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1.
Mean sea surface heights and residual radial orbit errors are estimated simultaneously in a single global crossover adjustment
of multiple cycles of satellite altimetry data. The rank defect inherent in the estimation problem is explicitly identified
and treated in various ways to give solutions that minimise (in norm) either orbit errors or mean sea surface heights. The
rank defect gives rise to geographically correlated orbit error, consisting of those components of the orbit error or those
components of the map of sea surface heights which fall within the nullspace of the estimation problem and which cannot be
distinguished as orbit error or ocean signal. We show that, in the case of Topex/Poseidon data, the geographically correlated error consists largely of long-wavelength and long-period sea surface fluctuations, which
in the past has often been assigned as orbit error.
Received 11 September 1995; Accepted 2 September 1996 相似文献
2.
The crossover adjustment plays a central role in the processing of satellite altimeter measurements. The usual procedure
is to form sea surface height differences at crossover points, solve for the radial orbit error (with due attention to the
singular nature of the estimation problem) and then to construct altimetric sea-level maps using the mean sea surface heights
at the crossover points. Our approach is very different, to make direct use of measurements at crossover points without differencing
and to estimate simultaneously orbit parameters, mean sea surface height and sea surface height variability in a single, unified
adjustment. The technique is suited for repeat data over an area small enough that adjoining passes may be considered to be
parallel and to permit the solution of a set of linear equations of dimension equal to the number of crossover points. The
size of the numerical problem is almost independent of the number of repeat cycles of the altimeter mission. Explicit recognition
is given to the rank defect of the least-squares estimation problem; we show that, for an orbit model with r parameters, the rank defect of the local crossover problem is exactly r
2. The defect may be overcome by choosing an appropriate set of constraints – either giving a best fit of mean sea surface
heights to a reference surface, or minimising orbit parameters, or a minimum norm solution in which both mean sea surface
heights and orbit parameters are minimised. There is no need to choose a reference pass, all passes are treated equally and
data gaps are easily accommodated. Numerical results are presented for the south-western Indian Ocean, based on the first
2 years of altimeter data from the Geosat Exact Repeat Mission.
Received: 31 May 1996 / Accepted: 19 April 1997 相似文献
3.
M. C. Kim 《Journal of Geodesy》1997,71(12):749-767
The fundamental geometry of satellite ground tracks and their crossover problem are investigated. For idealized nominal ground
tracks, the geometry is governed by a few constant parameters whose variations lead to qualitative changes in the crossover
solutions. On the basis that the theory to locate crossovers has not been studied in sufficient detail, such changes are described
in regard to the number of crossover solutions in conjunction with their bifurcations. Employing the spinor algebra as a tool
for establishing the ground-track crossing condition, numerical methodologies to locate crossovers appearing in general dual-satellite
ground-track configurations are also presented. The methodologies are applied to precisely determined orbital ephemerides
of the GEOSAT, ERS-1, and TOPEX/POSEIDON altimeter satellites.
Received: 19 November 1996 / Accepted: 12 May 1997 相似文献
4.
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
5.
The goal of the OSIRIS-REx mission is to return a sample of asteroid material from near-Earth asteroid (101955) Bennu. The role of the navigation and flight dynamics team is critical for the spacecraft to execute a precisely planned sampling maneuver over a specifically selected landing site. In particular, the orientation of Bennu needs to be recovered with good accuracy during orbital operations to contribute as small an error as possible to the landing error budget. Although Bennu is well characterized from Earth-based radar observations, its orientation dynamics are not sufficiently known to exclude the presence of a small wobble. To better understand this contingency and evaluate how well the orientation can be recovered in the presence of a large 1\(^{\circ }\) wobble, we conduct a comprehensive simulation with the NASA GSFC GEODYN orbit determination and geodetic parameter estimation software. We describe the dynamic orientation modeling implemented in GEODYN in support of OSIRIS-REx operations and show how both altimetry and imagery data can be used as either undifferenced (landmark, direct altimetry) or differenced (image crossover, altimetry crossover) measurements. We find that these two different types of data contribute differently to the recovery of instrument pointing or planetary orientation. When upweighted, the absolute measurements help reduce the geolocation errors, despite poorer astrometric (inertial) performance. We find that with no wobble present, all the geolocation requirements are met. While the presence of a large wobble is detrimental, the recovery is still reliable thanks to the combined use of altimetry and imagery data. 相似文献
6.
