Remote sensing of Earth’s surface water is crucial to the study of climate change and its impact to society.  Radar remote sensing is particularly important because it penetrates cloud cover, providing observations under all weather conditions.  Forty years ago, Seasat, the first satellite designed for studying the ocean from space, laid the foundation of radar remote sensing of the ocean with radar altimeter, scatterometer, and synthetic aperture radar (SAR). The first two have become the pillars of a global observing system that has revolutionized oceanography. Precise measurement of sea surface height by radar altimetry has provided a modern record of global sea level change and the state of ocean circulation, but its spatial resolution is limited by the large radar footprint (~20 km) and measurement noise, making it difficult to study small-scale, rapidly changing ocean processes, especially near coasts.

While SAR provides high-resolution images of many features of the ocean and land waters, it is difficult to derive quantitative information to study the underlying dynamics. Using the phase differences of consecutive SAR observations (a technique called radar interferometry) has allowed determination of the slow movement of ice sheets since the early 1990s. In the early 2000s, a mission was conducted onboard the Space Shuttle to map the earth’s land topography. The concept of applying radar interferometry onboard a satellite for oceanography and land hydrology was developed in the 2000s. Twenty years later the global mission called Surface Water and Ocean Topography (SWOT) was launched in December 2022.

We will present early results from SWOT with a focus on the ocean. The fundamental advancement of SWOT is the capability of observing the elevation of the ocean surface and with the resolution of SAR.  The spatial resolution of the resolved ocean dynamics more than an order of magnitude better than in conventional altimetry, enabling the study of small-scale ocean eddies and fronts that are essential to the ocean’s heat and carbon uptake from the atmosphere. The increased resolution will also advance the study of near shore processes to assess the coastal impact of sea level rise and severe weather.

How to cite: Fu, L.-L., Morrow, R., Farrar, J. T., and Wang, J.: A breakthrough of radar remote sensing of the ocean: the  Surface Water and Ocean Topography (SWOT) Mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12599, https://doi.org/10.5194/egusphere-egu24-12599, 2024.

The Surface Water and Ocean Topography (SWOT) mission is primarily designed to measure Sea Surface Height in two dimensions at an unprecedented resolution thanks to its innovative Ka-band radar interferometer KaRIn. In addition to the topography measurements derived from the phase difference between the images acquired at each of the two antennas separated by 10 meters, KaRIn can also provide information about the sea state, by exploiting the measured power in each of the SAR images and the interferometric correlation between both acquisition channels.

This last quantity, sometimes referred to as interferometric coherence, is directly affected by the presence of surface waves. This provides a fantastic opportunity to measure, for the first time at a global scale, Significant Wave Height at kilometric resolutions (well below the reach of nadir altimeters) and in two dimensions. This, however, requires estimating all other sources of decorrelation of instrumental origin with an exquisite precision to avoid misinterpreting instrumental effects as geophysical signals.

In this talk, I will briefly describe how the interferometric acquisitions by KaRIn are calibrated and processed to obtain SWH maps in 2D at various km-scale resolutions (typically 2x2 km or 5x5 km), and discuss how the accuracy at which we need to estimate all the other sources of decorrelation varies with cross-track distance and actual SWH to highlight the most challenging regimes for the inversion. I will then present comparisons between the KaRIn two-dimensional SWH measurements and several independent sets of validation data, including data from SWOT’s nadir altimeter, from the SAR nadir altimeter on-board Sentinel-3, from MASS’s lidar, and from in-situ data. I will finish by discussing various physical features that can be observed in the retrieved SWH fields to illustrate that the high resolution and the two-dimensional character of SWOT measurements really open the door to the quantitative study of the processes that contribute to sea-state variations at small scales.

How to cite: Bohe, A., Chen, A., Chen, C., Dibarboure, G., Dubois, P., Fore, A., Hajj, G., Legresy, B., Lenain, L., Molero, B., Peral, E., Raynal, M., and Stiles, B.: Measuring Significant Wave Height fields in two dimensions at kilometric scales with SWOT, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10457, https://doi.org/10.5194/egusphere-egu24-10457, 2024.

