An Ocean Wave Spectrum Derived from Polarimetric Microwave Radiometer Data
ABSTRACT This paper presents a detailed analysis of a simplified Two-Scale Model for ocean surface polarimetric microwave emission, and investigates the extent to which varying ocean surface length scales contribute to brightness temperature zeroth and second azimuth harmonics. The Two-Scale Model can be expressed as a weighting function M0,2 multiply ocean surface curvature spectrum C0,2. This implies a simple way to investigate the effect of curvature spectrum on ocean emission. It is found that ocean waves with wavelengths both comparable to and much greater than the electromagnetic wavelength can contribute to these harmonics, depending on the value of the ocean surface spectrum in these length scales. An ocean wave spectrum was derived from polarimetric microwave radiometer data according to constrained linear least-squares method.
AN OCEAN WAVE SPECTRUM DERIVED FROM POLARIMETRIC
MICROWAVE RADIOMETER DATA
Xiaobin Yin1, Zhenzhan Wang1, Lei Han2, Qing Xu3
Center for Space Science and Applied Reserch, Chinese Academy of Sciences, Beijing, 100080
First Institute of Oceanography, State Oceanic Administration, Qingdao, 266061
Institute of Space and Earth Information Science, The Chinese University of Hong Kong, Hong Kong
Oceanic emission and scattering model is critical in remote sensing wind vector using passive polarimetric
microwave radiometer [1, 2]. This paper presents a detailed analysis of a simplified Two-Scale Model for ocean surface
polarimetric microwave emission and derives an ocean wave spectrum from polarimetric microwave radiometer data.
The two-scale model states that brightness temperatures observed by a radiometer at observation angle ? can be
written as :
TT dSdSSP SSRE
Based on an efficient two-scale model  , we derive an even simpler express of (1) as:
(k )(k )
Where, M0 and M2 are weighting functions. C0 and C2 are zeroth and second cosine harmonics of the curvature
spectrum, which relate to the spectrum of the small-scale ocean wave W as:
( , )C k( , )( ) cos(2 )C k
( )k W kC k
Fig. 1 shows M0 and M2 for all four Stokes parameters versus log10(k) at 18.7GHz.
Fig. 1 Weighting functions of 0°, 90° and 180° azimuth angle at 18.7GHz and 55.3° incidence angle.
Several resonance type behaviors of the weighting functions are observed for wavelength scales comparable to half
and twice the electromagnetic wavelength at 18.7GHz, as indicated by Fig. 1. It is found that ocean waves with
wavelengths both comparable to and much greater than the electromagnetic wavelength can contribute to these
harmonics, depending on the shape of the ocean wave spectrum in these length scales [6~8].
As indicated by (2), obtaining a final prediction of emission requires inclusion of the product of the weighting
function M0 and M2 and ocean curvature spectrum harmonics C0 and C2. This implies a simple way to investigate the
effect of ocean surface parameters and curvature spectrum on ocean emission separately. Base on (2), an ocean wave
spectrum was derived using all four Stokes emission data of WindSat and WindRad at 10.7GHz, 18.7GHz and 37GHz
[9~11]. This spectrum is thought to be more accurate in a wide range of wave numbers.
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