HS6.8
Water level, storage and discharge from remote sensing and assimilation in hydrodynamic models

HS6.8

EDI
Water level, storage and discharge from remote sensing and assimilation in hydrodynamic models
Convener: Jérôme Benveniste | Co-conveners: J.F. Crétaux, Fernando JaramilloECSECS, Angelica Tarpanelli
vPICO presentations
| Mon, 26 Apr, 13:30–15:00 (CEST)

vPICO presentations: Mon, 26 Apr

Chairpersons: Jérôme Benveniste, Angelica Tarpanelli, J.F. Crétaux
River
13:30–13:35
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EGU21-12476
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ECS
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solicited
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Mounir Mahdade, Nicolas Le Moine, and Pierre Ribstein

River discharge is an essential component in the hydrological cycle. It is used to monitor rivers, the atmosphere, and the ocean through in-situ measurements, acquired on the surface, or from remote sensing to characterize natural disasters such as floods.

Estimating discharge in ungauged rivers with remote sensing data such as the Surface Water and Ocean Topography (SWOT) mission but without any prior in-situ information is difficult to solve, especially in the case of unknown bathymetry, friction, and lateral river flows. However, the current literature suggests that a better knowledge of bathymetry could considerably facilitate roughness and discharge inferring. SWOT observes water surface elevations, slopes, river widths for several overpasses. We propose an inverse method to estimate discharge in a non-uniform steady-state, maintaining longitudinal (alternating pool-riffle) and lateral (meanders) morphological variability of the river. The idea is to build a rating curve (water level - discharge relationship) at the reach scale using hydraulic signatures (quantities not related to a particular section of the reach, which characterize an aspect of the overall hydraulic behavior: e.g., flooded area as a function of Q, mean water level as a function of Q). The inverse approach requires building a model that produces rating curves that optimally correspond to the hydraulic signatures. It requires a direct hydraulic model and a geometric simplification to facilitate the resolution of the inverse problem.

The approach is based on the geomorphology of rivers. Indeed, the geometry of natural rivers presents high-frequency variability, characterized by alternating flow units: fast-flowing flow units in rectilinear and shallow areas (riffles), slow-flowing flow units in deeper areas (pools at alternating banks or inner side of meandering bends). This variability generates a variability of the hydraulic variables that covary at the reach scale. However, a simplification into a uniform geometry without spatial variability reappears as a bias in the frictional parameters, thus reducing the inversion's accuracy. For this, we propose a periodic approach that consists of representing the reach equivalent geometry by sinusoidal functions.

This direct periodic model is used to create a whole periodic geometry (curved based asymmetry sections, Kinoshita curves to model the meander planform) and then solve the Saint-Venant equations in the 2D Basilisk hydraulic model (http://basilisk.fr), which is based on finite volume methods with adaptive grid refinement.

This model does not require boundary conditions (use of periodic boundary conditions) and provides the ability to model floodplains and thus flood mapping. In the end, there are few parameters to adjust in the model (use of parameters covariances).

How to cite: Mahdade, M., Le Moine, N., and Ribstein, P.: How to build reach-averaged rating curves for remote sensing discharge estimation? The potential of periodic geometry hypotheses, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12476, https://doi.org/10.5194/egusphere-egu21-12476, 2021.

13:35–13:40
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EGU21-979
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solicited
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Albert Kettner, Robert Brakenridge, and Sagy Cohen

Historical and current information regarding river discharge is essential, not only from a water management, energy, or global change perspective but also to better analyze, control and forecast flooding. However, globally the number of ground-based gauging stations declines, and data that is measured by ground-based gauging stations is often not, or shared with a considerable delay.

It has been demonstrated that existing satellite sensors can be utilized for useful discharge measurements without requiring ground-based information. The DFO – Flood Observatory uses the Advanced Microwave Scanning Radiometer band at 36.5 GHz (e.g. TRMM, AMSR‐E, AMSR2, GMP), pre-processed by the Joint Research Center (JRC) to estimate discharges. With a nearly-daily repeat interval, this microwave signal has been successfully applied to measure water discharge at a global scale, where the calibration of the microwave discharge signal to discharge units is accomplished by comparison to results from a global hydrological numerical model, the Water Balance Model (WBM), for a calibration period. Once calibrated, daily discharge can be back-calculated to January 1998, providing a daily discharge record for more than 20 years.

Here we present the methods used to utilize remote sensing to measure discharge. We indicate the challenges and how to overcome these when using a multiple sensor approach to capture daily discharges for over a 20-year period. And we show an example for the Amazon river, comparing the remote sensed discharge data with ground observations for multiple locations. Additionally, applications are shown on how this discharge can be combined with flood extent maps to analyze flood frequency.

How to cite: Kettner, A., Brakenridge, R., and Cohen, S.: Remote sensed water discharge to analyze flood frequency, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-979, https://doi.org/10.5194/egusphere-egu21-979, 2021.

13:40–13:42
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EGU21-3809
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ECS
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Pai-Feng Teng and John Nieber

Flooding is one of the most financially devastating natural hazards in the world. Studying storage-discharge relations can have the potential to improve existing flood forecasting systems, which are based on rainfall-runoff models. This presentation will assess the non-linear relation between daily water storage (ΔS) and discharge (Q) simulated by physical-based hydrological models at the Rum River Watershed, a HUC8 watershed in Minnesota, between 1995-2015, by training Long Short-Term Memory (LSTM) networks and other machine learning (ML) algorithms. Currently, linear regression models do not adequately represent the relationship between the simulated total ΔS and total Q at the HUC-8 watershed (R2 = 0.3667). Since ML algorithms have been used for predicting the outputs that represent arbitrary non-linear functions between predictors and predictands, they will be used for improving the accuracy of the non-linear relation of the storage-discharge dynamics. This research will mainly use LSTM networks, the time-series deep learning neural network that has already been used for predicting rainfall-runoff relations. The LSTM network will be trained to evaluate the storage-discharge relationship by comparing two sets of non-linear hydrological variables simulated by the semi-distributed Hydrological Simulated Program-Fortran (HSPF): the relationship between the simulated discharges and input hydrological variables at selected HUC-8 watersheds, including air temperatures, cloud covers, dew points, potential evapotranspiration, precipitations, solar radiations, wind speeds, and total water storage, and the dynamics between simulated discharge and input variables that do not include the total water storage. The result of this research will lay the foundation for assessing the accuracy of downscaled storage-discharge dynamics by applying similar methods to evaluate the storage-discharge dynamics at small-scaled, HUC-12 watersheds. Furthermore, its results have the potentials for us to evaluate whether downscaling of storage-discharge dynamics at the HUC-12 watershed can improve the accuracy of predicting discharge by comparing the result from the HUC-8 and the HUC-12 watersheds.

