Spaceborne GNSS Reflectometry for Retrieving Sea Ice Concentration Using TDS-1 Data
Yongchao Zhu, Tingye Tao, Jingui Zou, Kegen Yu, Jens Wickert, Maximilian Semmling
Abstract
A geophysical model function (GMF) for sea ice concentration (SIC) retrieval is developed based on the spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) data measured by the TechDemoSat-1 (TDS-1) satellite. The spreading characteristics of onboard processed delay-Doppler maps (DDMs) change with the surface roughness, which can be related to the SIC. A GNSS-R observable termed as differential delay waveform (DDW) generated from DDM is first used in this article to estimate SIC. Collocated SIC data from the Advanced Microwave Scanning Radiometer 2 (AMSR2) are used as the ground truth to develop and evaluate the SIC model based on the right edge waveform summation (REWS) of DDW. All usable TDS-1 data collected from February 2015 to February 2016 are adopted, and data collected over land were excluded. SIC models of the northern and southern hemispheres (SH) are developed, respectively, for avoiding the impact of geometry. In general, the REWS-based model can achieve a root mean square error (RMSE) of 11.78% and a bias of 1.67% for the northern hemisphere, and 12.10% and 1.94% for the SH, respectively. This article demonstrates the capabilities of the spaceborne GNSS-R in SIC retrieval.