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1.
计算交叉点是卫星测高数据处理中的重要基础性工作。扩展了交叉点存在的判断条件,可用于判断任意两条卫星地面轨迹是否有交叉点。提出了一种快速计算交叉点的数值算法--矩形收缩算法。采用一个周期的Topex/Poseidon（T/P）卫星模拟轨道和一条海洋二号（HY-2）卫星实际轨迹设计了两个算例,以验证算法的精度和效率。结果表明矩形收缩法可以快速、高精度地计算出全部交叉点。以Envisat数据为例验证了算法计算近极轨道两极交叉点的适用性。该方法不仅可以计算单一卫星轨迹的交叉点,也可计算两个不同倾角卫星的轨迹交叉点,具有很强的通用性。 相似文献
2.
We can presently construct two independent time series of sea level, each at a precision of a few centimeters, from Geosat
(1985–1988) and TOPEX/Poseidon (1992–1995) collinear altimetry. Both are based on precise satellite orbits computed using
a common geopotential model, JGM-2 (Nerem et al. 1994). We have attempted to connect these series using Geosat-T/P crossover
differences in order to assess long-term ocean changes between these missions. Unfortunately, the observed result are large-scale
sea level differences which appear to be due to a combination of geodetic and geopotential error sources. The most significant
geodetic component seems to be a coordinate system bias for Geosat sea level (relative to T/P) of −7 to −9 cm in the y-axis (towards the Eastern Pacific). The Geosat-T/P sea height differences at crossovers (with JGM-2 orbits) probably also
contain stationary geopotential-orbit error of about the same magnitude which also distort any oceanographic interpretation
of the observed changes. We also found JGM-3 Geosat orbits have not resolved the datum errors evident from the JGM-2 Geosat
-T/P results. We conclude that the direct altimetric approach to accurate determination of sea level change using Geosat and
T/P data still depends on further improvement in the Geosat orbits, including definition of the geocenter.
Received: 11 March 1996; Accepted: 19 September 1996 相似文献
3.
A detailed accuracy assessment of the geopotential model Jgm3 is made based on independent single- and dual-satellite sea-height
differences at crossovers from altimetry with Jgm3-based orbits. These differences, averaged over long time spans and in latitude
bands, are converted to spectra (latitude-lumped coefficients) by least-squares estimation. The observed error spectra so
obtained are then compared directly to error projections for them from the Jgm3 variance–covariance matrix. It is found from
these comparisons that Jgm3 is generally well calibrated with respect to the crossover altimetry of and between Geosat, TOPEX/Poseidon
(T/P), and Ers 1. Some significant discrepancies at a few lower orders (namely m=1 and 3) indicate a need for further improvement of Jgm3. A companion calibration (by order) of the geopotential model Jgm2
shows its variance–covariance matrix also to be generally well calibrated for the same single- and dual-satellite altimeter
data sets (but based on Jgm2 orbits), except that the error projections for Geosat are too pessimistic. The analysis of the
dual-satellite crossovers reveals possible relative coordinate system offsets (particularly for Geosat with respect to T/P)
which have been discussed previously. The long-term detailed seasonally averaged Geosat sea level with respect to T/P (covering
1985–1996) should be useful in gauging the relative change in sea level between different parts of the ocean over the single
4-year gap between these missions (1988–1992).
Received: 16 February 1998 / Accepted: 25 November 1998 相似文献
4.
The round-trip travel time measurements made by spacecraft laser altimeters are primarily used to construct topographic maps
of the target body. The accuracy of the calculated bounce point locations of the laser pulses depends on the quality of the
spacecraft trajectory reconstruction. The trajectory constraints from Doppler and range radio tracking data can be supplemented
by altimetric “crossovers”, to greatly improve the reconstruction of the spacecraft trajectory. Crossovers have been used
successfully in the past (e.g., Mars Orbiter Laser Altimeter on Mars Global Surveyor), but only with single-beam altimeters.
