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1.
Tide gauge records of Hong Kong covering the past 45 years (1954.0–1999.0) are adopted to analyze the basic features of sea
level changes in the region. Data sets of atmospheric pressure, southern oscillation index and sea surface temperature during
the same time span are also used to determine the possible link between the sea level changes in Hong Kong and local and global
geophysical processes. Results indicate that the sea level of Hong Kong has a rising trend of 1.9 ± 0.4 mm per year, and that
there is an upward offset of about 15 cm in the pre-1957.0 tide gauge records. The effect of local atmospheric pressure variations
on the amplitude of the annual sea level change is about 30% of the amplitude that is calculated after the effect is corrected.
It is also found that the interannual variations in the sea level of Hong Kong are related to El Ni?o and La Ni?a events that
happen frequently in the tropical Pacific.
Received: 27 October 1999 / Accepted: 15 August 2000 相似文献
2.
In the southwest of China, one of the greatest threats to local ecosystem is the area expansion of an invasive species, i.e.,
Eupatorium adenophorum Spreng (EAS). In this study, the remote-sensing technology was used to detect and map the spatial distribution
of EAS in Guizhou Province, China. A series of vegetation indices, including normalized difference vegetation index (NDVI),
simple ratio index (SRI) and atmospherically resistant vegetation index (ARVI), were used to identify EAS from HJ-A Chninese
satellite data. According to the analysis results of fieldworks from March 21 to 22, 2009, it was found that the vegetation
index of {1.9589 ≤ SRI ≤ 4.1095}∩{0.2359 ≤ ARVI ≤ 0.5193} was the optimal remote-sensing parameter for identifying EAS from
HJ-A data. According to the spatial distribution of EAS estimated from HJ-A data, it was found that EAS was rather more in
southwest of Guizhou Province than in northeast. EAS became sparse from southwest to northeast gradually, and the central
Guizhou Province was the ecological corridor linking EAS in southwest to that in northeast. By comparison with validated data
collected by the government of Guizhou Province, it was found that the uncertainty of remote-sensing method was 18.52%, 29.31%,
8.77% and 9.46% in grassland, forest, farmland and others respectively, and the mean uncertainty was 13.29%. Owing to the
lower height of EAS than many plants in forest, the uncertainty of EAS was the greatest in forest than that in grassland,
farmland and so on. 相似文献
3.
The 2 arc-minute × 2 arc-minute geoid model (GEOID96) for the United States supports the conversion between North American
Datum 1983 (NAD 83) ellipsoid heights and North American Vertical Datum 1988 (NAVD 88) Helmert heights. GEOID96 includes information
from global positioning system (GPS) height measurements at optically leveled benchmarks. A separate geocentric gravimetric
geoid, G96SSS, was first calculated, then datum transformations and least-squares collocation were used to convert from G96SSS
to GEOID96.
Fits of 2951 GPS/level (ITRF94/NAVD 88) benchmarks to G96SSS show a 15.1-cm root mean square (RMS) around a tilted plane (0.06 ppm,
178∘ azimuth), with a mean value of −31.4 cm (15.6-cm RMS without plane). This mean represents a bias in NAVD 88 from global mean
sea level, remaining nearly constant when computed from subsets of benchmarks. Fits of 2951 GPS/level (NAD 83/NAVD 88) benchmarks
to GEOID96 show a 5.5-cm RMS (no tilts, zero average), due primarily to GPS error. The correlated error was 2.5 cm, decorrelating
at 40 km, and is due to gravity, geoid and GPS errors. Differences between GEOID96 and GEOID93 range from −122 to +374 cm
due primarily to the non-geocentricity of NAD 83.
Received: 28 July 1997 / Accepted: 2 September 1998 相似文献
4.
Unification of vertical datums by GPS and gravimetric geoid models with application to Fennoscandia 总被引：3，自引：0，他引：3
The second Baltic Sea Level (BSL) GPS campaign was run for one week in June 1993. Data from 35 tide gauge sites and five
fiducial stations were analysed, for three fiducial stations (Onsala, Mets?hovi and Wettzell) fixed at the ITRF93 system.