联合TOPEX/Poseidon与Geosat/ERM测高资料建立区域潮汐模型的研究 总被引：2，自引：1，他引：2
利用近十年的T/P测高数据来反演南海(8°~23°N,109°~120°E)九个主要分潮的潮汐参数,并计算了Geosat/ERM卫星对应的各主分潮的混叠周期及Rayleigh周期。根据潮汐参数提取的要求,选取了7个主分潮,为了克服混叠影响,将T/P沿迹点处的主要分潮间的5组差比关系引入到Geosat沿迹点处,并利用T/P提供的Sa模型去除Sa对M2的扰动影响。精度估计的结果表明,Geosat/ERM反演的潮汐参数的精度与传统的月分析结果的精度相近;因差比关系的捆绑,整个全日和半日潮族迟角偏差相近,这主要和Geosat/ERM的轨道设计有关。本文的方法可以应用于利用轨道调整后的T/P卫星的测高数据提取潮汐参数。 相似文献
7.
This study evaluates the performance of two widely used GRACE solutions (CNES/GRGS RL02 and CSR RL04) in deriving annual and
inter-annual water mass variations in the Black Sea for the period 2003–2007. It is demonstrated that the GRACE derived water
mass variations in the Black Sea are heavily influenced by the leakage of hydrological signals from the surrounding land.
After applying the corresponding correction, we found a good agreement with water mass variations derived from steric-corrected
satellite altimetry observations. Both GRACE and altimetry show significant annual water mass variations of roughly 7 cm amplitude
peaking in May and a semi-annual signal of roughly 3 cm peaking in June and in December. The amplitude of the annual water
mass signal varies significantly from year to year and is significantly larger during 2004–2006 than in 2003 and 2007. This
is also in agreement with the steric corrected altimetry. 相似文献
8.
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
9.
The global positioning system (GPS) model is distinctive in the way that the unknown parameters are not only real-valued,
the baseline coordinates, but also integers, the phase ambiguities. The GPS model therefore leads to a mixed integer–real-valued
estimation problem. Common solutions are the float solution, which ignores the ambiguities being integers, or the fixed solution,
where the ambiguities are estimated as integers and then are fixed. Confidence regions, so-called HPD (highest posterior density)
regions, for the GPS baselines are derived by Bayesian statistics. They take care of the integer character of the phase ambiguities
but still consider them as unknown parameters. Estimating these confidence regions leads to a numerical integration problem
which is solved by Monte Carlo methods. This is computationally expensive so that approximations of the confidence regions
are also developed. In an example it is shown that for a high confidence level the confidence region consists of more than
one region.
Received: 1 February 2001 / Accepted: 18 July 2001 相似文献
10.
The single- and dual-satellite crossover (SSC and DSC) residuals between and among Geosat, TOPEX/Poseidon (T/P), and ERS
1 or 2 have been used for various purposes, applied in geodesy for gravity field accuracy assessments and determination as
well as in oceanography. The theory is presented and various examples are given of certain combinations of SSC and DSC that test for residual altimetry data errors, mostly of non-gravitational origin, of the order of a few centimeters.
There are four types of basic DSCs and 12 independent combinations of them in pairs which have been found useful in the present
work. These are defined in terms of the `mean' and `variable' components of a satellite's geopotential orbit error from Rosborough's
1st-order analytical theory. The remaining small errors, after all altimeter data corrections are applied and the relative
offset of coordinate frames between altimetry missions removed, are statistically evaluated by means of the Student distribution.
The remaining signal of `non-gravitational' origin can in some cases be attributed to the main ocean currents which were not
accounted for among the media or sea-surface corrections. In future, they may be resolved by a long-term global circulation
model. Experience with two current models, neither of which are found either to cover the most critical missions (Geosat &
TOPEX/Poseidon) or to have the accuracy and resolution necessary to account for the strongest anomalies found across them,
is described. In other cases, the residual signal is due to errors in tides, altimeter delay corrections or El Ni?o. (Various
examples of these are also presented.) Tests of the combinations of the JGM 3-based DSC residuals show that overall the long-term
data now available are well suited for a gravity field inversion refining JGM 3 for low- and resonant-order geopotential harmonics
whose signatures are clearly seen in the basic DSC and SSC sets.
Received: 15 January 1999 / Accepted: 9 September 1999 相似文献
11.
Aliasing of the diurnal and semi-diurnal tides is a major problem when estimating the ocean tides from satellite altimetry.