How to cite: Teng, P.-F. and Nieber, J.: Toward Downscaling Storage-Discharge Dynamics: Training Long Short-Term Memory (LSTM) model for Simulating Nonlinear Storage-Discharge Relations at The Rum River Watershed, MN, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3809, https://doi.org/10.5194/egusphere-egu21-3809, 2021.

13:42–13:44
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EGU21-8716
Angelica Tarpanelli and Alessio Domeneghetti

The flow duration curves (FDCs) represent the relationship between river discharges observed at a given cross-section and the percent of time (duration) they are exceeded, or equaled, over an historical reference period. The FDC provides a comprehensive description of the hydrological regime of a catchment and its knowledge is fundamental for many water-related applications (e.g., water management and supply, human and irrigation purposes, etc.). However, relying on historical streamflow records, FDCs are constrained to gauged stations and, thus, typically available for a small portion of the world’s rivers. In this context, satellite data can support our monitoring capability and being considered as a valuable and additional source for the observation of the Earth’s physical parameters.

Recent studies demonstrated the efficiency of the surface reflectance in the Near Infrared (NIR) for the river discharge estimation. The high temporal resolution (almost daily), the high-medium spatial resolution (10 - 300 m) and the global coverage observing in a continuous way the range of 90-90 latitude encourage to extend the use of the NIR bands also for hydrology-related purposes. Here we tested the potential of MODIS 500 m 8-day product in providing discharge estimation for the construction of FDCs at 13 sites along the Mississippi River. In particular, this work considers records of river discharge from January 2003 to December 2019, calibrating and validating the FDCs for a period of 13 and 4 years, respectively. The aim is to test the ability to estimate the hydrological regime of a river at a given location using satellite data.

Results highlight the potential of the NIR bands to provide a realistic reconstruction of the flow regimes at different locations. Higher errors are obtained at the FDC tails, where extremely high or low flows have a low likelihood of being observed, mainly due to the limit of the sensor to see below the clouds during the flood events or to capture small water body. Better performances are obtained for the medium flows, encouraging the use of the satellite for the water resources management at ungauged river sites.

How to cite: Tarpanelli, A. and Domeneghetti, A.: Testing the potential of Near Infrared band for the estimation of flow duration curves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8716, https://doi.org/10.5194/egusphere-egu21-8716, 2021.

13:44–13:46
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EGU21-12034
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ECS
Zhenwu Wang, Rolf Hut, Natthachet Tangdamrongsub, and Nick van de Giesen

Assimilating surface soil moisture data or GRACE data, retrieved from satellite, into hydrological models has been proven to improve the accuracy of hydrological model estimations and predictions. For data assimilation applications in hydrology, the ensemble Kalm filter(EnKF) is the most commonly used data assimilation(DA) method. Particle filters are a type of non-Gaussian filter that doesn’t need the normality assumption that the EnKF needs. Adding localization defeats the curse of dimensionality that is a problem in normal particle filters. In the present study, we investigated our adaption of the local particle filter based on the Gamma test theory(LPF-GT) to improve discharge estimates by assimilating SMAP satellite soil moisture into the PCR-GLOBWB hydrological model. The study area is the Rhine river basin, driven by forcing data from April 2015 to December 2016. The improved discharge estimates are obtained by using DA to adjust the surface soil moisture in the model. The influence of DA to discharge is not direct but works through the dynamics of the hydrological model.  To explore the potential of LPF-GT, serval sensitivity experiments were conducted to figure out the impact of localization scales and the number of particles on DA's performance. The DA estimates were validated against in situ discharge measurements from gauge stations. To demonstrate the benefit of LPF-GT, EnKF was used as a benchmark in this research. Increases in Nash-Sutcliffe (0.05%– 38%) and decreases in normalized RMSE (0.02%–3.4%) validated the capability of LPF-GT. Results showed that localization scales' impact was substantial. The optimal value of the localization scale was obtained by tuning. LPF-GT achieved a satisfactory performance when only using a few particles, even with as little as five particles. The sample errors posed an adverse impact on the open-loop results. Further improvement could be achieved by considering reduce sample errors due to a small number of particles.

How to cite: Wang, Z., Hut, R., Tangdamrongsub, N., and van de Giesen, N.: Data assimilation of SMAP soil moisture into the PCR-GLOBWB hydrological model to improve discharge estimates via A Novel Local Particle Filter, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12034, https://doi.org/10.5194/egusphere-egu21-12034, 2021.

13:46–13:48
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EGU21-13378
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ECS
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Heidi Ranndal, Karina Nielsen, and Ole B. Andersen

The data from NASA’s Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) mission offer a unique opportunity to map rivers and lakes with an unprecedented number of observations in areas where previous missions have failed to provide valuable water level estimates. ICESat-2 carries just one instrument, the Advanced Topographic Laser Altimeter System (ATLAS), which is a green wavelength, photon-counting lidar, and several data products are available, such as the ATL03 product, which holds the photon data, and the ATL13 product which contains estimated inland water surface heights and statistics for water bodies across the world. The along-track resolution of the ATL03 product is less than 1 m, and with the three pairs of beams, i.e. six beams in total, the mission provides exceptional opportunities for inland water studies in areas with mountainous topography.

In general, inland water altimetry in mountainous areas has proven to be a challenge for both conventional Low Resolution Mode (LRM) and Synthetic Aperture Radar (SAR) altimetry, causing issues not only with waveforms, but also the position of the range window. In this study, we present the ability of ICESat-2 to obtain water levels in several mountainous rivers in China, where even SAR missions such as CryoSat-2 and Sentinel-3 have been unsuccessful. Results are shown for both the ATL03 and the ATL13 version 4 products to evaluate their performances.

