我国重力基本网若干技术问题

本文介绍我国新的国家重力基本网1985系统(新网)。新网由57个点组成,其中包括6个绝对重力点,用拉科斯特·隆贝格(LCR—G)重力仪进行相对观测,并与国外多个已知重力基准系统作了联测,共获得各类观测数据近万个。新网重力值平均中误差为±8微伽[10~(-8)ms~(-2)],经外部检核,实际精度达20微伽。1985年通过国家鉴定。经过两年来使用证明,新网达到设计要求,具有国际先进水平。本文还讨论了重力网平差、我国旧网精度及转换、LCR—G重力仪的特性和国际重力基准等问题。     

利用卫星重力梯度数据确定地球重力场的单层位模型

本文提出了处理卫星重力梯度数据以确定高分辩力重力场模型的单层位法并对其中的独立估计法进行了误差分析，数字结果显示：当卫星高度为200km，卫星数据网格宽度为15′，卫星重力梯度数据的精度为2×10~(-3)E时，利用独立估计法可得到分辩力为1°×1°（100km）的全球重力场模型，其重力异常精度小于1（mgal）；若卫星高度降至160km，卫星重力梯度数据的精度达到3×10~(-4)E，则获得的重力场模型的分辩力可提高到0.5°×0.5°（50km），其重力异常精度仍小于1（mgal）。     

相对重力测量的现状

地面作业方式的相对重力测量在一百年来实施期间,精度已提高了三个数量级。在野外正常条件下,目前100毫伽左右的重力差已能以±20～30微伽的精度测定。但由于绝对重力测量用于建立现代重力基本控制网已获得±1～10微伽精度,而且地球动力研究中所提出的问题也要求达到类似的精度,因此,相对重力测量的改进势在必行。通过对拉喀斯特——隆贝格(LCR)重力仪的误差分配表进行探讨,作者发现,使用高精度方法可以减少大部分仪器误差和外部误差,使一次重力差观测的精度达到±10微伽左右。主要的误差源来自至今未能模型化的温度效应和振动效应。用专门的隔离装置能进一步减小这两项误差,但真正的突破也许只有通过把弹簧原理改成无偏移相依系统。如果用几台LCR重力仪重复观测,并采取各种已知的预防措施,地区性重力网的建立可达±3～10微伽的精度,而局部网更可达1微伽级。连测或复测中测站重力的重现力问题,对绝对和相对重力测量是个共同性问题。它意味着需要对局部的近地面质量进行监测并模型化,这点至今仍无法以微伽级的精度解决。     

我国重力基本网(1985)的基准与平差

本文通过分析绝对重力测量点的精度和分布，为我国重力基本网（1985）系统科学地选择了可靠的绝对基准。分析LOR-G型重力仪的特性，采用合理的数据处理方法有助于提高重力基本网的精度。从而建立了点重力值中误差为±5～±13微伽的国家重力基本网（1985）系统。通过外部检核证实了该网的可靠性。     

黄河干流GPS网的布测与精度分析

概述黄河干流 GPS控制网的布测方案、数据处理和精度分析。结果表明 : 、 级网点的相对定位精度达到 10 - 7;在 ITRF96地心坐标系中的精度优于± 10 cm; 级网点的中误差小于± 4mm,相对精度为± 1.3× 10 - 6 D     

北京至东京、巴黎、香港首次国际重力联测评介

一九八四年四、五月间使用6台拉科斯特隆贝格(LCR-G)重力仪,在国家重力基本网1985系统(85网)与位于东京、巴黎、香港的分属于多个可靠已知重力基准系统之间,并在日本境内的若干城市间进行了高精度相对重力联测。这次联测的目的在于:1)建立外部条件以检核85网的实际精度;2)利用可靠的已知国际点对85网已知点不足的地区加强控制,并通过与85网的一并平差使85网与国际基准取得一致;3)精化LCR-G重力仪的格值函数。在23个点上所获得的约3000个观测数据参加了与85网的一并平差。计算分析表明:85网平差精度平均达土10微伽[10~(-8)ms~(-2)],外部检核精度达20微伽。网的尺度和基准可靠且与国际系统一致。北京点作为首先国际化的重力点,其重力值精确。LCR-G重力仪灵敏度与点位重力值有关;局部磁场给观测带来不可忽视的误差。本文还分析比较了有关国际重力系统的数据处理方法和计算结果,简评了1985年国家地震局与日本中川一郎教授合作进行的区域性重力测量结果。指出东京B点重力值不稳定。     

