共查询到20条相似文献，搜索用时 938 毫秒
1.
Abstract Using GPS phase observations in the kinematic mode, we are able to achieve centimeter accuracy in relative three‐dimensional coordinates. This could be verified even for fast‐moving sensors in aircraft, such as airborne photogrammetric cameras, at the time of exposure. Sophisticated kinematic software has been developed resolving cycle slips and carrier‐phase ambiguities during motion. To determine the instantaneous sea surface, the GPS receiver is placed in a free‐drifting buoy with the antenna on top. Differencing the 1‐Hz observations, wave heights can be determined as well as velocity and direction of ocean (tidal) currents. This article deals with the experiences from a test for the practical realization of this proposal. Hardware installation, software, and data analysis are described. Plans to use such an observational scenario of a GPS buoy array in the North Sea for the calibration of the radar altimeter of the European satellite ERS‐1 are presented. 相似文献
2.
Abstract A project was initiated in 1986 to investigate an apparent significant discrepancy between geodetic and oceanographic leveling determinations of mean sea level around the coast of Great Britain. In oceanographic terms this discrepancy is equivalent to a sea slope in a North‐South direction. The project, which lasted for 3 years, has been carried out in conjunction with research groups at the University of Edinburgh, the Proudman Oceanographic Laboratory, and the Ordnance Survey of Great Britain. It has involved combining Global Positioning System (GPS)‐derived ellipsoidal height differences with a high‐precision geoid, leading to an independent determination of the orthometric heights of tide gauges along the east coast of Great Britain. A major GPS campaign was observed in May 1988. Measurements were made at time gauges between Leith and Lowestoft while simultaneously making measurements at fiducial sites. The results of the 1988 and subsequent campaigns are presented and discussed, and details are given of further observation campaigns to monitor the vertical movement of tide gauges around the coast of Britain by GPS. 相似文献
3.
Nigel R. L. Gooding 《Marine Geodesy》2013,36(3-4):197-203
Abstract The historical development of positioning in relation to the nautical chart is described. Present nautical charts are largely based on geodetic surveys which date from the nineteenth and early twentieth centuries. This gave rise to the use of many local datums and there has been a need to provide the mariner with information to enable him to transfer his position from one chart to an adjacent one on a different datum. The availability of the Global Positioning System (GPS) and the World Geodetic System 1984 (WGS84) datum enables positioning on a single worldwide datum to become a reality. The important factors affecting the adoption of WGS84 as the datum for nautical charts—namely, data availability and the practical and political considerations—are discussed. New developments in the use of nautical charts, the electronic chart display and information systems, and the delineation of international boundaries and territorial limits all give rise to the requirement for improved positional accuracies. Recent experience in the use of GPS both in the provision of control for shore stations of electronic position‐fixing systems and the provision of position for hydrographic surveys is briefly discussed. 相似文献
4.
Abstract During May 1985, a comprehensive GPS and acoustic navigation data set was collected off the Monterey, California coast. Three types of GPS units, a LORAN‐C, and a Miniranger operated concurrently with an OCEANO acoustic system to resolve state‐of‐the‐art accuracies for at‐sea geodetic positioning. This report details the acoustic system which displayed baseline errors of only ±0.25 m over distances to 2600 m. Unfiltered point‐to‐point acoustic navigation errors had a standard deviation of ± 1.25 m, which included ship motion errors in addition to surveying errors. Ninety percent of the stations had navigation standard deviations below ±0.75 m The experiment showed that sub‐meter acoustic surveying is the state‐of‐the‐art. 相似文献
5.
This study concerns the determination of a regional geoid model in the North Atlantic area surrounding the Azores islands by combining multi-mission altimetry from the ERS (European Remote Sensing) satellites and surface gravity data. A high resolution mean sea surface, named AZOMSS99, has been derived using altimeter data from ERS-1 and ERS-2 35-day cycles, spanning a period of about four years, and from ERS-1 geodetic mission. Special attention has been paid to data processing of points around the islands due to land contamination on some of the geophysical corrections. A gravimetric geoid has been computed from all available surface gravity, including land and sea observations acquired during an observation campaign that took place in the Azores in October 1997 in the scope of a European and a Portuguese project. Free air gravity anomalies were derived by altimetric inversion of the mean sea surface heights. These were used to fill the large gaps in the surface gravity and combined solutions were computed using both types of data. The gravimetric and combined solutions have been compared with the mean sea surface and GPS (Global Positioning System)-levelling derived geoid undulations in five islands. It is shown that the inclusion of altimeter data improves geoid accuracy by about one order of magnitude. Combined geoid solutions have been obtained with an accuracy of better than one decimetre. 相似文献
6.
