Environmental Sensing A Revolution in GNSS Applications

J U L Y / A U G U S T 2 0 1 4 www.insidegnss.com In the past 20 years GPS has simultaneously revolutionized both our modern infrastructure (by providing real-time navigation, mapping, and timing support) and our geodetic/ surveying capabilities (by providing millimeter/centimeter-level positioning). At this point, most of the GNSS innovations we expect to see in the next decade will come from calculating positions more accurately and faster, while expanding from GPS to use of all available GNSS signals. Twenty years ago, in an article in ESA Journal (see Additional Resources section near the end of this article) Manual Martin-Neira presented a new application for GNSS. Instead of processing the direct GNSS signals for positioning, timing, and atmospheric studies, Martin-Neira suggested employing reflected GNSS signals as the measurement. The first GNSS reflection experiments were focused on altimetry, ocean winds, and soil moisture; later researchers evaluated GNSS reflectometry for sensing snow/ice and measuring vegetation growth. Each of these reflection studies used GNSS instruments specially designed to measure reflected signals. In contrast, geodesists and surveyors use GNSS instruments that we know are designed to suppress reflected signals (more commonly referred to as multipath). While these reflections are known to affect the accuracy of positions derived from these instruments, there is still no standardized approach that models (and eliminates) the effect of reflections. Increasingly sophisticated uses of GNSS observables have led to a new era in remote sensing. A team of researchers describe the results of the applications of interferometric reflectometry to measure snow depth, vegetation water content, and soil moisture. Environmental Sensing A Revolution in GNSS Applications