平均重力异常的计算及精度分析

本文介绍了测绘科学研究所研制的重力数据库中存储的平均空间重力异常的计算方法。并分析了不同格网(5′×5′,15′×15′,30′×30′等)平均重力异常的精度。选取北纬25°～32°,东经100°～107°作为试验区进行了研究。计算证明,利用参数拟合法,在我国一般地区,可以求得优于±10毫伽的5′×5′以上格网的平均空间异常。特殊困难地区,经特殊处理后可以求得优于±10毫伽的15′×15′以上格网的平均空间异常。     

成都市城区彩色航空影像及其应用

由四川省测绘局委托中国四维测绘技术总公司摄制的成都市城区彩色航空影像 ,经成都军区进行了保密处理 ,并由四川省测绘局用专业影像扫描仪将彩色航空影像扫描成影像数据。近日 ,四川省基础地理信息中心正式对外提供该影像数据的彩喷图像。该影像航摄比例尺 1 :40 0 0 ,绝对航高 1 1 0 0米 ,航片规格 2 3ｃｍ× 2 3ｃｍ ,覆盖范围为东经 1 0 3°5 6′1 5″～ 1 0 4°1 1′1 5″、北纬 30°35′0 0″～ 30°45′0 0″ ,覆盖面积包括三环路在内约 45 0平方公里。由于其地面分辨率高达 0 1米 ,且色彩效果好、影像清晰 ,因此 ,该影像在各领域具…     

NAV－5000GPS接收机在南极冰盖大陆导航定位中的应用

ＮＡＶ－５０００ＧＰＳ接收机在南极冰盖大陆导航定位中的应用１测区概况及导航定位目的意义中国南极科学考察站──中山站建立在南极州的拉斯曼丘陵上的米洛半岛。拉斯曼丘陵位于东经７６°～７６°３０′，南纬６９°２０′～６９°４０′之间，主要由米洛半岛、勃洛克...     

西沙群岛可开发的旅游资源

中国版图最南端的南海之中 ,有一块尚待开发的旅游处女地———西沙群岛。笔者应有关部门之邀 ,飞赴西沙 ,考察了那里极具魅力的旅游资源。西沙概况西沙群岛古名七洲洋、千里长沙、万里石塘 ,是我国南海四大群岛之一。共有 40多个岛礁 ,星罗棋布在北纬 1 5°43′～ 1 7°0 8′,东经1 1 1°1 0′～ 1 1 2°5 4′之间约 5 0万ｋｍ2 的海区内。岛屿总面积约 1 0ｋｍ2 ,礁盘面积达 1 .5万ｋｍ2 。西沙群岛属亚热带地区 ,温暖湿润 ,气压适宜 ,雾日罕见 ,能见度良好。全年主要受热带海洋气团控制 ,极端最高气温 34 .9℃ ,最低气温 1 5 .3℃ ,年平…     

联合多种测高数据建立高分辨率中国海平均海面高模型

利用经过编辑和环境改正后的多代卫星测高资料，通过联合交叉点平差以削弱径向轨道误差和不同卫星测高任务之间的系统偏差等因素的影响，建立了中国海域及邻海（1°N～41°N，103°E～137°E）2.5′×2.5′平均海平面高模型，并将其与CLS-SHOM98.2、GFZMSS95A和OSUMSS95平均海平面高模型进行了比较。     

中国似大地水准面

采用移去-恢复技术,利用我国高分辨率DTM和重力资料推算我国大陆重力大地水准面;然后再和我国GPS水准所构成的高程异常控制网拟合,推算具有分米级精度,15′×15′分辨率的我国大陆大地水准面.利用全国地壳运动监测网络的80余个高精度GPS水准点进行外部检核,检核结果证实和原设计精度完全一致即该大陆大地水准面的绝对精度,在东经120°以东,高于±0.3 m,在东经120°以西,北纬36°以北,±0.4 m, 36°以南,±(0.4～0.6) m.利用卫星测高数据计算垂线偏差,反解我国海域大地水准面.为了检核,由测高垂线偏差反演为重力异常,与海上万余点船测重力值进行了外部检核;同时将上述反演的重力异常推算大地水准面,与直接解得的相应结果进行比较作为内部检核.由重力和GPS水准数据推算的上述大陆大地水准面,和主要由卫星测高数据确定的海洋大地水准面,二者之间一般都存在以系统误差为主的拼接差.顾及这一现象和结合我国在陆海大地水准面拼接区重力资料稀疏的实际,研究提出了扩展拼接技术,即在沿海选取部分陆海毗邻的局部地区,在这局部地区内,陆地用实测平均重力格网数据,海洋用测高平均重力格网数据,统一推算陆海局部重力大地水准面.然后利用这一局部大地水准面的陆地部分和已经GPS水准校正的陆地大地水准面进行拟合.最后将拟合参数校正中国全部海域的测高重力大地水准面,而保持陆地部分大地水准面不变,以最大限度的削弱拼接点和测高海洋大地水准面的系统误差.     

