SST Dependence of Ku- and C-Band Backscatter Measurements

Wang, Zhixiong; Stoffelen, Ad; Fois, F.; Verhoef, Anton; Zhao, Chunjiang; Lin, Mingsen; Chen, Ge

doi:10.1109/jstars.2016.2600749

Cited by 57 publications

(39 citation statements)

References 29 publications

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“…The variation of

σ^{0}

due to SST changes at a given wind speed

V

, wind direction,

θ

p

, and

λ

was investigated theoretically using a physics‐based radar backscatter model and empirically using a data set of collocated ASCAT‐B and RapidScat measurements [ Wang et al ., ]. No evidence was found for any SST dependency of ASCAT‐retrieved winds.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper, we derive a sea surface temperature (SST)‐dependent Ku‐band wind retrieval geophysical model function (GMF) for the National Aeronautics and Space Administration (NASA) RapidScat scatterometer on board the International Space Station (ISS), following the assessment of Wang et al . [] of SST‐dependent errors in GMF‐simulated vertical (VV) and horizontal (HH) copolarization backscatter values.…”

Section: Introductionmentioning

confidence: 99%

“…A GMF can been written as:

σ^{0} = normalG normalM normalF (|, V_{10 s}, ϕ, θ, p, λ, S S T, \dots)

where

V_{10 s}

is the stress‐equivalent wind speed at a height of 10 m [ Edson , ; Liu and Tang , ; De Kloe et al ., ],

ϕ

is the wind direction with respect to the radar range direction,

p

is the radar emitted and received polarization,

θ

is the incidence angle, and

λ

is the radar wavelength [ Wentz et al ., ; Wentz and Smith , ; Brown , ; Gohil et al ., ; Hersbach et al ., ; Ricciardulli and Wentz , ]. Several studies have shown that it is necessary to take SST into account for a Ku‐band GMF, while for C‐band SST effects are much smaller [ Grodsky et al ., ; Bentamy et al ., ; Bentamy et al ., ; Wang et al ., ].…”

Section: Introductionmentioning

confidence: 99%

“…But this situation changed in September 2014 when NASA mounted the Ku‐band RapidScat scatterometer on the ISS, which is in a nonsun‐synchronous orbit. RapidScat provides measurements at different local times of the day and represents a unique opportunity to acquire collocated RapidScat and ASCAT scatterometer winds in large numbers at low and mid‐latitudes [ Wang et al ., ], allowing accurate attribution of various correlated geophysical effects. Despite the nonpolar ISS orbit, the sampling is over the full range of global geophysical conditions, in particular SST ranges from 0°C to 30

° C

.…”

Section: Introductionmentioning

confidence: 99%

“…The SST dependence of Ku‐band and C‐band backscatter measurements has been illustrated in Wang et al . [], and as a follow‐on of that paper, we aim to quantitatively estimate the SST dependence and to include it into the current NSCAT‐4 Ku‐band GMF for RapidScat wind retrievals in this paper. Both vertical ( p = VV) and horizontal ( p = HH) copolarization NRCS GMFs are modeled at their respective RapidScat incidence angles (assumed constant), as it has been shown that VV and HH have different SST dependence [ Wang et al ., ].…”

Section: Introductionmentioning

confidence: 99%

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An SST‐dependent Ku‐band geophysical model function for RapidScat

et al. 2017

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A new Ku‐band geophysical model function (GMF), which includes sea surface temperature (SST) dependence, named NSCAT‐5, is developed for improved RapidScat wind retrieval. The RapidScat scatterometer instrument mounted on the International Space Station (ISS) provides near‐global wind data over the oceans. Starting from the existing NSCAT‐4 GMF, the variation of σ0 is approximated as a second‐order Taylor expansion in sea surface temperature T for each given wind speed V, and the fitting coefficients are obtained from both observed and simulated radar cross sections, using ASCAT winds, of either vertical or horizontal polarizations. Furthermore, an intercalibration is performed which aligns the distribution of RapidScat wind speeds to that of ASCAT. NSCAT‐5 is obtained by correcting NSCAT‐4 with SST dependencies and intercalibration information. Validation of the new RapidScat wind products retrieved using NSCAT‐5 shows clear improvements over those obtained with NSCAT‐4: Wind inversion residuals no longer depend on SST, and the wind speed Probability Density Functions (PDFs) are closely overlapping with those of ASCAT. Also, RapidScat NSCAT‐5 minus ASCAT wind speed differences show no SST dependence. The work presented here opens a door for further improving the quality of wind products from Ku‐band backscatter measurements, and helps to build a long‐term and consistent essential Climate Data Record (CDR) of scatterometer winds.

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“…The variation of