The routine measurement of sea ice, an essential climate variable, is urgently needed for improving seasonal sea ice forecasting and tracking ocean-ice-atmosphere interactions. Over the last few decades, ocean remote sensing techniques have revealed significant and rapid declines in both the extent and volume of Arctic sea ice, driven by accelerated warming at high northern latitudes. The Surface Water Ocean Topography (SWOT) mission delivers innovative wide-swath Ka-band synthetic aperture radar (SAR) interferometry and coincident Ku-band altimetry and provides, for the first time, swath mapping of sea ice from a space-based system. The novel SWOT technology can be exploited to advance knowledge of sea ice processes and properties. Although SWOT’s latitudinal limit of coverage is 78° N, this is nevertheless sufficient for mapping the seasonal sea ice zone in the Arctic which develops, grows and deforms in winter and typically reaches a maximum in the month of April. SWOT can obtain measurements across ~9-10 million square kilometers of Arctic sea ice in April. It's high-resolution swath-mapping approach captures sea ice surface topography in two dimensions, both along- and across-track. This new capability allows us to determine the areal fraction and shape of individual sea ice floes, map the 2D structure of leads, identify the ice edge location in higher fidelity than has heretofore been possible, and simultaneously measure sea ice height, from which sea ice freeboard and hence thickness may be derived. Here we show the results of our initial assessment of SWOT data collected during the 1-day fast repeat orbit phase. This particular sampling strategy allows us to track individual sea ice floes and derive high resolution estimates of ice drift velocity. SWOT backscatter signatures over sea ice are also used to discriminate between rough sea ice floes and smooth, specular  leads. We evaluate SWOT backscatter using high-resolution measurements of sea ice roughness derived from spatially-coincident ICESat-2 laser altimetry data.  We also show the feasibility of using the 2D swath-mapping capabilities of SWOT in concert with ICESat-2 sea ice height profiles to map the joint floe size-ice thickness distribution. Our results demonstrate the many benefits of swath mapping altimetry for polar sea ice studies.

How to cite: Farrell, S. L., Fischer, R., Duncan, K., Yi, D., Kuhn, J. M., Leuliette, E., and Connor, L.: Early Assessment of SWOT’s Swath-mapping Capabilities over Arctic Sea Ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13614, https://doi.org/10.5194/egusphere-egu24-13614, 2024.

The SWOT satellite measures sea surface height at an unprecedented resolution about ten times better than conventional altimetry products. SWOT data offer a unique opportunity of observing very fine-scale (~few km) surface dynamics from space. In situ samplings, aside from complementing the 2D picture, also provide a 3D view of the observed fine scale dynamics essential for interpretation of bio-physical interaction processes. Nevertheless, exploring this regime during field experiments remains challenging due to the difficulty to precisely locate fine-scale features in real time. A shift of a few km may not be of critical importance when sampling a large structure such as an eddy with a radius of about 100 km. However a similar sampling error could obviously lead to severe misinterpretations in the case of a 10 to 20 km wide eddy. The problem is even exacerbated by the fact that the lifetime typically decreases with the size of eddies and filaments. One way to address this problem with field experiments at the SWOT scales is therefore to update and adapt the sampling location and shape, with synoptic near-real time information of the sea state provided by available high resolution remote sensing (SST and Chlorophyll), and analysis of altimetry and model assimilation. Although vulnerable to cloud coverage and/or limited in resolution, this information can be complemented by near-real time Lagrangian analysis of the surface geostrophic fields providing finer diagnostics of the sampling site dynamics. Early SWOT data also filled some gaps in terms of parameters and spatiotemporal coverage. By using the BIOSWOT-Med cruise as an example, here we review the tools offered by the SWOT AdAC Consortium to the field experiments that have been deployed during the SWOT fast-sampling phase (March-June 2023). After evaluating synergies and shortcomings with in situ platforms, we will discuss how adaptive sampling strategies may evolve in the future to assist field experiments during the SWOT Science phase.

