR, JPL and GFZ) use a transplant technique applying GRACE-C accelerometer data to replace that of GRACE-D. To improve the accuracy of non-gravitational measurements acting on the satellites, the GRACE-FO SDS centers recently released an updated hybrid-transplant accelerometer data for GRACE-D, which uses measurements from both satellites. Accordingly, updated (RL06.1) Level-2 (L2) monthly gravity solutions using the new accelerometer data are being released. In this work, we will present our results on quantification of the changes/improvements in the RL06.1 L2 solutions from all three SDS centers relative to RL06. We also explore the possibility of validating the changes using independent datasets. We first compare the low-degree harmonic coefficients C_{20} and C_{30} with those from SLR (TN-14) and examine their agreement at seasonal and interannual timescales. Using various spectral-domain analysis tools, we detect the spectral bands of spherical harmonic degrees and orders where the major changes in RL06.1 are observed. We then quantify the impact of such spherical harmonic coefficients on surface mass change estimates over the GRACE-FO period. Moreover, we quantify the noise reduction in monthly mass change solutions from RL06.1 (relative to RL06) over open oceans. For the latter analysis, we also detect the spatial regions as well as months which show the largest noise reduction and discuss the possible causes behind that. Our work is aimed at helping the GRACE-FO SDS to evaluate the improvement by new accelerometer transplant data.

How to cite: Ghobadi-Far, K., Werth, S., Shirzaei, M., Loomis, B., Horwath, M., Willen, M. O., and Döhne, T. A.: Comparison of GRACE Follow-On Level-2 data from RL06 and RL06.1: Assessing the impact of the new accelerometer transplant data, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-53, https://doi.org/10.5194/gstm2022-53, 2022.

16:57–17:09
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GSTM2022-54
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On-site presentation
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Impact of GRACE-FO LRI and the updated accelerometer transplant product (ACH1B) on the estimated static Earth gravity field 
Grigorios Kalimeris, Roland Pail, and Thomas Gruber

The impact of the GRACE-FO Laser Ranging Interferometer (LRI) and the updated transplant product ACH1B is evaluated on the static part of the Earth gravity field by solving the gravity field determination problem with the least-squares estimation approach.

In order to evaluate the impact of the LRI (first application) and the ACH1B product (second application), the type of observation sets is based on the range-acceleration measurements derived from the LRI and the K-Band Ranging (KBR) systems of the GRACE-FO satellites and from the LRI system only respectively.

The type of solution selected for the two applications is the approximate solution of the acceleration approach. The Earth gravity field used as reference is the GOCO06s model truncated to degree and order 120.

Two monthly observation sets are created per application by correcting the LRI/KBR range-acceleration measurements with:

  • the light time correction (LTC) for LRI and KBR
  • the antenna offset correction (AOC) for KBR only
  • the “accelerations correction term” (ACT) which includes the line-of-sight (LOS) relative accelerations caused by the solid Earth tides, the ocean tides, the third body attraction, the non-gravitational forces and the effect of general relativity
  • the “correction term” (CT) which includes the impact of the residual centrifugal acceleration (Ghobadi-Far K, et al., 2018)
  • outliers removal

The above described data processing, leads to range-accelerations which include the effect of the Earth's gravitational forces only. For the calculation of the LOS relative accelerations of the ACT, a modified version of the “High Precision Orbit Propagator” software developed by (Mahooti, 2022) is applied with the exception of the LOS relative accelerations caused by the non-gravitational forces.

The aforementioned accelerations are derived by using the ACT1B product only for both of the observation sets of the first application and for the first observation set of the second application. The ACT1B (for GRACE C satellite) and the ACH1B (for GRACE D satellite) products are used for the second observation set of the second application.

After performing the gravity field determination by using each of the two observation sets per application, the square root of the degree difference variances (DDVs) between the datasets and the GOCO06s model and the datasets themselves are examined on the high-frequency domain from which promising results are derived regarding the impact of the LRI and the new ACH1B product on the static Earth gravity field.

How to cite: Kalimeris, G., Pail, R., and Gruber, T.: Impact of GRACE-FO LRI and the updated accelerometer transplant product (ACH1B) on the estimated static Earth gravity field, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-54, https://doi.org/10.5194/gstm2022-54, 2022.

17:09–17:21
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GSTM2022-86
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On-site presentation
Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing 
Petro Abrykosov, Roman Sulzbach, Roland Pail, Henryk Dosblaw, and Maik Thomas

Due to its high-frequency, high-amplitude nature the ocean tide (OT) signal poses a core limitation within the GRACE/GARCE-FO data processing, as its temporal undersampling ultimately results in the typical striping pattern. To some degree this issue can be resolved by employing a-priori de-aliasing based on an OT background model. However, due to model errors and imperfections some residual effects inevitably remain within the resulting gravity product.

So far, the background models have been assumed as error-free within the data processing. Since ocean tide models feature distinct, time-invariant spatial error patterns (low uncertainties in open oceans, high uncertainties in coastal and high-latitude regions), it is reasonable to assume that weighting the observations based on the underlying spatial error shall result in a more homogenous gravity solution.

Thus, error co-variance matrices are derived for the spherical harmonic coefficients representing the eight principal tides based on a set of five modern-day OT models and propagated onto the level of observations. This error information is then employed within the least-squares parameter estimation for the final gravity product. The functionality of this approach is verified through closed-loop simulations and its limitations are discussed. Results are presented for single-pair-based gravity retrieval scenarios.

How to cite: Abrykosov, P., Sulzbach, R., Pail, R., Dosblaw, H., and Thomas, M.: Treatment of ocean tide background model errors in the context of GRACE/GRACE-FO data processing, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-86, https://doi.org/10.5194/gstm2022-86, 2022.

17:21–17:33
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GSTM2022-16
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On-site presentation
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Reduction of aliasing errors in gravity field recovery by means of covariance information for ocean tide models 
Josefine Wilms, Natalia Panafidina, Markus Hauk, Christoph Dahle, Roman Sulzbach, and Frank Flechtner

The GRACE and GRACE-FO missions are fundamental in establishing a near-continuous time series of global mass transport since 2002. However, monthly gravity field recovery using these mission data includes errors limiting the spatial and temporal resolution of the estimated gravity field solutions. The major error contributions, besides the noise of the accelerometer instruments, arise from temporal aliasing errors due to undersampling of signals to be recovered (e.g. hydrology), uncertainties in the de-aliasing models (e.g., non-tidal atmosphere and ocean) and imperfect ocean tide models. Especially the latter will also remain one of the most limiting factors in determining high-resolution temporal gravity fields from Next-Generation Gravity Missions (NGGM).

