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1.
Based on the gravity field models EGM96 and EIGEN-GL04C, the Earth＇s time-dependent principal moments of inertia A, B, C are obtained, and the variable rotation of the Earth is determined. Numerical results show that A, B, and C have increasing tendencies; the tilt of the rotation axis increases 2.1×10^ 8 mas/yr; the third component of the rotational angular velocity, ω3 , has a decrease of 1.0×10^ 22 rad/s^2, which is around 23% of the present observed value. Studies show in detail that both 0 and ω3 experience complex fluctuations at various time scales due to the variations of A, B and C.  相似文献   

2.
Summary The geopotential on and outside the earth is represented as a series in surface harmonics. The principal terms in it correspond to the solid harmonics of the external potential expansion with the coefficients being Stokes’ constantsC nm andS nm . The additional terms which occur near the earth’s surface due to its non-sphericity and topography are expressed in terms of Stokes’ constants too. This allows performing downward continuation of the potential derived from satellite observations. In the boundary condition which correlates Stokes’ constants and the surface gravity anomalies there occur additional terms due to the earth’s non-sphericity and topography. They are expressed in terms of Stokes’ constants as well. This improved boundary condition can be used for upward and downward continuations of the gravity field. Simple expressions are found representingC nm andS nm as explicit functions of the surface anomalies and its derivatives. The formula for the disturbing potential on the surface is derived in terms of the surface anomalies. All the formulas do not involve the earth’s surface in clinations.  相似文献   

3.
Modern models of the Earth's gravity field are developed in the IERS (International Earth Rotation Service) terrestrial reference frame. In this frame the mean values for gravity coefficients of the second degree and first order, C 21(IERS) and S 21(IERS), by the current IERS Conventions are recommended to be calculated by using the observed polar motion parameters. Here, it is proved that the formulae presently employed by the IERS Conventions to obtain these coefficients are insufficient to ensure their values as given by the same source. The relevant error of the normalized mean values for C 21(IERS) and S 21(IERS) is 3×10−12, far above the adopted cutoff (10−13) for variations of these coefficients. Such an error in C 21 and S 21 can produce non-modeled perturbations in motion prediction of certain artificial Earth satellites of a magnitude comparable to the accuracy of current tracking measurements. Received: 14 September 1998 / Accepted: 20 May 1999  相似文献   

4.
    
The methods of using earth satellites for determining the motion of the earth’s axis of rotation and of the earth’s principal axis of maximum inertia are discussed. Some simple formulae are also presented for evaluating the influence of various error sources in the orbital calculations on the pole coordinates and these offer some explanations of the frequencies found in the spectrum of the pole coordinates obtained by Anderle and Beuglass (1970). Initial calculations with existing laser data were attempted but the results were quite unsatisfactory due to the poor distribution of the data along the orbit. Some conclusions have however been drawn from these calculations that may be useful for future studies when better distributed data becomes available.  相似文献   

5.
Time variations in the Earths gravity field at periods longer than 1 year, for degree-two spherical harmonics, C21, S21, and C20, are estimated from accurately measured Earth rotational variations. These are compared with predictions of atmospheric, oceanic, and hydrologic models, and with independent satellite laser ranging (SLR) results. There is remarkably good agreement between Earth rotation and model predictions of C21 and S21 over a 22-year period. After decadal signals are removed, Earth-rotation-derived interannual C20 variations are dominated by a strong oscillation of period about 5.6 years, probably due to uncertainties in wind and ocean current estimates. The model-predicted C20 agrees reasonably well with SLR observations during the 22-year period, with the exception of the recent anomaly since 1997/1998.  相似文献   

6.
Rotation of the Earth as a Triaxial Rigid Body   总被引：2，自引：6，他引：2  
The Earth is taken as a triaxial rigid body, which rotates freely in the Euclidian space. The starting equations are the Euler dynamic equations, with A smaller than B and B smaller than C. The Euler equations are solved, and the numerical results are provided. In the calculations, the following parameters are used: (C-B)/A=0.003 273 53; (B-A)/C=0.000 021 96; (C-A)/B=0.003 295 49, and the mean angular velocity of the Earth's rotation, ω =0.000 072 921 15 rad/s. Calculations show that, besides the self-rotation of the Earth and the free Euler procession of its rotation, there exists the free nutation: the nutation angle, or the angle between the Earth's momentary rotation axis and the mean axis that periodically change with time. The free nutation is investigated.  相似文献   

