Miniature interferometer terminals for earth surveying

Counselman, C. C.; Shapiro, I. I.

doi:10.1007/bf02521086

Cited by 31 publications

(3 citation statements)

References 11 publications

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“…In the 1970s, a system of "miniature interferometer terminals for Earth surveying" was suggested, where "each receiver detects radio signals from low-power transmitters on Earth-orbiting satellites" (Counselman and Shapiro, 1979). This idea was inspired by Very-Long-Baseline Interferometry (VLBI), where radio signals from distant stars are observed at several positions on Earth.…”

Section: Passive Reception Of Microwave Signals: Global Navigation Sa...mentioning

confidence: 99%

Atomic clocks for geodesy

et al. 2018

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We review experimental progress on optical atomic clocks and frequency transfer, and consider the prospects of using these technologies for geodetic measurements. Today, optical atomic frequency standards have reached relative frequency inaccuracies below 10, opening new fields of fundamental and applied research. The dependence of atomic frequencies on the gravitational potential makes atomic clocks ideal candidates for the search for deviations in the predictions of Einstein's general relativity, tests of modern unifying theories and the development of new gravity field sensors. In this review, we introduce the concepts of optical atomic clocks and present the status of international clock development and comparison. Besides further improvement in stability and accuracy of today's best clocks, a large effort is put into increasing the reliability and technological readiness for applications outside of specialized laboratories with compact, portable devices. With relative frequency uncertainties of 10, comparisons of optical frequency standards are foreseen to contribute together with satellite and terrestrial data to the precise determination of fundamental height reference systems in geodesy with a resolution at the cm-level. The long-term stability of atomic standards will deliver excellent long-term height references for geodetic measurements and for the modelling and understanding of our Earth.

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Section: Passive Reception Of Microwave Signals: Global Navigation Sa...mentioning

confidence: 99%

Atomic clocks for geodesy

et al. 2018

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“…The satellite and receiver "clock" errors are easily and accurately dealt with using the method of double differencing, or its equivalent [e.g., Counselman and Shapiro, 1979;Wells et al, 1986], which uses between-station and between-satellite differences to estimate these quantities.…”

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confidence: 99%

Geodesy using the Global Positioning System: The effects of signal scattering on estimates of site position

Elósegui¹,

Davis²,

Jaldehag³

et al. 1995

J. Geophys. Res.

177

126

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Analysis of Global Positioning System (GPS) data from two sites separated by a horizontal distance of only ∼2.2 m yielded phase residuals exhibiting a systematic elevation angle dependence. One of the two GPS antennas was mounted on an ∼1‐m‐high concrete pillar, and the other was mounted on a standard wooden tripod. We performed elevation angle cutoff tests with these data and established that the estimate of the vertical coordinate of site position was sensitive to the minimum elevation angle (elevation cutoff) of the data analyzed. For example, the estimate of the vertical coordinate of site position changed by 9.7±0.8 mm when the minimum elevation angle was increased from 10° to 25°. We performed simulations based on a simple (ray tracing) multipath model with a single horizontal reflector which demonstrated that the results from the elevation angle cutoff tests and the pattern of the residuals versus elevation angle could be qualitatively reproduced if the reflector were located 0.1–0.2 m beneath the antenna phase center. We therefore hypothesized that the elevation‐angle‐dependent error was caused by scattering from the horizontal surface of the pillar, located a distance of ∼0.2 m beneath the antenna phase center. We tested this hypothesis by placing microwave absorbing material between the antenna and the pillar in a number of configurations and by analyzing the changes in apparent position of the antenna. The results indicate that (1) the horizontal surface of the pillar is indeed the main scatterer, (2) both the concrete and the metal plate embedded in the pillar are significant sources of scattering, and (3) the scattering can be reduced greatly by the use of microwave absorbing materials. These results have significant implications for the accuracy of global GPS geodetic tracking networks which use pillar‐antenna configurations identical or similar to the one used for this study at the Westford WFRD GPS site.

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“…The recognition that GPS could be utilized to achieve geodetic accuracies several orders of magnitude better than was originally conceived is usually attributed to Counselman and Shapiro [29]. Applying astronomical techniques developed for very long baseline interferometry (VLBI), they proposed using the carrier phase as the main GPS observable rather than the pseudorange.…”

Section: Data Analysis Strategiesmentioning

confidence: 99%

Geodetic techniques for time and frequency comparisons using GPS phase and code measurements

2005

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We review the development and status of GPS geodetic methods for high-precision global time and frequency comparisons. A comprehensive view is taken, including hardware effects in the transmitting satellites and tracking receiver stations, data analysis and interpretation, and comparisons with independent results. Other GPS techniques rely on single-frequency data and/or assume cancellation of most systematic errors using differences between simultaneous observations. By applying the full observation modelling of modern geodesy to dual-frequency observations of GPS carrier phase and pseudorange, the precision of timing comparisons can be improved from the level of several nanoseconds to near 100 ps. For an averaging interval of one day, we infer a limiting Allan deviation of about 1.4 × 10 −15 for the GPS geodetic technique. The accuracy of time comparisons is set by the ability to calibrate the absolute instrumental delays through the GPS receiver and antenna chain, currently about 3 ns. Geodetic clock measurements are available for most of the major timing laboratories, as well as for many other tracking stations and the satellites, via the routine products of the International GPS Service.

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Miniature interferometer terminals for earth surveying

Cited by 31 publications

References 11 publications

Atomic clocks for geodesy

Atomic clocks for geodesy

Geodesy using the Global Positioning System: The effects of signal scattering on estimates of site position

Geodetic techniques for time and frequency comparisons using GPS phase and code measurements

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