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1.
《测量评论》2013,45(66):174-176
Abstract

It has been shown in an earlier number of the Empire Survey Review (iv, 24, 70) that if an observer whose eye is at sea level in a calm sea sees an object at a distance s, so that it appears to be on the horizon, then the height of that object above sea level is given by <mml:math><mml:mrow><mml:mi>h</mml:mi><mml:mo>=</mml:mo><mml:mi>K</mml:mi><mml:msup><mml:mi>s</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow></mml:math> where <mml:math><mml:mrow><mml:mi>K</mml:mi><mml:mo>=</mml:mo><mml:mfrac><mml:mrow><mml:mfrac><mml:mn>1</mml:mn><mml:mn>2</mml:mn></mml:mfrac><mml:mo>?</mml:mo><mml:mi>k</mml:mi></mml:mrow><mml:mi>r</mml:mi></mml:mfrac></mml:mrow></mml:math>; being the coefficient of refraction and r the mean radius of the earth.  相似文献   

2.
《测量评论》2013,45(23):38-41
Abstract

Many surveyors, even those of wide experience, would, if questioned, assert that, at any given pointing of a theodolite, all points in the field of view which lie on the horizontal wire are at equal angular altitudes above the horizon, provided that the horizontal wire is in correct adjustment to the trunnion axis.  相似文献   

3.
Abstract

The seasonal and interannual variation of upwelling along the east coast of India between 6°N and 22°N was studied for the period 1985–2003 using NOAA–AVHRR sea surface temperature data. The seasonal migration of pronounced upwelling, which follows the seasonal shift of the winds in transition period and northeast monsoon, was confined. The temporal mean sea surface temperature images clearly show the upwelling season, as does the seasonal sea surface temperature anomaly. These dominant features of the upwelling system are also the most variable, with most of the variance being explained by the seasonal cycle. Quasi-cyclic behaviour of sea surface temperature on interannual scales has also been observed.  相似文献   

4.
Abstract

The Electronic Chart and the Electronic Chart Display Information System are integrating technologies requiring accurate position fixing using GPS, assessment of current sea surface situation using radar and high quality display in map form. The latter aspect is addressed here with an emphasis on operational requirements for such shipboard cartography including colour and symbolisation.  相似文献   

5.
《测量评论》2013,45(93):290-303
Abstract

In order to reduce the shoran distance to geodetic distance, it is necessary to know the following: (a) the height above sea level of the ground stations, (b) the elevation of the airborne station at the time of transits and (c) the path and velocity of the radar wave through the atmosphere.  相似文献   

6.
《The Cartographic journal》2013,50(3):211-221
Abstract

The progressive projection is by origin a manual cartographic technique, traditionally used by panoramic landscape painters; however, it is rarely encountered in digitally created three-dimensional (3D) maps. In this article, the advantages of this specific projection when designing 3D maps are presented, the processes involved in its manual construction, as well as the existing and potential digital implementation approaches, are reviewed. A new algorithmic solution is described, allowing for user-friendly interactive bending of a terrain model into a progressive view, with options to add a curved horizon, to vertically exaggerate the terrain, and to create a 360° strip panorama. The resulting software, Terrain Bender, is freely available for download.  相似文献   

7.
《测量评论》2013,45(24):68-69
Abstract

The following points occurred to me when reading the interesting paper on crustal equilibrium in E.S.R. No. 23. The principle of compensation or isostasy necessarily involves the idea of two different kinds of rock structure—one strong, the other weak or in extreme cases fluid; for example, there is the familiar case of the strong iceberg resisting change of shape in the liquid sea. In dealing with crustal problems of the earth then, we should make up our minds which part is to be considered as strong, e.g. the granite crust, and which part as weak or fluid, e.g. material at a depth x km. (say roo km.); by weak or fluid I mean that a possibility exists of horizontal movement.  相似文献   