测量仪器

CH20040783 用GWR-C032超导重力仪观测资料实施对LCR-ET20重力仪格值的精密测定/陈晓东(中国科学院测量与地球物理研究所)…∥测绘学报.-2003,32(3) .-219-223 利用我国武汉国际重力潮汐基准站GWR-C032超导重力仪与LCR-ET20重力仪的同址观测资料,采用多线性回归方法(Multi-linear Regression Technique)实施对ET20重力仪格值的精密测定,获得的格值为42.293 2±0.008 0×10~(-8)m×s~(-2)/V。用获得的格值对ET20重力     

iGrav-007超导重力仪格值的精密测定

iGrav超导重力仪是当前世界上最新型的便携式相对重力仪,可提供最稳定和最高精度的连续相对重力测量。利用武汉九峰台站FG5-112绝对重力仪与iGrav-007超导重力仪连续3天的同址观测结果,基于最小二乘线性回归和迭代算法,精密确定iGrav-007的格值。数据处理结果表明,iGrav-007的格值为(-91.640 2±0.085 2)×10-8 m·s-2/V,相对标定精度为0.092 9%,连续1天的FG5绝对重力观测获得的格值精度优于0.2%,连续3天的FG5绝对重力观测获得的格值精度优于0.1%。     

海潮负荷对自由核章动参数拟合的影响

基于武汉基准台超导重力仪重力潮汐观测资料 ,利用根据不同海潮模型获得的负荷重力改正值对观测数据作海潮改正 ,拟合了地球自由核章动 ( FCN)共振参数。结果表明 FCN的本征周期为 435 .2恒星日 ,品质因子为 4730 ,复共振强度为 ( - 6.34× 1 0 - 4,- 0 .0 9× 1 0 - 4)°/h。不同的海潮模型对 FCN本征周期和共振强度实部计算结果的影响很小 ,差异分别不超过± 1 .6%和± 7.7% ,对品质因子 Q值和共振强度虚部拟合结果的影响非常显著。基于 Ori96全球海潮模型得到的重力改正值可以很好地解释武汉基准台周日重力潮汐观测残差。     

略论珠穆朗玛峰重力值的推估

仅根据邻近点的重力与高程资料,采用了4种有关公式,有效地推估了珠穆朗玛峰顶上的重力值,该值为(976 970±7)×10-5m     

我国国家重力网的系统转换

本文分析了我国１９５７年国家重力网的精度和问题，探讨了国家重力网的系统转换模式，利用现有的新旧重力网的重合点实际数据进行了回归分析、方差分析和系统误差检验，结果表明在“５７网”与“８５网”之间，除了—１３．５８ｍｇａｌ的平均基准差之外，并不存在其它明显的系统误差，特别是看不出有尺度系统差的影响，也不存在差值随纬度变化的任何规律。因此认为将“５７网”系统转换成“８５网”系统时，可以不必加“尺度系统差改正”，更不用考虑“非线性系统差改正”，建议一律只加一项“基准系统差改正”，其数值应该采用—１３．５８ｍｇａｌ。     

Vector gravimetry using GPS in free-fall and in an Earth-fixed frame

The Global Positioning System (GPS) is considered in conjunction with a strapdown Inertial Measurement Unit (IMU) for measuring the gravity vector. A comparison of this system in space and on an airborne platform shows the relative importance of each system element in these two different acceleration environments. With currently available instrumentation, the acceleration measurement accuracy is the deciding factor in space, while on an Earth-bound (including airborne) platform, the attitude error of the IMU is most critical. A simulation shows that GPS-derived accelerations in space can be accurate to better than 0.1mgal for a 30s integration time, leading to estimates of 1° mean gravity anomalies on the Earth's surface with an accuracy of 4–5 mgal. On an airborne platform, the horizontal gravity estimation error is tightly coupled to the attitude error of the platform, which can only be bounded by external attitude updates. Horizontal gravity errors of 5mgal are achievable if the attitude is maintained to an accuracy of 1arcsec.     

