Combined Wind Vector and Sea State Impact on Ocean Nadir-Viewing Ku- and C-Band Radar Cross-Sections

Abstract

Abstract:The authors report the first results in studying the polarization anisotropy of the microwave backscatter from nadir observations provided by Jason-1 altimeter in both Kuand C-band. A small but clear wind direction signal for wind speeds above 6 m/s is revealed. These azimuthal variations of radar cross-section increase with increasing wind speed up to 14 m/s. The signatures then level off at higher winds. These results extend, for the first time, recent theoretical improved scattering approximation, and point some similarities between scattering and emission mechanisms at nadir. The observed directional effect can thus be interpreted as a signature of the curvature anisotropy of wind-generated short-scale waves. Sensitivities to both wind speed and sea state are also reported in the present analysis.

Analysis of Dual-Frequency Ocean Backscatter Measurements at Ku- and Ka-Bands Using Near-Nadir Incidence GPM Radar Data

“…But if the mean squared curvature correction term increases and/or Q z decreases, then α will increase and the PO model departs from GO. While weak, polarization sensitivity ( [18]) is also expected. Accordingly, the key parameter controlling GO-departure is α, and this parameter will be much larger for Ku-than for Ka-band measurements (Q z effect).…”

Jason-1/Jason-2 Metocean Comparisons and Monitoring

“…This is done to control the solar illumination on the spacecraft, hence the period coinciding with a known alias of the solar day. Through a comparison of Jason-1 altimetry and wind vectors from weather reanalyses, Tran and Chapron (2006) had shown that the direction of wind would have a small impact (~0.05 dB) at wind speeds of around 6-7 ms -1 (which correspond to the σ 0 C values around 15.3-15.6 dB used here). The results in Fig.…”

A new algorithm for wind speed at low incidence angles using TRMM Precipitation Radar data

“…This modulation generally increases with increasing wind speed and incidence angle. While for nadir º and mss, Tran and Chapron [12] concluded from Jason-1 altimeter data that directional signal is rather small in nadir both Ku-band and C-band º, the peak-to-peak directional signal is lower than 0.1 dB. Hauser et al [13] after examining C-band VV-polarized aircraft rotating radar data (7°to 16°), concluded that the anisotropy of the radar-filtered mss is small and its dependence with wind is weak.…”