NASA - National Aeronautics and Space Administration

The NASA-Langley GPS remote sensing (GPSRS) instrument simultaneously correlates the unique satellite pseudo-random noise (PRN) code in a given satellite signal with an instrument-generated copy of the code. For each surface measurement, the reflected signal is correlated at 14 successive delay times (or delay bins) relative to the arrival of the signal from the specular point. The correlation results are squared as part of instrument signal processing and recorded for later analysis.

Two GPS-derived classification features are merged with visible image data to create terrain-moisture (TM) classes, or visibly identifiable terrain or landcover classes containing a surface/soil moisture component. As compared to using surface imagery alone, classification accuracy is significantly improved for a number of visible classes when adding the GPS-based signal features. Since the strength of the reflected GPS signal is proportional to the amount of moisture in the surface, use of these GPS features provides information about the surface that is not obtainable using visible wavelengths alone. Application areas include hydrology, precision agriculture, and wetlands mapping.