8.
In November 1968, a marine geodetic control point was established in the Pacific Ocean at a water depth of6,200 feet. The control point (reference point) consists of three underwater acoustic transponders, two of which are powered with lead-acid batteries and the third with an underwater radioisotope power source “URIPS” with a10- to20- year life expectancy. Four independent measuring techniques (LORAC airborne line-crossing, satellite, ship inertial, and acoustic techniques) were used to measure and determine the coordinates of the control point. Preliminary analysis of the acoustic and airborne data indicates that high accuracies can be achieved in the establishment of geodetic reference points at sea. Geodetic adjustment by the method of variation of coordinates yielded a standard point error of±50 to±66 feet in determining the unknown ship station. The original location of the ship station as determined by shipboard navigation equipment was off by about1,600 feet. Paper previously published in the Proceedings of the Second Marine Geodesy Symposium of the Marine Technology Society.  相似文献   

9.
《测量评论》2013,45(13):391-395
Abstract

In January, 1934, a report was received from the Royal Research Ship Discovery II that the positions of Inaccessible and Nightingale Islands in the Tristan d'Acunha group were incorrectly shown on British Admiralty chart No. 1769. The report originated from local information, and was to some extent confirmed by patent log distances run by Discovery II, and by sea sights, but no really definite evidence as to the correct position of the two islands was received. In effect, the report merely stated that both Inaccessible and Nightingale Islands were considerably nearer to Tristan Island than as charted.  相似文献   

10.
《测量评论》2013,45(49):99-107
Abstract

The problem of dividing the circle into equal parts has occupied the minds of astronomers and instrument makers from the earliest times, but little is known of the methods adopted by such renowned observers as Hevelius or Tycho Brahe, who are said to have divided their own instruments (I). It is possible, however, to trace the various steps by which progress was made and to appreciate the urgent need that was felt, particularly throughout the eighteenth century, for improvement in the accuracy of astronomical instruments, if only to satisfy the increasing demands for navigational charts and for the means of determining the position of a ship at sea.  相似文献   

11.
Abstract

The southern part of the Caspian Sea shoreline in Iran with a length of 813 km has different topographic conditions. Owing to sea fluctuation, these zones have various dimensions in different times. During the last years, the Caspian Sea experienced enormous destructive rises. The historical information and tidal gauge measurements showed different ranges of sea rise from ?30 m to ?22 m from the mean sea level. On the other hand, the probable flooding zone is related to slope gradient of coasts. To help the determination of the probable flooding area owing to sea level rises, the coastal zones can be modelled using geographic information system (GIS) environment as vulnerability risk rates. These rates would be useful for making decisions in coastal management programs. This study examined different scenarios of sea rise to determine hazard-flooding rates in the coastal cities of the Mazandaran province and classified them based on vulnerability risk rates. The 1:2000 scale topographic maps of the coastal zones were prepared to extract topographic information and construct the coastal digital elevation model. With the presumption of half-metre sea rise scenarios, the digital elevation models classified eight scenarios from ?26 to ?22 m. The flooding areas in each scenario computed for 11 cities respectively. The vulnerability risk rate in each rise scenario was computed by dividing the flooded area of each scenario to city area. The results showed that in the first four scenarios, from ?26 to ?24 m, the Behshahr, Joibar, Neka and Babolsar cites would be more vulnerable than other cites. Moreover, for the second four scenarios from ?24 to ?22 m sea level rise scenario, only the coastal area of Chalous city would be vulnerable. It was also observed that the coastal region of Behshahr would be critical in total scenarios. Further studies would be necessary to complete this assessment by considering social-economic and land use information to estimate the exact hazardous and vulnerable zones.  相似文献   

12.
《测量评论》2013,45(15):14-16
Abstract

THE mapping of flat country from the ground always entails much more work than the mapping of hilly country for the obvious reason that the nearness of the horizon, coupled with the obstruction of trees, buildings, and vegetation, restricts the view, and long lines are not possible. In contrast to this, mapping from air-photographs becomes much more simple when the country is flat, for the photographic projection is not complicated by height distortions, and it is only necessary to correct for distortions caused by the impossibility of keeping the camera perfectly horizontal at the instant of exposure. During the past four years in Bengal and the United Provinces, where the alluvial plains scarcely vary a foot from monotonous flatness, many thousands of square miles have been surveyed photographically, and excellent maps have been made on a scale of 16 inches to 1 mile and are being used by Settlement Officers for purposes of land assessment.  相似文献   

