GPS Precise Point Positioning Software for Ground Control Point Establishment in Remote Sensing Applications

In practice, the coordinates necessary in geometric rectification are usually derived from medium scale maps such as $1:\mathrm{50,000}$ or $1:\mathrm{25,000}$ scale topographic maps. However, the total positional error of any point on these maps may exceed 1.0 mm due to pointing uncertainty, position shift, and exaggeration from cartographic generalization, paper shrinkage, etc. As spatial resolution of satellite imagery such as Landsat 7 panchromatic, ASTER VNIR, Spot 5 are now in the range of 5–15 m, ground control point (GCP) coordinates derived from medium scale maps are no longer acceptable since the magnitude of positional error may be up to several pixels. Larger scale maps may be used, but their coverage is limited to urban and high-density areas. This problem may be alleviated by adopting differential global positioning system (DGPS) techniques which can provide coordinates of up to 1 m accuracy. However, the technique is effective only for short baselines because the unmodeled errors are directly proportional to the baseline length. The need for at least two GPS receivers to operate simultaneously during data acquisition renders the technique less than desirable for most remote sensing applications. Developing a GPS technique that not only requires the operation of a single GPS receiver, but also provides accurate positioning results suitable for GCP establishment of medium and high resolution satellite imagery is the focus of this research. Interest in single receiver positioning has been rekindled by the recent availability of postmission satellite clock and ephemeris information generated by various data analysis centers, as byproducts of the data processing carried out under the auspices of the International GPS Service. This paper describes how postmission information and advanced data processing techniques are introduced into the precise point positioning software to improve the positioning accuracy. The results presented in this paper clearly demonstrate that an accuracy of better than 1 m in horizontal components can be achieved over a 15 min observation period using a dual-frequency GPS receiver.