On a time-scale of 5 days, precision was several parts in 109 for the horizontal and vertical components. Accuracies were about 1 cm in comparison with the International GPS Geodynamical
Service (IGS) coordinates in three directions. To connect the Swedish and the Finnish height systems, our numerical application
utilises three approaches: a rigorous approach, a bias fit and a three-parameter fit. The results between the Swedish RH70
and the Finnish N 60 systems are estimated to −19.3 ± 6.5, −17 ± 6 and −15 ± 6 cm, respectively, by the three approaches.
The results of the three indirect methods are in an agreement with those of a direct approach from levelling and gravity measurements.
Received: 3 April 1996 / Accepted: 4 August 1997 相似文献
5.
Atmospheric modelling in GPS analysis and its effect on the estimated geodetic parameters 总被引：4，自引：2，他引：2
Permanently operating Global Positioning System (GPS) receivers are used today, for example, in precise positioning and determination
of atmospheric water vapour content. The GPS signals are delayed by various gases when traversing the atmosphere. The delay
due to water vapour, the wet delay, is difficult to model using ground surface data and is thus often estimated from the GPS
data. In order to obtain the most accurate results from the GPS processing, a modelling of the horizontal distribution of
the wet delay may be necessary. Through simulations, three such models are evaluated, one of which is developed in this paper.
In the first model the water vapour is assumed to be horizontally stratified, thus the wet delay can be described by only
one zenith parameter. The second model gives the wet delay with one zenith and two horizontal gradient parameters. The third
model uses the correlation between the wet-delay values in different directions. It is found that for large gradients and
strong turbulence the two latter models yield lower errors in the estimated vertical coordinate and wet-delay parameters.
For large gradients this improvement is up to 7 mm in the zenith wet-delay parameter, from 9 mm down to 2 and 4 mm for the
second and third models, respectively.
Received: 7 May 1998 / Accepted: 1 March 1999 相似文献
6.
7.
This paper discusses a modeling approach for spatial-temporal prediction of environmental phenomena using classified satellite
images. This research was prompted by the analysis of change and landscape redistribution of petroleum residues formed from
the residue of the burning oil wells in Kuwait (1991). These surface residues have been termed “tarcrete” (El-Baz et al. 1994).
The tarcrete forms a thick layer over sand and desert pavement covering a significant portion of south-central Kuwait. The
purpose of this study is to develop a method that utilizes satellite images from different time steps to examine the rate-of-change
of the oil residue deposits and determine where redistribution is are likely to occur. This problem exhibits general characteristics
of environmental diffusion and dispersion phenomena so a theoretical framework for a general solution is sought. The use of
a lagged-clique, Markov random field framework and entropy measures is deduced to be an effective solution to satisfy the
criteria of determination of time-rate-of-change of the surface deposits and to forecast likely locations of redistribution
of dispersed, aggraded residues. The method minimally requires image classification, the determination of time stationarity
of classes and the measurement of the level of organization of the state-space information derived from the images. Analysis
occurs at levels of both the individual pixels and the system to determine specific states and suites of states in space and
time. Convergence of the observed landscape disorder with respect to an analytical maximum provide information on the total
dispersion of the residual system.
Received: 5 September 2000 / Accepted: 10 July 2001 相似文献
8.
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
9.
Current activities and recent progress on constructive approximation and numerical analysis in physical geodesy are reported
upon. Two major topics of interest are focused upon, namely trial systems for purposes of global and local approximation and
methods for adequate geodetic application. A fundamental tool is an uncertainty principle, which gives appropriate bounds
for the quantification of space and momentum localization of trial functions. The essential outcome is a better understanding
of constructive approximation in terms of radial basis functions such as splines and wavelets.
Received: 4 May 1999 / Accepted: 21 May 1999 相似文献
10.
Observations of gravity and atmospheric pressure variations during the total solar eclipse of 11 July 1991 in Mexico City
are presented. An LCR-G402 gravimeter equipped with a feedback system and a digital data acquisition system scanned gravity
and pressure every second around the totality. On the pressure record an oscillation, starting at the totality, with a peak
to peak amplitude of 0.5 hPa and a periodicity of 40 to 50 min, can clearly be seen. This oscillation results from the thermal
shock wave produced by the Moon shadow travelling at supersonic speed. At the 0.1 μGal (1 nm · s−2) level all gravity perturbations are explained by the atmospheric pressure effect.