Error Propagation Modeling in Raster GIS: Adding and Ratioing Operations

The purpose of this paper is to identify error properties arising when source maps that individually contain error are added or when the ratio of one map with respect to another is computed. The research approach to the problem combines mathematical analysis and simulation where source maps and error processes have been constructed with specified properties. Geman and Geman's corruption model is used to represent error in individual source maps. The paper reports spatial and aspatial error properties arising from adding and ratioing error-corrupted maps. These are identified as functions of the true characteristics of the individual source maps and the errors inherent within them; the relative contribution of these two components to the errors in maps is quantified by regression (for addition) and ANOVA (for ratioing). The paper considers the broader usefulness of this type of experimental analysis in using artificially constructed maps in geographic information science.     

Comparison of undulation difference accuracies using gravity anomalies and gravity disturbances

Errors are considered in the outer zone contribution to oceanic undulation differences as obtained from a set of potential coefficients complete to degree 180. It is assumed that the gravity data of the inner zone (a spherical cap), consisting of either gravity anomalies or gravity disturbances, has negligible error. This implies that error estimates of the total undulation difference are analyzed. If the potential coefficients are derived from a global field of 1°×1° mean anomalies accurate to ε_Δg=10 mgal, then for a cap radius of 10°, the undulation difference error (for separations between 100 km and 2000 km) ranges from 13 cm to 55 cm in the gravity anomaly case and from 6 cm to 36 cm in the gravity disturbance case. If ε_Δg is reduced to 1 mgal, these errors in both cases are less than 10 cm. In the absence of a spherical cap, both cases yield identical error estimates: about 68 cm if ε_Δg=1 mgal (for most separations) and ranging from 93 cm to 160 cm if ε_Δg=10 mgal. Introducing a perfect 30-degree reference field, the latter errors are reduced to about 110 cm for most separations.     

小型消费级无人机地形数据精度验证

低空遥感是近几年快速发展、应用非常广泛的新兴技术。小型消费级无人机集成可见光传感器,具有快速、灵活、高性价比等优势,受到广泛关注。然而目前有关该类无人机综合测量精度的研究不足,影响其进一步的推广应用。为此,本文开展了针对大疆(Phantom 3 professional)小型消费级无人机地形测量数据精度验证工作,设定6种航高(50 m、60 m、70 m、80 m、90 m和100 m)获取研究区的立体像对,生成影像点云(point cloud)、数字表面模型(DSM)以及数字正射影像图(DOM)等结果。在测量精度验证中,首先,在标准实验场均匀布设地面控制点(GCP),利用差分GPS测出GCP的高精度3维坐标;然后,通过GCP对立体像对进行绝对定位;最后,利用误差统计方法分析上述结果的测量精度。验证表明,在50—100m航高时,无人机影像结果的分辨率为2.22—4.23 cm,水平方向平均误差为±0.51 cm,垂直方向平均误差为±4.39 cm,相对均方根误差(RMSE)水平方向为±2.79 cm,垂直方向为±9.98 cm。研究结果表明,小型消费级无人机在飞控系统下的测量精度可达厘米级,这不仅为野外地理和生态调查工作者提供一种低成本、快速、灵活与精确获取地形信息的新型测量手段,同时还对使用此类无人机做航测应用及飞行参数设置提供一定参考。     

Shipborne high-accuracy heading determination method using INS- and GPS-based heading determination system

The heading accuracy of an existing shipborne inertial navigation system (INS) is affected by the oscillatory heading error caused by the misalignment angles between the gyro case and gyro axes. The accuracy of the heading determination system (HDS), which consists of two quadruple GPS antenna arrays, an INS, a total station surveying apparatus (TSSA), and two vessels, is affected by jump errors because of the degradation of tracking performance of the TSSA servo system in high dynamic conditions. Given that only pitch and roll of the INS are utilized in the HDS, we propose a high-accuracy heading determination system that combines the heading rate of the INS and linear fit of the heading difference between INS and HDS, to compensate for jump errors of HDS and oscillatory heading error of the INS. With the designed equipment, both jump errors and the oscillatory heading error can be suppressed effectively. The standard deviations of the heading errors are reduced from ±6 to ±2 and from ±8 to ±5 arcsec in mooring and sea tests, respectively, and a high accuracy of shipborne heading determination can be achieved since the oscillatory heading error is reduced to the 1 arcsec level.     