As a result of aliasing, the tides become correlated and many years of altimeter observations may be needed to seperate them.
For the three major satellite altimetry missions to date i.e., GEOSAT, ERS-1, and TOPEX/POSEIDON (T/P), the alias periods
as well as the Rayleigh periods over which the tides decorrelate can be identified. Especially in case of GEOSAT and ERS-1,
severe correlation problems arise. However, it is shown by means of covariance analyses that the tidal phase advance differences
on crossing satellite groundtracks can significantly reduce the correlations among the diurnal and semi-diurnal tides and
among these tides and the seasonal cycles of ocean variability. Therefore, it has been attempted to solve a multi-satellite
response tidal solution for the diurnal and semi-diurnal bands from a total of 7 years of altimetry. Unfortunately, it could
be shown that the GEOSAT and ERS-1 orbit errors are too large to improve a 3-year T/P tidal solution with about 2 years of
GEOSAT and 2 years of ERS-1 altimeter observations. However, these results are preliminary and it is expected that more accurate
orbits, which have become available recently for ERS-1, and additional altimeter data from ERS-2 and the GEOSAT Follow-On
(GFO) should lead to an improved T/P tidal model.
Received: 4 May 1999 / Accepted: 24 January 2000 相似文献
12.
Georges Blaha 《Journal of Geodesy》1982,56(3):209-219
The main goal of this paper is to show that the solution obtained by adjusting a free network via the inner adjustment constraint
method is the minimum norm solution. The latter is a special case of the class of “minimum trace” solutions, where the trace
of the variance-covariance matrix for the adjusted parameters is a minimum. The derivations are carried out in terms of pseudo-inverses,
the various other forms of generalized inverses having been left out of consideration. 相似文献
13.
A kinematic GPS methodology for sea surface mapping,Vanuatu 总被引：1，自引：0，他引：1
Marie-Noelle Bouin Valérie Ballu Stéphane Calmant Jean-Michel Boré Eric Folcher Jérôme Ammann 《Journal of Geodesy》2009,83(12):1203-1217
During the past few decades, satellite altimetry has brought tremendous new knowledge about the spatial and temporal variations
of sea surface heights over the Earth’s oceans. However, the precision is limited over short wavelengths and in coastal areas,
and other methods such as kinematic GPS may be needed to fill in this information. We present kinematic GPS work aimed at
mapping the sea surface height, with special attention to the precision one can expect. Active marine subduction zones, like
the Vanuatu archipelago, may present short wavelength, high amplitude undulations of the sea surface height that are difficult
to map with satellite altimetry. This paper presents the methodology used around Santo Island, in Vanuatu, to obtain a well-resolved
local sea surface map with a precision of 5–15 cm limited by the sea conditions and the distance from the coastal reference
station. We present the results of three campaigns in 2004, 2006 and 2007. Careful observation of the ship behaviour along
the surveys as well as simultaneous recording of the ship attitude variations is mandatory to obtain reliable results. We
show that the ship GPS antenna height varies with the ship’s velocity and we suggest a method to correct this effect. The
final precision is estimated using the crossover differences method. 相似文献
14.
The analysis of the time and space distribution of specular (reflecting) points in bistatic altimetry between GPS and CHAMP
satellites or SAC-C (taken as examples) is extended from Wagner and Klokočník (2003 J. Geod 77: 128–138). We demonstrate a
significantly higher number and density of reflecting points in bistatic altimetry in comparison with traditional monostatic
altimetry. After an outline of our older accuracy assessment for the vertical position of the reflecting point, we add a new
independent derivation and compare both approaches. We account for orbit errors of both the transmitters (GPS) and receiver
(CHAMP) satellites, and the measurement (delay) error. We found that the accuracy of the vertical position of the reflecting
point decreases only slowly with increasing off-nadir angle and that the orbit errors must be accounted for if decimeter and
better accuracy is required. In this paper, we do not study errors such as state of the ocean, technical parameters of the
receiving system, and atmospheric corrections. 相似文献
15.
The second European Remote Sensing satellite ERS-2, launched in 1995, is supported by satellite laser ranging (SLR), the
German precise range and range-rate equipment (PRARE) microwave tracking system, and radar altimetry (RA). SLR, PRARE and
crossover RA observations (XO/RA) from May, June, and July 1996 have been analyzed using the GEOSAT software developed at
Forsvarets forskningsinstitutt (FFI, The Norwegian defence research establishment). Orbits computed with the JGM3 gravity
model and the more recent EGM96 gravity model have been compared with orbits from other analysis centers. Based on these comparisons
in addition to the post-fit observation residuals, and results from internal orbital overlaps, we conclude that the radial
component of the ERS-2 orbit can be determined with a precision of 6 cm.