How to cite: Rousselet, L., Doglioli, A., Petrenko, A., Barrillon, S., Berta, M., Bosse, A., Berline, L., Fuda, J.-L., Rolland, R., Bouruet-Aubertot, P., Gastauer, S., Grégori, G., and d'Ovidio, F.: Adapting in situ sampling strategies to SWOT-scale studies: The BioSWOT-Med campaign example as part of the SWOTAdopt-a-Crossover Consortium, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7789, https://doi.org/10.5194/egusphere-egu24-7789, 2024.

The field experiment C-SWOT-2023 was carried out in North-Western Mediterranean Sea and aimed to support the new-generation SWOT altimeter (NASA/CNES) calibration and validation during its fast sampling phase. The daily overflight of the satellite between Marseille and Menorca was the opportunity to revisit the main aspects of the ocean circulation in the North-Western Mediterranean sub-basin such as the North Current, the Balearic Front or the eddy soup in the winter convection area.  The originality of the field experiment lies in the deployment of two research vessels (the R/V Thetys II for IFREMER and the R/V Atalante for the SHOM) that sailed along together to explore statistics of the surface ocean dynamics (vorticity, strain, divergence) that are seldomly accessible in fine scale observations. High resolution transects recording velocities, temperature and salinity in the first four hundred meters under the SWOT swaths were performed in order to disentangle the geostrophic and the ageostrophic part of the circulation. Dozens of drifting buoys have been dropped to assess the lagrangian aspect of the dynamics. A short overview of the 3D observations dataset will be proposed before focusing on the comparison between the dynamics experienced in situ and those observed remotely by SWOT.

How to cite: Garreau, P., Dumas, F., Ponte, A., Garnier, V., Pairaud, I., Ndiaye, K. S., and Demol, M.: C-SWOT2023: a Mediterranean intensive field experiment in the framework of the SWOT fast sampling phase, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10813, https://doi.org/10.5194/egusphere-egu24-10813, 2024.

The BioSWOT-Med cruise focused on the Western Mediterranean Sea, known for its rich plankton biodiversity under oligotrophic and moderate energy conditions. The cruise aimed to investigate the role of fine-scale circulation as a driver of plankton diversity, coinciding with the SWOT satellite's daily "fast-sampling" orbit over the same region. SWOT, with its high-resolution 2D observations of sea surface height at 15-120km spatial scale, offered a unique perspective on ocean dynamics.
Mesoscale and submesoscale currents play a crucial role in ocean-atmosphere interaction and marine biosphere processes. The SeaSTAR satellite mission concept (former ESA Earth Explorer 11 candidate at phase 0), is designed to observe small-scale ocean surface dynamics with a remarkable 1 km resolution, contributing to our understanding of carbon, water, energy, gases, and nutrient exchanges across various Earth systems.
To prepare for the SeaSTAR mission, the OSCAR (Ocean Surface Current Airborne Radar) airborne instrument was developed, providing a synoptic 2D view of ocean and atmosphere dynamics, including currents, waves, and winds, at fine scale. During the SEASTARex campaign in May 2022 over the Iroise Sea in Brittany, France, OSCAR demonstrated excellent performance against various measurements, including marine radar, ADCP, and HF radar.
Building on OSCAR's success, a campaign was organized in May 2023, coinciding with the Bio-SWOT campaign, to fly together with SWOT over a non-tidal dominated area, mapping small-scale dynamics. Satellite SAR images from various sources, including RCM, TerraSAR-X, Sentinel-1, RadarSat-2, and PAZ SAR, were collected for comparative analysis with OSCAR and SWOT data.
Initial comparisons between OSCAR and satellite data, spanning remote sensing instruments like SWOT, SAR imagers, and optical sensors, showed a high level of agreement. SWOT data, analyzed with a diverse dataset, promises to enhance understanding and characterization of dynamics observed in the new 2D images.
OSCAR's Doppler and scatterometry capabilities offer a fresh perspective on dynamic processes, particularly at fine scales, bridging the gap between in-situ point measurements and space-based sensors. The ongoing synergy between OSCAR and satellite data holds potential to advance our understanding of oceanic and atmospheric phenomena, addressing critical challenges related to climate, weather, and marine ecosystems.

