2007 Vol. 32, No. 1
Since 60's of the 20 Century China has carried out six geodetic campaigns(1966,1975,1992,1998,1999 and 2005 respectively) for measuring the height of Qomolangma(Mt.Everest,ME) and the crustal movement in its northern surrounding area(area in shorter),independently or in cooperation with foreign countries.Large scale geodetic field work,data processing and scientific research have been done,dealing with positioning,height determination,gravimetry,astronomical measurement and atmospheric reflection observation etc.The height variation of the snow summit of ME and the crustal movement,horizontal and vertical,of the area determined with GPS and leveling techniques in this passing years have been briefly reviewed and analyzed.The height variation of the ME snow summit is,according to the GPS measurement in 1992 and 2005,that 25 cm has been descending in the past 13 years,i.e.with the descending rate of 1.8 cm/a.The average horizontal crustal movement in the area,according to the GPS measurement in 1992,1998 and 2005,moves in the direction of 45 NE at the speed of 4 cm/a.The average vertical crustal movement in the area is,according to the multi terms re-leveling between 1966 and 2005,that the ascending rate is 1.8 mm/a.A non-stationary phenomenon both in time and space of the horizontal and vertical crustal movement in the area is found.
The lunar satellite's kinematic law and dynamic partial equation are described,the applicability of dynamic method and kinemetic method in lunar satellite orbit determination are discussed,the computation mode and optimization algorithm to determine lunar gravity field from observation are summarized.Based on concluding the computation flow of lunar gravity field recovery,the method of dealing with the difficulty of unobservable to farside of lunar are analyzed on emphases.Finally,considering the point that our national "Chang'e 1" will be launched with a laser altimetry on it,the idea and its flow chart to determinate lunar gravity field model with the stronger correlation as a restriction between lunar topography and gravity field is proposed.
In order to solve the problems that The satellite-ground double differential phase observation of onboard GPS is given to determine the earth gravity model from GPS phase data onboard CHAMP and observations of 48 IGS tracking sites.The Cowell II numerical orbit integration and the partitioned Bayesian least squares estimation are used to calculate the spherical harmonic coefficients of the earth gravity field to 70 degrees.The maximum difference of geoid undulation between the model and EGM96(to 70 degrees) is 2.872 m.The difference accuracy of geoid undulation is 0.522 m and the average difference is(-0.003 m.) These indicate that there is no systematic difference between the model and EGM96.
Based on the theory of GPS/gravity boundary value problem,the errors caused gravity disturbances with by different precision are simulated and analyzed using numerical simulation methods,and some significative conclusions are obtained,which may direct practice.
By using of GEODYNⅡ from GSFC/NASA/USA and newly lunar gravity model LP165P from JPL/NASA/USA,the effects on the orbit revolutionary from different models by truncation to some degree and order are simulated and computed,the orbit revolutionary and analysis of orbital lifetime under different height,inclination and ellipticity with same lunar gravity model are computed.The results show that high inclination circular high orbit(150 km or 200 km) has better performance,with its orbit lasting more than one year without(alignment,) and its orbit can be computed with gravity model truncated in degree and order 100 without losing its accuracy.
In the case that the accurate coordinates of the monitoring point and reference station are known,a new method for integer ambiguity resolution—DC(direct calculation) is introduced.The results of tests indicate that the above algorithm can solve precisely and fast for the integer ambiguity.It is a good method for integer ambiguity resolution in GPS deformation monitoring.
A method is put forward,which is based on single point positioning to(eliminate) the satellite constellation revolving errors round the earth and systematic error ΔΩ in all satellite clocks in making autonomous orbit determination with distance and velocity observations among satellites.When all navigation satellites revolve an angel ΔΩ round the earth,the longitude of the station given by point positioning will deviate the same angel.According to this principle,we can determine the angel ΔΩ on ground station with accurate coordinates.When all satellite clocks contain the same systematic error,the clock bias of receiver determined by point positioning also contains the same time error Δt.Then the error Δt can be determined by comparing with standard time.The results of several examples show that the methods is feasible and practicable.
The coefficients in the empirical exponential function are estimated by using the residual of measurements,hence the stochastic model more realistically describes the noise and bias in measurements.By using of GPS data and broadcast ephemeris,the numerical results indicate the RMS with 0.81 m,1.21 m and 1.72 m in east,north,and up are obtained.
The problem of GPS single-point positioning in view point of nonlinear least square and the superiority of GA in solving GPS nonlinear optimization problems are analyzed.The results of the practical data processing show that it is feasible for GPS single-point positioning based on genetic algorithm to attain the precision of meters' level.Compared with the results of linear least square method,the results of genetic algorithm are in the same level of positioning precision.
The commonly-used GPS cycle-slip detecting observations are used to detect cycle slips by wavelet method.The minimum cycle slips that can be detected by wavelet transform are obtained,and the wavelet method is compared with high order time differences.Double-difference phase data of cycle slip occurring twice in short time is calculated.Results prove that wavelet method works also well.A method about how to repair cycle slips based on wavelet transform is presented.Then tests are carried out.Results indicate that the method is feasible.
