Analysis of reflected global positioning system signals as a method for the determination of soil moisture

The use of GPS signals reflected form the Earth has been proposed as an alternative method to remotely sense soil moisture. The determination of soil moisture through remote sensing offers a clear advantage over ground-based measurements for applications that requires either frequent measurements or measurements over large geographic areas. Using a Delay Mapping Receiver (DMR), a set of reflected signals were collected over Las Cruces, New Mexico, an area known to have low soil moisture contents throughout the year. This area is also characterized by small vegetation density. The amplitude of the reflected signals were analyzed and compared to the direct signals to determine soil moisture. In addition, the collected data is referenced to physical bodies (i.e. rivers, lakes, dry land) to show a correlation of the amplitude of the reflections to water content. Although the accuracy of this method is still to be determined, the data studied was found to vary proportionally to soil moisture contents. In addition, a method that incorporates terrain irregularities is briefly discussed as a means to reduce possible error sources. The usage of GPS reflections to detect soil moisture may be used as an aircraft-based passive remote sensing tool