7.
Abstract

This study investigated the effects of some physicochemical properties of sediments on the accumulation of heavy metals in portions of the Musa creek coasts (Jafari and Petrochemical creeks). Effective properties such as pH, EC, texture, GS, γd, n, CaCO3 and OM were determined. All variables showed a normal distribution and general trends of NW–SE and NE–SW. After detrending the variables, ordinary kriging was used for modelling. The C0/σ2, C0/σ2, and search radius criteria were used to select the best semivariogram. All the variables displayed a spatial structure with different intensities. The IDW method was also used for estimation. The cross-validation showed that the results of both IDW and kriging methods are almost similar. Distribution of the sand particle, GS, n and OM decreases with distance from the waterways, whilst clay–silt deposits. In the center of the studied area, CaCO3 has the highest value and EC has the lowest value.  相似文献   

8.
A variational principle for the Stokesian boundary value problem is derived using the Euler-Lagrange theory. The resulting variational principle is then transformed into an equation determining the semi-major axis of the best fitting ellipsoid which fulfills the conditionU 0 =W 0 . The computations using three different geopotential models yields the semi-major axis of the earth ellipsoid asa=6378145.4 metres for the flatteningf=1/298.2564. The corresponding equatorial gravity and the geopotential number are computed as γa=978029.59 mgals andU 0=W 0=6.26367371 106 kgalmeters respectively.  相似文献   

9.
 Harmonic coefficients of the 2nd degree are separated into the invariant quantitative (the 2nd-degree variance) and the qualitative (the standardized harmonic coefficients) characteristics of the behavior of the potential V 2(t). On this basis the evolution of the Earth's dynamical figure is described as a solution of the time-dependent eigenvalues–eigenvectors problem in the canonical form. Such a canonical quadratic form is defined only by temporal variations of the harmonic coefficients and always remains finite, even within an infinite time interval. An additional condition for the correction or the determination of temporal variations of the 2nd degree is obtained. Temporal variations of the fully normalized sectorial harmonic coefficients are estimated in addition to ˙Cˉ 20, ˙Cˉ 21, and ˙Sˉ 21 of the EGM96 gravity model. In addition, a non-linear hyperbolic model for Cˉ 2m (t), Sˉ 2m (t) is constructed. The trigonometric form of the hyperbolic model leads to the consideration of the potential V 2(ψ) instead of V 2(t) within the closed interval −π/2≤ψ≤+π/2. Thus, it is possible to evaluate the global trend of V 2(t), the Earth's principal axes and the differences of the moments of inertia within the whole infinite time interval. Received: 25 September 1998 / Accepted: 28 June 2000  相似文献   

10.
The present study evaluates the effectiveness and suitability of cover management factors (C factor) generated through different techniques like land use/land cover-based arbitrary value (CLULC), Normalised Different Vegetation Index-based methods CNDVI1 and CNDVI2 and Modified Soil Adjusted Vegetation Index 2-based method (CMSAVI2). The C factors generated using these four methods were tested in the calculation and assessment of annual average soil loss from an upland forested subwatershed in the Baram river basin using the Revised Universal Soil Loss Equation (RUSLE). The four cover management factor maps generated by this analysis show some variation among the results. The LULC method uses a single arbitrary value for each LULC type mapped in the subwatershed. The other three methods show a range of C values within each mapped LULC type. The effects of these variations were tested in the RUSLE by keeping the factors such as rainfall erosivity (R), soil erodibility (K), slope-length and steepness (LS) constant. The maximum annual average soil loss is 1191 t. ha?1. y?1 based on the CLULC. Soil losses estimated with other three methods are very different compared to those estimated with the CLULC method. The highest calculated soil loss values were 1832, 1674 and 1608 t. ha?1. y?1 in the study area based, respectively, on CNDVI1, CNDVI2 and CMSAVI2 C factors. These maximum values represent the worst pixel scenario values of soil loss in the region. The statistical analysis performed indicates different relationship between the parameters and suggests the acceptance of the methodology based on CNDVI2 for the study area, instead of a single value method such as CLULC. Among the other two methods, the CMSAVI2 was found to be more consistent than the CNDVI1 method, but both methods lead to over-prediction of annual soil loss rate and therefore need to be reconsidered before applied in the RUSLE.  相似文献   