The same algorithms can be used with a multi-beam laser altimeter, but we present a method using the unique cross-track topographic
information present in the multi-beam data. Those crossovers are especially adapted to shallow (small angle) intersections,
as the overlapping area is large, reducing the inherent ambiguities of single-beam data in that situation. We call those “swath
crossovers”. They prove particularly useful in the case of polar-orbiting spacecraft over slowly rotating bodies, because
all the non-polar crossovers have small intersection angles. To demonstrate this method, we perform a simplified simulation
based on the Lunar Reconnaissance Orbiter (LRO) and its five-beam Lunar Orbiter Laser Altimeter. We show that swath crossovers
over one lunar month can independently, from geometry alone, recover the imposed orbital perturbations with great accuracy
(5 m horizontal, < 1 m vertical, about one order of magnitude smaller than the imposed perturbations). We also present new
types of constraints that can be derived from the swath crossovers, and designed to be used in a precision orbit determination
setup. In future work, we will use such multi-beam altimetric constraints with data from LRO. 相似文献
5.
A new method, called the fixed full-matrix method (FFM), is used to compute height changes at crossovers of satellite altimeter ground tracks. Using the ENVISAT data in East Antarctica, FFM results in crossovers of altimeter heights that are 1.9 and 79 times more than those from the fixed half method (FHM) and the one-row method (ORM). The mean standard error of height changes is about 14 cm from ORM, which is reduced to 7 cm by FHM and to 3 cm by FFM. Unlike FHM, FFM leads to uniform errors in the first-half and second-half height-change time series. FFM has the advantage in improving the accuracy of the change of height and backscattered power over ORM and FHM. Assisted by the ICESat-derived height changes, we determine the optimal threshold correlation coefficient (TCC) for a best correction for the backscatter effect on ENVISAT height changes. The TCC value of 0.92 yields an optimal result for FFM. With this value, FFM yields ENVISAT-derived height change rates in East Antarctica mostly falling between \(-3\) and 3 cm/year, and matching the ICESat result to 0.94 cm/year. The ENVISAT result will provide a constraint on the current mass balance result along the Chinese expedition route CHINARE. 相似文献
6.
Latitude-lumped coefficients (LLC) are defined, representing geopotential-orbit variations for dual-satellite crossovers (DSC). Formulae are derived for their standard errors from the covariances of geopotential field models. Numerical examples are
presented for pairs of the altimeter-bearing satellites TOPEX/Poseidon, ERS 1, and Geosat, using the error matrices of recent
gravity models. The DSC, connecting separate missions, will play an increasingly important role in oceanography spanning decades
only when its nonoceanographic signals are thoroughly understood. In general, the content of even the long-term averaged DSC
is more complex then their single satellite crossover (SSC) counterpart. The LLC, as the spatial spectra for the geopotential-caused
crossover effects, discriminate these source-differences sharply. Thus, the zero-order LLC in DSC data contains zonal gravity
information not present in SSC data. In addition, zero- and first-order LLC of DSC data can reveal a geocenter discrepancy
between the orbit tracking of the separate satellite missions. For example, DSC analysis from orbits computed with JGM 2 show
that the y-axis of the geocenter for Geosat in 1986–1988 is shifted with respect to T/P by 6–9 cm towards the eastern Pacific. Also,
where the time-gap is necessarily large (as between, say, Geosat and T/P missions) oceanographic (sea-level) differences in
DSC may corrupt the geopotential interpretation of the data. Most importantly, as we illustrate, media delays for the altimeter
(from the ionosphere, wet troposphere and sea-state bias) are more likely sources of contamination across two missions than
in SSC analyses. Again, the LLC of zero order best shows this contrast. Using the higher-order LLC of DSC for both Geosat-T/P
and ERS 1-T/P as likely representation of geopotential-only error, we show by comparison with the predicted standard errors
of JGM 2 that the latter's previously calibrated covariance matrix is generally valid.
Received: 14 February 1996 / Accepted: 27 March 1997 相似文献
7.
In the linear estimation problem associated with an experiment that is exactly repeated a number of times, the estimation
parameters may naturally be partitioned into two groups, those that are common to all repetitions, and those that are particular
to each repeat experiment. We derive least-squares solutions that minimise in norm either group of parameters, as also the
trace of the corresponding covariance matrix. These solutions are applied to the station adjustment of triangulation surveying,
and to the estimation problem of satellite radar altimetry: to estimate simultaneously mean sea surface heights and residual
radial orbit errors, while minimising the norm of either group of parameters. This altimetry problem is considered in the
cases of collinear, local crossover and global crossover data.
