Abstract
Wind speed and direction are important essential climate variables (ECVs). GNSS-R is an emerging remote sensing technique that can be potentially used to retrieve wind speed from space. However, few studies have addressed the wind direction retrieval from spaceborne GNSS-R observables, namely the Delay Doppler map (DDM). In this study, the feasibility of retrieving wind direction from the synthetic DDMs is analyzed. First, the simulation tool P2EPS is used to generate the DDMs under different geometry configurations, wind speed, and wind direction. Then, DDM changes caused by the wind direction are investigated, and two metrics are proposed to retrieve the wind direction from the DDM shape changes. The influence on wind direction retrieval of the wind speed, receiver’s elevation, and azimuth is further discussed. Finally, the sensitivity of DDM changes to noise is investigated, as well as the impact of noise on these two metrics.
Highlights
Wind speed and direction are important essential climate variables (ECVs)
When signal-to-noise ratio (SNR) reaches to 11 dB, no more significant improvement can be seen with the further increase of SNR
This study has theoretically investigated the possibility to retrieve wind direction from spaceborne global navigation satellite system-reflectometry (GNSS-R) observables
Summary
Wind speed and direction are important essential climate variables (ECVs). Wind speed and direction drive the air-sea interaction and have an impact on the ocean’s surface, the evaporation rate, the mixing of surface waters, and the development of seiches and storm surges. After the UK-DMC, several other GNSS-R satellites followed, including the UK TechDemoSat-1 (TDS-1) launched in 2014 [2], UPC’s 3Cat-2 satellite [3], and NASA’s Cyclone Global Navigation Satellite System (CYGNSS) constellation [4] launched in 2016 Another opportunistic GNSS-R instrument turned to be the Soil Moisture Active Passive (SMAP) satellite launched in 2015, after the failure of its radar transmitter. Komjathy et al [33] retrieved ocean surface wind speed and wind direction using reflected GPS signals. All the above studies of wind direction either focused on reflected GPS-R airborne measurements [31,32,33,34] or its effects on the GNSS-R radar cross-section [35,36,37]. The sensitivity of the DDM changes caused by wind direction is discussed under the presence of noise, as well as the impact of noise on the two metrics
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