In this context, recent developments have been made within the Research Unit NEROGRAV (New Refined Observations of Climate Change from Spaceborne Gravity Missions) funded by the German Research Foundation DFG. One of the projects within NEROGRAV deals with the stochastic modeling regarding ocean tide background models by the utilization of covariance information for eight major tidal constituents. The repeatable pattern of the tidal signal enables the extraction of uncertainty information by an ensemble of different ocean tide models. This information can be introduced into the gravity field recovery process in terms of a covariance matrix while expanding the parameter space by additional tidal parameters to be estimated.

This presentation provides an overview of the recovered monthly gravity fields from GRACE/GRACE-FO when applying covariance information of ocean tide errors. Furthermore, results from simulations representing a GRACE-FO type mission as well as an NGGM double-pair scenario (polar plus inclined pair) are presented. The results show reduced tidal aliasing errors as well as more realistic formal uncertainties.

How to cite: Wilms, J., Panafidina, N., Hauk, M., Dahle, C., Sulzbach, R., and Flechtner, F.: Reduction of aliasing errors in gravity field recovery by means of covariance information for ocean tide models, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-16, https://doi.org/10.5194/gstm2022-16, 2022.

17:33–17:45
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GSTM2022-94
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Virtual presentation
New developments in Earth systems mass change studies with GRACE and GRACE Follow-On for monitoring of extreme events 
Khosro Ghobadi-Far and Shin-Chan Han

The conventional data products from GRACE and GRACE Follow-On (GRACE-FO) are global snapshots of time-variable gravity or surface mass change, providing “average” fields of these quantities over a certain period like one month or 10 days. In this presentation, we propose an alternative approach based on along-orbit analysis of inter-satellite ranging residuals which represent “instantaneous” gravitational changes at satellite altitude due to mass changes happening beneath the satellites at the Earth surface. We first present the key improvement in distinguishing small-scale gravitational signals by GRACE-FO LRI (relative to KBR) associated with high-resolution (1) static gravity (global) and (2) time-variable gravity (mainly at polar regions). We then demonstrate that our approach opens new opportunities in Earth system mass change studies for monitoring of extreme, transient events. We do so by presenting multiple rapidly-changing geophysical applications: (1) GRACE KBR observations of large tsunamis with their unique characteristics in detecting the large-scale variability of tsunami wave field, (2) GRACE-FO LRI observations of the high-frequency gyre in the Argentine Basin and their validation with satellite altimetry, (3) GRACE-FO LRI observations of a rapid mass change in the Gulf of Carpentaria during a cyclone in 2019 and their application for validation of high-frequency ocean models (used for de-aliasing in satellite gravimetry), and (4) gravitational changes of Earth’s free oscillations excited by the 2004 Sumatra earthquake, their mapping into inter-satellite tracking explained by the Kaula theory and the potential detectability of gravitational oscillations related to Earth’s football mode by GRACE KBR data. The above transient mass changes cannot be adequately studied using the conventional data products of average snapshots (maps). Thus, the along-orbit analysis technique offers a unique opportunity to broaden the scope of geodetic and geophysical applications that can be addressed by GRACE and GRACE-FO satellites.

How to cite: Ghobadi-Far, K. and Han, S.-C.: New developments in Earth systems mass change studies with GRACE and GRACE Follow-On for monitoring of extreme events, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-94, https://doi.org/10.5194/gstm2022-94, 2022.

17:45–17:57
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GSTM2022-56
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Virtual presentation
The GRACE Plotter, a useful tool for intercomparison 
Stéphane Bourgogne and Jean-Michel Lemoine

A quick reminder of the GRACE Plotter comparing capabilities, and a presentation of its brand new functionalities. Try it yourself at https://thegraceplotter.com.

How to cite: Bourgogne, S. and Lemoine, J.-M.: The GRACE Plotter, a useful tool for intercomparison, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-56, https://doi.org/10.5194/gstm2022-56, 2022.

Orals: Wed, 19 Oct | Lecture Hall, Building H

08:30–08:42
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GSTM2022-41
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On-site presentation
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Towards a new release of the ITSG-Grace gravity field solutions: New investigations and first results 
Felix Öhlinger, Torsten Mayer-Gürr, Andreas Kvas, Sandro Krauss, Barbara Süsser-Rechberger, and Patrick Dumitraschkewitz

The Institute of Geodesy of the Graz University of Technology produces high quality GRACE/GRACE-FO gravity fields using an in-house developed software, the Gravity Recovery Object Oriented Programming System (GROOPS). We are currently working on a new release which will be based on the reprocessed Level-1A Release 05 Grace data the AOD1B Release 07 dealiasing product covering the complete GRACE/GRACE-FO time-span. Like its predecessor (ITSG-Grace2018) the new release will include a static field, unconstrained monthly, as well as Kalman smoothed daily solutions.

New investigations and improvements comprise: (a) A revision of the Level 1a to Level 1b processing focusing on the determination of the accelerometer transplant. 
(b) Updated background models which include an improved model of the thermosphere with higher temporal resolution as well as an optimized tide model. 
(c) The inclusion of LRI measurements in the gravity field recovery using optimal weighting achieved through stochastic modeling.

How to cite: Öhlinger, F., Mayer-Gürr, T., Kvas, A., Krauss, S., Süsser-Rechberger, B., and Dumitraschkewitz, P.: Towards a new release of the ITSG-Grace gravity field solutions: New investigations and first results, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-41, https://doi.org/10.5194/gstm2022-41, 2022.

08:42–08:54
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GSTM2022-87
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On-site presentation
Time-variable gravity field determination from GRACE Follow-On data usingthe Celestial Mechanics Approach extended by empirical noise modelling 
Martin Lasser, Ulrich Meyer, Daniel Arnold, and Adrian Jäggi

We study gravity field determination from GRACE Follow-On satellite-to-satellite tracking using the inter-satellite K-band link and kinematic positions of the satellites as observations and pseudo-observations respectively. A key component of any model is the accurate specification of its quality. In the case of gravity field modelling from satellite data with the Celestial Mechanics Approach (CMA) a least-squares adjustment is performed to obtain a monthly solution of the Earth’s gravity field. However, the jointly estimated formal errors usually do not reflect the error level that could be expected but provides much lower error estimates.
We present gravity field solutions computed with the CMA and extend it by an empirical modelling of the noise based on the post-fit residuals between the final GRACE Follow-On orbits, that are co-estimated together with the gravity field, and the observations, expressed in position residuals to the kinematic positions and in K-band range-rate residuals.
We compare and validate the solutions that use empirical modelling with solutions from the operational GRACE Follow-On processing at AIUB by examining the stochastic  behaviour of the respective post-fit residuals, by investigating areas where a low noise is expected and by inspecting the mass trend estimates in certain areas of global interest. Finally, we investigate the influence of the empirically weighted solutions in a combination of monthly gravity fields based on other approaches as it is done by the Combination Service for Time-variable Gravity fields (COST-G) and make use of noise and signal assessment applying the quality control tools routinely used in the frame of COST-G.