Received: 6 January 1997 / Accepted: 21 December 1998 相似文献
8.
P. Moore 《Journal of Geodesy》2001,75(5-6):241-254
Dual satellite crossovers (DXO) between the two European Remote Sensing satellites ERS-1 and ERS-2 and TOPEX/Poseidon are
used to (1) refine the Earth's gravity field and (2) extend the study of the ERS-2 altimetric range stability to cover the
first four years of its operation. The enhanced gravity field model, AGM-98, is validated by several methodologies and will
be shown to provide, in particular, low geographically correlated orbital error for ERS-2. For the ERS-2 altimetric range
study, TOPEX/Poseidon is first calibrated through comparison against in situ tide gauge data. A time series of the ERS-2 altimeter
bias has been recovered along with other geophysical correction terms using tables for bias jumps in the range measurements
at the single point target response (SPTR) events. On utilising the original version of the SPTR tables the overall bias drift
is seen to be 2.6±1.0 mm/yr with an RMS of fit of 12.2 mm but with discontinuities at the centimetre level at the SPTR events.
On utilising the recently released revised tables, SPTR2000, the drift is better defined at 2.4±0.6 mm/yr with the RMS of
fit reduced to 3.7 mm. Investigations identify the sea-state bias as a source of error with corrections affecting the overall
drift by close to 1.2 mm/yr.
Received: 25 May 2000 / Accepted: 24 January 2001 相似文献
9.
Parametric least squares collocation was used in order to study the detection of systematic errors of satellite gradiometer
data. For this purpose, simulated data sets with a priori known systematic errors were produced using ground gravity data
in the very smooth gravity field of the Canadian plains. Experiments carried out at different satellite altitudes showed that
the recovery of bias parameters from the gradiometer “measurements” is possible with high accuracy, especially in the case
of crossing tracks. The mean value of the differences (original minus estimated bias parameters) was relatively large compared
to the standard deviation of the corresponding second-order derivative component at the corresponding height. This mean value
almost vanished when gravity data at ground level were combined with the second-order derivative data set at satellite altitude.
In the case of simultaneous estimation of bias and tilt parameters from ∂2
T/∂z
2“measurements”, the recovery of both parameters agreed very well with the collocation error estimation.
Received: 10 October 1996 / Accepted 25 May 1998 相似文献
10.
Isaac Dadzie 《地球空间信息科学学报》2007,10(1):27-32
A new computational procedure for derivation of marine geoid on a 2.5′×2.5′grid in a non-tidal system over the South China Sea and the Philippine Sea from multi-satellite altimeter sea surface heights is discussed. Single-and dual-satellite crossovers were performed, and components of deflections of the vertical were determined at the crossover positions using Sand-well's computational theory, and gridded onto a 2.5′×2.5′resolution grid by employing the Shepard's interpolation procedure. 2.5′×2.5′grid of EGM96-derived components of deflections of the vertical and geoid heights were then used as reference global geopotential model quantities in a remove-restore procedure to implement the Molodensky-like formula via 1D-FFT technique to predict the geoid heights over the South China Sea and the Philippine Sea from the gridded altimeter-derived components of deflec-tions of the vertical. Statistical comparisons between the altimeter-and the EGM96- derived geoid heights showed that there was a root-mean-square agreement of ±0.35 m between them in a region of less tectonically active geological structures. However, over areas of tectonically active structures such as the Philippine trench, differences of about -19.9 m were obtained. 相似文献
11.
An algorithm （differential mode） is presented for the improvement of harmonic tidal analysis along T/P tracks, in which the differences between the observed sea surface heights at adjacent points are taken as observations. Also, the observation equations are constrained with the results of the crossover analysis; the parameter estimations are performed at 0.1° latitude intervals by the least squares. Cycle 10 to 330 T/P altimeter data covering the China Sea and the Northwest Pacific Ocean （2°-50° N,105°-150° E） are adopted for a refined along-track harmonic tidal analysis, and harmonic constants of 12 constituents in 8 474 points are obtained, which indicates that the algorithm can efficiently remove non-tidal effects in the altimeter observations, and improve the precision of tide parameters. Moreover, parameters along altimetry tracks represent a smoother distribution than those obtained by traditional algorithms. The root mean squares of the fitting errors between the tidal height model and the observations reduce from 11 cm to 1.3 cm. 相似文献
12.