How to cite: Ranndal, H., Nielsen, K., and Andersen, O. B.: Evaluation of ICESat-2 ATL03 and ATL13 River Levels in Mountainous Areas of China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13378, https://doi.org/10.5194/egusphere-egu21-13378, 2021.

13:48–13:50
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EGU21-13857
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Luciana Fenoglio-Marc, Elena Zahkavova, Matthias Gärtner, Bahtiyor Zohidov, Salvatore Dinardo, and Quang Duong

River discharge is a key variable to quantify the water cycle and its flux.  This study focuses on the river Rhine, of width between 200 and 500 meters. River discharge is evaluated in this paper from the Sentinel-3 altimeter water level using various approches, which are the empirical rating curve method, the semi-empirical Bjerklie method and the physically-based method based on hydraulic equations.

The Sentinel-3 GPOD ESA products from the SAMOSA+ retracker perform better than the standard Copernicus products that use the OCOG and ocean retrackers. Root-mean-square errors (RMSEs) between altimetry and in-situ stations are between 0.10 m and 0.30 m at 10 of the 17 virtual tide gauge locations. The empirical rating curve method applied to the altimetric water level and in-situ discharge provides estimates of the water discharge with accuracy of 3-7% (expressed as RMSE normalized with the mean of the discharge).

The performance of the semi-empirical Bjerklie method and of the physically-based Manning algorithm to estimate the river discharge is assessed from water surface slope, elevation and top width data for different part of the river and flow conditions. Firstly, daily synthetic water surface slopes and elevations are generated from selected in-situ gauges and mean top river widths. Secondly the input to the discharge algorithm comes from the 1D-hydrodynamic model Sobek. Various choises for reach lengths and for number of observed time-series are considered. Different time sampling are used to study the effect of the repeat cycle of nadir altimeter and SWOT missions. The effect of the priori information on the accuracy of the flow water discharge is investigated.

How to cite: Fenoglio-Marc, L., Zahkavova, E., Gärtner, M., Zohidov, B., Dinardo, S., and Duong, Q.: Discharge of the river Rhine from multi-sensor data from empirical and physical methods, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13857, https://doi.org/10.5194/egusphere-egu21-13857, 2021.

13:50–13:52
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EGU21-14175
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ECS
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Stefania Camici, Gabriele Giuliani, Luca Brocca, Christian Massari, Angelica Tarpanelli, Marco Restano, and Jérôme Benveniste

STREAM -SaTellite based Runoff Evaluation And Mapping- is a conceptual hydrological model able to derive daily river discharge and runoff estimates from satellite soil moisture, precipitation and terrestrial water storage anomalies observations. The model is very simple and versatile: It requires a limited number of parameters (only eight) to simulate river discharge.

The model simulates river discharge and gridded runoff at daily time scale with a 25 km spatial resolution. Forced by TRMM 3B42 rainfall data and ESA CCI soil moisture data and GRACE over five pilot large basins (Mississippi, Amazon, Niger, Danube and Murray Darling) the model already provided good runoff estimates especially over Amazon basin, with a Kling-Gupta efficiency (KGE) index greater than 0.92 both at the basin outlet and over several inner stations in the basin. Good results have been also obtained for Mississippi, Niger and Danube with KGE index greater than 0.75 for all the gauging stations.

By considering the good performances of the STREAM model and by the continuous availability (in space and time) of satellite observations, this work presents an attempt to regionalize the STREAM model parameters. The Mississippi river basin has been taken as case study and specific relationships between model parameters and different predictors (climate variables such as precipitation and evaporation, soil vegetation and topography characteristics) have been developed. By using these relationships, STREAM parameter values have been directly obtained from readily available climatic and physiographic basin characteristics and model performances are still satisfactory (median KGE over the basin equal to 0.60). The capability to use these relationships in other hydrologically similar catchments will be investigated for the Danube and Amazon river basins. The final target is to obtain global relationships as to provide to provide daily, 25 km, global runoff maps from the STREAM approach.

How to cite: Camici, S., Giuliani, G., Brocca, L., Massari, C., Tarpanelli, A., Restano, M., and Benveniste, J.: Global runoff estimation through a regionalized STREAM model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14175, https://doi.org/10.5194/egusphere-egu21-14175, 2021.

Lake
13:52–13:54
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EGU21-2785
Estel Cardellach, Weiqiang Li, Dallas Masters, Takayuki Yuasa, Franck Borde, John Shirlaw, and Manuel Martin-Neira

Recently, different studies have shown evidence of signals transmitted by the Global Navigation Satellite Systems (GNSS), coherently reflected over some parts of the ocean, and received from cubesats. In particular, strong coherent scattering has been reported in regions with low water surface roughness as those near continental masses and in atolls. Over open ocean, few coherent signals were reported to be found, although the data sets were somewhat limited and certainly not exhaustive. The level of coherence in reflected GNSS signals depends on the roughness of the  surface (i.e. significant wave height and small scale ripples and waves induced by the wind), the viewing geometry (i.e. incidence angle, or equivalently, elevation angle of the GNSS satellite as seen from the point of reflection), propagation effects (namely ionospheric disturbances) and on the frequency (i.e. particular GNSS band, like L1/E1, L2 or L5/E5). These coherent measurements over ocean follow earlier evidence of coherent GNSS reflections over sea ice which date back to 2005, the time of UK-DMC mission. More recently, Sea Ice Thickness (SIT) retrievals have also been carried out with this technique, at an accuracy comparable to that of SMOS.

All the observations referred so far were done at a single frequency, L1/E1. So, there is an interest to explore the coherence at the other main GNSS bands, i.e. L2 and L5/E5 as well as to the widelane combinations between them (linear combinations of carrier-phase measurements, of longer effective wavelength). Spire Global radio occultation cubesats work at L1 and L2 frequency bands, and therefore provide unique dual-frequency raw data sets of reflected signals over open ocean, sea ice and inland water bodies. With these, it is possible to study the coherence of these targets at each of the bands and at their widelane combination, as well as the performance of altimetric retrievals at grazing angles of observation (very slant geometries, which facilitate coherence properties of the scattering). The dual-frequency observations can correct the ionospheric effects, and their widelane combinations, of longer effective wavelength, might expand the conditions for coherence. The fact that this new approach is fully compatible with small GNSS radio occultation payloads and missions, might represent a low cost source of precise altimetry to complement larger dedicated missions.