How to cite: Lasser, M., Meyer, U., Arnold, D., and Jäggi, A.: Time-variable gravity field determination from GRACE Follow-On data usingthe Celestial Mechanics Approach extended by empirical noise modelling, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-87, https://doi.org/10.5194/gstm2022-87, 2022.

08:54–09:06
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GSTM2022-66
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On-site presentation
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Current status of CNES RL05 time series of solutions from GRACE and GRACE-FO data 
Jean-Michel Lemoine, Stéphane Bourgogne, and Alejandro Blazquez

The status of current work at CNES on GRACE/GRACE-FO data processing will be presented

Some details of the processing will be discussed, in particular:

- The negative impact of the unprecedented high altitude of GRACE-FO on the number of stable-resolved gravity field coefficients 

- An analysis of the range and range-rate residuals anomalies during entering and exiting eclipses

- The inclusion of the current LEGOS ensemble-solution of water-mass change in the set of evaluated solutions enables to analyze hydrology and ocean mass changes

How to cite: Lemoine, J.-M., Bourgogne, S., and Blazquez, A.: Current status of CNES RL05 time series of solutions from GRACE and GRACE-FO data, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-66, https://doi.org/10.5194/gstm2022-66, 2022.

09:06–09:18
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GSTM2022-78
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On-site presentation
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Analysis of recent LUH GRACE / GRACE-FO gravity field processing results 
Jakob Flury, Igor Koch, Mathias Duwe, and Nina Fletling

We show results of both the LUH operational GRACE-FO gravity field processing and of our recent reprocessing of the full GRACE mission. Since 2021, the LUH group at IfE is recognized as Analysis Center in the IAG Combination Service for Time Variable Gravity Fields (COST-G). Quality measures demonstrate that the LUH solutions are close to those of other analysis centers in COST-G and in the GRACE / GRACE-FO Science Data System (SDS). We discuss the current standards and strategy of our processing. We have studied range-rate residuals for the two complete missions, with a focus on specific spatial and temporal patterns. This helps to identify and analyze detailed signatures of anomalous systematic effects, such as shadow transition anomalies, star camera stray light effects, and KBR signal to noise ratio drops. Results could be used to reassess the system integration of the satellite-to-satellite tracking sensor system. We discuss the validation of our spherical harmonic solutions using specific geophysical signals, and we also show and discuss recent LUH LRI-based gravity solutions. 

How to cite: Flury, J., Koch, I., Duwe, M., and Fletling, N.: Analysis of recent LUH GRACE / GRACE-FO gravity field processing results, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-78, https://doi.org/10.5194/gstm2022-78, 2022.

09:18–09:30
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GSTM2022-75
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Virtual presentation
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COST-G: towards a new GRACE and GRACE-FO combination 
Ulrich Meyer, Martin Lasser, Neda Darbeheshti, Adrian Jäggi, Frank Flechtner, Christoph Dahle, Christoph Förste, Andreas Güntner, Torsten Mayer-Gürr, Andreas Kvas, Saniya Behzadpour, Jean-Michel Lemoine, Igor Koch, Jakob Flury, Stephane Bourgogne, and Wei Feng

The combination service for time-variable gravity fields (COST-G) provides the full time-series of monthly GRACE gravity fields: COST-G GRACE RL01, combined in reprocessing mode, and a steadily growing time-series of monthly GRACE-FO gravity fields: COST-G GRACE-FO RL01 OP, combined on an operational basis. Both time-series are currently considered for re-combination. In case of GRACE, new high-quality time-series from Chinese analysis centers are available for combination. In case of GRACE-FO, a revision of the weighting scheme, developed in the frame of the Horizon2020 project Global Gravity-based Groundwater Product (G3P), and the availability of reprocessed GRACE-FO time-series from AIUB, CSR, GFZ, and JPL, lead to a significant improvement of the combined gravity fields.

We present the preliminary re-combined GRACE and GRACE-FO time-series and quantify the differences with respect to the COST-G RL01 series in terms of signal and noise content.

How to cite: Meyer, U., Lasser, M., Darbeheshti, N., Jäggi, A., Flechtner, F., Dahle, C., Förste, C., Güntner, A., Mayer-Gürr, T., Kvas, A., Behzadpour, S., Lemoine, J.-M., Koch, I., Flury, J., Bourgogne, S., and Feng, W.: COST-G: towards a new GRACE and GRACE-FO combination, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-75, https://doi.org/10.5194/gstm2022-75, 2022.

09:30–09:42
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GSTM2022-32
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Virtual presentation
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150 km ANU mascon solutions 
Paul Tregoning, Rebecca McGirr, Anthony Purcell, and Sebastien Allgeyer

We present updated mascon solutions of the temporal gravity field, derived from the analysis of Level-1B GRACE and GRACE-FO data using the range acceleration observable. Our previous solutions contained significant noise in particular regions of high mass loss (e.g. West Antarctica), which was caused by inappropriate levels of regularisation. Here we show a new approach of both iteration and regularisation of the solutions which generates more reliable estimates of the mass variations across the whole Earth, with both temporal and spatial consistency despite not applying any temporal or spatial inter-mascon constraints. We compare mascon solutions at spatial resolutions from 300 km to 100 km, show estimates of ocean mass increase and mass loss in ice-covered regions as well as assess the C20 time series estimated directly from GRACE data alone. Our new mascon estimates, at ~200 km x 200 km spatial resolution, are now publicly available.

How to cite: Tregoning, P., McGirr, R., Purcell, A., and Allgeyer, S.: 150 km ANU mascon solutions, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-32, https://doi.org/10.5194/gstm2022-32, 2022.

09:42–09:54
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GSTM2022-95
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On-site presentation
Initial results from five-day GRACE/GRACE-FO mascon solutions from CSR 
Himanshu Save, Emad Hasan, Ashraf Rateb, Mark Tamisiea, Alexander Sun, and Bridget Scanlon

This study will focus on the 5-day global mascon solution produced from GRACE/GRACE-FO satellite tracking data. This paper will discuss the techniques used and challenges encountered with production of such a global total water storage and ocean bottom pressure product with high temporal sampling. This paper will discuss the results from the analysis performed over hydrological and ocean basins to validate the higher frequency signals captured in this product. Out of many uses of this product, one important use is producing high temporal resolution GRACE/GRACE-FO signals with a latency of a few days for ingestion into automated machine learning algorithms for flood detection applications

How to cite: Save, H., Hasan, E., Rateb, A., Tamisiea, M., Sun, A., and Scanlon, B.: Initial results from five-day GRACE/GRACE-FO mascon solutions from CSR, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-95, https://doi.org/10.5194/gstm2022-95, 2022.