中国新一代高精度、高分辨率大地水准面的研究和实施

采用移去恢复技术，利用我国高分辨率DTM和重力资料推算我国大陆重力大地水准面;然后再和我国GPS水准所构成的高程异常控制网拟合,推算了具有dm级精度、15′×15′分辨率的我国大陆大地水准面。利用全国地壳运动监测网络的80余个高精度GPS水准点进行外部检核，检核结果证实和原设计精度完全一致，即该大陆大地水准面的绝对精度,在东经102°以东高于±0.3m，在东经102°以西、北纬36°以北为±0.4m，36°以南为±(0.4～0.6)m。利用卫星测高数据计算垂线偏差，反解我国海域大地水准面。为了检核，由测高垂线偏差反演为重力异常，与海上万余点船测重力值进行了外部检核；同时用上述反演的重力异常推算大地水准面，与直接解得的相应结果进行比较作为内部检核。由重力和GPS水准数据推算的上述大陆大地水准面，和主要由卫星测高数据确定的海洋大地水准面，二者之间一般都存在以系统误差为主的拼接差。顾及这一现象并结合我国在陆海大地水准面拼接区重力资料稀疏的实际，研究提出了扩展拼接技术，即在沿海选取部分陆海毗邻的局部地区，在这局部地区内，陆地用实测平均重力格网数据，海洋用测高平均重力格网数据，统一推算这陆海局部重力大地水准面。然后利用这一局部大地水准面的陆地部分和已经用GPS水准校正的陆地大地水准面进行拟合。最后用拟合参数校正中国全部海域的测高重力大地水准面，从而保持陆地部分大地水准面不变，最大限度地削弱拼接点和测高海洋大地水准面的系统误差。     

ENVISAT测高卫星沿轨大地水准面梯度的海洋垂线偏差法研究

研究了利用沿轨大地水准面梯度数据计算海洋垂线偏差的最小二乘法,首先对ENVISAT测高数据进行各项地球物理改正得到近似测高大地水准面,然后计算沿轨大地水准面的梯度,接着用最小二乘法计算格网垂线偏差东西分量和南北分量的平均值。最后,用该方法计算了南中国海区域及其邻近海域(4°N～25°N,104°E～120°E)的5′×5′垂线偏差南北分量和东西分量,其精度优于7″,并与EGM96模型计算的垂线偏差值进行了比较,证明了该方法的有效性。     

我国陆地均匀重力测量补点问题的研究

推导了重力布点公式，应用全国重力点检验了原有代表误差系数的可靠性，估计了我国目前和将来5′×5′平均高的精度，阐述了陆地重力测量布点系统的建立方法和应用方法，给出了我国陆地重力点补测方案，应用它即可确定我国陆地每个5′×5′内应补测的重力点数及其分布。     

用FFT计算川西地区的高程异常

川西地区地势复杂,进行常规测绘工作很艰难。若采用GPS作为1:5万航测图的控制,既可以减轻大地测量工作的困难,也有很好的经济效益。但在高程方面,必须将GPS测定的大地高转换为正常高。如此需有高分辨率的似大地水准面。本文用平面近似的Stokes公式,并顾及Molodensky一阶项,用FFT计算了Δφ=14°Δλ=12°川西地区5′×5′的似大地水准面,结果与该区的天文重力水准及GPS水准比较,精度约为±1米,并认为顾及剩余重力异常较单纯用位系数模型的结果精度高20％。此外,还认为用0.5′×0.5′的DTM,再顾及Molodensky一阶项,精度还可提高20％。     

NOTES ON GEODETIC WORK IN THE GOLD COAST

Abstract

The Gold Coast, including that portion of Togoland which is mandated to Great Britain, comprises an area of 91,843 square miles lying between the parallels 4° 45′ N. and 11°N. and the meridians 1° 10′ E. and 3° 10′ W. The greater part of the southern area is covered with dense forest, but in the north the forest gradually opens out to more open “orchard-bush”, while in the extreme north the country consists of rolling plains covered with tall elephant-grass.     

