A scheme for reducing the effect of selective availability on precise geodetic measurements from the Global Positioning System

Abstract

From March to August 1990, the signals transmitted by the Block II satellites of the Global Positioning System (GPS) were dithered under a policy of “Selective Availability” (SA). The dithering appears as a ∼10−10 deviation of the satellite oscillator frequency, which, when accumulated over several minutes, can produce an error of ∼100 cycles (∼20 m) in the model for carrier beat phase. Differencing between simultaneously sampling receivers minimizes the error. If, however, the receivers do not sample simultaneously, it is necessary to model the frequency deviation, which we estimate from the phase observed at a station with a stable local oscillator. We apply such a model to data collected in March 1990 by TI4100 and Minimac receivers sampling at times separated by 0.92 s. Applying the algorithm significantly improves the root mean square (RMS) scatter of the estimated relative position vectors. The RMS scatter from a data set including dithered satellites is similar for both simultaneously and non‐simultaneously sampling receivers, a result which indicates that SA can be adequately modeled.

A unified analysis of crustal motion in Southern California, 1970-2004: The SCEC crustal motion map

“…The weaknesses of these early data are the sparse constellation of satellites and sparse network of global tracking stations used for orbits. For data collected in 1990 and 1991, processing became more challenging because of higher ionospheric activity; the limitations of codeless receivers used in both global tracking networks and in California surveys; and a difference of 0.08 s in the sampling times of different types of receivers [ Feigl et al , 1991]. To address these last two problems, we processed separately the global and regional data from each group of receivers that shared a common time tag, and combined the solutions through orbit and Earth orientation parameters.…”

Distribution of slip at the northern Sumatran fault system

“…Nevertheless, we were able to obtain good dual-frequency data froln the remaining (TI-4100) GPS receivers. In-1990 the combined adverse effects of GPS selective availability (SA) and unsynchronized global tracking [Feigl et al, 1991] reduced geodetic precision compared to surveys in subsequent years. These later surveys also benefited from improved receiver technology, increasingly favorable satellite constellation, and the establishment of the International GPS Service in 1992 with a robust global GPS tracking network [Beutler et al, 1993].…”

“…Nevertheless, we were able to obtain good dual-frequency data froln the remaining (TI-4100) GPS receivers. In-1990 the combined adverse effects of GPS selective availability (SA) and unsynchronized global tracking [Feigl et al, 1991] …”

Space Geodetic Measurements of Plate Boundary Deformation in the Western U.S. Cordillera

“…The first step, which involved reduction of the raw space geodetic data, was largely performed by others (Table 1). GAMIT employs a model for doublydifferenced carrier phase and a weighted least-squares algorithm [King et al, 1985;Bock et al, 1986;Schaffrin and Bock, 1988;Dong and Bock, 1989;Feigl et al, 1991] to derive estimates of site positions, 15-parameter satellite state vectors, Earth orientation parameters, time variable (piecewise linear) azimuthally asymmetric atmospheric delays, and integer phase biases. All analyses of GPS phase data were performed with the GAMIT software [King and Bock, 1999].…”