A compendium of transformation formulas useful in GPS work 总被引：9，自引：1，他引：8
T. Soler 《Journal of Geodesy》1998,72(7-8):482-490
In order properly to apply transformations when using data derived from different GPS solutions, the effects of plate motion
on the coordinates should be accurately taken into consideration. Only then can a rigorous comparison be established between
results observed at different epochs. Equations are given to relate GPS-derived Cartesian coordinates and velocities affected
by changes of their reference frames and epochs.
Received: 16 June 1997 / Accepted: 22 April 1998 相似文献
13.
Gravity gradient modeling using gravity and DEM 总被引：2，自引：0，他引：2
A model of the gravity gradient tensor at aircraft altitude is developed from the combination of ground gravity anomaly data
and a digital elevation model. The gravity data are processed according to various operational solutions to the boundary-value
problem (numerical integration of Stokes’ integral, radial-basis splines, and least-squares collocation). The terrain elevation
data are used to reduce free-air anomalies to the geoid and to compute a corresponding indirect effect on the gradients at
altitude. We compare the various modeled gradients to airborne gradiometric data and find differences of the order of 10–20 E
(SD) for all gradient tensor elements. Our analysis of these differences leads to a conclusion that their source may be primarily
measurement error in these particular gradient data. We have thus demonstrated the procedures and the utility of combining
ground gravity and elevation data to validate airborne gradiometer systems. 相似文献
14.
Knowledge of the local direction of multipath at a particular site is important for a number of reasons. For example, such
information can be used to study site selections or during monument design for GPS installations. We present a MATLAB program
for creating colorized polar maps of high-frequency multipath using TEQC report files of single-epoch data. The maps, although
not necessarily indicating the actual local direction of multipath on the ground, give the orientation with respect to the
geometry of the satellites in the sky. This information can aid the interpretation of ground multipath geometry at the site.
We give an example of short-span data with ∼0.05 Hz multipath (i.e. repeat period ≈ 20 s) although the program can be modified
for long-term measurements as well. 相似文献
15.
嫦娥一号激光高度计数据交叉点分析与平差处理 总被引：1，自引：1，他引：0
本文对嫦娥一号激光高度计进行了轨道交叉点分析和平差方法研究。根据获取的912万个激光高度测量点进行交叉点计算,产生了整个月球表面140多万个轨道交叉点,对交叉点的位置分布特点与交叉点不符值的时间分布特性进行了系统分析,并运用4种基于时间的函数模型对交叉点不符值进行平差处理和对比分析。在试验区(0°N~60°N, 50°W~0°W)内,4种交叉点平差模型均能使交叉点高程不符值中误差从平差前的62.1m降至37m以内,在此基础上产生的DEM条带现象消失或减弱,表明交叉点平差能明显改进DEM的质量。 相似文献
16.
A technique is presented for the development of a high-precision and high-resolution mean sea surface model utilising radar
altimetric sea surface heights extracted from the geodetic phase of the European Space Agency (ESA) ERS-1 mission. The methodology
uses a cubic-spline fit of dual ERS-1 and TOPEX crossovers for the minimisation of radial orbit error. Fourier domain processing
techniques are used for spectral optimal interpolation of the mean sea surface in order to reduce residual errors within the
initial model. The EGM96 gravity field and sea surface topography models are used as reference fields as part of the determination
of spectral components required for the optimal interpolation algorithm. A comparison between the final model and 10 cycles
of TOPEX sea surface heights shows differences of between 12.3 and 13.8 cm root mean square (RMS). An un-optimally interpolated
surface comparison with TOPEX data gave differences of between 15.7 and 16.2 cm RMS. The methodology results in an approximately
10-cm improvement in accuracy. Further improvement will be attained with the inclusion of stacked altimetry from both current
and future missions.
Received: 22 December 1999 / Accepted: 6 November 2000 相似文献
17.