Airborne vector gravimetry using precise,position-aided inertial measurement units

Vector gravimetry using a precise inertial navigation system continually updated with external position data, for example using GPS, is studied with respect to two problems. The first concerns the attitude accuracy requirement for horizontal gravity component estimation. With covariance analyses in the space and frequency domains it is argued that with relatively stable uncompensated gyro drift, the short-wavelength gravity vector can be estimated without the aid of external attitude updates. The second problem concerns the state-space estimation of the gravity signal where considerable approximations must be assumed in the gravity model in order to take advantage of the ensemble error estimation afforded by the Kalman filter technique. Gauss-Markov models for the gravity field are specially designed to reflect the attenuation of the signal at a specific altitude and the omission of the long-wavelength components from the estimation. With medium accuracy INS/GPS systems, the horizontal components of gravity with wavelengths shorter than 250 km should be estimable to an accuracy of 4–6 mgal (µg); while high accuracy systems should yield an improvement to 1–2 mgal.     

Estimation and exclusion of multipath range error for robust positioning

In integrated systems for accurate positioning, which consist of GNSS, INS, and other sensors, the GNSS positioning accuracy has a decisive influence on the performance of the entire system and thus is very important. However, GNSS usually exhibits poor positioning results in urban canyon environments due to pseudorange measurement errors caused by multipath creation, which leads to performance degradation of the entire positioning system. For this reason, in order to maintain the accuracy of an integrated positioning system, it is necessary to determine when the GNSS positioning is accurate and which satellites can have their pseudorange measured accurately without multipath errors. Thus, the objective of our work is to detect the multipath errors in the satellite signals and exclude these signals to improve the positioning accuracy of GNSS, especially in an urban canyon environment. One of the previous technologies for tackling this problem is RAIM, which checks the residual of the least square and identifies the suspicious satellites. However, it presumes a Gaussian measurement error that is more common in an open-sky environment than in the urban canyon environment. On the other hand, our proposed method can estimate the size of the pseudorange error directly from the information of altitude positioning error, which is available with an altitude map. This method can estimate even the size of non-Gaussian error due to multipath in the urban canyon environment. Then, the estimated pseudorange error is utilized to weight satellite signals and improve the positioning accuracy. The proposed method was tested with a low-cost GNSS receiver mounted on a test vehicle in a test drive in Nagoya, Japan, which is a typical urban canyon environment. The experimental result shows that the estimated pseudorange error is accurate enough to exclude erroneous satellites and improve the GNSS positioning accuracy.     

Establishment of precise gravity network of airport stations in India

A precise gravity network of thirty-five stations based on the first order gravity station at Palam airport, New Delhi (979.13433 gals—University of Wisconsin 1969 value) was established during April–June 1971, covering the entire country, in order to use them as reference bases for any future gravity surveys in India with a repeatability of ±0.05 mgal or less. The instrument, a LaCoste-Romberg geodetic gravimeter No. G-84, was transported by air over the network of airport stations embracing Trivandrum in the south, Srinagar in the north, Bombay in the west and Mohanbari in the east. The four airport stations in New Delhi, Calcutta, Madras and Bombay which were more precisely established by a large number of repeat observations were utilised as base stations for facilitating easy occupation of the remaining thirty-one stations within their respective zones. The observations were reduced by procedure which permits automatic removal of instrumental drift from the observed readings. According to the depicted drift curve, the instrumental drift though comparatively small, is found not exactly linear due to the possible tare effect observed at the initial stage and also the resulting creep drift that might have been developed during transportation of the gravimeter by air. The final results along with their probable errors of the order of ±0.01 mgal for base stations and ±0.03 mgal for other stations relative to the adopted value at Palam airport, are given in Table 1. Fourteen of the sites occupied are reoccupations of stations already established by the University of Wisconsin in 1963, and the results of the old and the new measurements as given in Table 2, are in remarkable agreement, which ensures the correctness of the calibration factors of the present instrument relative to that of the Wollard's LaCoste-Romberg gravimeter No. G-1-A actually employed in the 1963 measurements.