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Development of a geophysical model function for HY-2 satellite microwave scatterometer wind retrievals

  • role： First author第一作者
  • Affiliation：

    School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

  • Email：wangzhixiongcn@163.com
  • Introduction：王志雄，研究方向为卫星海洋遥感、极地遥感、卫星资料同化。E-mail： wangzhixiongcn@163.com
WANG Zhixiong13,  
  • role： Corresponding author通信作者
  • Affiliation：

    Southern Marine Science and Engineering Guangdong Laboratory, Guangzhou 511458, China

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

    National Satellite Ocean Application Service, Beijing 100081, China

  • Email：zoujuhong@mail.nsoas.org.cn
  • Introduction：邹巨洪，研究方向为卫星海洋遥感与应用。E-mail： zoujuhong@mail.nsoas.org.cn
ZOU Juhong234*,  
  • Affiliation：

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

    National Satellite Ocean Application Service, Beijing 100081, China

LIN Mingsen34,  
  • Affiliation：

    School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

LIN Wenming13,  
  • Affiliation：

    Southern Marine Science and Engineering Guangdong Laboratory, Guangzhou 511458, China

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

    National Satellite Ocean Application Service, Beijing 100081, China

ZHANG Yougunag234,  
  • Affiliation：

    School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

LI Xiuzhong13,  
  • Affiliation：

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

    National Satellite Ocean Application Service, Beijing 100081, China

FENG Qian34,  
  • Affiliation：

    School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing 210044, China

    Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Beijing 100081, China

HE Yijun13

résumé

The Geophysical Model Function (GMF) is indispensable in space-born scatterometer wind retrieval data processing because it is the main factor that dominates the error characteristics of retrieved winds. In this study, a new Ku-band GMF (named NSCAT-5.HY-2), which includes Sea Surface Temperature (SST) dependence, is developed for improved HY-2 satellite scatterometer (HSCAT) wind retrieval. Based on the existing NSCAT-4 GMF, the dependence of σ0 on wind speed and direction will be refined, and that of σ0 on SST is then added. The sea surface winds from the C-band advanced scatterometer (ASCAT) onboard the MetOp-B and C satellites are of high quality and have no dependence on SST. Accordingly, the ASCAT winds are used as reference for developing the NSCAT-5.HY-2 GMF. HY-2C and HY-2D are in non-sun-synchronous orbits with a 66.0° inclination, and their equator crossing times shift each orbit. The HY-2C or HY-2D scatterometer represents a unique opportunity to acquire closely collocated HSCAT and ASCAT scatterometer winds at different times of the day. In this study, the wind vector cells between HSCAT and ASCAT are matched by limiting the spatial distance within km and time differences within 45 min. The close collocations of HSCAT and ASCAT winds allow accurate attribution of the different correlated residual geophysical effects of wind speed bias and distribution, SST, sea state, rain, wind variability, and geographical sampling biases. Here, we explore the opportunity of close collocations of HSCAT-C and ASCAT and develop an SST-dependent Ku-band GMF for HY-2 scatterometers. The wind speed corrections as a function of wind speed can be calculated by using the cumulative distribution function matching technique, which aligns the Probability Density Function (PDF) of HSCAT wind speeds with the referenced PDF. During the wind direction modulations, five terms of the Fourier series are used, and the harmonic coefficients are derived utilizing ASCAT wind direction as reference. The variations of σ0 as a function of SST are given as a polynomial expansion for each given wind speed, and the polynomial coefficients are obtained from the observed and simulated radar cross-sections using closely collocated ASCAT winds of either vertical or horizontal polarizations. The validation of the new HSCAT wind products retrieved using NSCAT-5.HY-2 GMF shows clear improvements over those obtained with NSCAT-4 GMF. The consistency between HSCAT and ASCAT winds is much improved by at least 10%, and wind speed differences no longer depend on SST.

mots-clés

Remote sensing of sea surface wind vectors;HY-2 microwave scatterometer;ASCAT scatterometer;geophysical model function;sea surface temperature

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