Characteristics and Applications of the Ground-Based X Band Low Elevation Angle Brightness Temperatures under Low Sea State Based on Measured Data

Zhongqing Cao; Lixin Guo; Shifeng Kang; Xianhai Cheng; Qingliang Li; Leke Lin; Yusheng Zhang

doi:10.3390/rs12111736

Remote Sensing (May 2020)

Characteristics and Applications of the Ground-Based X Band Low Elevation Angle Brightness Temperatures under Low Sea State Based on Measured Data

Zhongqing Cao,
Lixin Guo,
Shifeng Kang,
Xianhai Cheng,
Qingliang Li,
Leke Lin,
Yusheng Zhang

Affiliations

Zhongqing Cao: School of Physics and Optoelectronic Engineering, Xidian University, No. 2, Taibai Road, Xi’an 710071, China
Lixin Guo: School of Physics and Optoelectronic Engineering, Xidian University, No. 2, Taibai Road, Xi’an 710071, China
Shifeng Kang: National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave, Propagation, Qingdao 266107, China
Xianhai Cheng: National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave, Propagation, Qingdao 266107, China
Qingliang Li: National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave, Propagation, Qingdao 266107, China
Leke Lin: National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave, Propagation, Qingdao 266107, China
Yusheng Zhang: National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave, Propagation, Qingdao 266107, China

DOI: https://doi.org/10.3390/rs12111736
Journal volume & issue: Vol. 12, no. 11
p. 1736

Abstract

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In ground-based microwave radiometer remote sensing, low-elevation-angle (−3°~3°) radiation data are often discarded because they are considered to be of little value and are often difficult to model due to the complicated mechanism. Based on the observed X-band horizontal polarization low elevation angle microwave radiation data and the meteorological data at the same time, this study investigated the generation mechanism of low elevation angle brightness temperature (LEATB) and its relationship with meteorological data, i.e., temperature, humidity, and wind speed, under low sea state. As a result, one could find that the LEATB was sensitive to the atmosphere at the elevation angle between 1° to 3°, and a diurnal variation of the LEATB reached up to 10 K. This study also found a linear relationship between the LEATB and sea surface wind speed under low sea state at an elevation range from −3° to 0°, i.e., the brightness temperature decreased as the wind speed increased, which was inconsistent with the observations at the elevation angle from −10° to −5°. The variation of the LEATB difference according to the change in the over-the-horizon detection capability (OTHDC) of the shipborne microwave radar was examined to identify the reason for this phenomenon theoretically. The results showed that the LEATB difference was significantly influenced by a change in the OTHDC. Further, this study examined a remote sensing method to extract the sea surface wind speed data from experimental LEATB data under low sea state. The results demonstrated that the X-band horizontal polarization LEATBs were useful to retrieve the sea surface wind speed data at a reasonable accuracy—the root mean square error of 0.02408 m/s. Overall, this study proved the promising potential of the LEATB data for retrieving temperature profiles, humidity profiles, sea surface winds, and the OTHDC.

Published in Remote Sensing

ISSN: 2072-4292 (Online)
Publisher: MDPI AG
Country of publisher: Switzerland
LCC subjects: Science
Website: http://www.mdpi.com/journal/remotesensing/

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