Abstract
Global Navigation Satellite System Reflectometry (GNSS-R) is a rapidly developing Earth observation technology that makes use of signals of opportunity from Global Navigation Satellite Systems that have been reflected off the Earth’s surface. The Cyclone Global Navigation Satellite System (CyGNSS) is a constellation of eight small satellites launched by NASA in 2016, carrying dedicated GNSS-R payloads to measure ocean surface wind speed at low latitudes (±35° North/South). The ESA ECOLOGY project evaluated CyGNSS v3.0 products, which were recently released following various calibration updates. This paper examines the performance of the new calibration by evaluating CyGNSS v3.0 Level-1 Normalised Bistatic Radar Cross Section (NBRCS) and Leading Edge Slope (LES) data from individual CyGNSS units and different GPS transmitters under constant ocean wind conditions. Results indicate that L1 NBRCS from individual CyGNSS units are well inter-calibrated and remarkably stable over time, a significant improvement over previous versions of the products. However, prominent geographical biases reaching over 3 dB are found in NBRCS, linked to factors including the choice of GPS transmitter and the bistatic geometry. L1 LES shows similar anomalies as well as a secondary geographical pattern of biases. These findings provide a basis for further improvement of CyGNSS Level-2 wind products and have wider applicability to improving the calibration of GNSS-R sensors for the remote sensing of non-ocean Earth surfaces.
Highlights
Following the first proposal of the Global Navigation Satellite System Reflectometry (GNSS-R) principle for scatterometry in the late1980s [1], and later in the early 1990s for ocean altimetry [2], the technology was later demonstrated from low-Earth-orbit altitudes by the UK-Disaster Monitoring Constellation (UK-DMC) [3] and UK TechDemoSat-1 (TDS-1) missions [4,5]
This work provides an assessment of Cyclone Global Navigation Satellite System (CyGNSS) L1 v3.0 products, which have been recently updated to feature a novel calibration approach that includes the capability to exploit data collected from the zenith front-end to account for the variability of available
Analysis of the CyGNSS L1 normalised bistatic radar cross-section (NBRCS) shows good temporal stability and negligible inter-receiver and inter-antenna biases, which are constrained to ~0.1 dB and
Summary
1980s [1], and later in the early 1990s for ocean altimetry [2], the technology was later demonstrated from low-Earth-orbit altitudes by the UK-Disaster Monitoring Constellation (UK-DMC) [3] and UK TechDemoSat-1 (TDS-1) missions [4,5]. It has since been implemented as a dedicated mission with the NASA CyGNSS constellation of small satellites [6]. The normalised bistatic radar cross-section (NBRCS) describes the strength of the signal scattered of the rough surface in the direction
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