An ESA research study involving Spire Global and IEEC aims at studying this new potential altimetric technique. Raw data acquisitions from limb-looking antennas of Spire’s cubesat constellation were selected to be geographically and time collocated with ESA Sentinel 3A and 3B passes in order to compare the results of coherence and altimetry. For this study, the raw data at two frequencies, acquired at 6.2 Mbps, are shifted to intermediate frequencies and downloaded to the ground without any further processing. In-house software receivers are then applied to generate the reflected echoes or waveforms, and to track the phase of the carrier signals. Precise altimetry (a few cm in 20 ms integration) is then possible from these observables. The results of this activity will be shown, focusing on altimetric retrievals over large lakes.

How to cite: Cardellach, E., Li, W., Masters, D., Yuasa, T., Borde, F., Shirlaw, J., and Martin-Neira, M.: Precise carrier phase altimetry over lakes using dual-frequency reflected signals of the Global Navigation Satellite Systems (GNSS), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2785, https://doi.org/10.5194/egusphere-egu21-2785, 2021.

13:54–13:56
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EGU21-2890
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ECS
Saeid Aminjafari and Fernando Jaramillo

Sweden has approximately 100,000 lakes covering roughly nine percent of the country’s surface area. These lakes are one of the important sources of fresh water for urban, industrial, and agricultural use, further providing a wide range of ecosystem services. In order to conserve and protect the lakes from the impacts of climate change, hydrologic monitoring should ideally be conducted in all of these lakes. However, it is almost impossible to gauge all of these lakes on a regular basis, due to economical and logistic constraints. Radar altimetry has been successfully used to obtain water levels from specific lakes; however, the technology can only be used in large lakes that are located precisely under the orbit of the satellite, thus excluding most Swedish lakes. We here develop a new procedure based on the application of differential interferometric synthetic aperture radar (DInSAR) on sequential image pairs with short temporal baseline to measure the water level of 36 lakes. We processed Sentinel-1 twin satellite data with 6-day revisiting intervals, pair by pair, from March 2019 to November 2019. In total, we constructed 41 interferograms considering only the pixels with coherence values greater than 0.2 in all interferograms to ensure consistent scattering and good coherence in all images. We found that the pixels located near tree trunks in flat areas or near steep cliffs in mountainous areas showed a steady phase change in all interferograms that could be converted to water level change. In some of these lakes, the water level changes derived from this methodology correlated well with the in-situ water level of the gauge stations provided by the Swedish Meteorological and Hydrological Institute. We believe that this methodology has good potential for monitoring water level data in small lakes that cannot be monitored by radar altimetry, and serves as evidence of the unknown potential of DInSAR to track hydrological changes in open water surfaces.

How to cite: Aminjafari, S. and Jaramillo, F.: Water level changes in Swedish lake systems using pixel-specific Sentinel-1 phase change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2890, https://doi.org/10.5194/egusphere-egu21-2890, 2021.

13:56–13:58
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EGU21-6850
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ECS
Sebastián Palomino-Ángel, Raúl F. Vázquez, Henrietta Hampel, Jesús A. Anaya-Acevedo, Pablo V. Mosquera, and Fernando Jaramillo

Spatiotemporal characteristics of physical responses of lakes to external and environmental changes are still largely unknown due to the consistent lack of monitoring of water level and corresponding changes in water storage in lakes. Understanding these changes is a fundamental step in advancing regional management of natural and anthropogenic systems that depend on the water resources of lakes. As an illustrative example, we here report a case study involving lakes of the headwater topical Andes mountain range, which, despite guaranteeing water security to millions of downstream inhabitants, still remain significantly ungauged. We present a novel evaluation of the potential of Differential Interferometric Synthetic Aperture Radar DInSAR techniques for the spatiotemporal analysis of patterns of water level change in lakes such as the ones comprising these ungauged high-altitude lake systems. Time series of Sentinel-1B data for the years 2017 and 2018 were used to generate continuous interferograms representing water level changes in twenty-four lakes of the Cajas National Park, Ecuador. The relation of these water level changes with climatic and topographical factors were analyzed to validate the methodology, and determine any patterns of change and response to climatic drivers. We found relatively high Pearson correlation coefficients between regional precipitation and water level change as estimated from the interferograms. Furthermore, we found an important negative relationship between water level change, as obtained from the DInSAR phase, and lake surface area. The study revealed a spatial trend of this correlation in terms of the altitude of the lakes at the basin scale; that is, lower correlation values were found in the headers of the basins, whilst higher correlation values were found at lower basin altitudes. The results of the present study demonstrate the potential of DInSAR techniques based on Sentinel-1 data for the monitoring of hydrologic changes in open water surfaces, and the possible validation of the DInSAR results with precipitation when gauged water level data is missing. These results are a basis to propose monitoring strategies in ungauged high-altitude lake systems in regions with similar data gauging constraints. Future work will encompass the integration of ongoing water level gauging for further validation of the herein depicted lake water level estimation approach.

How to cite: Palomino-Ángel, S., Vázquez, R. F., Hampel, H., Anaya-Acevedo, J. A., Mosquera, P. V., and Jaramillo, F.: Spatiotemporal change of water level in ungauged high-altitude tropical lakes: a DInSAR approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6850, https://doi.org/10.5194/egusphere-egu21-6850, 2021.

13:58–14:00
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EGU21-8615
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ECS
Dung Trung Vu, Thanh Duc Dang, and Stefano Galelli

Being a part of the Water Tower of Asia, the Mekong River originates from the Tibetan Plateau and flows through China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. Its upper portion, also called the Lancang River, has abundant hydropower potential, which has been largely exploited during the three recent decades. To date, there are 11 operational dams (10 of them have a volume larger than 100 MCM) on the mainstream of the Lancang, controlling about 40% of the annual flow at Chiang Saen (the most upstream station of the Lower Mekong). The amount of water withheld in these dams is a potential source of controversy between China and downstream countries because it affects both the timing and volume of available water. Assessing the real impacts of these dams is a challenging task owing to the chronic lack of data on reservoirs' storage and operating patterns. To overcome this challenge, we exploit satellite images and altimetry data. The analysis focuses on 10 reservoirs and is conducted in three steps. First, we estimate the relationship between water elevation and surface area (E-A curve) for each reservoir. For this purpose, we either use DEM data or water surface area data (derived from satellite images) paired with altimetry-derived water levels. Second, with the Elevation-Area-Storage curve converted from each E-A curve, we calculate storage variability over time by using satellite image-derived reservoir water surface area. The result is collated with storage variability derived from altimetry data. In the last part of our analysis, focusing on the period 2008-2020, we show how the total withheld storage changed over time, we determine the rule curve of each reservoir and elucidate the role of reservoir filling strategies.