Quantitative monitoring of land use changes in relation to hydrology of Bhavani basin using remote sensing techniques — a case study

The paper summarises a part of the results of an on-going project for quantifying the land use changes in Bhavani basin (Geographic co-ordinates N lat 10°55′ - 11°45′,E Long. 76°30′ - 77°45′). Landsat and aerial data have been used in monitoring the dynamic changes in land use patterns. Visually interpreted Landsat MSS data of two different dates in conjunction with the historic data acquired from the Survey of India topographic maps and field data were used in this investigation. Also land use changes over two test-sites in the basin were studied using aerial photographs. During the study, it has been observed that a direct correlation exists between the rainfall and the area irrigated. The repetitive coverage of the satellite data are found to be quite remarkable, especially the 1:250,000 False Colour Composites (FCC) in assessing rapidly the temporal land use changes of a region at a cheaper cost.     

GEOGRAPHICAL POSITIONS IN MALAYA AND SIAM

Abstract

Malaya.—The geographical positions of points in the “Primary Triangulation of Malaya”, published in 1917, depend upon latitude and azimuth determinations at Bukit Asa and on the longitude of Fort Cornwallis Flagstaff, Penang, the latter being supposed to be 100° 20′ 44″.4 E. This value was obtained by Commander (later Admiral) Mostyn Field in H.M.S. Egeria 1893, by the exchange of telegraphic signals with Mr Angus Sutherland at Singapore, Old Transit Circle. The longitude, 103° 51′ 15″.75 E., accepted for Singa- pore in order to arrive at this determination of Fort Cornwallis Flagstaff, was based upon that of an Observation Spot, 103° 51′ 15″.00 E., fixed in 1881 by Lieutenant Commander Green, United States Navy, by meridian distance from the transit circle ofMadras Observatory, the corresponding longitude of the latter being taken as 80° 14′ 51″.51 E.     

TRIGONOMETRICAL LEVELLING ACROSS THE INLAND ICE IN NORTH GREENLAND

Abstract

As part of the scientific work of the British North Greenland Expedition (1952–1954), a programme of trigonometrical levelling was carried out from the east to the west coast of Greenland, along a line across the inland ice between latitudes 76° 40′ N., and 78° 10′ N. The primary purpose of the work was to determine accurately the heights above sea level of a series of gravity stations, the gravity measurements being made in connection with determinations of ice thickness. For meteorological purposes it was necessary to know also the altitude of the Expedition's central station, situated in latitude 78° 04′ N., longitude 38° 29′ W. The accuracy necessary for the purpose of the gravity survey was a few metres for the altitudes, while the latitude of each gravity station had to be determined with an accuracy of ± 0.1 minute.     

Photogeologic mapping north of Khairwara,Udaipur district,Rajasthan

Photogeologic mapping of a sample area defined by latitudes 24° O to 6′N and longitudes 73° 30′ to 45′ E from a part of the Aravalli orogen, illustrates the advantages, as well as limitations, of photo-interpretation (PI) in terrains comprsing, highly deformed ancient rock formations. Discrimination between psammitic and pelitic metasediments is easy, using micro-relief and drainage parameters as PI elements; but that between pelites, ultra-basic schists and impure marbles is difficult and less reliable. Trends of foliations, several sets of joints and faults are distinct on the aerial photographs, but complete reconstruction of the superposed fold geometry is not possible. Within the area studied, dominantly pelitic, psammitic and a little clacareous metasediments, intruded by ultra-basics, exhibit a prominent and persistent NNE trend defined by lithologic contacts, bedding and foliations, with steep northwesterly dips. In its central part, bands of psammites within the pelites exhibit a hook shaped fold interference pattern (type 3 of Ramsay, 1967) with the later upright (Fleuty, 1964) fold axial trace trending northwesterly.     

