稳健估计在GNSS高程拟合中的粗差探测

由于最小二乘法不能有效地抵抗粗差,而控制点的平面坐标和高程异常值中不可避免地含有误差,对应用最小二乘法和稳健估计法在GNSS高程拟合中的粗差探测进行探讨。通过对不同数量控制点的高程异常观测值中加入粗差,采用两种算法在求解GNSS高程拟合中的精度进行分析比较,并对粗差在稳健估计中的干扰范围进行研究,结果表明,稳健估计具有抵抗多个粗差的能力。     

低矮植被的无人机激光雷达测高精度分析

针对无人机激光雷达估测低矮植被高度的精度大小,本文以3m以下低矮树木为研究对象,通过数值模拟方法得到不同航高、不同扫描角情况下激光脚点坐标和点云估测单一树木高度的最大测量误差值;对比实测树高,分析了激光点云估测树高的精度。结果表明,在航高为30m、扫描范围为(-50°,5°)的情况下,无人机激光雷达获取的激光脚点坐标误差和由激光点云估测低矮树高(3m以下)的误差均可以达到cm级;激光点云估测单一树木高度与实测高度的决定系数为0.977,均方根差为5cm,标准均方根差为4%。因此,应用无人机激光雷达数据可以快速、精确获取低矮植被高度信息,进而为反演植被生物量和植被长势信息监测提供重要依据。     

邵阳市区域尺度GPS高程异常分析

针对工程测量中GPS大地高代替水准正常高的问题,该文根据邵阳市实测GPS、水准数据,采用二次曲面拟合模型得到了该地区高程拟合参数。通过正常高与拟合高程进行比较,最大拟合残差为3.9cm,最小为0cm,高程异常模型拟合中误差为1.85cm,证明了该区域GPS高程拟合参数可以满足工程建设中大地高代替正常高的要求。根据GPS高程拟合参数得到的邵阳市辖区及周边地区高程异常曲面具有由西北至东南递减且变化梯度逐渐递减的特征,该区域最大高程异常15.65m,最小高程异常14.75m。     

水平距离和海拔高度对雷达估测降水影响及订正

以石家庄2006—2008年77次降水过程为例,分析了海拔高度和距雷达站水平距离对定量估测降水的影响,给出了估测降水时反射率因子取值的最佳高度以及距离高度订正值。对比了经验公式法和最优化法分别在有无距离高度订正4种情况下的估测效果,依据估测效果,设计了雷达定量估测降水最佳方案:若反射率因子小于30 dBz,则不进行距离高度订正,仅采用最优化法估测降水;若反射率因子大于30 dBz,则首先对反射率因子进行距离高度订正,然后采用最优化法估测降水。实例检验表明,该方案对单站10 mm·h~(-1)以上的强降水、过程降水量和区域降水量估测效果较好。     

Simultaneously simulate vertical and horizontal expansions of a future urban landscape: a case study in Wuhan,Central China

While there are extensive studies of urban 2D forms, research on the varying geometric features and spatial distribution patterns of urban 3D spaces is comparatively rare. In this paper, we propose a coupled model, known as BPANN-CBRSortCA, which is based on a back propagation artificial neural network (BPANN) and case-based reasoning technology with sort cellular automaton (CBRSortCA) to simulate future urban building heights and their spatial distribution. BPANN–CBRSortCA uses BPANN to predict the vertical extrusion of building heights and uses CBRSortCA to simulate horizontal urban expansion. The BPANN–CBRSortCA model is innovative because of its capabilities to simultaneously project urban growth in the vertical and horizontal dimensions. The proposed model also overcomes the limitations of the traditional cellular automata models that cannot simulate ‘diffused’ urban expansion. This research used Wuhan City as a case study to simulate vertical and horizontal urban expansion from 2015 to 2025. The results showed the following: (1) in the next 10 years, new build-up will mainly appear along the edge of Hongshan and Hanyang Districts or will occupy bare land in the form of ‘filling’ and (2) the tallest buildings will be mainly located to the south of East Lake in Hongshan District and on undeveloped land within the city. These simulation results can provide a reference for future urban planning.     

对我国35年来珠峰高程测定成果的思考

20世纪60年代以来，我国曾单独或与外国合作，在1966年，1975年，1992年，1998年及1999年对珠穆朗玛峰高程进行了5次测定，开展了大规模的大地测量外业作业、数据处理和科学研究，其中包括天文、重力、平面、高程和气象等方面。本文对我国近35年来的珠峰高程测定的成果和最新进展作分析研究，将我国35年来所精确测定的珠峰峰顶雪面高程值取中数，以我国60(似)大地水准面为基准面，得珠峰海拔高为8849.0m±0.5m；若以接近全球高程系统的EGM96大地水准面为基准面，珠峰海拔高为8850.1m±0.5m。     

卫星测高数据的沿轨迹重力异常反演法及其应用

本文给出了一套基于直角坐标系下的垂线偏差求解重力异常公式 ,并将之发展成为一套新的沿轨迹重力异常求解公式。与其他方法相比 ,本方法无须求解交叠点处沿轨迹和跨轨迹方向的海面高斜率 ,仅需计算沿轨迹方向的海面高斜率 ,因而更为简洁、有效 ,而且分辨率可以更高并可与真正的沿航迹实际船测重力相比较、验证。据此 ,利用 Geosat/GM、ERS-1 /35天及TOPEX/Poseidon三种测高数据 ,反演了南中国海域 (0°～ 2 5°N,1 0 5°～ 1 2 2°E)的 2′× 2′重力异常—— IGG-S。通过与实际船测资料和国际同行提供的重力模型相比 ,IGG-S总体精度达到1 0× 1 0 - 5ms- 2。     

An Approximate Analytical Solution For The Baroclinic And Variable Eddy Diffusivity Semi-Geostrophic Ekman Boundary Layer

The WKB method has been used to develop an approximate solutionof the semi-geostrophic Ekman boundary layer with height-dependenteddy viscosity and a baroclinic pressure field. The approximate solutionretains the same simple form as the classical Ekman solution. Behavioursof the approximate solution are discussed for different eddy viscosityand the pressure systems. These features show that wind structure inthe semi-geostrophic Ekman boundary layer depends on the interactionbetween the inertial acceleration, variable eddy viscosity and baroclinicpressure gradient. Anticyclonic shear has an acceleration effect on theair motion in the boundary layer, while cyclonic shear has a decelerationeffect. Decreasing pressure gradient with height results in a super-geostrophicpeak in the wind speed profile, however the increasing pressure gradient withheight may remove the peak. Anticyclonic shear and decreasing the variableeddy viscosity with height has an enhanced effect on the peak.Variable eddy viscosity and inertial acceleration has an important role in thedivergence and vorticity in the boundary layer and the vertical motion at the top of the boundary layer that is called Ekman pumping. Compared to the constanteddy viscosity case, the variable eddy diffusivity reduces the absolute value ofEkman pumping, especially in the case of eddy viscosity initially increasing with height. The difference in the Ekman pumping produced by different eddy diffusivity assumptions is intensified in anticyclonic flow and reduced in cyclonic flow.     

Precise geoid determination over Sweden using the Stokes–Helmert method and improved topographic corrections

 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     

高精度GPS水准高程求解算法研究

为了改善GPS大地高向正常高转换的精度和计算速度，坐标转换、顾及非格网数据考虑地形改正的几何方法和龙贝格加速积分法被采用，实践验证，该方法是正确的。