How to cite: Trung Vu, D., Duc Dang, T., and Galelli, S.: Using space observations to monitor reservoir operations in the Lancang River, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8615, https://doi.org/10.5194/egusphere-egu21-8615, 2021.

14:00–14:02
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EGU21-12738
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Florence Sylvestre, Jean-François Crétaux, Muriel Berge-Nguyen, Binh Pham Duc, Abdallah Mahamat Nour, Camille Bouchez, Frédéric Frappart, and Fabrice Papa

In a near future, the Sahara and Sahelian regions could experience more rainfall than today as a result of climate change. Wetter conditions in the hottest and driest place of the planet today raise the question of whether the near future might hold in store environmental transformations, particularly in view of the growing human-induced climate, land-use and land-cover changes. Reflecting an enhancement of the global hydrological cycle under warmer conditions, some experiments provide support for the notion of a strengthening of the monsoon in the future and more rainfall in central Sahel and Sahara. However, some remote forcing could counterbalance the decadal trend. Modeling experiments suggest that the freshwater discharge coming from Greenland melting could significantly impact the sea surface temperature of North Atlantic and induce a decrease in Sahel rainfall for the next decades, remaining left open the question how Sahara will be in a warmer climate?

By chance, Lake Chad, located at the southern edge of the Sahara, is recognized for being the best site in Africa for deciphering hydrological and climate change. After being ranked at the world’s sixth largest inland water body with an open water area of 25,000 km2 in the 1960s, it shrunk dramatically at the beginning of the 1970s and reached less than 2000 km2 during the 1980s, decreasing by more 90% in area. Because it provides food and water to 50 millions of people, it becomes crucial to observe precisely its hydrological cycle during the last 20 years.

Here by using a new multi-satellite approach combined with ground-based observations, we show that Lake Chad extent has remained stable during the last two decades, slightly increasing at 14,000 km2. We extend further this reconstruction by adding new data from the hydrological year 2019-2020, which is considered at an extreme in precipitation recorded over the Sahel. Moreover, since the 2000s, groundwater which contributes to 70% of Lake Chad’s annual water storage, is increasing due to water supply provide by its two main tributaries draining a catchment area 610,000 km2 wide. Because the current climate change seems to be characterize by a higher interannual variability affecting from year to year the amount of precipitation during the rainy season and increasing the vulnerability of the economy of the region mainly based of agropastoral activities, we investigate the yearly cycle and see how it is impacted the hydrological cycle of Lake Chad and changed over time.

How to cite: Sylvestre, F., Crétaux, J.-F., Berge-Nguyen, M., Pham Duc, B., Mahamat Nour, A., Bouchez, C., Frappart, F., and Papa, F.: Lake Chad hydrological cycle under current climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12738, https://doi.org/10.5194/egusphere-egu21-12738, 2021.

Groundwater
14:02–14:04
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EGU21-505
Sergii Kadurin, Elena Chuiko, and Kseniya Andreeva

Problems statement and purpose. Studied area has a high level of agricultural development. There are different irrigation and drainage systems located there. Significant part of the supplied water losses from the irrigation network because of filtration and reaches the groundwater level, which begins to rise. Raising of groundwater level can lead to waterlogging of the soil, secondary salinization and, as a consequence, to a decrease in crop yields. As result, the groundwater level is under intense technogenic impact. Control and analyses of groundwater level changes with remote sensing methods for Ovidiopol area is the main goal of that work. The object of study is the groundwater level regime in the territory of Lower Dniester irrigation system in Ovidiopol district, Odessa region. The subject of research is water indexes application for analyses of groundwater level changes.

Data and methods. The local system of groundwater observation includes 7 drillholes in Nadlimanskoe village and around. These drillholes located in different geomorphological, hydrogeological and technogenic conditions. The groundwater level was surveyed monthly in 2017.  Sentinel-2 2A images for each month from March 2017 to December 2017 were used for studied area. All satellite images has atmospheric correction. Three water indexes NDWI, MNDWI, NDPI were calculated for drillhole points for each month in 2017 year.

Results. Significant coefficients of correlation were obtained in comparison between groundwater level changes and water indexes in some drillholes points. The highest numbers of correlation connected with free of construction areas and for drillholes, which are located outside of villages. Water indexes have the same intra-annual dynamics of changing as groundwater level. NDWI is the most informative and representative index for studied area. Other types of indexes should be used for build-up areas analyses. However, existed water indexes can be used for groundwater level analyses in the open fields and in river slopes and valleys with developed irrigation system.

How to cite: Kadurin, S., Chuiko, E., and Andreeva, K.: Sentinel-2 water indexes application for the underground water level analyses in Ovidiopol area of Odessa region (Ukraine)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-505, https://doi.org/10.5194/egusphere-egu21-505, 2021.

14:04–14:06
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EGU21-3402
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ECS
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Mehdi Darvishi and Fernando Jaramillo

In the recent years, southern Sweden has experienced drought conditions during the summer with potential risks of groundwater shortages. One of the main physical effects of groundwater depletion is land subsidence, a geohazard that potentially damages urban infrastructure, natural resources and can generate casualties. We here investigate land subsidence induced by groundwater depletion and/or seasonal variations in Gotland, an agricultural island in the Baltic Sea experiencing recent hydrological droughts in the summer. Taking advantage of the multiple monitoring groundwater wells active on the island, we explore the existence of a relationship between groundwater fluctuations and ground deformation, as obtained from Interferometric Synthetic Aperture Radar (InSAR). The aim in the long-term is to develop a high-accuracy map of land subsidence with an appropriate temporal and spatial resolution to understand groundwater changes in the area are recognize hydroclimatic and anthropogenic drivers of change.

