Editorial Type:
Article
Article Type:
Research Article

Gravity–Capillary Wave Curvature Spectrum and Mean-Square Slope Retrieved from Microwave Radiometric Measurements (Coastal Ocean Probing Experiment)

Yu G. Trokhimovski NOAA/ERL/Environmental Technology Laboratory, Boulder, Colorado

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Print Publication:
01 Sep 2000
DOI:
https://doi.org/10.1175/1520-0426(2000)017<1259:GNCWCS>2.0.CO;2
Page(s):
1259–1270
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Abstract

Brightness temperature of the sea surface is determined by surface waves of different scales. Polarimetric measurements collected by microwave radiometers at several viewing angles and frequencies give an opportunity to convert the observed brightness temperatures to the mean-square slope of long waves and curvature spectral density in the gravity–capillary interval without a priori assumptions about the shape of spectrum. Such an inversion was made using radiometric data collected during the Coastal Ocean Probing Experiment (COPE’95) from a blimp. It is shown that at low and moderate wind speed conditions typical for COPE’95 (4–7 m s−1) the curvature spectrum has a maximum at wavenumber of about 4.5 rad cm−1, slightly higher than the wavenumber of the phase velocity minimum. The maximum corresponds to the wavenumber with the highest initial growth rate as predicted by theory for the growth rate of wind-induced gravity–capillary waves based on the Orr– Sommerfeld equation. The author’s estimation of the mean-square slope of surface waves is very close to the Cox and Munk values for stable and unstable atmospheric stratification. The radiometric results are compared with several gravity–capillary wave spectral models.

Corresponding author address: Dr. Yuri G. Trokhimovski, NOAA/Environmental Technology Laboratory, R/E/ET1, 325 Broadway, Boulder, CO 80303-3328.

Abstract

Brightness temperature of the sea surface is determined by surface waves of different scales. Polarimetric measurements collected by microwave radiometers at several viewing angles and frequencies give an opportunity to convert the observed brightness temperatures to the mean-square slope of long waves and curvature spectral density in the gravity–capillary interval without a priori assumptions about the shape of spectrum. Such an inversion was made using radiometric data collected during the Coastal Ocean Probing Experiment (COPE’95) from a blimp. It is shown that at low and moderate wind speed conditions typical for COPE’95 (4–7 m s−1) the curvature spectrum has a maximum at wavenumber of about 4.5 rad cm−1, slightly higher than the wavenumber of the phase velocity minimum. The maximum corresponds to the wavenumber with the highest initial growth rate as predicted by theory for the growth rate of wind-induced gravity–capillary waves based on the Orr– Sommerfeld equation. The author’s estimation of the mean-square slope of surface waves is very close to the Cox and Munk values for stable and unstable atmospheric stratification. The radiometric results are compared with several gravity–capillary wave spectral models.

Corresponding author address: Dr. Yuri G. Trokhimovski, NOAA/Environmental Technology Laboratory, R/E/ET1, 325 Broadway, Boulder, CO 80303-3328.

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Journal of Atmospheric and Oceanic Technology

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