Received: 10 February 1995 / Accepted: 7 June 1996 相似文献
11.
A 2×2 arc-minute resolution geoid model, CARIB97, has been computed covering the Caribbean Sea. The geoid undulations refer
to the GRS-80 ellipsoid, centered at the ITRF94 (1996.0) origin. The geoid level is defined by adopting the gravity potential
on the geoid as W
0=62 636 856.88 m2/s2 and a gravity-mass constant of GM=3.986 004 418×1014 m3/s2. The geoid model was computed by applying high-frequency corrections to the Earth Gravity Model 1996 global geopotential
model in a remove-compute-restore procedure. The permanent tide system of CARIB97 is non-tidal. Comparison of CARIB97 geoid
heights to 31 GPS/tidal (ITRF94/local) benchmarks shows an average offset (h–H–N) of 51 cm, with an Root Mean Square (RMS) of 62 cm about the average. This represents an improvement over the use of a global
geoid model for the region. However, because the measured orthometric heights (H) refer to many differing tidal datums, these comparisons are biased by localized permanent ocean dynamic topography (PODT).
Therefore, we interpret the 51 cm as partially an estimate of the average PODT in the vicinity of the 31 island benchmarks.
On an island-by-island basis, CARIB97 now offers the ability to analyze local datum problems which were previously unrecognized
due to a lack of high-resolution geoid information in the area.
Received: 2 January 1998 / Accepted: 18 August 1998 相似文献
12.
This paper illustrates the surveys and the results obtained in an experiment whose goal is to evaluate the Global Positioning
System (GPS) sensitivity and accuracy for deformation control on non-permanent network of different extensions. To this aim
a high-precision device was properly built to set up known displacements along three orthogonal axes of a GPS antenna. One
of the antennas in the considered GPS networks was moved according to centimeter and sub-centimeter displacements; after careful
GPS data processing, it was evaluated whether these simulated deformations were correctly a posteriori detected and at which
probability level. This experiment was carried out both on a local (baselines ranging between 3 and 30 km) and on a regional
(baselines ranging between 300 and 600 km) GPS network. The results show that in the local network it is possible to identify
the displacements at a level of 10 mm in height and at a level of 5 mm in horizontal position. The analysis of the regional
network showed that it is fundamental to investigate new strategies to model the troposphere; in fact, it is necessary to
improve the precision of the height in order to correctly identify displacements lower than 60–80 mm; on the contrary, horizontal
displacements can be evidenced at the level of 20 mm.
Received: 27 April 1998 / Accepted: 14 December 1998 相似文献
13.
An algorithm for very accurate absolute positioning through Global Positioning System (GPS) satellite clock estimation has
been developed. Using International GPS Service (IGS) precise orbits and measurements, GPS clock errors were estimated at
30-s intervals. Compared to values determined by the Jet Propulsion Laboratory, the agreement was at the level of about 0.1 ns
(3 cm). The clock error estimates were then applied to an absolute positioning algorithm in both static and kinematic modes.
For the static case, an IGS station was selected and the coordinates were estimated every 30 s. The estimated absolute position
coordinates and the known values had a mean difference of up to 18 cm with standard deviation less than 2 cm. For the kinematic
case, data obtained every second from a GPS buoy were tested and the result from the absolute positioning was compared to
a differential GPS (DGPS) solution. The mean differences between the coordinates estimated by the two methods are less than
40 cm and the standard deviations are less than 25 cm. It was verified that this poorer standard deviation on 1-s position
results is due to the clock error interpolation from 30-s estimates with Selective Availability (SA). After SA was turned
off, higher-rate clock error estimates (such as 1 s) could be obtained by a simple interpolation with negligible corruption.
Therefore, the proposed absolute positioning technique can be used to within a few centimeters' precision at any rate by estimating
30-s satellite clock errors and interpolating them.
Received: 16 May 2000 / Accepted: 23 October 2000 相似文献
14.