11.
Summary Let S be the (regular) boundary-surface of an exterior regionE e in Euclidean space ℜ3 (for instance: sphere, ellipsoid, geoid, earth's surface). Denote by {φn} a countable, linearly independent system of trial functions (e.g., solid spherical harmonics or certain singularity functions) which are harmonic in some domain containingE e ∪ S. It is the purpose of this paper to show that the restrictions {ϕn} of the functions {φn} onS form a closed system in the spaceC (S), i.e. any functionf, defined and continuous onS, can be approximated uniformly by a linear combination of the functions ϕn. Consequences of this result are versions of Runge and Keldysh-Lavrentiev theorems adapted to the chosen system {φn} and the mathematical justification of the use of trial functions in numerical (especially: collocational) procedures.  相似文献   

12.
The six-hourly values of the atmospheric angular momentum (AAM) functions computed by the U.S. National Meteorological Center (NMC) were used to estimate the effects of the atmospheric tides on the Earth's rotation. Variations of the equatorial components 1 and 2 of the AAM have periods close to gravitational tidesP 1 andK 1.The amplitudes of the detected variations in 1 and 2 functions have been found to be much larger than the theoretical ones, the reason of this amplification remains unexplained. According to theoretical formulations, these waves can be expressed only as retrograde motions. Because of frame effects, there is a correspondance between diurnal retrograde polar motion and precession-nutations and the atmospheric effect on polar motion cannot be detected from observations.The second part of this paper deals the effects of atmospheric tides in Earth rotation. High-frequency UT1 variations have been derived from VLBI and GPS techniques during the SEARCH'92 campaign (Study ofEarth-AtmosphereRapidCHanges) (Dickey et al. 1994). They have been compared to values derived by Ray et al. (1994) from global ocean tide model. The results obtained in the present paper show the existence of variations of thermal origin with an amplitude of about 1µs in Universal Time UT1. The agreement between observed and theoretical values is better when the determined thermal atmospheric tides are taken into account.Oceanic tidal signal explains a large part (60% of the signal variance) of the diurnal and sub-diurnal variations. Our results show that only a small part of the residuals (5%) accounts for the atmospheric tidal effects. The residual signal remains unexplained; it might be due to mismodelization of oceanic or atmospheric tides or effect of other geophysical phenomena.  相似文献   

13.
Ross-Li核驱动模型热点参数化及其校正—以POLDER数据为例   总被引：1，自引：1，他引：0  
半经验、核驱动二向性反射分布函数(BRDF)模型是多角度遥感领域的一个重要模型,其热点效应在应用BRDF反演其它地表参数时有重要作用。本研究针对树冠内部叶片的间隙对热点的影响,对几何光学核的重叠函数进行热点效应的改进,并利用POLDER多角度观测数据集,对改进热点效应后的不同核函数组合模型的最优热点参数进行了确定。通过最小均方根误差(RMSE)筛选出最优热点参数,进一步分析不同模型对热点参数的敏感性和RMSE随热点参数的变化情况。结果表明:(1)该热点参数化方法可用于Ross-Li核驱动模型不同核函数组合的情况,热点校正后的模型相对于原模型很好地改善了对热点反射率的拟合能力;(2)热点参数最优值在几何光学核为LSRC (LiSparseRChen)与LDRC (LiDenseRChen)组成的模型中出现明显差别,C1在LDRC模型中的值远小于LSRC模型,主要是因为LDRC核函数自身较好考虑了树冠尺度下的热点效应,所以该热点参数改进方法起到的补偿作用较小;(3)总体上,同一模型的C1参数比C2参数对热点的变化更敏感。本研究为Ross-Li核驱动模型的热点效应进一步校正及热点参数的取值范围提供了依据,对Ross-Li模型的推广有重要意义,改进热点效应后的模型可用于未来国产多角度卫星的数据处理流程中,以获取加精确的地物热点反射率信息。  相似文献   