Three functional models,polynomial,spectral analysis,and modified AR model,are fitted and compared in fitting and predicting the clock differences based on the data series derived from two-way satellite time and frequency transfer.A robust equivalent weight is applied,which controls the significant of outlying observations.Some conclusions show that the prediction precision of robust estimation is better than that of LS.The prediction precision calculated from smoothed observations is higher than that calculated from sampling observations.As a count of the obvious period variations in the time series,the prediction result of polynomial model is uncertainty.The prediction precision of spectral analysis is very low,but the main period variations can be determined.The 6-hour prediction RMS is 1 ns or so,when modified AR model is used.
The standardization of second order polynomial is described.The eigenvalues and eigenvectors of quadric coefficient matrix are used to describe the relation between surveying coordinates system and standardized coordinate system,in which conicoid equations are well expressed mathematically. The rotation angles are derived from eigenvector matrix.Then conicoid fitting model is developed using eigenvalues,rotation angles and shifts as parameters.The example shows the correctness of the model.
The adaptive sequential adjustment and the adaptive robust sequential adjustment are presented based on adaptive filtering and robust estimation principle.The estimation formula of the parameters for both the adaptive sequential adjustment and the adaptive robust sequential adjustment are derived.A numerical example is given.It is shown by the theory and calculation,that the adaptive sequential adjustment can balance the prior model information and the posterior observation information,and the adaptive robust sequential adjustment is not only simple in calculation but also can efficiently control the influences of the prior information disturbing of model parameters and the measurement outliers on the estimated parameters.
Height measurement accuracy is analyzed from InSAR basic theory based on the baseline projection both along horizontal direction and the line of sight direction.The effect formulas of slant range,baseline,phase and height etc.on height measurement accuracy are put forward both mutual influence and non-influence respectively,taking simultaneously into account the baseline projection along horizontal direction and the line of sight direction.It is shown from the formulas that the effect of these independent variables on height measurement accuracy is the special circumstances of non-independence.
The cause of azimuth base-line is described based on the characteristic of formation-flying satellites based InSAR system.The correcting method of phases is proposed,and the phase is produced by azimuth base-line.On the basis of this method,the phase correction of InSAR system of formation-flying satellites in the normal instance and the influence to the accuracy of InSAR DEM are analyzed.
The development of the image-based normalization technique used for Landsat Thematic Mapper/Enhanced Thematic Mapper Plus imagery is reviewed.The techniques perform radiometric calibration by converting the digital number of the Landsat imagery to at-satellite radiance and then to at-satellite reflectance using data normalization method.The validation case in this study shows that the illumination difference between the tested multitemporal Landsat TM images can be considerably reduced to one-third of that of the original DN-based image through the normalization technique.
A new 2D entropy image segmentation algorithm based on artificial immune is proposed.Experiment results on aerial images show good segmentation quality,and time consuming is cut down to as only 1.8% as that of the traditional method.It proves our algorithm's feasibility and validity on image segmentation.
A new approach for detecting and removing haze from panchromatic high-resolution remote sensing images based on undecimated wavelet transform is proposed.It involves detecting the haze areas and estimating its thickness from the scene by analyzing the low frequency information content,and rectifies the high frequency content by different amplitude according to different haze optical thickness.In our experiments,both visual inspection and statistical data show that the approach is valid.
The theoretical basis of complex wavelet is described together with its key properties;a new method for fusing remote sensing images based on complex wavelet is proposed.Experiment results show that the fusion method based on complex wavelet transform is remarkably better than that based on classical discrete wavelet transform.
An empirical algorithm is described,which is used to determine the case Ⅱ water from the MODIS image.The algorithm takes advantage of the characteristic that the apparent reflectance of the Case Ⅰ water and the Case Ⅱ water is same in SWIR band,but is considerably different in visible band.
An improved cone-shaped model is given in order to improve the old cone-shaped model.The new improved spatial direction-relation makes use of the ideas of both cone-shape model and direction-relation matrix model,which inherits their merits at same time,especially heightens the ability greately to express the spatial direction-relation between spatial objects effectively under the muilti-sacle circumstance,and the muilti-scale compatibility is considered.
Based on numerical calculation and error distribution mechanism of the linear entity in vector GIS,the modeling error theory of 2D generic curve in vector GIS has been researched.The concept named the equivalent probability density error model(Tepdem) is brought forward.The concepts and ascertaining methods on Scale factor used to determine the scale of Tepdem are presented.Based on the probability algorithm on a linear entity drops in its corresponding Tepdem and the probability confidence level,the scale of Tepdem to 2D generic curve are solved successfully.The theory and methods are provided,at the same time,the theory basis for GIS positional uncertainty research has been tamped to great extent.
The main fruits of hyper-graph's applications are summarized,the various spatio-temporal data model and spatio-temporal reasoning model are compared.Some new concepts of spatio-temporal model that is called spatio-temporal reasoning model based on hyper-graph theory are put forward.This model is used to the rotating planning management of tobacco in the Honghe Prefecture of Yunnan province.Through practice,this model has implemented the integration of space and time,having the complete connotation.