Least-squares prediction using an empirically deduced local covariance function was performed to investigate the temporal
change in the rates of vertical crustal movements in the Tohoku district, Japan. Levelling data covering an area of approximately
450 × 275 km2 observed between 1966 and 1995 were used and the results shown in the form of contour maps. Firstly we derived a covariance
function of the rates of vertical crustal movement with a Gaussian form function. We used this function to estimate the spatial
distribution of the rates of vertical crustal movements. By the present method, a steady tilt of the Tohoku district to the
east, toward the Japan Trench and an areal uplift in the southwestern part were well reproduced. Moreover, a significant temporal
change in vertical movement rates is clearly seen.
Received: 15 July 1996 相似文献
15.
One of the aims of the Earth Explorer Gravity Field and Steady-State Ocean Circulation (GOCE) mission is to provide global
and regional models of the Earth's gravity field and of the geoid with high spatial resolution and accuracy. Using the GOCE
error model, simulation studies were performed in order to estimate the accuracy of datum transfer in different areas of the
Earth. The results showed that with the GOCE error model, the standard deviation of the height anomaly differences is about
one order of magnitude better than the corresponding value with the EGM96 error model. As an example, the accuracy of the
vertical datum transfer from the tide gauge of Amsterdam to New York was estimated equal to 57 cm when the EGM96 error model
was used, while in the case of GOCE error model this accuracy was increased to 6 cm. The geoid undulation difference between
the two places is about 76.5 m. Scaling the GOCE errors to the local gravity variance, the estimated accuracy varied between
3 and 7 cm, depending on the scaling model.
Received: 1 March 2000 / Accepted: 21 February 2001 相似文献
16.
C. Vigny J. Chéry T. Duquesnoy F. Jouanne J. Ammann M. Anzidei J.-P. Avouac F. Barlier R. Bayer P. Briole E. Calais F. Cotton F. Duquenne K. L. Feigl G. Ferhat M. Flouzat J.-F. Gamond A. Geiger A. Harmel M. Kasser M. Laplanche M. Le Pape J. Martinod G. Ménard B. Meyer J.-C. Ruegg J.-M. Scheubel O. Scotti G. Vidal 《Journal of Geodesy》2002,76(2):63-76
The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical
investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely
unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic
problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation
between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address
these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale
GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at
each site. GPS data processing has been done by three independent teams using different software. The different solutions
have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and
2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally
smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem
to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence
between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation
of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea
that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation.
Received: 27 November 2000 / Accepted: 17 September 2001 相似文献
17.
R. P. Singh S. Rovshan S. K. Goroshi S. Panigrahy J. S. Parihar 《Journal of the Indian Society of Remote Sensing》2011,39(3):345-353
The monitoring of terrestrial carbon dynamics is important in studies related with global climate change. This paper presents
results of the inter-annual variability of Net Primary Productivity (NPP) from 1981 to 2000 derived using observations from
NOAA-AVHRR data using Global Production Efficiency Model (GloPEM). The GloPEM model is based on physiological principles and
uses the production efficiency concept, in which the canopy absorption of photosynthetically active radiation (APAR) is used
with a conversion “efficiency” to estimate Gross Primary Production (GPP). NPP derived from GloPEM model over India showed
maximum NPP about 3,000 gCm−2year−1 in west Bengal and lowest up to 500 gCm−2year−1 in Rajasthan. The India averaged NPP varied from 1,084.7 gCm−2year−1 to 1,390.8 gCm−2year−1 in the corresponding years of 1983 and 1998 respectively. The regression analysis of the 20 year NPP variability showed significant
increase in NPP over India (r = 0.7, F = 17.53, p < 0.001). The mean rate of increase was observed as 10.43 gCm−2year−1. Carbon fixation ability of terrestrial ecosystem of India is increasing with rate of 34.3 TgC annually (t = 4.18, p < 0.001). The estimated net carbon fixation over Indian landmass ranged from 3.56 PgC (in 1983) to 4.57 PgC (in 1998). Grid
level temporal correlation analysis showed that agricultural regions are the source of increase in terrestrial NPP of India.