The solani-ganga interfluve; an application of remote sensing technique on soil resource mapping for agricultural planning

The area of the Solani-Ganga interfluve, which lies between 29°16′N to 30°15′N latitude and 77°45′E to 78°15′E longitude was undertaken for the present study using LANDSAT imagery of band 5 and 7 and the false colour composite on the scale of 1:250,000 in combination with aerial photographs (1:25,000). Major geomorphic units, e.g., Siwalik Hills. Solani-upper alluvial plain, Solani lower alluvial plain, ‘Tarai’ and Ganga alluvial plain were delineated on LANDSAT and colour composite. Sample areas selected from LANDSAT were studied on aerial photographs in details and soil physiography relationship was developed. The soils on Siwalik hills are classified as Orthents. The soils of the pledmont plain and the recent terraces of Solani river and its tributaries were Psamments, Orthents, Fluvents, Orchrepts and Aquepts. The soils of upper alluvial tract of the Ganga plain is mostly Ustalfs with inclusion of Aqualfs, while the strong hydromorphic Tarai tract consists of partly Aquepts, Ochrepts (cultivated) and partly of Aquolls, Ustolls and Ustalfs (under forest). The present study aims to pin point the nature of soil relief relationship with the help of LANDSAT imagery and aerial photographs and diagnose the intensity of the depletion of soil resources (by prevailing factors like swift run off of biykderfed torrents, fast-flow of ground water, soil creep, mass wasting) through field studies and then treat them with ecological dose of soil conservation. For agronomic development of the region, it is worked out that the present crop-combination and crop-rotation systems should be slightly modified according to its ecosystem to prevent the depletion of soil nutrients.     

GIS application to determine the effect of topography on landuse in Ashwani Khad watershed

The landuse status of Ashwani Khad watershed has been obtained using 1RS-ID satellite data for 1999 and further topographic analysis has been carried out using GIS software-ARC/ INFO and ARCVIEW. It has been found that of the total geographical area (85.30 sq. km) of the Ashwani Khad watershed which lies between 30°50′ to 31°N latitude and 77°05′ to 77° 15′E longitude in Himachal Pradesh, 54.53 % constituted wasteland, 33.55% agriculture and least 11.92 % forest. The altitude, aspect and slope have exhibited marked effect on land utilization. Agriculture and wasteland have been found maximum in mid altitude (1300-1500 m) and moderate slopes (13.2-26.4 degree), whereas, agriculture and forest have been maximum in flat and north aspect.     

MAPPING OUT OF CROWN LANDS IN CEYLON

Abstract

The Island of Ceylon has an extent of 25,332 square miles, and a population of nearly seven millions; the range of latitude is from 5° 55′ to 9° 50′ North and of longitude 79° 42′ to 81° 53′ East.     

Spatial Variability and Precision Nutrient Management in Sugarcane

Investigations were carried out to develop precision nutrient management techniques for sugarcane. The study area (800 ha) comprised of Bijapur, Bilgi and Jamakhandi talukas that lie between 16° 34′–28° 10′ N latitudes and 75° 33′–75° 37′ E longitudes and located around Nandi Sahakari Sakkare Karkhane (NSSK) Niyamit, Galagali. The soils are medium to deep black with pH and EC ranging from 7.32 to 8.36 and 0.17 to 1.13 dS/m, respectively. The soils are low to medium in available nitrogen, medium in available phosphorus and high in available potassium content. Crop condition assessment was made through analysis of LISS-III satellite images using Erdas Imagine software. Fertigation with 300 kg N and 195 kg K per ha at fortnightly interval and soil application of 32 kg P per ha as basal, recorded higher sugarcane yield (167 Mg ha^?1) as compared to 124 Mg ha^?1 obtained with soil application of 250 kg N, 32 kg P and 156 kg K per ha and flood irrigation as per the package recommended by the University(POP). Fertigation of N and K at weekly interval recorded highest NDVI value (0.354) and soil application of nutrients as per POP resulted in the lowest NDVI of 0.219.     

GEOGRAPHICAL POSITIONS IN MAURITIUS AND RODRIGUEZ

Abstract

The desirability of determining as accurately as possible the latitudes and longitudes of a number of points in Mauritius appears to have first appealed to the French astronomer M. L'Abbé de la Caille, who was sent to the island by the French East India Company in 1753. His observatory was situated 4,730 feet east and 2,610 feet north of Port Louis Time Ball, and in addition to determining the geographical position of this. 0bservatory (the house, later demolished, of a Mr Mabile, where Mr D'Après had made observations the previous year)—

Latitude 20° 09′ 42″ S.; Longitude 55° 08′ 15″ E. of Paris—,

he succeeded in effecting a triangulation of the island. Four bases were measured with wooden scales which previously had been compared with an iron toise (6.394 feet—the French fathom) approved by the Academy of Sciences, Paris; a I4-inch quadrant fitted with micrometer was used to measure the angles.