Snow depth sensing using the GPS L2C signal with a dipole antenna
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RESEARCH
Open Access
Snow depth sensing using the GPS L2C signal with a dipole antenna Qiang Chen*, Daehee Won and Dennis M Akos
Abstract Prior research has shown that the currently deployed geodetic global positioning system (GPS) stations can be used to measure snow depth in an area around the antenna installation via GPS interferometric reflectometry (GPS-IR). Although such a technique provides the advantages of large spatial coverage and high temporal measurement sampling, there are also drawbacks in using geodetic equipment for this application. The geodetic antenna is costly and designed to mitigate the multipath signal, while for snow depth sensing, the reflective component contains the desired information regarding the environment. In this paper, the authors reviewed the principles of snow depth sensing via GPS-IR and show that the horizontally polarized electromagnetic wave is the desired signal for this application. A customized dipole antenna, which was designed to be horizontally polarized by properly adjusting its orientation, was built and evaluated in an experiment carried out at Table Mountain, Boulder, Colorado, during early February 2012. In this experiment, a universal software radio peripheral (USRP) is used to collect the raw data and a software-defined receiver (SDR) for L2C signal is used for data processing. Data and results from this dipole antenna/SDR implementation are compared with those from the geodetic GPS station and show an improvement for snow depth estimation. Keywords: Snow depth; GPS-IR; L2C; Dipole antenna; Remote Sensing
1 Introduction Seasonal snow cover is an important component in the investigation of the land surface climate and hydrology. The measurement of the amount of water stored in the snowpack and forecasting the rate of melt are essential for management of the water supply and flood control systems [1]. It has been shown that the current network of geodetic global positioning system (GPS) stations, which were installed for geophysical and surveying applications, are capable of measuring the snow depth in their vicinity using GPS interferometric reflectometry (GPS-IR) providing a large spatial footprint with a high update rate [2]. The principle for GPS-IR leverages the relationship between the variations of the GPS signal power, i.e., the signal-to-noise ratio (SNR) and the snow depth. Currently, there are 32 GPS satellites in operation and the period of a GPS satellite is approximately 24 h, which results in 64 available tracks (ascending and descending track) per day. The snow depth estimation via GPS-IR would process a * Correspondence: [email protected] Department of Aerospace Engineering and Sciences, University of Colorado, Boulder, CO 80309-0553, USA
period of SNR data within a particular elevation angle range and obtain a snow depth estimate for each track. Figure 1 from [2] shows the SNR before and after a 35-cm snowfall at Marshal, Colorado, from a geodetic GPS station. The signal coherently reflected off the ground coupled with the direct sign
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