Parts of forest regions (Himalayan in Nepal, north east India) are relatively less influenced over the study period and showed
lower or negative correlation (trend). Finding of the study would provide valuable input in understanding the global change
associated with vegetation activities as a sink for atmospheric carbon dioxide. 相似文献
18.
Four different implementations of Stokes' formula are employed for the estimation of geoid heights over Sweden: the Vincent
and Marsh (1974) model with the high-degree reference gravity field but no kernel modifications; modified Wong and Gore (1969)
and Molodenskii et al. (1962) models, which use a high-degree reference gravity field and modification of Stokes' kernel;
and a least-squares (LS) spectral weighting proposed by Sj?berg (1991). Classical topographic correction formulae are improved
to consider long-wavelength contributions. The effect of a Bouguer shell is also included in the formulae, which is neglected
in classical formulae due to planar approximation. The gravimetric geoid is compared with global positioning system (GPS)-levelling-derived
geoid heights at 23 Swedish Permanent GPS Network SWEPOS stations distributed over Sweden. The LS method is in best agreement,
with a 10.1-cm mean and ±5.5-cm standard deviation in the differences between gravimetric and GPS geoid heights. The gravimetric
geoid was also fitted to the GPS-levelling-derived geoid using a four-parameter transformation model. The results after fitting
also show the best consistency for the LS method, with the standard deviation of differences reduced to ±1.1 cm. For comparison,
the NKG96 geoid yields a 17-cm mean and ±8-cm standard deviation of agreement with the same SWEPOS stations. After four-parameter
fitting to the GPS stations, the standard deviation reduces to ±6.1 cm for the NKG96 geoid. It is concluded that the new corrections
in this study improve the accuracy of the geoid. The final geoid heights range from 17.22 to 43.62 m with a mean value of
29.01 m. The standard errors of the computed geoid heights, through a simple error propagation of standard errors of mean
anomalies, are also computed. They range from ±7.02 to ±13.05 cm. The global root-mean-square error of the LS model is the
other estimation of the accuracy of the final geoid, and is computed to be ±28.6 cm.
Received: 15 September 1999 / Accepted: 6 November 2000 相似文献
19.
Spherical cap harmonic analysis: a comment on its proper use for local gravity field representation 总被引：1，自引：0，他引：1
Spherical cap harmonic analysis is the appropriate analytical technique for modelling Laplacian potential and the corresponding
field components over a spherical cap. This paper describes the use of this method by means of a least-squares approach for
local gravity field representation. Formulations for the geoid undulation and the components ξ, η of the deflection of the
vertical are derived, together with some warnings in the application of the technique. Although most of the formulations have
been given by another paper, these were confusing or even incorrect, mainly because of an improper application of the spherical
cap harmonic analysis.
Received: 16 January 1996 / Accepted: 17 March 1997 相似文献
20.
Fast and accurate relative positioning for baselines less than 20 km in length is possible using dual-frequency Global Positioning
System (GPS) receivers. By measuring orthometric heights of a few GPS stations by differential levelling techniques, the geoid
undulation can be modelled, which enables GPS to be used for orthometric height determination in a much faster and more economical
way than terrestrial methods. The geoid undulation anomaly can be very useful for studying tectonic structure. GPS, levelling
and gravity measurements were carried out along a 200-km-long highly undulating profile, at an average elevation of 4000 m,
in the Ladak region of NW Himalaya, India. The geoid undulation and gravity anomaly were measured at 28 common GPS-levelling
and 67 GPS-gravity stations. A regional geoid low of nearly −4 m coincident with a steep negative gravity gradient is compatible
with very recent findings from other geophysical studies of a low-velocity layer 20–30 km thick to the north of the India–Tibet
plate boundary, within the Tibetan plate. Topographic, gravity and geoid data possibly indicate that the actual plate boundary
is situated further north of what is geologically known as the Indus Tsangpo Suture Zone, the traditionally supposed location
of the plate boundary. Comparison of the measured geoid with that computed from OSU91 and EGM96 gravity models indicates that
GPS alone can be used for orthometric height determination over the Higher Himalaya with 1–2 m accuracy.
Received: 10 April 1997 / Accepted: 9 October 1998 相似文献