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Correction of the tropospheric slant path delay of Tiangong-2 Interferometric Imaging Radar Altimeter

  • role： First author第一作者
  • Affiliation：

    CAS Key Laboratory of Microwave Remote Sensing, National Space Science Center, Beijing 100190, China

    University of Chinese Academy of Science, Beijing 100049, China

  • Email：chenjiehaojane@foxmail.com
  • Introduction：陈洁好，1994年生，女，硕士研究生，研究方向为雷达信号处理、数据挖掘与分析。E-mail:chenjiehaojane@foxmail.com
CHEN Jiehao12,  
  • role： Corresponding author通信作者
  • Affiliation：

    CAS Key Laboratory of Microwave Remote Sensing, National Space Science Center, Beijing 100190, China

    University of Chinese Academy of Science, Beijing 100049, China

  • Email：zhangyunhua@mirslab.cn
  • Introduction：张云华，1967年生，男，研究员，研究方向为微波遥感器、高分辨率雷达系统设计、信号处理、天线技术等。E-mail: zhangyunhua@mirslab.cn
ZHANG Yunhua12*,  
  • Affiliation：

    CAS Key Laboratory of Microwave Remote Sensing, National Space Science Center, Beijing 100190, China

DONG Xiao1

résumé

Launched on September 15, 2019, the Interferometric Imaging Radar Altimeter (InIRA) onboard the Chinese Tiangong-2 space laboratory is the first spaceborne interferometric radar altimeter that can obtain wide-swath ocean topography measurements by adopting small incidence angles from 1° to 8° with a short baseline. InIRA achieves various technological breakthroughs, meanwhile, it also brings some challenges in data processing because no radiometer is onboard the Tiangong-2 space laboratory. Considering signal path delays is a premise for InIRA to meet its geocoding and Sea Surface Height (SSH) measurement goals, a mathematical model-based method for tropospheric path delay correction should be developed. Unlike traditional nadir-looking altimeters, which only require the propagation delay related to the velocity variation along a line path, the Tiangong-2 InIRA must consider the additional bending of radio waves for its small incidence angles. In this study, a tropospheric slant path delay correction algorithm is developed using the ray-tracing technique based on Fermat’s principle and on the numeric weather model from the European Center for Medium-range Weather Forecasts. Two calibration campaigns are conducted in March 2017 and September 2018, which recorded 12 measurement data from 9 corner reflectors. Results show that the standard deviation of the residual error range after the tropospheric slant path delay correction is approximately 6.2 cm, which indicates that a centimeter-level range accuracy is realized. Therefore, the effectiveness and reliability of the proposed algorithm in different small incidence angles are validated.

mots-clés

Tiangong-2 Interferometric Imaging Radar Altimeter (InIRA);atmospheric path delay;slant path delay correction;Numeric Weather Model (NWM);bending of radio waves

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