13.
ABSTRACT

Surface roughness of sea ice is primary information for understanding sea ice dynamics and air–ice–ocean interactions. Synthetic aperture radar (SAR) is a powerful tool for investigating sea ice surface roughness owing to the high sensitivity of its signal to surface structures. In this study, we explored the surface roughness signatures of the summer Arctic snow-covered first-year sea ice in X-band dual-polarimetric SAR in terms of the root mean square (RMS) height. Two ice campaigns were conducted for the first-year sea ice with dry snow cover in the marginal ice zone of the Chukchi Sea in August 2017 and August 2018, from which high-resolution (4 cm) digital surface models (DSMs) of the sea ice were derived with the help of a terrestrial laser scanner to obtain the in situ RMS height. X-band dual-polarimetric (HH and VV) SAR data (3 m spatial resolution) were obtained for the 2017 campaign, at a high incidence angle (49.5°) of TerraSAR-X, and for the 2018 campaign, at a mid-incidence angle (36.1°) of TanDEM-X 1–2 days after the acquisition of the DSMs. The sea ice drifted during the time between the SAR and DSM acquisitions. As it is difficult to directly co-register the DSM to SAR owing to the difference in spatial resolution, the two datasets were geometrically matched using unmanned aerial vehicle (4 cm resolution) and helicopter-borne (30 cm resolution) photographs acquired as part of the ice campaigns. A total of five dual-polarimetric SAR features―backscattering coefficients at HH and VV polarizations, co-polarization ratio, co-polarization phase difference, and co-polarization correlation coefficient ―were computed from the dual-polarimetric SAR data and compared to the RMS height of the sea ice, which showed macroscale surface roughness. All the SAR features obtained at the high incidence angle were statistically weakly correlated with the RMS height of the sea ice, possibly influenced by the low backscattering close to the noise level that is attributed to the high incidence angle. The SAR features at the mid-incidence angle showed a statistically significant correlation with the RMS height of the sea ice, with Spearman’s correlation coefficient being higher than 0.7, except for the co-polarization ratio. Among the intensity-based and polarimetry-based SAR features, HH-polarized backscattering and co-polarization phase difference were analyzed to be the most sensitive to the macroscale RMS height of the sea ice. Our results show that the X-band dual-polarimetric SAR at mid-incidence angle exhibits potential for estimation of the macroscale surface roughness of the first-year sea ice with dry snow cover in summer.  相似文献   

14.
The advantages and disadvantages of measuring ocean wave heights in the surf zone by using terrestrial photogrammetry are outlined. Difficulties arising from a lack of control points can be overcome by using the apparent horizon to provide camera orientations about two axes, provided that the apparent horizon is the sea surface and that an unconventional orientation of the camera axis system is adopted. Following practical tests and error simulation studies, height differences were determined for 12 points in the breaking wave zone off a Newcastle (New South Wales) beach. It is hoped that the method can be developed as a convenient means of collecting wave data.  相似文献   

15.
《测量评论》2013,45(18):194-203
  相似文献   

16.
《测量评论》2013,45(1):33-35
Abstract

For some years past the work of the Hydrographic Service of H.M. Navy afloat has been carried out by eight of H.M. Surveying Vessels. These ships, of which four are employed abroad and four in home waters, work at sea for about eight months in the year and are refitted during the remaining four months, usually during the winter or bad-weather season. Whilst the ships are being refitted for further service the officers are employed in drawing the fair charts of the season's work and in preparing Sailing Directions and other work in connection with the Survey.  相似文献   

17.
In general the observations within a continental levelling network have been made during day time when the sun is above the horizon. In Northern countries levelling observations have often been made during the summer months and in the morning and the evening, when the sun may be to the North of the prime vertical. This entails that special mean tidal perturbations by the sun on a levelling network may deviate with not quite negligible quantities from general mean tidal influence by the sun on the sea. For the moon the corresponding deviation will be nearly zero. The variance of the levelling (REUN 1960) between the tidal stations M-28 Fredericia and M-48 Genova is (±33 mm x kiloGal)2. The author (1965) has found for this line (hypothetical levelling 19/5–2/6 1950 on the Yielding Earth) possiblespecial mean tidal correction by the moon +27.5 mm possiblespecial mean tidal correction by the sun −4.2 mm ― in total +23.3 mm deviating 22.5 mm fromgeneral mean tidal correction of the seafor both moon and sun} +45.8 mm The deviation 22.5 mm between tidal corrections for Mean Sea Level, MSL, and for levelling line is not quite negligible.  相似文献   

