Sensing the earth with the SGR-ReSI multi-antenna space GPS/GNSS receiver

SSTL has undertaken pioneering work in spaceborne GPS and GNSS, ranging from miniaturised space GPS receivers, to the GIOVE-A Galileo demonstrator satellite, which itself carried an experimental GEO GPS receiver. Recent activities in GNSS remote sensing undertaken by SSTL have included new reflected GNSS measurements over the poles from the experiment on the UK-DMC satellite, and in-orbit ionospheric scintillation measurements in connection with the Shrewsbury School instigated POISE experiment. SSTL with partners from The National Oceanographic Centre, the University of Bath and the Surrey Space Centre have been developing a new generation GNSS instrument, with funding from the UK Centre for Earth Observation Instrumentation (CEOI), to further exploit GNSS potential for remote sensing in the fields of ocean and atmospheric monitoring. GNSS-Radio Occultation is a technique that is already well established and current satellite missions are providing valuable data to scientists around the world. GNSS Reflectometry, on the other hand, is a relatively new application and this technique seeks to derive information about the Earth by looking at GNSS signals that have been reflected off the Earth's surface and subsequently received by a satellite in low Earth orbit. In the process of reflecting, these signals are distorted by the reflecting surface and, through the use of inversion models, it is possible to subsequently derive information about that surface from the signals. The driving application for this development is the monitoring of the Earth's oceans and, in particular, information about ocean roughness and wind speeds could be derived. Reflections off land and ice have also been detected and potentially contain a wealth of useful information. While the concept has been proven, more data from orbit is required to improve the models; the development of the SGR-ReSI (Space GNSS Receiver - Remote Sensing Instrument) seeks to address this. At its heart, the SGR-ReSI is a highly versatile, multi-frequency GNSS navigation receiver. With the addition of multiple front-ends, reconfigurable DSP capabilities, asmall data recorder and specialised antennas, the SGR-ReSI will support both Reflectometry and Radio Occultation applications. Building on SSTL's small satellite expertise and using state of the art technology, the instrument aims to provide a highly capable yet relatively compact and affordable way of studying the Earth from orbit, with core technology that can be reused for a new family of navigation-grade receivers.