09:54–10:06
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GSTM2022-45
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On-site presentation
GRACE-FO and SLR updates from GSFC 
Bryant Loomis, Michael Croteau, Terry Sabaka, and Kenny Rachlin

We present a summary of our recent work on time-variable gravity estimates derived from GRACE/GRACE-FO and satellite laser ranging (SLR). We will show analyses summarizing the impacts of the improved accelerometer transplant product on our unregularized monthly spherical harmonics and regularized mascons. Additionally, we will discuss new efforts to leverage our high-resolution regression approach to capture short-term mass changes and climatology signals with enhanced spatial resolution and improved signal recovery. For our SLR work, we will present recent analysis of the impacts of the background gravity models on the C20 and C30 solutions provided in Technical Note 14, where considered models include a low degree expansion trend and seasonal regression model (current approach), GRACE/GRACE-FO RL06, and GRACE-FO RL06.1. New combined GRACE/GRACE-FO/SLR estimates are also presented and discussed. This work seeks to assess the reliability of Technical Note 14, and to investigate the potential benefit and impact of “quick-look” and “final” estimates of C20 and C30.

How to cite: Loomis, B., Croteau, M., Sabaka, T., and Rachlin, K.: GRACE-FO and SLR updates from GSFC, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-45, https://doi.org/10.5194/gstm2022-45, 2022.

10:06–10:18
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GSTM2022-48
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On-site presentation
SLR sliding window solutions with daily sampling for replacing GRACE/GRACE-FO C20 and C30 
Zhigui Kang, John Ries, Mark Tamisiea, Srinivas Bettadpur, and Himanshu Save

The recovery of Earth’s time variable gravity field from satellite data relied on Satellite Laser Ranging (SLR) before missions like the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (FO). Currently, the monthly gravity solutions from GRACE/GRACE-FO provide amazing information about the temporal variations of gravity field.  However, coefficients C20 and C30 derived from GRACE/GRACE-FO are unreliable. The coefficients, on the other hand, can be reasonably well determined using SLR data and can be used to replace the unreliable values from GRACE/GRACE-FO. In the future, GRACE-FO will provide 28-day sliding widow gravity solutions with weekly sampling. The corresponding SLR solutions should be also provided. Based on this motivation, we study the SLR 30-day sliding window solutions with daily sampling. The new SLR products can be used to replace unreliable coefficients C20 and C30 of both GRACE-FO monthly and sliding window products. This study presents the strategies of gravity recovery from SLR data and discusses the results.

How to cite: Kang, Z., Ries, J., Tamisiea, M., Bettadpur, S., and Save, H.: SLR sliding window solutions with daily sampling for replacing GRACE/GRACE-FO C20 and C30, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-48, https://doi.org/10.5194/gstm2022-48, 2022.

10:18–10:30
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GSTM2022-17
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On-site presentation
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EOF analysis of the monthly gravity fields from GRACE and GRACE-FO 
Minkang Cheng and John ries

Empirical Orthogonal Function (EOF) analysis is applied to study the spatial structure and temporal feature of the time series of the global EWH from GRACE/GRACE-FO-derived gravity fields. The scaled PC time series for the corresponding trend spatial structure of GRACE appears to change from initially linearly decreasing to increasing around June 2013, while the trend is continuously increasing for GRACE-FO. The EOF spatial structure from the GRACE or GRACE-FO derived SHC (spherical harmonic coefficients) with size of 6x6 can improve recovering the time series of C30/C50 from the SLR data over the period prior to March 2012 when the LARES data were not available. With the EOF technique and a time variable gravity model applied for the higher degrees, a new time series of C20 and C30 is determined based on the temporal feature from SLR and the better EOF spatial structure determined from the SHC in GRACE (or GRACE-FO) solutions, which are less influenced by the higher-degree aliasing. The EOF-based estimates of C20 andC30 may provide an estimate better unified with the higher-degree part of the GRACE (for C20) and GRACE-FO gravity fields.

How to cite: Cheng, M. and ries, J.: EOF analysis of the monthly gravity fields from GRACE and GRACE-FO, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-17, https://doi.org/10.5194/gstm2022-17, 2022.

Coffee break
11:00–11:12
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GSTM2022-29
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On-site presentation
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A joint inversion of gravimetry, altimetry and GNSS to improve spatial resolution of Earth system mass change 
David Wiese, Donald Argus, Alex Gardner, Matthias Ellmer, Felix Landerer, Johan Nilsson, Athina Peidou, and Nicole Schlegel

Knowledge of Earth system mass change is limited to spatial scales of approximately 300 km x 300 km, as this is near the native resolution of the data collected from the GRACE and GRACE-FO (G/GFO) satellite gravimetry missions.  Measurements of surface height change at much finer spatial scales can additionally be exploited to derive mass change, albeit with the proper treatment of the data.  Here, we jointly invert inter-satellite range-rate measurements from GRACE and GRACE-FO, surface height changes measured by in-situ GNSS receivers, and surface elevation changes from a multi-mission synthesis of radar and laser satellite altimeters to estimate mass change at spatial scales of 100 km x 100 km within a Bayesian framework over the time period 2002 - 2021.  In this talk, we will focus on results over North America, where nearly 3,000 in-situ GNSS measurements are processed in combination with G/GFO, and over Antarctica, where Envisat, ICESat, CryoSat-2, and ICESat-2 measurements have been processed in combination with G/GFO.  We find agreement between the geodetic data combination solution and the G/GFO-only solution at large basin scales, but unique knowledge of mass change is gained with the geodetic data combination solution at smaller spatial scales not observed by satellite gravimetry alone.

How to cite: Wiese, D., Argus, D., Gardner, A., Ellmer, M., Landerer, F., Nilsson, J., Peidou, A., and Schlegel, N.: A joint inversion of gravimetry, altimetry and GNSS to improve spatial resolution of Earth system mass change, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-29, https://doi.org/10.5194/gstm2022-29, 2022.