14.
Global plate tectonics and the secular motion of the Pole   总被引：1，自引：0，他引：1  
Astronomical data compiled during the last 70 years by the international organizations (ILS/IPMS, BIH) providing the coordinates of the instantaneous pole, clearly shows a continuous drift of the “mean pole” (≡barycenter of the wobble cycle with respect to the Conventional International Origin (CIO). This study was undertaken to investigate the possibility of an actual secular motion of the barycenter (approximated by the earth's maximum principal moment of inertia axis or axis of figure) due to differential mass displacements from lithospheric plate rotations. The method assumes the earth's crust modeled as a mosaic of 1°×1° blocks, each one moving independently with their corresponding absolute plate velocities. The differential contributions to the earth's second-order tensor of inertia were computed, resulting in no significant displacement of the earth's axis of figure. In view of the above, the possibleapparent displacement of the “mean pole” as a consequence of station drifting due to absolute plate motions was also analyzed, again without great success. As a further step the old speculation of the whole crust possibly sliding over the upper mantle is revived and the usefulness of the CIO is questioned. Presented at the IAU Symposium No. 78, “Nutation and the Earth Rotation”, Kiev, 22–29, May, 1977.  相似文献   

15.
THE SPECIFIC CHARACTER OF LIMIT ERRORS IN CLOSE RANGE PHOTOGRAMMETRY   总被引：1，自引：0，他引：1  
1　ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅａｐｐｌｉｃａｔｉｏｎｏｆｃｌｏｓｅ＿ｒａｎｇｅｐｈｏｔｏｇｒａｍｍｅｔｒｙｉｓｔｏｄｅｔｅｒｍｉｎｅｔｈｅｆｏｒｍａｎｄｓｉｚｅ ,ｒａｔｈｅｒｔｈａｎｔｈｅａｂ ｓｏｌｕｔｅｐｏｓｉｔｉｏｎ ,ｏｆａｎｏｂｊｅｃｔｉｎｔｈｅｆｉｅｌｄｏｆａｒｃｈｉｔｅｃ ｔｕｒｅ ,ｉｎｄｕｓｔｒｙａｎｄｂｉｏｍｅｄｉｃｉｎｅ .Ａｎｙｉｎｔｅｇｒａｌｔｒａｎｓ ｌａｔｉｏｎａｎｄｒｏｔａｔｉｏｎｃａｕｓｅｄｂｙｄｉｆｆｅｒｅｎｔｏｐｅｒａｔｉｏｎｐｒｏｃｅｓｓｉｎｃｌｏｓｅ＿ｒａｎｇ…  相似文献   

16.
Given the second radial derivative Vrr（P） ｜δs of the Earth＇s gravitational potential V（P） on the surface δS corresponding to the satellite altitude, by using the fictitious compress recovery method, a fictitious regular harmonic field rrVrr（P）^＊ and a fictitious second radial gradient field V：（P） in the domain outside an inner sphere Ki can be determined, which coincides with the real field V（P） in the domain outside the Earth. Vrr^＊（P）could be further expressed as a uniformly convergent expansion series in the domain outside the inner sphere, because rrV（P）^＊ could be expressed as a uniformly convergent spherical harmonic expansion series due to its regularity and harmony in that domain. In another aspect, the fictitious field V^＊（P） defined in the domain outside the inner sphere, which coincides with the real field V（P） in the domain outside the Earth, could be also expressed as a spherical harmonic expansion series. Then, the harmonic coefficients contained in the series expressing V^＊（P） can be determined, and consequently the real field V（P） is recovered. Preliminary simulation calculations show that the second radial gradient field Vrr（P） could be recovered based only on the second radial derivative V（P）｜δs given on the satellite boundary. Concerning the final recovery of the potential field V（P） based only on the boundary value Vrr （P）｜δs, the simulation tests are still in process.  相似文献   

