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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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As part of TOPEX altimeter verification, the Global Positioning System has been used to measure the baseline between the verification site at oil platform Harvest and a GPS antenna collocated with the satellite laser ranging site at Quincy, California.
Study of the September-October 1997 Umbria-Marche earthquakes that took place in Italy. Use joint inversion of GPS and SAR interferometry data.
This paper talks about how 2 spacecraft launches add two new instrumetns for climate monitoring and GPS radio occultations.
The IGS network today consists of 364 stations managed by about, 100 different agencies worldwide. The RINEX observations are contributed to the IGS Data Centers, which permanently archive the data and make it freely available to all users. The primary customer of the data set is the IGS Analysis Centers, which acquire the data for generation of precise GPS products such as ephemerides, clocks, earth orientation parameters, and station position and velocities.
GPS measurements collected between 1999 and 2002 in Marie Byrd Land, West Antarctica indicate no significant present motion between East and West Antarctica greater than 1-2 nm/yr.
The vertical temperature structure of the tropical atmosphere has been explained as controlled by the combined effect of three green house gases: water vapor, carbon dioxide, and ozone. Absorption by water vapor of the light reflected off the Earth's surface would determine the temperature lapse rate in the lower troposphere up to the bottom of the Tropical Transition Layer (TTL); radiative absorption by carbon dioxide would dominate the temperature lapse rate between the bottom of the TTL and the coldest point in the upper-troposphere, the cold point tropopause (CPT), and; absorption of incoming solar radiation by ozone would control the temperature above the CPT. The TTL region can thus be very sensitive to changes in the relative abundances of these greenhouse gases. In this contribution we describe the seasonal evolution of temperature profiles in the TTL and their longitudinal structure using GPS radio occultation.
Advancements in Global Positioning System (GPS) technology and its contributions to the evolution of surveying and geodesy are highlighted.
GPS tutorial presentation given by GSFC at NIST time and frequency seminar for more than the past 10 years. Minor updates from last year to keep current.
An autonomous GPS array is being implemented in the Transantarctic Mountains, sponsored by NSF and NASA, for the purpose of measuring uplift resulting from post-glacial rebound (PGR).
We present the first spaceborne observation of a Global Positioning System (GPS) signal reflected from the Earth's surface, specifically from the Pacific Ocean.
To provide delay corrections to single frequency users, wide area differential GPS systems depend upon accurate determination of ionospheric total electron content (TEC).
GPS observations in Costa Rica from 1994-1997 reveal a complex pattern of motion consistent with the superposition of seismic cycle and secular plate margin deformation.
Geopotential heights of constant pressure surfaces are retrieved from GPS radio occultation data. In order to assess accuracy, a subset of data obtained by GPS/MET during spring and summer 1995 are compared to the output of the ECMWF global model...
The International GPS Service for Geodynamics is an international scientific service which began formal operation at the beginning of 1994, following several years of planning and 1-1/2 year pilot service.
Based on realistic modeling of the electron density of the ionosphere and using a dipole moment approximation for the earth magnetic field, we are able to estimate the effect of the ionosphere on the GPS signal for a ground user. Our study implies reduction of the second-order ionospheric error to less than 2 mm on the average and, therefore, potential improvement of orbit determination and baseline solutions.
After a decade of preparation, the GPS precise orbit determinatin (POD) experiment on TOPEX/Poseidon is now yielding definite results.
Tomographic imaging of the ionosphere is examined using singular value decomposition analysis. The interdependency of the obtainable resolution, the accuracy of the solution and the noise data is explained. A simulation is illustrated where a true 2-D ionospheric structure is generated, and a tomographic inversion of the structure is carried out. Inclusion of data taken in an occultation geometry reveals the strength that is added by these data. The effect of the ionosphere on a GPS signal as viewed by a user in space is examined. Under somewhat strong solar conditions, the absolute bending of the signal is of the order of 0.01 degrees for the L1 signal; the phase advance can be as large as 90 meters.
In this paper we present results for CHAMP POD using the precise GPS measurements collected by the BlackJack receiver through the up-looking antenna. We will describe the quality of the tracking data, the tuning of the reduced-dynamic model for the 400-km orbit, and the various methods of evaluating the orbit accuracy.