Swath altimetry simulations with Radarspy, in preparation of Copernicus mission Sentinel-3 Next Generation - Topography

We wish to present the CNES contribution to the Sentinel-3 Next Generation - Topography (S3NG-T) project. In the wake of the SWOT mission, which pioneered the use of SAR interferometry for surface water altimetry, ESA is considering using this new approach for the successor to its current operational mission Sentinel-3 (S3), S3NG. Such so-called “swath altimetry” enables the access to two-dimensional features on water surfaces, much more directly than traditional Nadir altimetry (such as that used aboard S3) does, but it must also stand the test of accuracy requirements.

Scheduled to take flight in 2033, the altimetry component of S3NG, called S3NG-T, is wrapping up its development phase B1 wherein two consortia designed their proposal of a swath altimetry mission, and during which SWOT’s very promising first data released. A Mission Gate Review in early 2024 should lead to the definitive decision whether to adopt this new measurement technique for S3NG-T or not. Rich with the heritage of their contribution to SWOT and convinced of the potential of swath altimetry, the CNES teams bring a technical expertise to the S3NG table.

As such, we developed evolutions for Radarspy, our in-house simulator of swath altimeter data, in order to assess S3NG’s performances over oceans and inland waters. The swath altimetry instrument aboard S3NG-T, called SAOOH, differs from SWOT’s instrument mainly in its 3-meter baseline, its multiple receptors (four per swath – left or right – in order to flatten the gain pattern), and its interleaved observation pattern, where bursts of 128 Radar pulses are sent alternatively left and right. We wish to present the results of our simulations, which test SAOOH over scenes of various reflectivity, water content and topography. These simulations yield encouraging first results and let us see how some choices made in its on-board processing algorithm affect the random noise, the water detection performance and the point-target response.