This study concerns the determination of a regional geoid model in the North Atlantic area surrounding the Azores islands by combining multi-mission altimetry from the ERS (European Remote Sensing) satellites and surface gravity data. A high resolution mean sea surface, named AZOMSS99, has been derived using altimeter data from ERS-1 and ERS-2 35-day cycles, spanning a period of about four years, and from ERS-1 geodetic mission. Special attention has been paid to data processing of points around the islands due to land contamination on some of the geophysical corrections. A gravimetric geoid has been computed from all available surface gravity, including land and sea observations acquired during an observation campaign that took place in the Azores in October 1997 in the scope of a European and a Portuguese project. Free air gravity anomalies were derived by altimetric inversion of the mean sea surface heights. These were used to fill the large gaps in the surface gravity and combined solutions were computed using both types of data. The gravimetric and combined solutions have been compared with the mean sea surface and GPS (Global Positioning System)-levelling derived geoid undulations in five islands. It is shown that the inclusion of altimeter data improves geoid accuracy by about one order of magnitude. Combined geoid solutions have been obtained with an accuracy of better than one decimetre. 相似文献
7.
Tad Murty 《Marine Geodesy》2013,36(4):331-332
Optimal interpolation in the spatial domain is limited by computer storage requirements and the computational effort to invert the autocovariance matrix. The procedure can be simplified by use of the fast Fourier transform (FFT), where matrix inversion is replaced by a quotient of power spectral density (PSD) functions in the spectral domain. Such a methodology is developed and utilized to estimate an altimetric mean sea surface from a single 35‐day cycle of ERS‐1. ERS‐1 radial orbit error is first reduced by minimizing dual crossover residuals with TOPEXIPoseidon through solution for a sinusoidal correction for each ascending and descending arc along with the relative altimeter bias. A regular grid for ascending (descending) arcs is then formed by use of the equator‐crossing longitudes and the along‐track displacement. Gaps in the altimeter data set are filled by use of a reference model. PSDs derived from the data and reference surface enable computation of the least‐Squares estimator in the spectral domain, from which the optimally interpolated surface heights for ascending (descending) arcs are derived by the inverse Fourier operator. The resolution is bounded across track by the Nyquist frequencies, which for the 35‐day repeat period correspond to 1.44° longitudinal spacings or 160 km. For consistency, the along‐track resolution is reduced to a comparable level. The combination of the ascending and descending sea surface heights yields a surface up to the isotropic frequency that corresponds to surface spherical harmonics of degree and order 250. Comparisons show that the model performs almost as well as the Ohio State University model present on the TOPEXIPoseidon CD‐ROMs. 相似文献
8.
J. Gómez-Enri M. A. Srokosz C. P. Gommenginger P. G. Challenor M. P. Milagro-Pérez 《Marine Geodesy》2013,36(3):217-233
An adequate conceptual definition of the geoid is essential for the unambiguous combination of satellite tracking data, satellite al‐timetry, and surface gravity measurements to obtain sea surface topography. The factors influencing the selection of a particular level surface of the earth's gravity field include the purpose(s) for which the geoid is to be used at the 5‐cm level, and the types of data to be used in achieving these objectives. The principal reasons for high precision determinations of the shape of the geoid are: the determination of sea surface topography for applications in oceanography; and the unification of leveling datums with a resolution equivalent to that of first order geodetic leveling. A conceptual definition of the geoid acceptable to oceanographers would be: The geoid for a selected epoch of measurement is that level surface of the earth's gravity field in relation to which the average non‐tidal (or quasi‐stationary) sea surface topography is zero as sampled globally in ocean regions. In the geodetic context, it would be convenient, though not essential, to modify this definition in such a way that the global sea surface topography had zero mean as sampled for evaluations of the geodetic boundary value problem. In either case, a basis exists for unifying all leveling datums serving areas in excess of 106 km2, using either gravity anomaly data for the regions or precise determinations of position at first order bench marks. Unfavorable signal‐to‐noise ratios can pose problems when dealing with datums serving smaller areas. Elevation and gravity data banks must be correctly referenced to leveling datums prior to use in sea surface topography determinations. A recent attempt to upgrade the Australian gravity anomaly data bank indicates that all current data banks of this type are inadequate for the task. It is unlikely that time variations in the radial position of the geoid as conceptually defined above, will exceed ±5 cm per century, provided the rate of earth expansion was less than 1 part in 1010 yr‐l and there is no dramatic change in the present rate of secular change in Mean Sea Level. 相似文献
9.
