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991.
992.
J. R. Smith 《The Photogrammetric Record》1998,16(91):157-157
993.
994.
G. M. Appleby 《Journal of Geodesy》1998,72(6):333-342
In this paper we describe the results of an analysis of a 2.5-year set of satellite laser range observations of the two Etalon
geodetic satellites. We fit continuous orbits to the range observations, and map the range residuals into series of equivalent
orbital element residuals, considering in detail the orbital longitude, eccentricity and nodal residuals. We use the longitude
residuals to study thermal effects acting on the satellites and compare the results with those published for the Lageos satellites.
We discuss the differences between the two series of eccentricity residuals, and again compare the results with those from
Lageos. Finally we use the nodal residuals to investigate the potential for determination of UT1 of the reference frame defined
by the orbits of the Etalon satellites.
Received: 30 January 1997 / Accepted: 11 December 1997 相似文献
995.
We have calculated vertical velocities and their change in time from three precise levellings in Finland, with central epochs
1902, 1946, and 1986. Models with and without simultaneous determination of heights give the same results for velocities.
Evidence for velocity change in time appears at first sight strong but on closer examination turns out to be inconclusive.
We offer an alternative explanation in terms of levelling errors and estimate them. A new uplift map closely reproduces main
features of earlier maps from partial data, but does not support some details in them.
Received: 27 January 1997/ Accepted: 20 April 1998 相似文献
996.
A. H. W. Kearsley R. Forsberg A. Olesen L. Bastos K. Hehl U. Meyer A. Gidskehaug 《Journal of Geodesy》1998,72(10):600-605
Two detailed geoids have been computed in the region of North Jutland. The first computation used marine data in the offshore
areas. For the second computation the marine data set was replaced by the sparser airborne gravity data resulting from the
AGMASCO campaign of September 1996. The results of comparisons of the geoid heights at on-shore geometric control showed that
the geoid heights computed from the airborne gravity data matched in precision those computed using the marine data, supporting
the view that airborne techniques have enormous potential for mapping those unsurveyed areas between the land-based data and
the off-shore marine or altimetrically derived data.
Received: 7 July 1997 / Accepted: 22 April 1998 相似文献
997.
A fast algorithm is proposed to integrate the trajectory of a low obiter perturbed by the earth's non-sphericity. The algorithm
uses a separation degree to define the low-degree and the high-degree acceleration components, the former computed rigorously,
and the latter interpolated from gridded accelerations. An FFT method is used to grid the accelerations. An optimal grid type
for the algorithm depends on the trajectory's permissible error, speed, and memory capacity. Using the non-spherical accelerations
computed from EGM96 to harmonic degree 360, orbit integrations were performed for a low orbiter at an altitude of 170 km.
For a separation degree of 50, the new algorithm, together with the predict-pseudo correct method, speeds up the integration
by 145 times compared to the conventional algorithm while keeping the errors in position and velocity below 10−4 m and 10−7 m/s for a 3-day arc.
Received: 28 July 1997 / Accepted: 1 April 1998 相似文献
998.
A sparse matrix method is developed for computing variance factors for block-diagonal, bordered systems of equations using
MINQUE (Minimum Norm Quadratic Unbiased Estimation). This method greatly reduces the computational effort required to apply
MINQUE, thus making it practical to compute variance factors for some very large systems of equations. The computer implementation
of the method is described and applied to the computation of variance factors for a combination of 1609 VLBI (Very Long Baseline
Interferometry) observing sessions. The purpose of this test was to compute a variance factor for each of the data sets and,
perhaps, to obtain more realistic variance estimates to replace those in common use for the analysis of VLBI data. It was
found that the method is satisfactory for use with such large problems, and the test served to verify that the variances in
current use in VLBI data adjustments are adequate.
Received: 26 November 1996 / Accepted: 12 December 1997 相似文献
999.
The first author commenced his experiences with aerial photography in 1945, when he joined the Royal Air Force (RAF). The aerial cameras used at that time were the Williamson F24 and F52, with Ilford HP3 and FP3 panchromatic films. Subsequently the Williamson F95 camera was tested against the USAF Sonne 11 camera. During his final years in the RAF, a variety of film types was employed: colour, monochrome infra-red and false colour infra-red. Additional experience was gained when the author was employed by the International Training Centre (ITC), The Netherlands and he saw the further development of the air camera from the Wild RC8 and Zeiss (Oberkochen) RMK 15/23 to the Wild RC20, Zeiss (Jena) LMK and Zeiss (Oberkochen) RMK TOP. He predicts that the future lies with digital cameras.
The second author started working with aerial photography in the 1950s. Details are given of cameras, visual navigation sights and survey aircraft dating from that period. Overseas operations, carried out mainly by Hunting Surveys and Fairey Surveys, posed particular problems because the majority of the work there was undertaken without the aid of existing maps. The introduction of external navigation systems is described, from the Decca ship navigation system, through the GNS-200 VLF/Omega low frequency radio system to INS, the Inertial Navigation System. The author later joined the ITC, which enabled him to participate in trials of the Computer-controlled Photo Navigation System. Eventually practical experience was gained with differential GPS, particularly in countries in southeast Asia. Aerial photography currently appears to benefit less from financial investment than the photographic, aviation and survey industries. However, the satisfaction of making a significant contribution to major overseas development projects outweighs the frustration of lack of acceptance of plans for the future of the air survey industry. 相似文献
The second author started working with aerial photography in the 1950s. Details are given of cameras, visual navigation sights and survey aircraft dating from that period. Overseas operations, carried out mainly by Hunting Surveys and Fairey Surveys, posed particular problems because the majority of the work there was undertaken without the aid of existing maps. The introduction of external navigation systems is described, from the Decca ship navigation system, through the GNS-200 VLF/Omega low frequency radio system to INS, the Inertial Navigation System. The author later joined the ITC, which enabled him to participate in trials of the Computer-controlled Photo Navigation System. Eventually practical experience was gained with differential GPS, particularly in countries in southeast Asia. Aerial photography currently appears to benefit less from financial investment than the photographic, aviation and survey industries. However, the satisfaction of making a significant contribution to major overseas development projects outweighs the frustration of lack of acceptance of plans for the future of the air survey industry. 相似文献
1000.
During a project concerned with DEM generation using SPOT stereoscopic imagery, difficulties were experienced when using Level 1B stereopairs for the task. This paper presents a mathematical solution to overcome this problem which has been implemented at the University of Glasgow. Results are included from experimental tests which were carried out over a test field in Jordan using this solution. These tests used five SPOT Level 1B stereopairs together with a single SPOT Level 1A stereopair for comparative purposes. The residual errors at the ground control points and independent check points are given and show that a satisfactory solution was achieved. 相似文献