Abstract's details
Sentinel-3 Next Generation Topography Mission Performance and Uncertainty Assessment (S3NGT-MPUA)
Event: 2025 SWOT Science Team Meeting
Session: Hydrology: Open Science & Applications
Presentation type: Poster
The Sentinel-3 Next Generation Topography (S3NGT) mission is designed to ensure the continuity of the existing Copernicus Sentinel-3 nadir-altimeter measurements from 2030 to 2050 while also improving measurement capabilities and performance. This mission consists of two large spacecrafts equipped with an across-track interferometer swath altimeter (SAOOH), a synthetic aperture radar (SAR) nadir altimeter (Poseidon-5 (POS-5)), a multi-channel microwave radiometer, and a precise orbit determination suite. The SAOOH instrument builds upon the swath altimetry advancements pioneered by the Surface Water and Ocean Topography (SWOT) mission, launched in December 2022 with the KaRIn instrument. However, the SAOOH instrument differs from KaRIn in several key aspects, including a shorter baseline (3 m instead of 10 m) and a different Signal-to-Noise-Ratio (SNR) of the antenna compared to SWOT/KaRIn's. Given these differences, it is imperative to pay utmost attention to the performance of the S3NGT mission before its launch to ensure its success.
The ESA-supported S3NGT preliminary mission performance and uncertainty assessment (S3NGT-MPUA) study is ongoing. In this study, we have made significant progress since its initiation in May 2023. Here, we outline the key achievements for each objective of this project.
The first objective of the study is to conduct a preliminary assessment of the performance of S3NGT Level-2 products before the mission's launch. This assessment focuses on ocean surfaces and inland waters. To achieve this, we first developed a strategy to generate S3NGT-like data. For ocean surfaces, we employed a strategy that utilized inflight data from the SWOT mission (level-3 products) to create a first dataset and an Ocean General Circulation Model (OGCM) to simulate S3NGT-like data for a second dataset. We introduced S3NGT-specific instrumental uncertainties into the OGCM data and SWOT inflight level-3 data using a scientific simulator developed by ODL. These two complementary approaches provide respectively lower and upper bounds of S3NGT performances. Additionally, we evaluated the behavior of swath measurements for high sea state conditions by degrading SWOT Level-1B data with instrumental characteristics that are similar to SAOOH ones. For inland waters, we developed a similar strategy to generate S3NGT-like data from SWOT L2 Pixel cloud products, incorporating specific S3NGT uncertainties. All these three SWOT-derived datasets are examples of applications of SWOT data and help gain knowledge in swath altimetry. This activity also included defining key metrics to describe the mission’s performance for several variables including sea surface height, sea state, systematic errors, and inland water surface elevation. We evaluated these metrics with our generated S3NGT-like data and compared these results to the S3NGT Mission Requirements Document (MRD). This approach provides valuable insights into the expected capabilities of S3NGT products and highlights areas where the mission design can be refined to meet operational requirements.
The second study objective is to develop a comprehensive uncertainty model and budget following established metrological principles. The first part entails a metrological assessment of the S3NGT mission, while the second part focuses on verifying and validating the S3NGT uncertainty budget. This has involved creating a clear metrological traceability diagram representing the Swath altimeter and using this to identify (and later quantify) individual sources of uncertainty.
The third study objective is to evaluate options for in-orbit calibration of the S3NG-TOPO mission. This includes methods such as using orbit crossovers to correct for known systematic errors in water elevation over the ocean and inland water bodies. The evaluation must consider the different latencies of the S3NG-TOPO products. Indeed, given the stricter latency requirements for the S3NG-TOPO mission than for SWOT, the number of available orbit crossovers for cross-calibration measurements is limited.
The final study objective is to assess the uncertainty in cross-calibrating S3NG-TOPO with the current S3 constellation and reference mission (S6) using established or innovative methods. The primary goal is to ensure the continuity of S3NGT measurements, including an effective cross-calibration between the current S3 constellation and the future S3NG-TOPO constellation, particularly for the nadir altimeter system incorporating the microwave radiometer (MWR).
The ESA-supported S3NGT preliminary mission performance and uncertainty assessment (S3NGT-MPUA) study is ongoing. In this study, we have made significant progress since its initiation in May 2023. Here, we outline the key achievements for each objective of this project.
The first objective of the study is to conduct a preliminary assessment of the performance of S3NGT Level-2 products before the mission's launch. This assessment focuses on ocean surfaces and inland waters. To achieve this, we first developed a strategy to generate S3NGT-like data. For ocean surfaces, we employed a strategy that utilized inflight data from the SWOT mission (level-3 products) to create a first dataset and an Ocean General Circulation Model (OGCM) to simulate S3NGT-like data for a second dataset. We introduced S3NGT-specific instrumental uncertainties into the OGCM data and SWOT inflight level-3 data using a scientific simulator developed by ODL. These two complementary approaches provide respectively lower and upper bounds of S3NGT performances. Additionally, we evaluated the behavior of swath measurements for high sea state conditions by degrading SWOT Level-1B data with instrumental characteristics that are similar to SAOOH ones. For inland waters, we developed a similar strategy to generate S3NGT-like data from SWOT L2 Pixel cloud products, incorporating specific S3NGT uncertainties. All these three SWOT-derived datasets are examples of applications of SWOT data and help gain knowledge in swath altimetry. This activity also included defining key metrics to describe the mission’s performance for several variables including sea surface height, sea state, systematic errors, and inland water surface elevation. We evaluated these metrics with our generated S3NGT-like data and compared these results to the S3NGT Mission Requirements Document (MRD). This approach provides valuable insights into the expected capabilities of S3NGT products and highlights areas where the mission design can be refined to meet operational requirements.
The second study objective is to develop a comprehensive uncertainty model and budget following established metrological principles. The first part entails a metrological assessment of the S3NGT mission, while the second part focuses on verifying and validating the S3NGT uncertainty budget. This has involved creating a clear metrological traceability diagram representing the Swath altimeter and using this to identify (and later quantify) individual sources of uncertainty.
The third study objective is to evaluate options for in-orbit calibration of the S3NG-TOPO mission. This includes methods such as using orbit crossovers to correct for known systematic errors in water elevation over the ocean and inland water bodies. The evaluation must consider the different latencies of the S3NG-TOPO products. Indeed, given the stricter latency requirements for the S3NG-TOPO mission than for SWOT, the number of available orbit crossovers for cross-calibration measurements is limited.
The final study objective is to assess the uncertainty in cross-calibrating S3NG-TOPO with the current S3 constellation and reference mission (S6) using established or innovative methods. The primary goal is to ensure the continuity of S3NGT measurements, including an effective cross-calibration between the current S3 constellation and the future S3NG-TOPO constellation, particularly for the nadir altimeter system incorporating the microwave radiometer (MWR).
Contribution: ST2025HS6-Sentinel-3_Next_Generation_Topography_Mission_Performance_and_Uncertainty_Assessment__S3NGT-MPUA_.pdf (pdf, 1503 ko)
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