How to cite: Martin, A., Lemerle, E., Mccann, D., Macedo, K., Andrievskaia, D., Gommenginger, C., and Casal, T.: Towards mapping total currents and winds during the BioSWOT-Med campaign with the OSCAR airborne instrument, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16040, https://doi.org/10.5194/egusphere-egu24-16040, 2024.

During the SWOT fast sampling phase in spring 2023, the BioSWOTMed cruise (https://doi.org/10.17600/18002392) sampled for four weeks a front located on both the western and eastern swaths of the 003 SWOT pass, about 100 km northeast of Menorca, in the Western Mediterranean Sea. The front coincided to a portion of the north Balearic front. The front was modulated by the presence of eddies of small Rossby radius (of the order of 20-30km), not visible in conventional altimetry maps. The availability of cloud-free images of ocean color (OLCI) for five consecutive days also revealed the presence of various submesoscale structures and part of their life cycle. The front consisted of a strong roughly eastward meandering jet, separating cold, salty and more productive waters (modified Atlantic Water) in the north from warm, fresher and more oligotrophic waters (younger Atlantic Water) in the south. In addition to classical hydrological, glider, drifters/floats and moving vessel profiler (MVP) measurements, 3D oceanic velocities were measured by 3 ship-mounted acoustic Doppler current profilers (ADCPs), 2 lowered-ADCPs, 1 free-falling newer generation 5-beam ADCP and 2 autonomous vertical velocity profilers. The jet had horizontal velocities up to ~0.35 m.s^-1 (0-300 m average), with a cross-jet distance of ~40 km and a vertical extension of 200 m. 1m-surface drifters deployed in the core of the jet traveled at a speed of ~0.5 m.s^-1. Two northerly storms generated intense near-inertial waves interacting in the mesoscale field of several eddies sampled by the ship. Cyclogeostrophic velocities derived from SWOT are in good agreement with the measured ADCP (horizontal) velocities. The normalized relative vorticity provides a regional view of the complex oceanic circulation of the jet meandering between various mesoscale eddies and interacting with submesoscale structures. The high variability of vertical velocities (+/- 1.5 cm.s^-1) of various origins masks the expected cross-frontal ageostrophic circulation. The finescale 3D circulations observed and well captured at the surface by SWOT are also associated with complex biological content distribution.

How to cite: Petrenko, A. A., Arnaud, M., Barrillon, S., Comby, C., Fuda, J.-L., Berline, L., Bosse, A., Rousselet, L., Rolland, R., Bouruet-Aubertot, P., Oms, L., Demol, M., Didry, M., Gastauer, S., Pacciaroni, M., Berta, M., d'Ovidio, F., Gregori, G., and Doglioli, A.: Complex 3-D oceanic velocities at SWOT scales exhibited during the spring 2023 BioSWOTMed cruise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17343, https://doi.org/10.5194/egusphere-egu24-17343, 2024.

Studying ocean tides from satellite altimetry has traditionally been difficult in coastal regions, mainly due to the complexity of tides in these regions, limited spatial coverage, and land contamination of the radar returns. The Cal/Val phase and the science orbit phase of SWOT provide unique observations which can be exploited for tidal analysis. The nadir data provided by this mission complements other traditional altimetry missions and will serve the refinement of global ocean tide models well in future studies. The KaRIn data, however, is beneficial for evaluating the spatial variability of ocean tides at much smaller scales than previously possible from altimetry or in-situ measurements. In addition, areas very close to the shoreline can also be monitored. Analysing tides in complex coastal regions, such as fjords and inlets, is now also possible thanks to the increased spatial coverage of SWOT. 