11:12–11:24
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GSTM2022-31
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On-site presentation
Error characterization of GNSS vertical land displacements for use in GNSS-GRACE joint inversion 
Athina Peidou, Felix Landerer, David Wiese, Donald Argus, and Matthias Ellmer

Quantification of uncertainty in surface mass change signals derived from GNSS measurements poses challenges, especially when dealing with large datasets with continental or global coverage. Our aim is to assign weights to GNSS estimates of vertical land displacement (VLD), which will be used in a future joint solution with GRACE observations. Thus, we study the structure and quantify the uncertainty present in VLD estimates derived from 3045 GNSS stations distributed across the continental US. Monthly means of daily positions are available for 15 years. First, we remove outliers by performing a 3σ test, and data screening via a number of correlation metrics between the input GNSS VLD estimates and external validation datasets (i.e., VLD predicted from GRACE/GRACE-FO and hydrology models). Afterwards, we employ various processing schemes to characterize the uncertainty of VLD through stochastic modeling and quantification of the spatially correlated errors. In particular, we test for white, colored and spatially correlated noise. When only white noise is considered nearly 30% of the stations exhibit noise level < 2 mm, 65% noise between 2-4 mm and 5% noise > 4 mm.  In case of colored noise, error smaller than 2 mm, between 2-4 mm and >4mm, is mapped in 20%, 60% and 20% of the stations, respectively. Spatially correlated noise is in family but slightly smaller in magnitude compared to colored noise.

How to cite: Peidou, A., Landerer, F., Wiese, D., Argus, D., and Ellmer, M.: Error characterization of GNSS vertical land displacements for use in GNSS-GRACE joint inversion, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-31, https://doi.org/10.5194/gstm2022-31, 2022.

11:24–11:36
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GSTM2022-65
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On-site presentation
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Investigating differences between GRACE mass change estimation methods using their inherent sensitivity kernels 
Thorben Döhne, Martin Horwath, Andreas Groh, and Eric Buchta

Estimates of mass changes from GRACE spherical harmonic (SH) solutions arrive at different results even for the same regions and timeframes. These differences can be attributed to two parts of the estimation. The first part is the preparation of a SH input dataset based on the GRACE solutions. This includes amendments to low-degree components and corrections for modelled geophysical signals. The second part, and topic of this presentation, is the estimation method itself. Studies assessing these estimation methods were mostly based on the resulting mass change estimates from a limited number of test signals. We propose to use the inherent sensitivity kernels (SKs) of estimation methods for comparison and assessment of methods. The SK describes the weighting function that is used to integrate a surface mass density representation of the prepared input dataset. It can be represented in either the spatial or SH domain. Alternative terms for the SK used in previous studies include 'averaging kernel', 'averaging function' or 'weight function'. For methods of the direct approach the SK is obvious. These methods directly construct the SK, mostly starting from modification of a simple region function. For methods of the inverse approach the SKs are less obvious. In this approach patterns of mass changes are defined which are then fitted to observations of the gravity field variations. However, SKs are also inherent to inverse methods and may be made explicit. In fact, certain implementations of both approaches have identical SKs when rigorously incorporating the same signal and error covariance information. Under this conditions both approaches are equivalent. Based on the SKs it is straight-forward to assess leakage errors and GRACE error propagation not only in the resulting mass change estimation. Publishing the SKs associated to a method also enables any user to investigate the method without deeper knowledge of the implementation details. We illustrate this by presenting SKs for our implementation of four different methods to estimate Greenland Ice Sheet mass changes. The SKs show similarities as well as striking differences which can be attributed to the underlying differences in the methods.

How to cite: Döhne, T., Horwath, M., Groh, A., and Buchta, E.: Investigating differences between GRACE mass change estimation methods using their inherent sensitivity kernels, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-65, https://doi.org/10.5194/gstm2022-65, 2022.

11:36–11:48
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GSTM2022-34
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Virtual presentation
Interplay of altitude, ground track coverage, noise and regularisation in the spatial resolution of GRACE gravity field models 
Rebecca McGirr, Paul Tregoning, Sebastien Allgeyer, Herb McQueen, and Anthony Purcell

Models of the temporal gravity field derived from space gravity missions are typically produced with monthly temporal resolution and ~300 km spatial resolution. However, variations in instrument performance and altitude of the GRACE mission impact the spatial resolution that can be achieved month-to-month. As the altitude of the orbits of the twin spacecraft vary throughout the mission, so does the ability of the observations to recover certain components of the temporal gravity field. The spatial resolution of GRACE observations should increase as the altitude decreases throughout the mission because the reduced altitude intensifies the gravity signals acting on the satellites. Simulations using actual GRACE altitude and ground track coverage and realistic noise levels confirm this predicted influence of the altitude of the satellites on the accuracy of the estimated solutions. Solutions with larger mass concentration elements (mascons) are more numerically stable as the satellite altitude decreases but they suffer from greater error caused by the inability to properly represent spatial variations of signals within mascons, referred to as intra-mascon variability. Mascons as small as ~150 x 150 km (i.e. ~1.5 arc-degree) reduce the intra-mascon variability and, with appropriate regularisation, yield the most accurate solutions, especially during the low-altitude periods of the GRACE mission. Importantly, unlike spherical harmonic solutions, regularised mascon solutions are not degraded during resonant orbit months, and are of comparable quality to months with full ground track coverage.

How to cite: McGirr, R., Tregoning, P., Allgeyer, S., McQueen, H., and Purcell, A.: Interplay of altitude, ground track coverage, noise and regularisation in the spatial resolution of GRACE gravity field models, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-34, https://doi.org/10.5194/gstm2022-34, 2022.

11:48–12:00
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GSTM2022-59
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Virtual presentation
Toward near-real time analysis of gravity change with the examples of flood and flash drought events 
Shin-Chan Han, Paul Tregoning, and Christopher McCullough

We discuss a methodology of scientifically utilizing high-precision laser ranging measurements (in addition to K-band microwave) for higher temporal sampling of surface mass changes.  The standard spatial analysis (i.e., global gravity field recovery) over a month period such as L2 and L3 data processing would produce a biased estimate when characteristic time scales of mass change processes are shorter than a month.  Our proposed time-domain (along-track) analysis will lead to better quantification of such processes.  Furthermore, we exploit the low-latency (within 1–3 days) Quick-Look (QL) L1B data to examine the feasibility of immediate assessment of extreme events such as flood and flash drought.  Such QL data processing can promote timely assessment of severe weather events and natural hazards as important applications of the GRACE-FO mission.  As examples, we present the data processing results for the 2019 South East US flash drought, the 2020 (unusually large) monsoonal flood in Bangladesh, and the 2021 Eastern Australia flood.  A new streamlined along-track data processing chain is proposed to facilitate utilization of superb laser ranging measurements for advanced quantification of rapid Earth system changes we experience recent years.

