Relationship Between Altimetric Quality and Along-Track Spatial Resolution for iGNSS-R Sea Surface Altimetry: Example for the Airborne Experiment

Zongqiang Liu,Guohua Kang,Xuezhi Sun,Fan Wu,Qiang Wang,Wei Zheng

doi:10.3389/feart.2021.730513

Abstract

The altimetric quality and the along-track spatial resolution are the critical parameters to characterize the performance of interferometric global navigation satellite systems reflectometry (iGNSS-R) sea surface altimetry, which is closely related to each other through signal processing time. Among them, the quality of sea surface height (SSH) measurement includes precision and accuracy. In order to obtain higher altimetric quality in the observation area, a longer signal processing time is needed, which will lead to the loss of spatial resolution along the track. In contrast, higher along-track spatial resolution requires more intensive sampling, leading to unsatisfactory altimetric quality. In this study, taking the airborne iGNSS-R observation data as an example, the relationship between the altimetric quality and the along-track spatial resolution is analyzed from the perspectives of precision and accuracy. The results indicate that the reduction in the along-track spatial resolution will improve the altimetric quality. The accuracy range is 0.28–0.73 m, and the precision range is 0.24–0.65 m. However, this change is not linear, and the degree of altimetric quality improvement will decrease as the along-track spatial resolution worsens. The research results in this paper can provide a scientific reference for the configuration of parameters for future spaceborne iGNSS-R altimetry missions.

Highlights

IntroductionAs an effective and innovative bistatic radar remote sensing technology, the global navigation satellite system reflectometry (GNSS-R) can measure a series of physical parameters of the earth’s surface by using GNSS reflected signals, including the sea surface wind speed (Garrison et al, 2002; Katzberg et al, 2006; Foti et al, 2015), the sea surface height (SSH) (Lowe et al, 2002; Rius et al, 2010; Cardellach et al, 2014; Gao et al, 2021) and the soil moisture (Masters et al, 2004; Rodriguez-Alvarez et al, 2009; Wu et al, 2021), etc
The power waveform is the database for obtaining the interferometric global navigation satellite systems reflectometry (iGNSS-R) altimetric quality
The altimetric precision is directly related to the signal-tonoise ratio (SNR) of the waveform, and the acquisition of the altimetric accuracy requires the power waveform retracking to calculate the delay of the specular points

Summary

Introduction

As an effective and innovative bistatic radar remote sensing technology, the global navigation satellite system reflectometry (GNSS-R) can measure a series of physical parameters of the earth’s surface by using GNSS reflected signals, including the sea surface wind speed (Garrison et al, 2002; Katzberg et al, 2006; Foti et al, 2015), the sea surface height (SSH) (Lowe et al, 2002; Rius et al, 2010; Cardellach et al, 2014; Gao et al, 2021) and the soil moisture (Masters et al, 2004; Rodriguez-Alvarez et al, 2009; Wu et al, 2021), etc. CGNSS-R needs to use the GNSS signals with known structure, such as L1C, L2C, L5 of GPS, B1I, B1C, B2a of BDS-3 et al the maximum bandwidth of the above signals can only reach 20.46 MHz, which limits the altimetric quality and the along-track spatial resolution (Cardellach et al, 2014). The iGNSS-R technology makes complex cross-correlation between the direct signal and reflected signal, which can fully use the spectral components in the GNSS signal, and the bandwidth can reach 25 to 50 MHz. The sharper autocorrelation function can be obtained using the wider bandwidth, which will significantly improve the altimetric quality and the along-track spatial resolution (Li et al, 2016)

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Conclusion