This presentation evaluates the pixel cloud data of the hydrological product and the ocean product provided by SWOT in three regions. These regions are selected to provide examples of the usefulness of these data in very complex environments. The regions are as follows:

• The Bristol Channel, on the west coast of the UK.
• The Sognefjord along the west coast of Norway.
• The Long Island Sound on the east coast of the USA.

These regions have relatively large tidal ranges and have been challenging for conventional altimetry, resulting in reduced accuracy in available ocean tide models. These regions are also well covered by in-situ measurements and are either covered by the Cal/Val phase or the nominal orbit of the SWOT mission. The resultant estimations will be contrasted with in-situ measurements and state-of-the-art global models.

How to cite: Hart-Davis, M., Schwatke, C., Andersen, O., Ray, R., Zaron, E., Bonaduce, A., Borck, H. S., and Dettmering, D.: Ocean tides from SWOT: insights in complex coastal regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1629, https://doi.org/10.5194/egusphere-egu24-1629, 2024.

Coastal-to-land sites are mostly affected by climate changes and are at multi-risks due to coastline retreat, flooding storms and river floods. New altimeter processing and new missions open new possibilities to observe fine-scale spatial changes in this region. Our hypothesis is that new altimetry remote sensing observations from the Delay Doppler nadir-altimetry and wide swath altimetry can make an unprecedented progress at monitoring the river-to-ocean continuum and understanding estuarine and coastal hydrodynamic processes.

Aim of this study is the interaction between river discharge and coastal sea level in the Elbe estuary and tidal river. Region of analysis are the German coasts and Elbe estuary and tidal river. This last is under the SWOT cal/val track. SWOT’s unique, high-resolution 2D observations, combined with the field campaign data, other satellite data and models, is expected to provide a new view of many dynamical phenomena from ocean and nearshore zones to coastal and estuarine contexts.

We consider the Fully-Focus (FF-SAR) processing near coast. We show that results depend on the retracking method and that land contamination is also affecting FF-SAR. The  SAMOSA+ retracker gives the best results for both FFSAR and unfocused SAR (USAR).

The ability of regional ocean models to reproduce tides and the high variability at fine spatial-scale is investigated. Ocean simulation sea level is compared to nadir-altimetry along the satellite ground tracks. We show that while the coverage of nadir-altimeter is limited by the number of ground-tracks, SWOT, that provides a uniform coverage, is less affected by land contamination. We investigate the SWOT mission data. First results with low resolution 2 km x 2 km data indicate good agreement with in-situ gauges with 20-30 cm standard deviation from in-situ tide gauge stations. SWOT enhanced resolution data at 250m x 250m and higher resolution data are further investigated to more accurately monitor nearshore, estuarine, and the sea-ice interface. Due to the differences between along-track and swath-altimetry, new methods to derive accuracy and precision of the measurements and derived ocean parameters are developed. Using a large network of in-situ, model and nadir-altimetry data we perform the calibration and the validation of the SWOT products assessing the relevance of SWOT for improving numerical models over all the Elbe tidal river.

We would be interested in submitting our presentation to a peer reviewed special issue in Ocean Sciences.

How to cite: Fenoglio-Marc, L.: Monitoring the Elbe estuary and coastal zone with SWOT and nadir-altimeters , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14849, https://doi.org/10.5194/egusphere-egu24-14849, 2024.

Improving our understanding and ability to represent surface oceanic dynamics is crucial for the study and forecast of the climate system, as it modulates air-sea interactions and marine ecosystem. 

The recently launched SWOT altimetric satellite is providing a 2D highly resolved vision of sea level (down to submesoscales) and may thus offer a brand new view on upper ocean circulation.

If geostrophy has historically allowed a global estimation of mesoscale and larger ocean surface circulation from classical altimetry, it is jeopardized at the scales resolved by SWOT by contributions from higher frequency processes such as internal tides, near-inertial waves and wind effect.

Drifters trajectories, which provide a high frequency  'ground-truth’ estimate of the upper ocean circulation and wind reanalysis products are thus highly complementary to altimetry to reconstruct surface ocean dynamic. 

