Showing papers by "Penina Axelrad published in 2000"
TL;DR: In this article, a theoretical model has been developed that describes the power of the reflected GPS signals for different time delays and Doppler frequencies as a function of geometrical and environmental parameters.
117 citations
01 Jan 2000
TL;DR: In this paper, a new research effort was described to extend the application of Global Positioning System (GPS) signal reflections, received by airborne instruments, to cryospheric remote sensing.
Abstract: This paper describes a new research effort to extend the application of Global Positioning System (GPS) signal reflections, received by airborne instruments, to cryospheric remote sensing. Their experimental results indicate that reflected GPS signals have potential to provide information on the presence and condition of sea and fresh-water ice as well as the freeze/thaw state of frozen ground. They show results from aircraft experiments over the ice pack near Barrow, Alaska indicating correlation between forward-scattered GPS returns and RADARSAT backscattered measurements.
103 citations
TL;DR: The analysis shows that a modest reduction in the acquisition threshold of the receiver enables reliable navigation performance even in very high orbits with unfavorable antenna placement restrictions.
Abstract: GPS is an enabling technology for autonomous spacecraft navigation, including mission concepts involving formation flying in highly eccentric orbits. However, to date most spaceborne GPS applications have been limited to low earth orbits or postprocessing applications. This paper describes the problems associated with using GPS in the high earth orbit (HEO) environment and presents a GPS receiver design optimized for these applications. The design builds upon the PiVoT receiver developed by Goddard Space Flight Center by incorporating the GPS Enhanced Orbit Determination (GEODE) navigation filter, a high-quality clock, and enhancements to basic receiver acquisition and tracking algorithms. Predicted navigation performance for several representative missions, including geosynchronous and geosynchronous transfer orbits, is presented. The analysis shows that a modest reduction in the acquisition threshold of the receiver enables reliable navigation performance even in very high orbits with unfavorable antenna placement restrictions.
37 citations
01 Jan 2000
TL;DR: In this article, initial estimates of ocean surface wind speed and direction based on observations of reflected GPS signals are presented and compared to QuikSCAT wind fields, and two wind speed estimates are generally in agreement to within 2-3 m/s, and under favorable conditions of well developed seas and stable winds, direction estimates agree to within 10 deg.
Abstract: Initial estimates of ocean surface wind speed and direction based on observations of reflected GPS signals are presented and compared to QuikSCAT wind fields. The two wind speed estimates are generally in agreement to within 2-3 m/s, and under favorable conditions of well developed seas and stable winds, direction estimates agree to within 10 deg. An overview of the GPS technique is presented as well as a presentation and discussion of these first results.
16 citations
24 Jul 2000
TL;DR: A satellite mission using reflected signals from GPS satellites to remotely sense ocean wind speed/direction and soil moisture has been proposed in this article, which relies on the measurements of forward scattered GPS waveforms which are sensitive to surface roughness and dielectric constant.
Abstract: A satellite mission using reflected signals from GPS satellites to remotely sense ocean wind speed/direction and soil moisture has been proposed. It relies on the measurements of forward scattered GPS waveforms which are sensitive to surface roughness and dielectric constant. By analyzing the distribution of the reflected signal in delay and Doppler, one can determine the surface characteristics. The proposed OWLS' satellite will host a set of nadir pointed antennas and a modified GPS receiver for making these measurements.
6 citations
17 Feb 2000
TL;DR: This final technical report summarizes the research performed by the Colorado Center for Astrodynamics Research for the Naval Research Laboratory on Spaceborne Differential GPS Applications over the period of September 1997 through 31 August 1999 on relative state estimation using GPS data from two vehicles.
Abstract: : This final technical report summarizes the research performed by the Colorado Center for Astrodynamics Research (CCAR) for the Naval Research Laboratory (NRL) on Spaceborne Differential GPS Applications over the period Ol September 1997 through 31 August 1999. The primary focus of our work was on relative state estimation using GPS data from two vehicles. Data from a spaceborne experiment conducted by NASA was used for algorithm development and performance analysis. An auxiliary area of research was the identification and reduction of multipath errors in GPS observations. This effort is key to full utilization of GPS for high precision applications such as attitude determination, differential GPS, and relative navigation. The report comprises three documents descrIbing the research. The first two are conference papers presented at ION GPS 99 describing the relative navigation and multipath research. The third is a doctoral dissertation research proposal written by Dolan Highsmith, summarizing his research on this project and plans for future work.