18.
极区海冰密集度AMSR-E数据反演算法的试验与验证   总被引：2，自引：2，他引：2  
海冰密集度是极区海冰监测的重要参数,目前分辨率最高的微波海冰密集度产品为德国Bremen大学发布的针对AMSR-E 89 GHz频段数据利用ASI算法反演的网格数据。为实现中国极区遥感产品从无到有的战略步骤,本文针对AMSR-E 89GHz频段微波数据的ASI算法,进行了插值算法、系点值和天气滤波器一系列试验。针对北极海区,着重对影响反演结果的主要参数——纯冰和纯水的亮温极化差异阈值,即系点值(P1和P0)进行了2009年全年的统计分析。研究表明,2009年北极纯冰和纯水的代表区域P1和P0年平均值分别为10.0 K和46.67 K;2 K以上的系点值差异引起的海冰密集度差别较为显著;同样的系点值差异在不同极化差异P取值范围对海冰密集度的影响也不同。通过统计确定的系点值推算并修正了海冰密集度反演公式,对2009年全年北极海冰密集度进行了反演,并与Bremen大学产品进行了比较。继而对白令海和楚科奇海12个晴空下MODIS可见光样本数据进行反演,以验证AMSR-E冰密集度反演结果,并对误差原因进行了分析。本研究反演结果与MODIS样本比对的误差略小于Bremen大学的反演产品,空间平均误差为3.84%,空间平均绝对误差10.83%。  相似文献   

19.
Impacts of geodynamic phenomena on systems for height and gravity   总被引：2，自引：1，他引：2  
Geodynamic phenomena of permanent or secular characters play a significant role when defining height systems and gravity systems. A treatment is here given of the permanent earth tide, postglacial land uplift, sea level changes and polar drift from this point of view.
1.  The various gravity and geoid concepts originating from differing ways of handling the permanent tide are treated, and transformations between them are given. Numerical applications are made to height and gravity systems in the Nordic countries, including determination of land uplift. The oceanographic deviation of mean sea level in the Baltic Sea is discussed with respect to the permanent tide. Problems caused by the permanent tide in height determination based onGPS are illustrated.
2.  The effects of postglacial land uplift and sea level changes are dealt with together. Again, numerical applications are made to height and gravity systems in the Nordic countries. It is discussed how sea level data should be included in the determination of land uplift. An attempt to estimate the remaining land uplift is made.
3.  A few words are said on the role of polar drift when defining a gravity system.
  相似文献   

20.
The main environmental problem in tracking a satellite through the atmosphere is in finding the most probable value of the mean refractive index. In this paper, the mean refractive index is computed as a four-part model. The troposphere is treated as one altitude range from sea level to 9 kilometers, and the stratosphere is divided into three altitude ranges, 9 to 18, 18 to 27, and 27 to 36 kilometers. At 36 kilometers, the N-value is approximately equal to two and reduces rapidly to zero. By the use of theEssen formula in radio wave application and the modifiedKohlrausch formula in light wave application, point-to-point values of the refractive index are computed through these altitude ranges. The polynomial expansion of second order from the basic exponential function is selected as the model, and the curve-fitting adjustments of the computed values are established separately to each altitude range to obtain coefficients A, B, and C. A model based on the U. S. Standard Atmosphere, 1962, is used as the reference to which four sets of actual soundings made in Lihue, Hawaii and Fairbanks, Alaska on February 3 and July 2, 1966, are compared. The results show that the parabolic adjustment has a very high reliability. In the use of standard atmosphere, the standard error of the refractive index through the total altitude range of 0 to 36 kilometers, and at the 70° zenith distance, equal only ±7 millimeters when radio waves are utilized, and ±3 millimeters when light waves are utilized. Paper presented at Conference on Refraction Effects in Geodesy and Electronic Distance Measurement, University of New South Wales, 5–8 November 1968. Hawaii Institute of Geophysics Contribution No. 239.  相似文献   

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