The horizontal surface momentum conservation is here reconstructed from historical altimetric data, drifters derived currents (Global Drifter Program) and atmospheric reanalysis products. We will present our ability at closing upper ocean momentum balance globally and quantify contributions from different terms involved (inertial acceleration, coriolis acceleration, pressure gradient and wind stress vertical divergence). This will allow to qualify and map the dominant dynamical balances, revealing the limit of geostrophy and the dominance of inertial balance in some areas. An error budget is also estimated. 

How to cite: Demol, M., Garreau, P., and Ponte, A.: Reconstructing ocean surface momentum conservation from altimetry, drifters and wind reanalysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3501, https://doi.org/10.5194/egusphere-egu24-3501, 2024.

The Surface Water and Ocean Topography (SWOT) mission offers two-dimensional measurements of Sea Surface Height (SSH), capturing scales of a few tens of kilometers and enabling the study of previously unobserved short mesoscale dynamical structures. However, the mission faces technical challenges in maximizing scientific benefits, particularly during the science phase with its 21-day repeat orbit, which limits observations of small-scale structure evolution over time.

To address the challenge of high spatial and low temporal samplings, we propose an original dynamic interpolation scheme that we call 4Dvar-QG. This innovative method combines a weakly constrained, reduced-order, 4-dimensional variational scheme with a quasi-geostrophic model. The weak constraint of the quasi-geostrophic model on the inversion procedure ensures that the estimated maps closely match the observations while preserving the space-time continuity of the reconstructed structures.

The 4Dvar-QG method is applied in the North Atlantic Ocean on a constellation of real conventional altimeters and SWOT, during both the SWOT’s fast sampling and science phases. Performance evaluations are conducted through Observing System Experiments, utilizing independent data (such as altimetric and drifter data) as ground truth and comparing results to operational products like the Multiscale Interpolation Ocean Science Topography product (MIOST). The 4Dvar-QG method significantly improves the mapping of short energetic structures, reducing the root mean square error by up to 50% and increasing the effective resolutions by up to 30% compared to MIOST, while maintaining good reconstruction of large-scale and/or low energetic structures.

How to cite: Ubelmann, C., Le Guillou, F., Ballarotta, M., Cosme, E., Metref, S., and Rio, M.-H.: Dynamical mapping of SWOT: performances from real observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10460, https://doi.org/10.5194/egusphere-egu24-10460, 2024.

Accessing vertical velocities and heat fluxes globally represents today a major gap in our understanding of the 3D ocean dynamics. SWOT is showing a great advance, namely a sea level resolution up to ten times better than traditional nadir-looking altimeters, allowing for the observation of fine-scale ocean dynamics. Mesoscale dynamics account for 80% of the total kinetic energy in the ocean and smaller mesoscales and sub-mesoscales contribute 50% of the total vertical velocity variance in the upper ocean. In this work, we explore the potential of using SWOT 2D surface topography data to reconstruct vertical velocities and vertical heat fluxes below the Southern Ocean mixed layer using surface Quasi-Geostrophic (sQG) theory for the vertical projection. The upper ocean 3D circulation is calculated from SWOT’s science phase 2D sea surface height (SSH) observations and validated with multi-sourced in-situ data (high-resolution XBT and CTD sections from the SURVOSTRAL and ACC-SMST SWOT CalVal campaigns in the Southern Ocean south of Tasmania). The performance of the SQG methodology, in terms of spatial and temporal correlation, is first assessed using the COAS coupled ocean-atmosphere simulation,  and we find that the SQG reproduces both the spatial distribution and the overall regional variability of the mesoscale structures below the Southern Ocean mixed layer. We then apply the SQG methodology to a high-resolution SSH regional mapping of 3 to 5 days of SWOT science phase data to obtain reconstructed vertical velocities and vertical heat fluxes. The results are validated over the in-situ XBT and CTD data collected in the same time period. The observable structures, resolved dynamics and errors involved in this fine-scale reconstruction are discussed.