We processed Sentinel-1 (S1) data, covering the time span of 2016-2019, by using the Small BAseline Subset (SBAS) to process 119 S1-A/B data (descending mode). The groundwater level of Nineteen wells distributed over the Gotland island were used to assess the relationship between groundwater depletion and the detected InSAR displacement. In addition to that, the roles of other geological key factors such as soil depth, ground capacity in bed rock, karstification, structure of bedrock and soil type in occurring land subsidence also investigated. The findings showed that the groundwater level in thirteen wells with soil depths of less than 5 meters correlated well with InSAR displacements. The closeness of bedrock to ground surface (small soil depth) was responsible for high coherence values near the wells, and enabled the detection land subsidence. The results demonstrated that InSAR could use as an effective monitoring system for groundwater management and can assist in predicting or estimating low groundwater levels during summer conditions.

How to cite: Darvishi, M. and Jaramillo, F.: Detecting land deformation due to groundwater changes with InSAR observations - the case of the island of Gotland, Sweden, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3402, https://doi.org/10.5194/egusphere-egu21-3402, 2021.

Wetland -- Chairs Fernando Jaramillo, Angelica Tarpanelli, Jean-François Crétaux
14:06–14:08
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EGU21-6768
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solicited
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Shimon Wdowinski, Heming Liao, and Boya (Paul) Zhang

Wetlands store roughly 10% of global surface water in the terrestrial portion of the water cycle, cover roughly 9% of the Earth’s surface, and provide critical habitat for a wide variety of plant and animal species. Over the past century, many wetland areas have been lost, degraded, or stressed mainly due to anthropogenic activities, as water diversion, agricultural development, and urbanization, but also in response to natural processes, as sea level rise and climate change. Global and regional monitoring of wetland health and response to their natural and anthropogenic stressors are important and are best conducted using space-based remote sensing techniques, due to wetlands’ vast extent and often inaccessibility.

Several space-based remote sensing technologies provide high spatial resolution observations of wetland water level and its changes over time. These techniques include Synthetic Aperture Radar (SAR), optical imagery, radar and laser altimetry, and Surface Water Ocean Topography (SWOT). SAR observations include two independent observables, amplitude and phase; each observable is sensitive to different hydrological parameters. Radar and laser altimetry missions provide cm-level accuracy water level measurements along the satellite track. The SWOT mission, which is scheduled for a February 2022 launch, will use radar interferometer for repeated measurements of cm-level water level measurements over a 50-100 km wide swaths. As part of a NASA supported project, we develop a space-based multi-sensor monitoring system of surface water level changes in wetlands. The multi-sensor system will generate detailed multi-temporal maps of wetland inundation extent, water levels, and water level changes. The development of the multi-sensor monitoring system will be conducted over the south Florida Everglades, which can be considered as a natural laboratory due to its variable land cover and the availability of ground-based hydrological observations. Preliminary results based on Interferometric Synthetic Aperture Radar (InSAR) observations yielded detailed maps of water level changes of the entire Everglades wetlands with 100 m spatial resolution and 3-4 cm accuracy level. After development, the system will be tested in two other wetland areas located in Louisiana, and Peace–Athabasca Delta (Alberta, Canada).

How to cite: Wdowinski, S., Liao, H., and Zhang, B. (.: A multi-sensor monitoring system of surface water level changes in wetlands, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6768, https://doi.org/10.5194/egusphere-egu21-6768, 2021.

14:08–14:10
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EGU21-3732
Sang-Hoon Hong, Shimon Wdowinski, and Sang-Wan Kim

High spatial resolution maps of relative water level changes in wetlands environment have been successfully generated using spaceborne interferometric synthetic aperture radar (InSAR) techniques. However, the wetland InSAR application has limited hydrological monitoring application, because it estimates water level changes not absolute water levels, which are used by hydrologists. TanDEM-X bistatic observations provide simultaneous phase measurements of water surfaces with a two-satellite constellation without temporal decorrelation. In this study, the TanDEM-X bistatic science phase observations with very large baseline (> 1.3 km) geometric configuration were evaluated to extract absolute water levels of the Everglades wetland in south Florida, U.S.A. Thanks to the large perpendicular baseline, spatial variation of water level surfaces with extremely low slope were estimated. We processed two datasets of TanDEM-X bistatic observations acquired on August 26 and 31, 2015. The perpendicular baselines are 1.43 km and 1.36 km and the ambiguity heights were calculated as 3.61 m and 3.90 m in each interferometric pair. The estimated absolute water level maps with 3.6 m and 7.4 m pixel spacing in range and azimuth directions (multilook factor of 4), respectively, show vast detailed variation of the water surfaces for each acquisition date. Hourly water level measurements obtained by stage stations, which are provided by the Everglades Depth Estimation Network (EDEN), were used for verifying the estimated absolute water levels. Some of stage stations, which are located in low interferometric coherence areas, such as dense vegetated and tree areas, were considered as outliers and were excluded from the comparison. The verification results show very good agreements (code of determination > 0.95) between the TanDEM-X derived absolute water levels and the stage station measurements. The root mean square error (RMSE) between the TanDEM-X results and stage records for the two datasets were 0.77 m and 0.66  m. Although, TanDEM-X bistatic observations have no temporal baseline, there are severe volume decorrelations over various tree types due to the very large perpendicular baseline. The TanDEM-L mission with longer wavelength of radar signal will enable us to generate more coherent interferometric phase observations over wetlands and, consequently, generate improved absolute water level maps.

How to cite: Hong, S.-H., Wdowinski, S., and Kim, S.-W.: Extraction of Absolute Water Level in the Florida Everglades Using TanDEM-X Bistatic Science Phase Observations with a Large Perpendicular Baseline, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3732, https://doi.org/10.5194/egusphere-egu21-3732, 2021.

