Improving CyGNSS-Based Land Remote Sensing: Track-Wise Data Calibration Schemes

Qingyun Yan,Yan Jia,Jian Wang,Shuanggen Jin,Weimin Huang,Tiexi Chen,Ting Hu

doi:10.3390/rs13142844

Abstract

Cyclone Global Navigation Satellite System (CyGNSS) data have been used for generating several intermediate products, such as surface reflectivity (Γ), to facilitate a wide variety of land remote sensing applications. The accuracy of Γ relies on precise knowledge of the effective instantaneous radiative power (EIRP) of the transmitted GNSS signals in the direction of the specular reflection point, the precise knowledge of zenith antenna patterns which in turn affects estimates of EIRP, the good knowledge of receive antenna patterns etc. However, obtaining accurate estimates on these parameters completely is still a challenge. To solve this problem, in this paper, an effective method is proposed for calibrating the CyGNSS Γ product in a track-wise manner. Here, two different criteria for selecting data to calibrate and three reference options as targets of the calibrating data are examined. Accordingly, six calibration schemes corresponding to six different combinations are implemented and the resulting Γ products are assessed by (1) visual inspection and (2) evaluation of their associated soil moisture retrieval results. Both visual inspection and retrieval validation demonstrate the effectiveness of the proposed schemes, which are respectively demonstrated by the immediate removal/fix of track-wisely noisy data and obvious enhancement of retrieval accuracy with the calibrated Γ. Moreover, the schemes are tested using all the available CyGNSS level 1 version 3.0 data and the good results obtained from such a large volume of data further illustrate their robustness. This work provides an effective and robust way to calibrate the CyGNSS Γ result, which will further improve relevant remote sensing applications in the future.

Highlights

Remote sensing using the emerging technique of Global Navigation Satellite System (GNSS)-Reflectometry (GNSS-R) has been widely adopted
With public access to massive data collected by the Cyclone GNSS (CyGNSS) mission covering the continents below latitudes of 40◦, researchers are offered an unprecedented opportunity to explore land remote sensing applications using spaceborne GNSS-R, e.g., wetland classification [13], inland water detection [14,15], flash flood monitoring [16], and soil moisture (SM) retrieval [17,18,19,20,21]
It should be noted that the reliability of bistatic radar cross section (BRCS)/Γ measurements depends on the good knowledge of the L1 Global Positioning System (GPS) effective instantaneous radiative power (EIRP) in the direction towards the specular point (SP) as well as the zenith and receiver antenna patterns

Summary

Introduction

Remote sensing using the emerging technique of Global Navigation Satellite System (GNSS)-Reflectometry (GNSS-R) has been widely adopted. With public access to massive data collected by the Cyclone GNSS (CyGNSS) mission covering the continents below latitudes of 40◦ , researchers are offered an unprecedented opportunity to explore land remote sensing applications using spaceborne GNSS-R, e.g., wetland classification [13], inland water detection [14,15], flash flood monitoring [16], and soil moisture (SM) retrieval [17,18,19,20,21]. It should be noted that the reliability of BRCS/Γ measurements depends on the good knowledge of the L1 Global Positioning System (GPS) effective instantaneous radiative power (EIRP) in the direction towards the specular point (SP) as well as the zenith and receiver antenna patterns. Wang et al proposed a dynamic calibration approach to compensate GPS

Methods

Results

Discussion

Conclusion