How to cite: Carli, E., Siegelman, L., Morrow, R., Legresy, B., and Vergara, O.: Reconstructing vertical velocities and heat fluxes in the Southern Ocean from SWOT SSH fields, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6805, https://doi.org/10.5194/egusphere-egu24-6805, 2024.

Observations from satellite altimeters are essential to mapping the marine gravity field and bathymetry. As most of the ocean basins are yet to be mapped by sonar, obtaining reliable data of sea surface height and sea surface slopes is key to improving our understanding of the marine gravity field and bathymetry. Improvement in altimeter systems has enabled the marine gravity field to be determined to a few mGal, however with conventional satellite altimetry, improvements are challenging.

The major challenge is the sampling geometry of conventional satellite altimeters, with along-track (majorly north-south) sea surface slopes being much better determined than across-track slopes (east-west). With the KaRIn instrument on the Surface Water and Ocean Topography (SWOT) satellite, swath-altimetry with 2-dimensional observations of the sea surface height is possible. From these observations, the directional sea surface slopes in both along-track and across-track can be determined. However, determining the resolution and precision with which the sea surface slope is determined, is of fundamental importance for the improvement of the mapping of the marine gravity field.

We present directional sea surface slopes associated with a major seamount using SWOT L2 data and with a minor seamount using SWOT pixel-cloud data, demonstrating the quantum leap forward possible with SWOT. With three parallel beams, ICESat-2 is another satellite that can determine the east-west sea surface slope. From observing the difference in sea surface height between beams, we can determine the directional sea surface slopes in north-south and east-west components, with auspicious results. With data from ICESat-2, we aim to validate the SWOT directional sea surface slopes at cross-overs between SWOT and ICESat-2 and determine the relative initial performance.

How to cite: Nilsson, B., Andersen, O. B., and Arildsen, R. L.: Mapping directional sea surface slopes associated with seamounts from SWOT and validation with ICESat-2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6062, https://doi.org/10.5194/egusphere-egu24-6062, 2024.

Disentangling balanced eddy and unbalanced wave motions from the oceanic Sea Surface Height (SSH) fields, is a complex problem made even more challenging due to their non-linear interactions. The high resolution SSH snapshots from the recently launched Surface Water and Ocean Topography (SWOT) program will include scales down to O(10) km and resolve internal gravity waves (IGWs). At these scales the IGW signatures co-existing with those of the balanced motions pose two major challenges: (i) disentangling IGWs from balanced motions at the ocean surface, a regime with small scale separation and Rossby number near unity, and (ii) detecting IGW signals from two-dimensional snapshots. Here we address these challenges by using state-of-art flow decomposition methods combined with machine learning (ML) for a range of flow regimes.

The currently available flow decomposition methods rely on three-dimensional flow fields and methods to separate these motions from two-dimensional snapshots are currently non-existent. Here we develop a novel method using supervised ML to extract IGWs from snapshots of a flow field and apply it to SWOT SHH field. The initial training and testing is done using Convolution Neural Network algorithms, often used for instance in image classification and pattern recognition problems. The neural network (NN) is trained to detect IGWs in different dynamical regimes based on the decomposition outputs of velocities and model-derived SSH fields from a suite of idealised ocean models outputs of rotating stratified flows with different flow decomposition methods: Higher order decomposition (Eden et al., 2019; Chouksey et al., 2022), Optimal Balance (Masur et al., 2020; Chouksey et al., 2023), and Time Averaged Optimal Balance (Rosenau et al., 2023). The trained NN predicts the flow components from SSH fields generated by the SWOT-simulator and SWOT observations. Analysis using TensorFlow in a shallow water model shows promising results in the prediction of balanced and unbalanced motions by the trained NN. This novel ML-based flow decomposition method is the first of its kind and will provide support for the retrieval of IGW signatures to the SWOT community. 

How to cite: Chouksey, M. and Brecht, R.: Detection of internal waves from oceanic SHH field using neural-network based flow decomposition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19694, https://doi.org/10.5194/egusphere-egu24-19694, 2024.