On May 22 and 24, 1995, a buoy, designed to float with the water surface and equipped with a GPS antenna, was deployed off the California coast at 16 locations near the Texaco oil platform, Harvest. The purpose of this deployment was threefold:.(1) to demonstrate the ability of this style of buoy to calibrate the TOPEXIPOSEIDON (TIP) altimeter range measurement as it overflew the platform: (2) to demonstrate the ability of the buoy to map the ocean's surface over a 10‐km‐diameter circle surrounding platform Harvest; and (3) to demonstrate the ability of the buoy to measure the sea state accurately. During the 1.6‐h period surrounding the time of the TIP overflight, the buoy‐measured sea level never differed by more than 1.5 cm from the sea level measured by the National Oceanic and Atmospheric Administration (NOAA) acoustic tide gauge on the platform. The good agreement demonstrated the capability of this style of buoy to calibrate altimetric satellites. A paraboloid was fitted to sea level from 16 buoy locations surrounding the platform with a 2.5‐cm rms residual. On a 10‐km‐diameter circle centered on the platform, the paraboloid was within 2.4‐cm rms of the Ohio State University Mean Sea Surface (OSUMSS95). H u3 values calculated around the overflight times from the GPS buoy vertical positions had a mean difference of 2 cm and a standard deviation of 18 cm from values calculated from the University of Colorado (CU) pressure gauge system. At the time of the overflight, H u3 was near 2 m, while 3‐m seas were observed by the CU pressure system during measurements later in the day. This experiment demonstrates that a simple wave‐rider buoy design can give comparable accuracies to that of more complex GPS platforms such as the University of Colorado's spar buoy, but is much easier to deploy and capable of being used in more severe weather conditions. Thus, such a buoy and derivative designs have great potential for calibrating altimetric experiments, and for oceanographic and geodetic mapping experiments. 相似文献
10.
《Marine Geodesy》2013,36(3-4):261-284
The double geodetic Corsica site, which includes Ajaccio-Aspretto and Cape Senetosa (40 km south Ajaccio) in the western Mediterranean area, has been chosen to permit the absolute calibration of radar altimeters. It has been developed since 1998 at Cape Senetosa and, in addition to the use of classical tide gauges, a GPS buoy is deployed every 10 days under the satellites ground track (10 km off shore) since 2000. The 2002 absolute calibration campaign made from January to September in Corsica revealed the necessity of deploying different geodetic techniques on a dedicated site to reach an accuracy level of a few mm: in particular, the French Transportable Laser Ranging System (FTLRS) for accurate orbit determination, and various geodetic equipment as well as a local marine geoid, for monitoring the local sea level and mean sea level. TOPEX/Poseidon altimeter calibration has been performed from cycle 208 to 365 using M-GDR products, whereas Jason-1 altimeter calibration used cycles from 1 to 45 using I-GDR products. For Jason-1, improved estimates of sea-state bias and columnar atmospheric wet path delay as well as the most precise orbits available have been used. The goal of this article is to give synthetic results of the analysis of the different error sources for the tandem phase and for the whole studied period, as geophysical corrections, orbits and reference frame, sea level, and finally altimeter biases. Results are at the millimeter level when considering one year of continuous monitoring; they show a great consistency between both satellites with biases of 6 ± 3 mm (ALT-B) and 120 ± 7 mm, respectively, for TOPEX/Poseidon and Jason-1. 相似文献
11.