How to cite: Han, S.-C., Tregoning, P., and McCullough, C.: Toward near-real time analysis of gravity change with the examples of flood and flash drought events, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-59, https://doi.org/10.5194/gstm2022-59, 2022.

12:00–12:12
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GSTM2022-52
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On-site presentation
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The forgotten second dimension of GRACE-like systems 
Matthias Weigelt

Intersatellite ranging systems as implemented in the GRACE and GRACE-FO mission are considered one-dimensional observation systems. Range or range-rate are observed in the direction of the line-of-sight and connected in the modelling process to the relative position and velocity projected on the line-of-sight, respectively. However, the observed range is also proportional to the relative velocity vector projected on the change of the line-of-sight vector which is by definition perpendicular to the line-of-sight vector. This vector is nearly in radial direction of a GRACE-like system thus implying that the range observation also contains information about the radial direction of the gravity field. This contribution will show the mathematical derivations and investigates the feasibility of the using the additional direction in the gravity field recovery process.

How to cite: Weigelt, M.: The forgotten second dimension of GRACE-like systems, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-52, https://doi.org/10.5194/gstm2022-52, 2022.

Posters: Wed, 19 Oct, 16:15–17:15 | Foyer, Building H

P1
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GSTM2022-6
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On-site presentation
TiME22: High-Frequency Gravity Potential Coefficients of Atmosphere and Ocean Tides 
Roman Sulzbach, Kyriakos Balidakis, Henryk Dobslaw, and Maik Thomas

The orbits of low-earth orbiting satellites have always repeat periods that are much longer than the diurnal and sub-diurnal frequencies of tides in the solid earth, ocean, and atmosphere. While unaccounted for, tides, therefore, cause aliasing artifacts, so it is an important step in the data processing chain of satellite gravity missions (e.g. GRACE and GRACE-FO) to reduce this effect of tidal aliasing. While solid Earth tides are well-understood in terms of (simple) theoretical models, predictions of the ocean and atmospheric tides need to consider observational data to reach sufficiently high accuracy to serve as background models for satellite gravimetry. Despite many research efforts in the past, tidal aliasing is currently still a limiting factor that prevents increasing the resolution of gravity field products and thus still needs to be improved.

Here we present the TiME22 catalog, comprising high-frequency tidal mass variability from atmosphere and ocean tides encoded in Stokes coefficients. The data set's atmospheric part (ATM) is obtained by performing a tidal analysis of 8 years of ERA5 surface pressure data, where 16 tidal constituents of diurnal to sixth-diurnal periods were extracted. While the obtained surface pressure fields represent periodic mass variability in the atmosphere, those fields also represent an effective, barotropic forcing mechanism for ocean tides.

The ocean component of TiME22 (OCN) is obtained from simulations of the barotropic ocean tide model TiME that considers a modern, non-local implementation of the effect of Self-Attraction and Loading (SAL) and dissipation by wave drag and bottom friction. The model is forced with barotropic excitation of the gravity potential and atmospheric pressure, as well as wind stress forcing. While the model is data-unconstrained, it is inherently less accurate than data-assimilating models for major tidal constituents like M2 or K1, where observational data is dense and of high quality. This is different for minor amplitude ocean tides, where the relative accuracy of data-constrained models is worse. Thus, the TiME22 ocean tide catalog comprises 52 tidal constituents of which many are not contained in state-of-the-art data-constrained atlases. This includes third-degree ocean tides (e.g. 3M1, 3M3), high-frequency atmospherically-excited tides (e.g. S3), and tidal constituents in the edges of tidal bands (e.g. OO1, 2Q1) that are usually estimated by linear admittance extrapolation. We will show, that the accuracy of several minor tides is improved when considering TiME solutions. Further, GRACE pre-fit residuals are reduced when considering TiME22 atmosphere and ocean mass variability from TiME22 compared to the background models applied in the GRACE GFZ RL06 monthly solutions. Stokes coefficients of TIME22 will be made publicly available for use in both precise orbit determination and gravity field estimation.

How to cite: Sulzbach, R., Balidakis, K., Dobslaw, H., and Thomas, M.: TiME22: High-Frequency Gravity Potential Coefficients of Atmosphere and Ocean Tides, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-6, https://doi.org/10.5194/gstm2022-6, 2022.

P2
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GSTM2022-15
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On-site presentation
Advanced processing strategies regarding an improved GFZ GRACE/GRACE-FO RL07 time series 
Markus Hauk, Christoph Dahle, Josefine Wilms, Murböck Michael, Natalia Panafidina, and Frank Flechtner

GFZ, as part of the GRACE/GRACE-FO Science Data System, is one of the official Level-2 processing centers routinely providing monthly gravity models. These models are used by a wide variety of geoscientists to infer mass changes mainly at the Earth’s surface. While the current release 6 (RL06) is still operationally processed, plans and internal tests for a reprocessed GFZ RL07 time series are already in progress.

In this context, advanced processing strategies are developed within the Research Unit (RU) NEROGRAV (New Refined Observations of Climate Change from Spaceborne Gravity Missions) funded by the German Research Foundation DFG. The main focus is on an improved stochastic modeling regarding both instrument data (accelerometer and inter-satellite ranging observations) as well as background models (e.g. by the utilization of covariance information for these models). At the same time, the solved-for parameter space, in particular regarding empirical accelerations, has been revised. Finally, also the potential benefit by adding observations of the laser-ranging interferometer (LRI) onboard GRACE-FO has been investigated.

This poster provides an overview of the developed advanced processing strategies, and their individual and combined impact on GFZ’s Level-2 products compared to current GFZ RL06 solutions.

How to cite: Hauk, M., Dahle, C., Wilms, J., Michael, M., Panafidina, N., and Flechtner, F.: Advanced processing strategies regarding an improved GFZ GRACE/GRACE-FO RL07 time series, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-15, https://doi.org/10.5194/gstm2022-15, 2022.

P3
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GSTM2022-22
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On-site presentation
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Disturbances in GRACE-FO LRI Ranging Data: Thruster Effects and Single Event Upsets 
Simon Bähre, Pallavi Bekal, Malte Misfeldt, Laura Müller, Vitali Müller, and Gerhard Heinzel

The range between the two spacecraft in the GRACE-FO mission is measured by the Laser Ranging Interferometer (LRI) and the Microwave Instrument (MWI). The measured signal has variations of gravitational and non-gravitational origins, and can also contain unphysical disturbances, which we regard as noise. Some sporadic and unphysical range errors in LRI are expected to arise from radiation-induced Single Event Upsets (SEUs) in the ranging processor. Another source of non-gravitational range variations are parasitic accelerations produced by the attitude control thrusters (ACTs), which are short-lived events that can dominate the LRI range spectrum for frequencies between 35 and 200 mHz.