Received: 30 June 1997 / Accepted: 4 February 1998 相似文献
16.
On aggregation in spatial econometric modelling 总被引：1，自引：1，他引：0
Jean H.P. Paelinck 《Journal of Geographical Systems》2000,2(2):157-165
The spatial aggregation problem – also termed the modifiable areal unit problem – has attracted regular attention in spatial
statistics and econometrics. In this study econometric aggregation analysis is used to investigate the formal composition
of meso-areal parameters given micro-areal underlying relations with spatial dependence. Impact on stochastic terms (possible
meso-areal spatial autocorrelation) is also studied. Finally consequences for meso-areal estimation are derived, the general
finding having been that spatial aggregation leads to meso-region specific parameter values, with the estimation problems
this implies. 相似文献
17.
Quasi-stationary sea surface topography estimation by the multiple input/output method 总被引：1，自引：0，他引：1
Multiple input/multiple output system theory (MIMOST) is briefly presented, and the application of the method to the quasi-stationary
sea surface topography (QSST) estimation and the filtering of the input observations are discussed. The repeat character of
satellite altimetry missions provides more than one sample of the measured sea surface height (SSH) field, and an approximation
of the input signal and error power spectral densities can be determined using this successive information. A case study in
the Labrador Sea is considered using SSHs from ERS1 phases C and G, ERS1-GM, ERS2 phase A and TOPEX/POSEIDON altimetric missions
in combination with shipborne gravity anomalies. The time period of the observations in this study is from 1993 to 1998. Some
comparisons between the techniques used for the power spectral density approximation are carried out and some remarks on the
properties of the estimated QSST are presented.
Received: 19 October 1999 / Accepted: 23 October 2000 相似文献
18.
M. Schmidt 《Journal of Geodesy》1999,73(3):109-117
Geodetic adjustment problems frequently require the solution of large systems of linear equations. An approximation method
is presented based on the decomposition of the estimated covariance matrix of the observation matrix, calculated in a pre-processing
step, into a system of eigenvalues and eigenvectors. Neglecting the non-dominant eigenvalues and the assigned eigenvectors,
the matrix of the residuals is approximated applying the synthesis formula of principal-component analysis. Although the number
of observation vectors in the multivariate Gauss–Markoff model is drastically reduced, all unknown parameters are estimated
approximately. The described method is tested using a numerical example of satellite altimetry.
Received: 6 January 1997 / Accepted: 16 November 1998 相似文献
19.
Robust estimation of geodetic datum transformation 总被引：18，自引：1，他引：17
Y. Yang 《Journal of Geodesy》1999,73(5):268-274
The robust estimation of geodetic datum transformation is discussed. The basic principle of robust estimation is introduced.
The error influence functions of the robust estimators, together with those of least-squares estimators, are given. Particular
attention is given to the robust initial estimates of the transformation parameters, which should have a high breakdown point
in order to provide reliable residuals for the following estimation. The median method is applied to solve for robust initial
estimates of transformation parameters since it has the highest breakdown point. A smooth weight function is then used to
improve the efficiency of the parameter estimates in successive iterative computations. A numerical example is given on a
datum transformation between a global positioning system network and the corresponding geodetic network in China. The results
show that when the coordinates are contaminated by outliers, the proposed method can still give reasonable results.
Received: 25 September 1997 / Accepted: 1 March 1999 相似文献
20.
The parameter distributions of the integer GPS model 总被引：6，自引：0，他引：6
P. J. G. Teunissen 《Journal of Geodesy》2002,76(1):41-48
A parameter estimation theory is incomplete if no rigorous measures are available for describing the uncertainty of the parameter
estimators. Since the classical theory of linear estimation does not apply to the integer GPS model, rigorous probabilistic
statements cannot be made with reference to the classical results. The fact that integer parameters are involved in the estimation
process forces a reappraisal of the propagation of uncertainty. It is with this purpose in mind that the joint and marginal
distributional properties of both the integer and non-integer parameters of the GPS model are determined. These joint distributions
can also be used to determine the distribution of functions of the parameters. As an important example, the distribution of
the vector of ambiguity residuals is determined.
Received: 30 January 2001 / Accepted: 31 July 2001 相似文献