Abstract
L-band active microwave remote sensing is one of the most important technical methods of ocean environmental monitoring and dynamic parameter retrieval. Recently, a unique negative upwind-crosswind (NUC) asymmetry of L-band ocean backscatter over a low wind speed range was observed. To study the directional features of L-band ocean surface backscattering, a new directional spectrum model is proposed and built into the advanced integral equation method (AIEM). This spectrum combines Apel’s omnidirectional spectrum and an improved empirical angular spreading function (ASF). The coefficients in the ASF were determined by the fitting of radar observations so that it provides a better description of wave directionality, especially over wavenumber ranges from short-gravity waves to capillary waves. Based on the improved spectrum and the AIEM scattering model, L-band NUC asymmetry at low wind speeds and positive upwind-crosswind (PUC) asymmetry at higher wind speeds are simulated successfully. The model outputs are validated against Aquarius/SAC-D observations under different incidence angles, azimuth angles and wind speed conditions.
Highlights
L-band microwaves have a high sensitivity to marine physical parameters such as salinity and wind field [1]
We proposed a new explanation of this special UC asymmetry
In the calculation process, the dielectric constants needed by the advanced integral equation method (AIEM) model were obtained from the K-S model [44]
Summary
L-band microwaves have a high sensitivity to marine physical parameters such as salinity and wind field [1]. Due to their long wavelength, L-band microwaves have a good penetrability to adapt to complex surface conditions. Aperture Radar (PALSAR) [6], the Aquarius/SAC-D mission [7] and the Soil Moisture Active-Passive (SMAP) mission [8]. The Aquarius/SAC-D and SMAP missions, which were both undertaken by the U.S National Aeronautics and Space Administration (NASA), have used L-band microwave radiometers and combined active/passive L-band instruments for ocean research
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