14:10–14:12
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EGU21-8021
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ECS
Hannah Tripp and Erik Crosman

The improved spatial, spectral, and temporal resolution of Sentinel-2 satellite imagery compared to widely used Landsat imagery allows for many small, variable bodies of water such as intermittent rivers, glacial lakes, rice paddies, and ephemeral wetlands to be studied in depth for the first time.  Across the Texas High Plains, USA, playa lakes are highly sensitive to wet/dry cycles, and are noted for their critical ecological importance in the region, providing habitat for many species of birds and other animals. The playas are also known to be important features for aquifer recharge in some areas. While sporadic aircraft studies and satellite evaluations of the larger playas in the region have been conducted previously from Landsat, no known study has utilized the improved capabilities of Sentinel-2 imagery to document the numerous smaller playas in the region. In this study, we analyze playa lakes across northwestern Texas, USA between 2016-2020  using high-resolution spectral satellite imagery from the European Space Agency’s Sentinel-2 mission. The Semi-Automatic Classification plugin for QGIS is used to document spatial and temporal changes in the areal extent of water in seasonal playa lakes in the High Plains region of Texas. Several case studies of the spatial and temporal evolution of the playa lakes from Sentinel-2 imagery will be presented, as well as applications for seasonal ecological monitoring and groundwater recharge monitoring.   Images taken of the same playa lakes at different times are compared to determine the rate at which the amount of water is changing. Using data from the nearest available weather stations, the amount of water loss due to evaporation is estimated. This is compared to the observed water loss to estimate the amount of water percolating into the ground where it may be contributing to aquifer recharge. This study aims to be a proof of concept for a method for operationally monitoring the state of playa lakes across the region for ecological applications, as well as to quantify potential groundwater recharge.

How to cite: Tripp, H. and Crosman, E.: Spatiotemporal Variations in West Texas Playa Wetlands Mapped from Sentinel-2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8021, https://doi.org/10.5194/egusphere-egu21-8021, 2021.

14:12–14:14
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EGU21-8737
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ECS
Stefan Schlaffer, Marco Chini, and Wouter Dorigo

The North American Prairie Pothole Region (PPR) consists of millions of wetlands and holds great importance for biodiversity, water storage and flood management. The wetlands cover a wide range of sizes from a few square metres to several square kilometres. Prairie hydrology is greatly influenced by the threshold behaviour of potholes leading to spilling as well as merging of adjacent wetlands. The knowledge of seasonal and inter-annual surface water dynamics in the PPR is critical for understanding this behaviour of connected and isolated wetlands. Synthetic aperture radar (SAR) sensors, e.g. used by the Copernicus Sentinel-1 mission, have great potential to provide high-accuracy wetland extent maps even when cloud cover is present. We derived water extent during the ice-free months May to October from 2015 to 2020 by fusing dual-polarised Sentinel-1 backscatter data with topographical information. The approach was applied to a prairie catchment in North Dakota. Total water area, number of water bodies and median area per water body were computed from the time series of water extent maps. Surface water dynamics showed strong seasonal dynamics especially in the case of small water bodies (< 1 ha) with a decrease in water area and number of small water bodies from spring throughout summer when evaporation rates in the PPR are typically high. Larger water bodies showed a more stable behaviour during most years. Inter-annual dynamics were strongly related to drought indices based on climate data, such as the Palmer Drought Severity Index. During the extremely wet period of late 2019 to 2020, the dynamics of both small and large water bodies changed markedly. While a larger number of small water bodies was encountered, which remained stable throughout the wet period, also the area of larger water bodies increased, partly due to merging of smaller adjacent water bodies. The results demonstrate the potential of Sentinel-1 data for long-term monitoring of prairie wetlands while limitations exist due to the rather low temporal resolution of 12 days over the PPR.

How to cite: Schlaffer, S., Chini, M., and Dorigo, W.: Remote Sensing of Surface Water Dynamics Between 2015 and 2020 in the Prairie Pothole Region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8737, https://doi.org/10.5194/egusphere-egu21-8737, 2021.

14:14–14:16
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EGU21-14620
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ECS
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Fernando Jaramillo, Dan Liu, Saeid Aminjafari, and Xuan Wang

Hydrological connectivity is a critical determinant of wetland functions and ecosystems by controlling the movement of biogeochemical elements within wetlands and the flow of water between their hydrological units. Hydrological barriers exist when this connectivity is impaired, either by man-made infrastructure, agriculture developments, or naturally restricted by soil and ground composition. Determining hydrological barriers in wetlands is challenging due to the costs of high-resolution and large-scale monitoring, but radar observations can become a useful tool for such task. We here use an Interferometric Synthetic Aperture Radar (InSAR) to identify hydrological barriers in several iconic wetlands worldwide, with particular focus on the Baiyangdian wetland system in Northern China. For the first, we use Sentinel 1A and 1B data covering the period 2016-2019, while for the rest we rely on ALOS PALSAR data. We calculated profiles of water level change across hydrological transects showing high coherence and visualized them in maps. For instance, in the case of the Baiyangdian wetland, we find that of the 70 transects studied, 11% of all transects are permanently disconnected by hydrological barriers across all interferograms and 58% of the transects are conditionally disconnected. The occurrence of hydrological barriers varies between wetlands, with permanent barriers more related to ditches, infrastructure and the specific wetland landscape, and conditional barriers more to low water levels during dry seasons. This study highlights the potential of the application of wetland InSAR to determine hydrological barriers for wetland management and restoration.

How to cite: Jaramillo, F., Liu, D., Aminjafari, S., and Wang, X.: Determining hydrological barriers in wetlands with InSAR methods: several iconic cases worldwide, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14620, https://doi.org/10.5194/egusphere-egu21-14620, 2021.

Instrument Processing
14:16–14:18
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EGU21-4129
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Simon Boitard, Sophie Le Gac, Denis Blumstein, Eric Munesa, François Boy, Eric Jeansou, Mathilde Cancet, Léo Grignon, Nicolas Picot, and Pierre Féménias

Fresh water is an essential resource that requires a close monitoring and a constant preservation effort. The evolution of hydrological bodies water level constitutes a key indicator on the available quantity of fresh water in a given region. The limited extent of the in situ networks currently deployed has generated a growing interest in using space borne altimetry as a complementary data source to increase the coverage of emerged fresh water stocks and ensure a more global and continuous monitoring of their water surface height.