SEUs are errors in the processed data due to a transient perturbation of electronic components in the processing chain by high-energy particles that exist in Earth’s magnetic field and relentlessly inundate all electronic devices on board the spacecraft. SEUs can manifest as temporary bit upsets in the registers of two low-pass FIR filters, propagating through a series of decimators and producing a distinct pattern in the LRI downlinked data. We investigate bitflips in any of the four downlinked channels on each spacecraft at a time.

Knowing the architecture of the LRI, we produce SEU templates of the internal filtering chain’s impulse response over the parameter space. The free parameters are the exact sub-sample timing, the register number within the 500- or 140-taps filter and the bit number of the 64-bit depth of each register. The output patterns are then compared to the observed glitches through a pattern matching algorithm to detect and characterize the SEUs. About 20 SEU events were successfully detected and modelled using this algorithm.

A much more frequent disturbance arises from the activation of ACTs which keep the satellites aligned. Even though ACTs should only induce rotational accelerations, slightly misaligned mounts and imperfections of the valves can cause a small coupling into linear accelerations. These linear accelerations are measured by the accelerometer in all three axes and by the LRI in the line-of-sight direction when the second time-derivative of the ranging data is formed. As long as both the accelerometer and LRI correctly measure these accelerations, they should not introduce errors when performing gravitational field recovery.

We present an approach to separate the effects of ACTs from the dominant gravitational signal in LRI ranging data and characterize and model the acceleration profiles in the line-of-sight direction of different ACTs to remove the signatures from LRI ranging data for diagnostic purposes. Our analysis excludes ACT-induced unphysical phase jumps in LRI data, which are handled separately.

Our ACT results help to understand the ACT response differences in the accelerometer and the LRI data products, while identifying and removing SEU models provides cleaner ranging datasets. Both aspects have relevance for the design of future missions and instruments and might, in principle, improve the recovered gravity fields in GRACE-FO.

How to cite: Bähre, S., Bekal, P., Misfeldt, M., Müller, L., Müller, V., and Heinzel, G.: Disturbances in GRACE-FO LRI Ranging Data: Thruster Effects and Single Event Upsets, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-22, https://doi.org/10.5194/gstm2022-22, 2022.

P4
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GSTM2022-30
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On-site presentation
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GRACE and GRACE-FO Level 2 RL07 data processing at JPL 
Matthias Ellmer, David Wiese, Da Kuang, Felix Landerer, Carmen Blackwood, Christopher McCullough, Dah-Ning Yuan, Eugene Fahnestock, and Athina Peidou

The RL07 series of GRACE gravity field products generated at JPL is a reprocessing of updated Level 1 data for the entire mission duration. Some aspects of the Level 2 processing have been updated from the RL06 series, in an effort to improve solution quality and uncertainty quantification.

Level 2 processing improvements include the co-estimation and use of full observation covariance matrices for both GPS and inter-satellite ranging KBR observations, and the use of an updated background field (GOCO06s) and other models. The updates ensure consistency and continuity with the GRACE-FO data record, which is processed using the same standards.

We present time series and analysis of these new fields, and compare them to the previously released JPL RL06 series of gravity field solutions, showing higher fidelity in formal errors, and improvements in solution noise levels. For the GRACE-FO time period, we compare KBR solutions with LRI fields processed using this new set of standards.

How to cite: Ellmer, M., Wiese, D., Kuang, D., Landerer, F., Blackwood, C., McCullough, C., Yuan, D.-N., Fahnestock, E., and Peidou, A.: GRACE and GRACE-FO Level 2 RL07 data processing at JPL, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-30, https://doi.org/10.5194/gstm2022-30, 2022.

P5
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GSTM2022-51
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On-site presentation
Analysis of GRACE and GRACE-FO post-fit range-rate residuals 
Nina Fletling, Jakob Flury, Mathias Duwe, and Igor Koch

The monthly gravity field models at LUH are computed with a generalized dynamic orbit determination approach utilizing precise range-rate measurements derived from the K-band ranging system as main observations. A by-product of the gravity field computations are time series of range-rate residuals which represent a complex superposition of different effects, for example of instrumental, environmental and geophysical nature. An analysis of the residuals helps to gain knowledge of the different systematics that can be used to improve the computation strategy and thus the accuracy of the gravity field models.

Since a similar processing strategy was applied to the analyzed GRACE and GRACE-FO residuals, the smaller and more homogenous GRACE-FO residuals mainly reflect improvements in hardware and software.

Some noticeable abnormalities recur at certain positions and orientations of the satellites relative to the Earth and Sun. The transitions between sunlight and the Earth’s shadow are recognizable as well as the blinding of the star cameras by the Sun in specific angles. Moreover, the simultaneous blinding of both star cameras at GRACE by Sun and Moon can cause peaks in the residuals due to the transient outage of precise attitude determination.

Other amplitudes can be related, for instance, to temporary mode changes of the AOCS during maneuvers or to specific combinations of the received frequency and the temperature at the K-band ranging assembly. Besides the systematic errors, the residuals also contain geophysical signals. This applies mainly for regions with strong annual variations as well as where the models of high-frequency signals are prone to errors.

How to cite: Fletling, N., Flury, J., Duwe, M., and Koch, I.: Analysis of GRACE and GRACE-FO post-fit range-rate residuals, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-51, https://doi.org/10.5194/gstm2022-51, 2022.

P6
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GSTM2022-67
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On-site presentation
Triangular grids on the sphere 
Josef Sebera, Aleš Bezděk, and Jörg Ebbing

Inverting LRI data from GRACE-FO (NASA/GFZ) is challenging from  multiple points of view. To benefit from the laser instrument, that provides a higher precision compared with the KBR ranging, the global basis functions such as spherical harmonics may not provide the best service for exploiting data the full potential. Because the regional analyses use surface elements such as mascons, we present two alternatives in terms of the spherical triangles that may also be used as target elements for the inversion. Since the spherical trigonometry can be used, a relatively easy manipulation and remeshing is possible if appropriate indexing is used. Furthermore, such grids are also used in the solid-Earth models models like LITHO1.0 and WINTER-C, and, thus they may provide an easy link from satellite gravimetry to solid-Earth disciplines. We show the properties of both grids, how to properly index them and how to reduce SST data for the continental part of the signal with the monthly solutions.

How to cite: Sebera, J., Bezděk, A., and Ebbing, J.: Triangular grids on the sphere, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-67, https://doi.org/10.5194/gstm2022-67, 2022.

