Abstract's details

Surface Measurements for Oceanographic Satellites: the SUMOS in-situ and airborne campaign

Cédric Tourain (CNES, France)


Raquel Rodriguez-Suquet (CNES, France); Danièle Hauser (LATMOS, France); Lotfi Aouf (Météo-France, France); Peter Sutherland (Ifremer, France); Louis Marié (Ifremer, France)

Event: 2022 Ocean Surface Topography Science Team Meeting

Session: CFOSAT

Presentation type: Type Forum only

As a supporting contribution to the validation of observations by the China-France Oceanography Satellite, CFOSAT, launched on 29 October 2018, the SUMOS campaign was conducted in February and March 2021 by CNES and a number of research teams from the CNRS, Météo-France and Ifremer.
This campaign was mainly oriented for SWIM product assessment. SWIM is an innovative wave scatterometer It is a Ku-band real aperture radar which illuminates the surface sequentially with 6 incidence angles: 0°, 2°, 4°, 6°, 8° and 10°, thanks to its rotating antenna (5.6 rpm), it acquires data in all azimuth orientations. From SWIM measurements are generated, among other: nadir significant wave height and wind speed, wave slope spectra given for 70*90 resolution cells.
The campaign was carried out in the Bay of Biscay between the 15th February and 4th March 2021. It was designed to collect a set of co-located observations of wind, waves and associated parameters (turbulent air-sea fluxes) by both in-situ and remote sensing means. The resulting data will be used to:
• improve CFOSAT/SWIM instrument data inversion methods,
• better identify the performance and limits of the parameters provided by CFOSAT/SWIM,
• advance mission objectives concerning the study of wave hydrodynamics and wind/wave/flux relationships in turbulent conditions.
The campaign also took advantage of the SKIM mission for multiscale monitoring of sea surface kinematics to acquire Ka-band Doppler radar scatterometry data via KaRADOC (an instrument developed by the IETR) to support concepts for future satellite missions using this technique.
Two national experimentation platforms were deployed in and over the Bay of Biscay: F-HTMO, the ATR 42 research aircraft operated by SAFIRE, the French facility for airborne research (Météo-France/CNRS/CNES) and the French Oceanographic research vessel L’Atalante operated by Genavir.
Data were acquired using these two platforms in coordination with CFOSAT passes over the Bay of Biscay. The operation plan included:
1. in-situ measurements of surface waves with 20 drifting buoys (SPOTTER) to measure directional wave spectra and 3 so-called “FLAME” drifting devices to measure wind, and the turbulent fluxes close to the surface; all these systems have been deployed by the L'Atalante ship.
2. measurements taken on board the ship itself using in particular an imaging X-band radar operated by Germany’s Helmholtz-Zentrum from Geesthacht. These measurements are used to estimate the directional spectrum of the waves and surface currents. In addition, a stereo video camera and a polarimetric imaging system was deployed by LOPS and collected about 50 hours of measurements to characterize the short and intermediate waves and study their relation with breaking and with remotely sensed parameters
3. airborne radar measurements using the Ku-band Radar for Observation of Surfaces (KuROS) developed and operated by LATMOS, were performed from the ATR 42 research aircraft so as to provide directional wave spectra using the same concept of measurement as used for SWIM.
4. airborne measurements with the KaRADOC radar developed and operated by the IETR, also carried by the ATR 42. These measurements are used in particular to study the concept of acquiring surface current data by applying a pulse-pair method to a Doppler radar signal. KaRADOC was designed as part of the SKIM project proposed by LOPS.
In all, the ATR 42 flew 17 times in perfect coordination with the in-situ measurements carried out on board the L'Atalante and the drifting buoys deployed from the vessel. Of these 17 flights, 13 were synchronized with CFOSAT satellite passes (SUMOS campaign) and the last 4 were used for the SKIM project.
Each flight provided between 3 and 4 hours of data over long distances across the Bay of Biscay. The research vessel was positioned at different points during this period according to the satellite's passes and the constraints of launching and recovering the drifting buoys.
A large set of high-quality data was acquired, and a wide range of weather conditions was observed, enabling campaign objectives to be reached.
The first results of this campaign are very positive. They show very close agreement between measurements from SWIM, the drifting buoys and the MFWAM model. Analysis from the full collocated data set is in progress with in particular studies devoted to the experimental estimation or validation of the Modulation Transfer Function which is used to invert SWIM observations into directional wave spectra.
The data set will be made available to the wider scientific community, including altimetry community, as soon as they become available.
The scientific altimetry community will be able to take advantage of these observations to validate the different products on wave height (SWH) at nadir.
Cédric Tourain