Orbit determination of the Lunar Reconnaissance Orbiter 总被引：3，自引：1，他引：2
We present the results on precision orbit determination from the radio science investigation of the Lunar Reconnaissance Orbiter
(LRO) spacecraft. We describe the data, modeling and methods used to achieve position knowledge several times better than
the required 50–100 m (in total position), over the period from 13 July 2009 to 31 January 2011. In addition to the near-continuous
radiometric tracking data, we include altimetric data from the Lunar Orbiter Laser Altimeter (LOLA) in the form of crossover
measurements, and show that they strongly improve the accuracy of the orbit reconstruction (total position overlap differences
decrease from ~70 m to ~23 m). To refine the spacecraft trajectory further, we develop a lunar gravity field by combining
the newly acquired LRO data with the historical data. The reprocessing of the spacecraft trajectory with that model shows
significantly increased accuracy (~20 m with only the radiometric data, and ~14 m with the addition of the altimetric crossovers).
LOLA topographic maps and calibration data from the Lunar Reconnaissance Orbiter Camera were used to supplement the results
of the overlap analysis and demonstrate the trajectory accuracy. 相似文献
18.
Assessment of long-range kinematic GPS positioning errors by comparison with airborne laser altimetry and satellite altimetry 总被引：3，自引：0，他引：3
Long-range airborne laser altimetry and laser scanning (LIDAR) or airborne gravity surveys in, for example, polar or oceanic
areas require airborne kinematic GPS baselines of many hundreds of kilometers in length. In such instances, with the complications
of ionospheric biases, it can be a real challenge for traditional differential kinematic GPS software to obtain reasonable
solutions. In this paper, we will describe attempts to validate an implementation of the precise point positioning (PPP) technique
on an aircraft without the use of a local GPS reference station. We will compare PPP solutions with other conventional GPS
solutions, as well as with independent data by comparison of airborne laser data with “ground truth” heights. The comparisons
involve two flights: A July 5, 2003, airborne laser flight line across the North Atlantic from Iceland to Scotland, and a
May 24, 2004, flight in an area of the Arctic Ocean north of Greenland, near-coincident in time and space with the ICESat
satellite laser altimeter. Both of these flights were more than 800 km long. Comparisons between different GPS methods and
four different software packages do not suggest a clear preference for any one, with the heights generally showing decimeter-level
agreement. For the comparison with the independent ICESat- and LIDAR-derived “ground truth” of ocean or sea-ice heights, the
statistics of comparison show a typical fit of around 10 cm RMS in the North Atlantic, and 30 cm in the sea-ice region north
of Greenland. Part of the latter 30 cm error is likely due to errors in the airborne LIDAR measurement and calibration, as
well as errors in the “ground truth” ocean surfaces due to drifting sea-ice. Nevertheless, the potential of the PPP method
for generating 10 cm level kinematic height positioning over long baselines is illustrated. 相似文献
19.
P. J. G. Teunissen 《Journal of Geodesy》1997,71(8):486-501
This contribution is the third of four parts. Based on the gain-number concept, canonical forms will be presented of the
ambiguity search spaces of the geometry-based model, the time-averaged model, and the geometry-free model. These forms reveal
the intrinsic geometry of the search spaces and allow one to study their size, shape, and orientation as function of data
precision, sampling rate, satellite redundancy, and change in receiver-satellite geometry. The canonical forms are also used
to address the problem of search halting. The phenomenon of search halting is explained and it is shown how decorrelating
ambiguity transformations can largely eliminate this computational burden.
Received: 16 July 1996 / Accepted: 14 November 1996 相似文献
20.
V. Kostoglodov R. W. Valenzuela A. Gorbatov J. Mimiaga S. I. Franco J. A. Alvarado R. Peláez 《Journal of Geodesy》2001,75(1):19-32
The Pacific coast of Guerrero state in Mexico is recognized as the `Guerrero seismic gap', with a high probability of producing
a large subduction earthquake (M > 8). A study of the vertical surface deformation was undertaken to understand the interseismic process of elastic strain
accumulation. Four leveling lines were installed in the states of Guerrero and Michoacán. Starting in 1995, several high-accuracy
leveling surveys have been carried out on those profiles once every year. The vertical uplift rate across the Guerrero coastal
region, as determined through the changes in repeated leveling surveys, suggests the accumulation of elastic strain at both
ends of the gap. In contrast, the sense of tilting in the middle of the gap is opposite to that observed at the ends and suggests
significant changes in the geometry of the locked zone and perhaps even slow strain release.
Received: 24 February 2000 / Accepted: 23 August 2000 相似文献