P. Bonnefond P. Exertier O. Laurain Y. M nard A. Orsoni G. Jan E. Jeansou 《Marine Geodesy》2003,26(3):261-284
The double geodetic Corsica site, which includes Ajaccio-Aspretto and Cape Senetosa (40 km south Ajaccio) in the western Mediterranean area, has been chosen to permit the absolute calibration of radar altimeters. It has been developed since 1998 at Cape Senetosa and, in addition to the use of classical tide gauges, a GPS buoy is deployed every 10 days under the satellites ground track (10 km off shore) since 2000. The 2002 absolute calibration campaign made from January to September in Corsica revealed the necessity of deploying different geodetic techniques on a dedicated site to reach an accuracy level of a few mm: in particular, the French Transportable Laser Ranging System (FTLRS) for accurate orbit determination, and various geodetic equipment as well as a local marine geoid, for monitoring the local sea level and mean sea level. TOPEX/Poseidon altimeter calibration has been performed from cycle 208 to 365 using M-GDR products, whereas Jason-1 altimeter calibration used cycles from 1 to 45 using I-GDR products. For Jason-1, improved estimates of sea-state bias and columnar atmospheric wet path delay as well as the most precise orbits available have been used. The goal of this article is to give synthetic results of the analysis of the different error sources for the tandem phase and for the whole studied period, as geophysical corrections, orbits and reference frame, sea level, and finally altimeter biases. Results are at the millimeter level when considering one year of continuous monitoring; they show a great consistency between both satellites with biases of 6 ± 3 mm (ALT-B) and 120 ± 7 mm, respectively, for TOPEX/Poseidon and Jason-1. 相似文献
12.
The Northwest Atlantic Regional Energetics Experiment (REX) will study the dynamics and energetics of the Gulf Stream and associated rings. Bottom‐moored inverted echo sounders with pressure gauges (IES/PGs) will collect in situ data which both complement and augment the GEOSAT altimeter measurements in the Northwest Atlantic. The primary objective of these data will be the intercomparison of satellite and IES/PG measured fluctuations in sea surface topography and mean ther‐mocline depth. However, more detailed and absolute intercom‐parisons of these data would be available if the IES/PG could be positioned in an inertial reference frame while the measurements were taken. This paper presents an error model for computing the accuracy of positioning with a bottom beacon of the IES/PG type. Equations for studying the use of acoustic range data for locating an IES/PG with respect to a ship's track are developed and presented. The ship's track is assumed to be located in inertial space to the 1‐ to 2‐m level by application of the GPS (Mohan, 1983, 1984). Effects of depth‐dependent acoustic speed are included. Although IES/PGs as presently deployed would have to be modified to function as the type of ranging device described in this paper, the representative parameter values that have been calculated for the Northwest Atlantic REX show that sub‐1‐meter accuracy in location determination can be expected. A crucial factor is the measurement pattern, and recommendations for optimal patterns are presented. 相似文献
13.
Andrzej S. Lenart 《Marine Geodesy》2013,36(4):309-323
Abstract Simplified geodetic formulas for very long and medium geodesies used in the sea and air navigation as well as methodology and formulas for investigating errors involved in these simplifictions for any hyperbolic system are presented. 相似文献
14.
GPS buoy and pressure transducer results from the August 1990 Texaco Harvest Oil Platform Experiment
The Texaco Harvest Oil Platform Experiment took place August 22–28, 1990, off Point Conception, California. This platform has been designated as the NASA/JPL verification site for the TOPEX radar altimeter, which is to be launched in mid‐1992. The purpose of the experiment was to obtain measurements from GPS and other instrumentation that will be used at the site for the verification activities, and to determine the potential effects of the platform environment on the quality of the measurements. In conjunction with this experiment, a buoy equipped with a GPS receiver was floated in the vicinity of the platform for the purpose of measuring sea‐level change and waves relative to a reference receiver located on the platform. A pressure transducer installed at the site also provided sea‐level change and wave measurements relative to the platform. We present the data collection, processing, and analysis results comparing the GPS‐buoy and pressure transducer data. The GPS‐determined sea‐surface height measurements show 1.3‐cm agreement when compared with transducer‐determined heights taken over the same period of time. Low‐rate (15‐s) data were used to measure the change in sea‐level height due to tides, while high‐rate (1‐s) measurements provided temporal resolution sufficient for determining wave spectra. 相似文献
15.
