Wet tropospheric path delay can be a major error source for Global Positioning System (GPS) geodetic experiments. We investigate strategies for minimizing this error using data from CASA Uno, the first major GPS experiment in Central and South America, where wet path delays may be both high and variable. We compared wet path delay calibration using water vapor radiometers (WVRs) and residual delay estimation, with strategies where the entire wet path delay is estimated stochastically without prior calibration, using data from a 270 km test baseline in Costa Rica. Both approaches yield centimeter‐level baseline repeatability and similar tropospheric estimates, suggesting that WVR calibration is not critical for obtaining high precision results with GPS in the CASA region.
High‐accuracy sea surface positioning is required for sea floor geodesy, satellite altimeter verification, and the study of sea level. An experiment to study the feasibility of using the Global Positioning System (GPS) for accurate sea surface positioning was conducted. A GPS‐equipped buoy (floater) was deployed off the Scripps pier at La Jolla, California during December 13–15, 1989. Two reference GPS receivers were placed on land, one within ∼100 m of the floater, and the other about 80 km inland at the laser ranging site on Monument Peak. The position of the floater was determined relative to the land‐fixed receivers using: (a) kinematic GPS processing software developed at the National Geodetic Survey (NGS), and (b) the Jet Propulsion Laboratory's GIPSY (GPS Inferred Positioning SYstem) software. Sea level and ocean wave spectra were calculated from GPS measurements. These results were compared to measurements made with a NOAA tide gauge and a ParosTM pressure transducer (PPT). GPS sea level for the short 100‐m baseline agrees with the PPT sea level at the 1‐cm level and has an rms variation of 5 mm over a period of 4 hours. Agreement between results with the two independent GPS analyses is on the order of a few millimeters. Processing of the longer Monument Peak ‐ floater baseline is in progress and will require orbit adjustments and tropospheric modeling to obtain results comparable to the short baseline.
We present analysis results for Global Positioning System (GPS) measurements made at sites in Costa Rica during two campaigns in February and July 1991. GPS solutions for 5 sites (Limon, Liberia, Bratsi, ETCG, and Vueltas) reveal significant horizontal and vertical displacements relative to their February positions. Horizontal displacements relative to Liberia, measured 244.7 ± 0.8, 89.2 ± 0.9, 12.4 ± 1.3, and 1.9 ± 0.9 cm at Limon, Bratsi, Vueltas, and ETCG respectively. Vertical displacements relative to Liberia measured 163 ± 2.1, 15.3 ± 3.0, −10.5 ± 4.4, and −0.6 ±2.1 cm at Limon, Bratsi, Vueltas, and ETCG respectively. We find differences in the GPS derived vertical and horizontal displacements compared to other types of geodetic measurements of uplift in the coastal region and their associated models. To address these differences we compute a dislocation model which fits the GPS measured displacements. A simple uniform planar slip model can not reconcile the differences between the coastal uplift data or the seismic moment, suggesting considerable complexity of the earthquake source.
This chapter introduces the book, which deals with philosophical ethics. It is filled with challenging and provocative discussions on a wide range of philosophical positions and problems. All of these discussions are at least loosely presented as being in the service of the search for the supreme principle of morality. This chapter comments on the suggestion that there is a single true morality, a suggestion that has both a metaethical and a normative aspect. It argues that there are tensions in our common moral thought at least some of which are reflected in the differences among Kantian, contractualist, and consequentialist perspectives. One such tension, which is frequently associated with the difference between Kantian and consequentialist ethics, is that between respect for autonomy and concern for optimific results. The chapter considers how this tension disappears when the author of this book transforms Immanuel Kant's theory. It also examines the tensions between contractualist and noncontractualist theories, as well as the importance (or unimportance) of finding a supreme principle of morality.
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