Spaceborne GNSS reflectometry for ocean winds: First results from the UK TechDemoSat‐1 mission

TLDR

TDS‑1 was launched in July 2014 and provides the first new spaceborne GNSS‑R data since 2003, but exploiting lower SNR signals requires accurate knowledge of the antenna beam, platform attitude, and instrument gain. This study demonstrates the capabilities of low‑cost, low‑mass, and low‑power GNSS‑R receivers ahead of their launch on the NASA Cyclone GNSS constellation in 2016. The authors developed and evaluated a wind‑speed algorithm using signal‑to‑noise ratio and the bistatic radar equation, calibrated against collocated ASCAT winds. First results show that TDS‑1 can retrieve ocean wind speeds up to 27.9 m/s with excellent data quality, and for SNRs above 3 dB the algorithm achieves unbiased retrievals with a precision of about 2.2 m/s between 3 and 18 m/s without calibration.

Abstract

Abstract First results are presented for ocean surface wind speed retrieval from reflected GPS signals measured by the low Earth orbiting UK TechDemoSat‐1 satellite (TDS‐1). Launched in July 2014, TDS‐1 provides the first new spaceborne Global Navigation Satellite System‐Reflectometry (GNSS‐R) data since the pioneering UK‐Disaster Monitoring Mission (UK‐DMC) experiment in 2003. Examples of onboard‐processed delay‐Doppler maps reveal excellent data quality for winds up to 27.9 m/s. Collocated Advanced Scatterometer (ASCAT) winds are used to develop and evaluate a wind speed algorithm based on signal‐to‐noise ratio (SNR) and the bistatic radar equation. For SNRs greater than 3 dB, wind speed is retrieved without bias and a precision around 2.2 m/s between 3 and 18 m/s even without calibration. Exploiting lower SNR signals, however, requires good knowledge of the antenna beam, platform attitude, and instrument gain setting. This study demonstrates the capabilities of low‐cost, low‐mass, and low‐power GNSS‐R receivers ahead of their launch on the NASA Cyclone GNSS (CYGNSS) constellation in 2016.