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A new application using reflected Global Positioning System (GPS) signals collected by a tightly integrated GPS receiver for ground object detection and soil moisture estimation is developed. Several operational considerations are discussed to successfully acquire and track the weakly reflected GPS signals from the ground surface. Both right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) antennas are employed so that the direct and reflected signals can be received simultaneously. The arrival direction of the signal may be along the reflected signal path or the line-of-sight of a particular satellite. Unlike most existing GPS reflection experiments, the goal of this paper is to exploit the carrier phase observables for soil moisture estimation and ground object detection. During the development and test stages, ground truth measurements are also performed for different soil water content over different surface roughness. The ground truth measurements are expected to be useful for the moisture content in a small sample to check with the moisture variations in the lots instead of using bulk samples. The roughness effect parameter is calibrated by accounting for the standard deviation of height on soil surface and reflective footprint from GPS RHCP/LHCP accurate positioning data.