P7
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GSTM2022-72
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On-site presentation
Merging GRACE Follow-On gravity fields with various approaches 
Artur Lenczuk, Anna Klos, and Janusz Bogusz

For the 2002–2017 period, an essential information about global monthly gravity variations was provided by the Gravity Recovery and Climate Experiment (GRACE) mission. Gravimetric mission have given a new opportunities to analyze fluctuations in the Earth's system, so GRACE observations is widely used in various fields of science. After a gap of almost a year, in May 2018, the GRACE mission successor, i.e., the GRACE Follow-On (GRACE-FO) mission was launched. Both mission observations are processed and supplied by various centers. Therefore, in the following research, we determine a monthly homogenous gravity fields for GRACE-FO mission based on recent Science Data System (SDS) solutions. We use all available 44 months (June 2018 to March 2022) of GRACE-FO monthly data in spherical harmonics form up to degree and order 96. Data is provided by SDS centers, i.e., the Center for Space Research (CSR; the United States), the German Research Center for Geosciences (GFZ) and the NASA’s Jet Propulsion Laboratory (JPL; the United States). To obtain merged gravity fields, we test algorithms based on non-iterative: (1) coefficient-wise and (2) field-wise weighting methods, and iterative: (3) variance component estimation (VCE) method, which help to eliminate signal noise left from each data sets after Gaussian spatial smoothing. In a case of weights, we obtained similar magnitude of them for three selected datasets for non-iterative methods, but CSR weights dominate for the VCE method. In the study, our solution was analyzed in spectral and spatial domain of gravity signal (spherical harmonics case) and land hydrology (total water storage case; TWS). The analysis of signal information contained in each degree and order of spherical harmonic coefficients notice that largest amount of information is contained up to 60 degree and order for SDS and weighted solutions. Above degree and order 60 is more than two times less information. The greatest signal differences between our and SDS solutions occur for the sectorial coefficients up to 40. We also show that the applied field-wise weights much more effectively remove remaining noise after spatial averaging than per-order/degree weighting. Moreover, the obtained values of signals variance for our solutions concur with the geophysical models. In case of land hydrology, the used weighting approaches reduce root mean square scatter of TWS by 5-15% for continental areas. The largest differences occur mainly in high latitudes for both hemispheres. Regional analyses (e.g. Amazon, Zambezi, Murray Darling river basins) show good agreement of monthly TWS series between original GRACE-FO (from SDS centers) and our solutions. We received the extreme TWS differences up to 15% depending on the data center (CSR, GFZ or JPL) and weighting method.

How to cite: Lenczuk, A., Klos, A., and Bogusz, J.: Merging GRACE Follow-On gravity fields with various approaches, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-72, https://doi.org/10.5194/gstm2022-72, 2022.

P8
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GSTM2022-83
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On-site presentation
Sub-monthly Antarctica surface mass changes from GRACE Follow-On Laser Ranging Interferometer measurements 
Mohsen Feizi, Mehdi Roofian Naeeni, and Shin-Chan Han

We present our on-going study of regional gravity field and surface mass change recovery with an example of Antarctica.  We use new parameterization based on spherical cap harmonic (SCH) functions that is suitable for modelling gravitational potential over a spherical cap region.  There are a few advantages of efficiency and flexibility in this approach.  (1) The nearly identical potential field based on spherical harmonic (SH) functions can be expressed with a substantially less number of parameters in terms of SCH functions.  (2) The region-specific constraints can be implemented.  (3) Temporal resolution of the gravity recovery can be flexible and adjusted depending of the satellite coverage.  We use the instantaneous gravitational data along the satellite orbit such as Line-of-sight Gravity Difference (LGD) time series that are computed directly from the laser ranging interferometer (LRI) measurements of range change between two satellites.  We will discuss the methodology and show initial inversion results every 10 days over the Antarctica and discuss possible sub-monthly surface mass variability that we can find from our 10-daily regional surface mass solutions from 2019.

How to cite: Feizi, M., Roofian Naeeni, M., and Han, S.-C.: Sub-monthly Antarctica surface mass changes from GRACE Follow-On Laser Ranging Interferometer measurements, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-83, https://doi.org/10.5194/gstm2022-83, 2022.

P9
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GSTM2022-84
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On-site presentation
LRI post-fit range rate residuals - analysis and comparison 
Mathias Duwe, Igor Koch, and Prof. Dr.-Ing. Jakob Flury

At the institute of geodesy (IfE) we are processing GRACE and GRACE-FO level 1B data to obtain the time variable monthly gravity field (TVG). For this we are using a 2 step variational equation approach (Koch et al. 2021) implemented in our inhouse developed and evolving software GRACE-SIGMA. The software determines different types of TVG: KBR only, LRI only and combined (KBR and LRI) L1B data based all in one step. This allowes an easier and faster intercomparison in terms of spectral and spatial analysis. After determining the gravity field our processing chain calculates the post-fit range-rage residuals which reveals uncertenties e.g. in sensor models, background models, etc. At IfE we are studying these residuals to explain some geophysical phenomena and sensor behavior anomalies. On my poster I focusing on sensor behaviours derived from LRI post-fit range rate residuals. In additon I will show our recent improvements in software. 

How to cite: Duwe, M., Koch, I., and Flury, P. Dr.-Ing. J.: LRI post-fit range rate residuals - analysis and comparison, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-84, https://doi.org/10.5194/gstm2022-84, 2022.

P10
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GSTM2022-91
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On-site presentation
Signals of geophysical nature in GRACE and GRACE-FO post-fit range-rate residuals 
Igor Koch, Mathias Duwe, Jakob Flury, and Nina Fletling

Post-fit residuals of satellite-to-satellite tracking measurements of the GRACE and GRACE-FO missions obtained after a common estimation of orbit and gravity field parameters should ideally contain measurement noise with a behavior that meets expectations for the involved sensors. In reality, obtained GRACE and GRACE-FO post-fit range-rate residuals represent a complex superposition of different effects, e.g. of instrumental, environmental and geophysical nature. In this contribution, we focus on the geophysical signals in the post-fit residuals of the LUH GRACE and GRACE-FO time series. We apply band-pass filtering to extract the geophysical signal buried in the residuals and analyze the most distinctive signatures for their spatial and temporal behavior.

How to cite: Koch, I., Duwe, M., Flury, J., and Fletling, N.: Signals of geophysical nature in GRACE and GRACE-FO post-fit range-rate residuals, GRACE/GRACE-FO Science Team Meeting 2022, Potsdam, Germany, 18–20 Oct 2022, GSTM2022-91, https://doi.org/10.5194/gstm2022-91, 2022.