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

Giuseppe Foti,Colette Robertson,Andrew Shaw,Josep Roselló,Martin Unwin,Christine Gommenginger,Philip Jales

doi:10.1002/2015gl064204

Abstract

AbstractFirst 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.

Highlights

Global Navigation Satellite System-Reflectometry (GNSS-R) is an innovative Earth observation technique that exploits signals of opportunity from Global Navigation Satellite System (GNSS) constellations after reflection on the Earth surface
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
First results were presented of ocean surface wind speed retrieval from reflected Global Positioning System (GPS) signals collected by the UK TechDemoSat-1 satellite launched in July 2014

Summary

Introduction

Global Navigation Satellite System-Reflectometry (GNSS-R) is an innovative Earth observation technique that exploits signals of opportunity from Global Navigation Satellite System (GNSS) constellations after reflection on the Earth surface. GNSS-R can provide geophysical information about a number of surface properties, its applications to Earth observation, including remote sensing of ocean roughness, soil moisture, snow depth, and sea ice extent [see, for example, Gleason, 2006; Cardellach et al, 2011]. With large and growing numbers of GNSS surface reflections available simultaneously at any point and time from GPS and other GNSS constellations (e.g., GLONASS, Galileo, Beidou, etc.), the technique offers the possibility of wide-swath sensing given appropriate receiver and antenna specifications. The final section highlights the specific technical constraints affecting GNSS-R wind retrieval on TDS-1 and indicates future work needed to fully demonstrate the wide-swath capabilities of the technique

GNSS-R on TechDemoSat-1

TDS-1 ReSI Data Collections

Wind Speed Inversion and the Bistatic Radar Equation

Geophysical Model Function and Early Validation Against ASCAT Winds

Findings

Summary and Conclusions