Revised ocean backscatter models at C and Ku band under high-wind conditions

• Published in: Journal of Geophysical Research, Washington, DC Vol. 104; no. C5; pp. 11485 - 11497
• Main Authors: Donnelly, William J., Carswell, James R., McIntosh, Robert E., Chang, Paul S., Wilkerson, John, Marks, Frank, Black, Peter G.
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 15-05-1999
• Subjects: Marine
• ISSN: 0148-0227; 2169-9275; 2156-2202; 2169-9291
• DOI: 10.1029/1998JC900030

A series of airborne scatterometer experiments designed to collect C and Ku band ocean backscatter data in regions of high ocean surface winds has recently been completed. More than 100 hours of data were collected using the University of Massachusetts C and Ku band scatterometers, CSCAT and KUSCAT. These instruments measure the full azimuthal normalized radar cross section (NRCS) of a common surface area of the ocean simultaneously at four incidence angles. Our results demonstrate limitations of the current empirical models, C band geophysical model function 4 (CMOD4), SeaSat scatterometer 2 (SASS 2), and NASA scatterometer 1 (NSCAT) 1, that relate ocean backscatter to the near‐surface wind at high wind speeds. The discussion focuses on winds in excess of 15 m s−1 in clear atmospheric conditions. The scatterometer data are collocated with measurements from ocean data buoys and Global Positioning System dropsondes, and a Fourier analysis is performed as a function of wind regime. A three‐term Fourier series is fit to the backscatter data, and a revised set of coefficients is tabulated. These revised models, CMOD4HW and KUSCAT 1, are the basis for a discussion of the NRCS at high wind speeds. Our scatterometer data show a clear overprediction of the derived NRCS response to high winds based on the CMOD4, SASS 2, and NSCAT 1 models. Furthermore, saturation of the NRCS response begins to occur above 15 m s−1. Sensitivity of the upwind and crosswind response is discussed with implications toward high wind speed retrieval.