A great effort has been carried out over the past decade to improve altimeters’ capability to acquire quality measurements over inland waters. In particular, the Open-Loop Tracking Command (OLTC), which consists in calibrating the altimeter signal acquisition window with a prior information on the overflown hydrological surface height, represents a major evolution of the tracking function. This tracking mode’s efficiency is such that it is now stated as operational mode for current Sentinel-3 and Jason-3 missions as well as the recently launched Sentinel-6A mission. The improvements brought to onboard tables contents in 2017 (Jason-3), 2018 (Sentinel-3B) and 2019 (Sentinel-3A) enhanced and confirmed the OLTC performances.

In 2020, the onboard OLTC tables of the Jason-3, Sentinel-3A and Sentinel-3B missions have benefitted from further new major upgrades. The first version of the Sentinel-6A onboard OLTC tables holds the same content as Jason-3. The tracking command defined over Jason-3 and Sentinel-6A repeat cycle now accounts for more than 30,000 hydrological targets which represents five times more targets than in the previous version. For each Sentinel-3, the number of water body surface heights coded into the OLTC has been increased by a factor of 3 to 70,000. This further major step is made possible by the analysis and merging of the most recent digital elevation models (SRTM, MERIT and ALOS/PalSAR) and water bodies databases (HydroLakes, GRaND v1.3, SWBD, GSW). This methodology ensures coherency and consistent standards between all nadir altimetry missions and types of hydrological targets.

A detailed description of the 2020 upgrades will be given as well as measurements validation results obtained since their upload. An overview of the global validation of Sentinel-6A measurements over hydrological targets will also be presented.

These 2020 OLTC upgrades constitute a great asset for building a valuable and continuous record of the water surface height of worldwide lakes, rivers, reservoirs and wetlands. In addition, for a continuous improvement of the OLTC tracking mode, the users can check the content of the onboard OLTC tables over hydrological targets for both Sentinel-3 missions on the https://www.altimetry-hydro.eu/ web portal. When relevant, they can correct existing water surface heights or submit new targets.

How to cite: Boitard, S., Le Gac, S., Blumstein, D., Munesa, E., Boy, F., Jeansou, E., Cancet, M., Grignon, L., Picot, N., and Féménias, P.: New upgrades of Open-Loop Tracking Command (OLTC) tables of nadir altimeters in 2020 and benefits for inland waters users, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4129, https://doi.org/10.5194/egusphere-egu21-4129, 2021.

14:18–14:20
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EGU21-12480
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Jérôme Benveniste, Salvatore Dinardo, Christopher Buchhaupt, Michele Scagliola, Marcello Passaro, Luciana Fenoglio-Marc, Giovanni Sabatino, Américo Ambrózio, and Marco Restano

The scope of this presentation is to feature and provide an update on the ESA G-POD/SARvatore family of altimetry services portfolio for the exploitation of CryoSat-2 and Sentinel-3 data from L1A (FBR) data products up to SAR/SARin Level-2 geophysical data products. At present, the following on-line & on-demand services compose the portfolio:

-       The SARvatore (SAR Versatile Altimetric TOolkit for Research & Exploitation) for CryoSat-2 and Sentinel-3 services developed by the Altimetry Team in the R&D division at ESA-ESRIN. These processor prototypes are versatile and allow the users to customize and adapt the processing at L1b & L2 according to their specific requirements by setting a list of configurable options. The scope is to provide users with specific processing options not available in the operational processing chains (e.g. range walk correction, stack sub-setting, extended receiving window, zero padding, high-posting rate and burst weighting at L1b & SAMOSA+, SAMOSA++ and ALES+ SAR retrackers at L2). AJoin & Share Forum (https://wiki.services.eoportal.org/tiki-custom_home.php) allows users to post questions and report issues. A data repository is also available to the Community to avoid the redundant reprocessing of already processed data (https://wiki.services.eoportal.org/tiki-index.php?page=SARvatore+Data+Repository&highlight=repository).

-       The TUDaBo SAR-RDSAR (Technical University Darmstadt – University Bonn SAR-Reduced SAR) for CryoSat-2 and Sentinel-3 service. It allows users to generate reduced SAR, unfocused SAR & LRMC data. Several configurable L1b & L2 processing options and retrackers (BMLE3, SINC2, TALES, SINCS) are available. The processor will be extended during an additional activity related to the ESA HYDROCOASTAL Project (https://www.satoc.eu/projects/hydrocoastal/) to account in the open ocean for the vertical motion of the wave particles (VMWP) in unfocused SAR and in a simplified form of the fully focused SAR called here Low Resolution Range Cell Migration Correction-Focused (LRMC-F).  

-       The ALES+ SAR for CryoSat-2 and Sentinel-3 service. It allows users to process official L1b data and produces L2 NetCDF products by applying the empirical ALES+ SAR subwaveform retracker, including a dedicated SSB solution, developed by the Technische Universität München in the frame of the ESA Sea Level CCI (http://www.esa-sealevel-cci.org/) & BALTIC+ SEAL Projects (http://balticseal.eu/).

-       The Aresys Fully Focused SAR for CryoSat-2 service. Currently under development, it will provide the capability to produce CS-2 FF-SAR L1b products thanks to the Aresys 2D transformed frequency domain AREALT-FF1 processor prototype. Output products will also include geophysical corrections and threshold peak & ALES-like subwaveform retracker estimates.

The G-POD graphical interface allows users to select, in all the services, a geographical area of interest within the time-frame related to the L1A (FBR) & L1b data products availability in the service catalogue.  

After the task submission, users can follow, in real time, the status of the processing. The output data products are generated in standard NetCDF format, therefore being compatible with the multi-mission “Broadview Radar Altimetry Toolbox” (BRAT, http://www.altimetry.info) and typical tools.

Services are open, free of charge (supported by ESA) for worldwide scientific applications and available, after registration and activation (to be requested for each chosen service to eo-gpod@esa.int), at https://gpod.eo.esa.int.

How to cite: Benveniste, J., Dinardo, S., Buchhaupt, C., Scagliola, M., Passaro, M., Fenoglio-Marc, L., Sabatino, G., Ambrózio, A., and Restano, M.: SAR, SARin, RDSAR and FF-SAR Altimetry Processing on Demand for CryoSat-2 and Sentinel-3 at ESA G-POD, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12480, https://doi.org/10.5194/egusphere-egu21-12480, 2021.

Meet the authors in their breakout text chats... (Convener's advice: Offer your own videoconference room link in the chat for better interactivity...)
14:20–15:00