Sea state effect on the sea surface emissivity at L-band

• Published in: IEEE transactions on geoscience and remote sensing Vol. 41; no. 10; pp. 2307 - 2315
• Main Authors: Miranda, J.J., Vall-llossera, M., Camps, A., Duffo, N., Corbella, I., Etcheto, J.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.10.2003; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Apertures; Applied geophysics; Brightness temperature; Earth sciences; Earth, ocean, space; Exact sciences and technology; Internal geophysics; L-band; Marine; Marine geology; Mathematical analysis; Mathematical models; Meteorology; Microwave radiometry; Ocean temperature; Salinity; Sea measurements; Sea states; Sea surface; SMOS mission; Soil moisture; Velocity measurement; Wind; Wind speed; microwaves; Nonstationary sea conditions; remote sensing; cartography; swells; surface water; swell effect; brightness temperature; ocean; sea surface spectrum; winds; sea surface emissivity at L-band; polarization
• ISSN: 0196-2892; 1558-0644
• DOI: 10.1109/TGRS.2003.817190

In May 1999, the European Space Agency (ESA) selected the Earth Explorer Opportunity Soil Moisture and Ocean Salinity (SMOS) mission to obtain global and frequent soil moisture and ocean salinity maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L-band two-dimensional aperture synthesis radiometer with multiangular observation capabilities. At L-band, the brightness temperature sensitivity to the sea surface salinity (SSS) is low, approximately 0.5 K/psu at 20/spl deg/C, decreasing to 0.25 K/psu at 0/spl deg/C, comparable to that to the wind speed /spl sim/0.2 K/(m/s) at nadir. However, at a given time, the sea state does not depend only on local winds, but on the local wind history and the presence of waves traveling from far distances. The Wind and Salinity Experiment (WISE) 2000 and 2001 campaigns were sponsored by ESA to determine the impact of oceanographic and atmospheric variables on the L-band brightness temperature at vertical and horizontal polarizations. This paper presents the results of the analysis of three nonstationary sea state conditions: growing and decreasing sea, and the presence of swell. Measured sea surface spectra are compared with the theoretical ones, computed using the instantaneous wind speed. Differences can be minimized using an "effective wind speed" that makes the theoretical spectrum best match the measured one. The impact on the predicted brightness temperatures is then assessed using the small slope approximation/small perturbation method (SSA/SPM).