17.
Applying remote sensing techniques to develop the retrieval models and further to obtain the spatiotemporal information of water quality parameters is necessary for understanding, managing, and protecting lake ecosystems. This study aimed to calibrate and validate the retrieval models for estimating the concentrations of chlorophyll a (CCHL), suspended particulate matter (CSPM), and dissolved organic carbon (CDOC) with the in situ hyperspectral measurements in Poyang Lake, China in 2010 and 2011. The model calibration and validation results indicated that: (1) for CCHL retrieval, significantly strong and moderate correlations existed between the measured and estimated values (with the correlation coefficient r = 0.92 and r = 0.76) using the exponential model and the three-band model, respectively, with biased estimation observed for the exponential model; (2) for retrieving CSPM, there was a strong correlation between the measured and estimated values (r = 0.95) using the exponential model; and (3) no significant correlation between measured and estimated CDOC values was found with our developed models. More work is needed to allow the water quality of Poyang Lake to be accurately and steadily estimated, especially for CCHL and CDOC.  相似文献   

18.
《测量评论》2013,45(50):158-160
Abstract

Apart from “stickiness” of the suspension and looseness of the sights, prismatic compasses are subject to three internal sources of error:- <list list-type="roman-lower"> <list-item>

Collimation error. This may be caused by <list list-type="alpha-lower"> <list-item>

magnetic axis not being parallel to the zero line of the graduated circle;</list-item> <list-item>

line of sight not passing through the axis of rotation.</list-item> </list> It is unnecessary to aftempt to distinguish between the above faults, which introduce constant errors into the compass readings.</list-item> <list-item>

Eccentricity error. This is caused by the axis of rotation failing to pass through the centre of the graduated circle. This introduces an error into the compass readings of E sin θ cosec I°/R where E is the eccentricity, R the radius of the graduated circle and θ the angle between the line of sight and the line joining the centre of the circle to the axis of rotation. Eccentricity error is completely eliminated by observing both forward and back bearings, but this is not always practicable.</list-item> <list-item>

Irregular division of the graduated circle. This error is negligible in any modern compass.</list-item> </list>  相似文献   

19.
Resolving the initial phase ambiguities of GPS carrier phase observations was always considered an important aspect of GPS processing techniques. Resolution of the so-called wide-lane ambiguities using a special linear combination of theL 1 andL 2 carrier and code observations has become standard. New aspects have to be considered today: (1) Soon AS, the so-called Anti-Spoofing, will be turned on for all Block II spacecrafts. This means that precise code observations will be no longer available, which in turn means that the mentioned approach to resolve the wide-lane ambiguities will fail. (2) Most encouraging is the establishment of the new International GPS Geodynamics Service (IGS), from where high quality orbits, earth rotation parameters, and eventually also ionospheric models will be available. We are reviewing the ambiguity resolution problem under these new aspects: We look for methods to resolve the initial phase ambiguities without using code observations but using high quality orbits and ionospheric models from IGS, and we study the resolution of the narrow-lane ambiguities (after wide-lane ambiguity resolution) using IGS orbits.  相似文献   

20.
The formulas for the determination of the coefficients of the spherical harmonic expansion of the disturbing potential of the earth are defined for data given on a sphere. In order to determine the spherical harmonic coefficients, the gravity anomalies have to be analytically downward continued from the earth's surface to a sphere—at least to the ellipsoid. The goal of this paper is to continue the gravity anomalies from the earth's surface downward to the ellipsoid using recent elevation models. The basic method for the downward continuation is the gradient solution (theg 1 term). The terrain correction has also been computed because of the role it can play as a correction term when calculating harmonic coefficients from surface gravity data. Theg 1 term and the terrain correction were expanded into the spherical harmonics up to180 th order. The corrections (theg 1 term and the terrain correction) have the order of about 2% of theRMS value of degree variance of the disturbing potential per degree. The influences of theg 1 term and the terrain correction on the geoid take the order of 1 meter (RMS value of corrections of the geoid undulation) and on the deflections of the vertical is of the order 0.1″ (RMS value of correction of the deflections of the vertical).  相似文献   

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