Sea Surface Determination Using Long-Range Kinematic GPS Positioning and Laser Airborne Depth Sounder Techniques 总被引：3，自引：0，他引：3
Precise long-range kinematic GPS positioning requires the use of carrier phase measurements, the data processing of which suffers from the technical challenges of ambiguity resolution and cycle slip repair. In this paper, the combination of an ambiguity recovery technique and a linear bias correction method has been used to overcome such problems. An experiment was conducted to test the utility of this technique to determine aircraft height to high accuracy, over very long baselines (of the order of one thousand kilometres), in support of the Laser Airborne Depth Sounder (LADS). From a comparison of four independently derived trajectories, this airborne GPS kinematic positioning experiment has confirmed that the sea surface can be determined to centimetre accuracy. The sea surface profiles thus obtained can be used to correct the errors introduced by long period ocean swells. 相似文献
16.
Precise long-range kinematic GPS positioning requires the use of carrier phase measurements, the data processing of which suffers from the technical challenges of ambiguity resolution and cycle slip repair. In this paper, the combination of an ambiguity recovery technique and a linear bias correction method has been used to overcome such problems. An experiment was conducted to test the utility of this technique to determine aircraft height to high accuracy, over very long baselines (of the order of one thousand kilometres), in support of the Laser Airborne Depth Sounder (LADS). From a comparison of four independently derived trajectories, this airborne GPS kinematic positioning experiment has confirmed that the sea surface can be determined to centimetre accuracy. The sea surface profiles thus obtained can be used to correct the errors introduced by long period ocean swells. 相似文献
17.
Route height connection across the sea by using the vertical deflections and ellipsoidal height data
Distance between the main land and island is so long that it is very difficult to precisely connect the height datum across the sea with the traditional method like the trigonometric leveling,or it is very expensive and takes long time to implement the height transfer with the geopotential technique.We combine the data of GPS surveying,astro-geodesy and EGM2008 to precisely connect the orthometric height across the sea with the improved astronomical leveling method in the paper.The Qiongzhou Strait is selected as the test area for the height connection over the sea.We precisely determine the geodetic latitudes,longitudes,heights and deflections of the vertical for four points on both sides across the strait.Modeled deflections of the vertical along the height connecting routes over the sea are determined with EGM2008 model based on the geodetic positions and heights of the sea segmentation points from DNSC08MSS model.Differences of the measured and modeled deflections of the vertical are calculated at four points on both sides and linearly change along the route.So the deflections of the vertical along the route over the sea can be improved by the linear interpolation model.The results are also in accord with those of trigonometirc levelings.The practical case shows that we can precisely connect the orthometric height across the Qiongzhou Strait to satisfy the requirement of order 3 leveling network of China.The method is very efficient to precisely connect the height datum across the sea along the route up to 80 km. 相似文献
18.
Y. Gao 《Marine Geodesy》2013,36(4):279-288
Global positioning system (GPS) has found applications in various areas including marine geodesy. GPS positioning accuracy, however, is greatly degraded by GPS ephemeris and clock errors, particularly errors due to Selective Availability (SA). Thus, it is crucial to use precise ephemeris and clock corrections for users who require high position accuracy. Presently, precise ephemeris and clock corrections are available only in post‐mission. This paper investigates the generation of precise real‐time ephemeris and clock corrections and the positioning accuracy using them. In this research, precise real‐time ephemeris is generated from accurate dynamic orbit prediction and clock corrections are calculated using instantaneous GPS measurements. Numerical analysis using data from an actual GPS tracking network is performed that indicates use of precise ephemeris and clock corrections can improve the positioning accuracy to the one meter level. This accuracy is attainable in real‐time as the precise real‐time ephemeris and clock corrections become available in the future. 相似文献
19.
20.
Theo Engelis 《Marine Geodesy》2013,36(1):45-69
Abstract A set of time‐averaged sea surface heights at 1° intervals, derived from the adjusted SEASAT altimeter data, and the GEML2 gravity field are used to estimate the long‐wavelength stationary sea surface topography. In order to reduce the leakage of energy in the estimated sea surface topography, the GEML2 field is augmented by the Rapp81 gravity field to generate geoidal undulations with wavelengths consistent with the ones of sea surface heights. These undulations are subtracted from the sea surface heights, and the resulting differences are subjected to filtering in order to recover sea surface topography with minimum wavelengths of 6000 km and an estimated accuracy of 20–25 cm. These estimates agree well with oceanographic and other satellite‐derived results. The direction of current flow can be computed on a global basis using the spherical harmonic expansion of sea surface topography. This is done not only for the SEASAT/GEML2 estimates, but also using the recent dynamic topography estimates of Levitus. The results of the two solutions are very similar and agree well with the major circulation features of the oceans. 相似文献