Estimation of wave spectra with SWIM on CFOSAT illustration on a real case C. Tison (1), C. Manent (2), T. Amiot (1), V. Enjolras (3), D. Hauser (2), L. Rey (3), P. Castillan (1) (1) CNES, Altimetry and Radar department, France (2) UVSQ, CNRS, LATMOS-IPSL, France (3) Thals Alenia Space, France IGARSS11 July, Overview of the presentation SWIM instrument and measures Performance budget SimuSWIM an end-to-end simulator A real sea state condition Results IGARSS11 July, The CFOSAT mission Status of the program: Conception and Development phase Launch planned end of 2014 SWIM Measurement of the oceanic wave properties Real-aperture radar with 6 beams (Ku band) SCAT Measurement of wind sea surface Real-aperture radar (bi polar, Ku band) KuROS Airborne sensor developed by LATMOS Validation of SWIM and SCAT More on the CFOSAT mission tomorrow session WE4.T10 Altimetry I China France Oceanography SATellite IGARSS11 July, SWIM instrument (1/2) SWIM: Surface Wave Investigation and Monitoring Ku-band radar (scatterometer) 6 beams IGARSS11 July, SWIM instrument (2/2) Wind sea Swell Nadir signal SWH and wind speed - Accuracy SWH: max(10% of SWH, 50 cm) -Accuracy wind speed: 2 m/s 10, 8 and 6 beams wave spectrum - spatial sampling of 70 x 70 Km - Detectable wave wavelength : ~ [ ] m - Azimuth accuracy: 15 - Energy accuracy: 15% All beams backscattering coefficient profiles: - Absolute accuracy < +/- 1 dB - Relative accuracy (between beams) < +/- 0.1 dB IGARSS11 July, Estimation of wave spectra Wave topography: (x,y) Directional wave spectrum F(k x,k y ) Modulation of the backscattering coefficient Signal modulation Modulation spectrum P m Received power Wave slopes Link slope/signal modulation IGARSS11 July, 2011 Simulations Simulations from the sea surface to the estimated signal Input = sea state conditions Output = wave spectrum computation of backscattered intensity and processing similar to the future ground segment use SWIM parameters End-to-end simulation tool: SimuSWIM 0246810 Max integration time (ms) Bc (MHz)320 PRF (Hz) 2125 fixed variable variable variable Nimp (fixed) SNR (dB) IGARSS11 July, Simulations End-to-end simulation tool: SimuSWIM Input spectrum (models, measurements) Surface computation Backscattered signal (knowing SWIM geometry and properties) At a given azimuth direction: -Computation of the N imp backscattered pulses 2 options: 1. Computation of the N imp pulses (with geometrical migrations and noises for each) 2. Computation of one pulse and additions of noise (thermal+speckle) to create the N imp pulses with central migrations -Addition of the N imp signals N imp pulses per cycles IGARSS11 July, Simulations End-to-end simulation tool: SimuSWIM Input spectrum (models, measurements) Surface computation Backscattered signal (knowing SWIM geometry and properties) Estimated modulation spectrum Quality criteria IGARSS11 July, Impact of migrations (1/2) N imp N imp /2 NR ER MR FR x MR Due to satellite advection and antenna rotation: MIGRATIONS range (of each target) different at each impulse -3 kinds of migration: -Centre migration -Migration along elevation -Migration along wave front -NB: at the cycle scale, no impact of antenna rotation Corrected by chirp scaling Non correctable Two ways of simulation (for computation time constraints): 1.With only central migrations and elevation migrations 2.With all migrations IGARSS11 July, Impact of migrations (2/2) (a) Reference 2D modulation spectrum (b) Estimated 2D modulation spectrum WITHOUT complete migration (c) Estimated 2D modulation spectrum WITH complete migrations DirectionWave- length Energy Swell0 0% 3% 13% 10% Wind sea11 14 27% 16% 19% 12% IGARSS11 July, 2011 A real sea state condition: Prestige case Case of November, 2002 storm in Atlantic ocean Lead to the sinking of the Prestige (oil tanker) Very different conditions during the day 00:00: low wind sea + dominant swell 06:00: very young wind sea (high wind) + dominant swell 08:00: mature wind sea + dominant swell 15:00: crossed wind seas (old + young) Wind sea rotated by about 120 Spain Galician coast BSAM/Douanes franaises IGARSS11 July, 2011 A real sea state condition: Prestige case IGARSS11 July, 2011 A real sea state condition: Prestige case Available data MFWAM output with ALADIN winds (Mto France models of wind and waves) 2D polar azimuth/frequency height spectrum converted into 2D cartesian wavenumber by bilinear interpolation Subset of results: 00, 06, 08, 10, 15 UTC (different wind and waves cases) Simulation conditions Incidence angle: 10 N imp = 237 pulses per cycle ( averaging for noise reduction) Rotation speed = 5.7 rpm ( 49 cycles / 360) IGARSS11 July, 2011 Simulation results 06:00 UTC Reference: 2D spectrum from WAM model CFOSAT/SWIM estimation (simulations from SimuSWIM) Same detection of swell and wind sea partitions Small underestimation IGARSS11 July, D modulation spectra 6h UTC Swell =135 (SE-NW look direction) Sea wind = 235 (NE-SW look direction) = angle between satellite track (assumed S-N) and radar look direction IGARSS11 July, :00 UTC06:00 UTC08:00 UTC15:00 UTC10:00 UTC Reference: 2D spectrum from WAM model CFOSAT/SWIM estimation (simulations from SimuSWIM) Hs: 6.5 m U: 17.3 m/s Hs: 6.1 m U: 8.8 m/s Hs: 5.8 m U: 22.2 m/s Hs: 5.1 m U: 11.7 m/s Hs: 6.5 m U: 21.0 m/s Prestige SOS 14:00 UTC IGARSS11 July, 2011 Performance quality SWELLWIND SEA E E 00h30%4%--- 06h00%13%1127%19% 08h01%7%1118%6% 10h08% 116%7% 15h312%6%719%5% Estimation errors on wave direction ( ), wave wavelength ( ) and energy (E):