Abstract
This paper presents the results of the first characterization of coincident Ku- and Ka-band ocean surface normalized radar cross section measurements at earth incidence angles 0°–18° using one year of wide swath Global Precipitation Measurement (GPM) mission dual frequency precipitation radar (DPR) data. Empirical geophysical model functions were derived for both bands, isotropic and directorial sensitivity were assessed, and finally, sea surface temperature (SST) dependence of radar backscatter, at both bands, were investigated. The Ka-band exhibited higher vector wind sensitivity for a low-to-moderate wind speeds regime, and the SST effects were also observed to be substantially larger at Ka-band than at Ku-band.
Highlights
A robust empirical model of the relationship between ocean surface normalized radar cross section and associated geophysical parameters is essential for the development of an accurate ocean vector wind (OVW) retrieval algorithm
Radar (DPR) on the follow-on Global Precipitation Mission (GPM) [3,4] measure ocean backscatter from space
This paper presents the first comparative results from the full-swath, collocated, GPM dual-frequency precipitation radar (DPR) measurements, and separate (Ku- and Ka-band) geophysical model function (GMF) are described for horizontal-polarization, which characterize the clear-sky, ocean surface σ0 as a function of earth incidence angles (EIA) and environmental parameters—namely, ocean surface wind speed (WS), wind direction (WD), and sea surface temperature (SST)
Summary
A robust empirical model of the relationship between ocean surface normalized radar cross section (known as σ0 ) and associated geophysical parameters (especially the ocean wind speed and direction and sea surface temperature) is essential for the development of an accurate ocean vector wind (OVW) retrieval algorithm. While the literature for ocean σ0 is extensive, the majority of studies concern either radar scatterometers at moderate earth incidence angles (EIA) or nadir-viewing radar altimeters that operate at the Ku- or C-band frequencies. Radar (DPR) on the follow-on Global Precipitation Mission (GPM) [3,4] measure ocean backscatter from space. These radars view the surface at near-nadir EIA, with cross track scans within ±18◦ ; this scenario offers a unique scientific opportunity to investigate air/sea interaction processes as a function of wind and wave parameters from non-sun synchronous, low-earth orbiting satellites. Notable among near-nadir ocean backscatter studies were: Freilich and Vanhoff (2003) [5], who established an empirical relation between ocean surface σ0 and wind speed for EIA 0◦ –18◦ using TRMM Ku PR measurements; Jones et al (2002) [6] and Souisvarn et al (2003) [7], who were the first to characterize the TRMM
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