Validation of SWOT data using airborne LiDAR off the coasts of Normandy during the fast sampling orbit phase

The Surface Water and Ocean Topography (SWOT) altimeter will perform a continuous global water survey with unprecedented resolution and accuracy across its 3-year mission. After being launched on December 16th 2022 with a SpaceX Falcon 9 rocket from Vandenberg in California, it was successfully commissioned followed by a Calibration and Validation (Cal/Val) phase that lasted approximately between April and July 2023. During this period, numerous in-situ measurements were performed across the globe to assess the altimeter’s performance. Airborne Light Detection And Ranging (LiDAR) campaigns were conducted off the coasts of Normandy, France as part of other measurements in this region. We carried out 4 different missions, 2 in May and 2 in June, using a Leica ALS 60 airborne sensor aboard 2 different planes, a Piper Navajo and a Swearingen Fairchild Merlin. The flight plans were designed below the SWOT Ka-band Radar Interferometer (KaRIn) along and across the 1-day fast sampling ground track. Ground Control Points (GCP) were acquired under the LiDAR coverage, close to the city of Cherbourg. The plane’s trajectory was processed using CNES GINS software, using the integer Precise Point Positioning (iPPP) mode, resulting in centimetric antenna phase positioning. LiDAR data were calibrated using the GCPs with a millimetric average accuracy. First results between SWOT data and airborne LiDAR indicate very good consistency. Indeed, the differences between the SWOT LR 2 km pre-cal product and LiDAR data, averaged over a similar 2 km grid, gives centimetric standard deviation.