SOME EFFECTS OF PULLEY ECCENTRICITY IN BASE MEASURING APPARATUS

Abstract

The comprehensive paper on the suspension of tapes by M. Hotine in the January, 1939, issue of the Empire Survey Review (v, 31, 2) did not contain any reference to this question, as was pointed out by A. J. Morley in a letter published on page 261 in the same volume (v, 34, 261). A brief analysis has been made by F. Yates of the theoretical effects of pulley eccentricity and misalignment (“Gold Coast Survey Department Records” VoL III, 1931, page 43) but I have not seen any further reference to the subject and have recently experienced the effects of such a defect in our own apparatus, so the followingnotes nlay be of interest. Before proceeding to details I will describe briefly those parts of the apparatus which are considered here and give a short summary of the whole paper.     

A PNEUMATIC APPARATUS FOR MEASURING THE FLATNESS OF PHOTOGRAPHIC PLATES

Abstract

The paper describes a simple pneuluatic apparatus, working at a pressure of about ½lb./in.², which enahles the flatness of photographic plates to be checked rapidly prior to their use in the camera. The errors of flatness are shown directly by the levels of coloured water columns in parallel manometer tubes; the magnification is 2,500 and the linear range is ±15μ (±0.0006 in.). The apparatus essentially measures departures from a prescribed form and has therefore other applications.     

TEMPERATURE MEASUREMENT AND SURFACE CHAINING FOR CADASTRAL PURPOSES

Abstract

The measurement of the temperature of a measuring band or bar has always been a major problem. A considerable a.mount of experimentation has been done on the morepreciseaspects of survey measurement, and attempts, ranging from packing measuring bars in ice to bimetallic apparatus, made to reduce temperature errors. At the present time electro-resistance thermometers are being used and an entire new field is being investigated using various waves for distance measurement. For at least some time in the future, however, these new techniques will not be sufficiently developed to be of practical or economic use to the cadastral surveyor. Nevertheless very much less interest is taken in what may be termed “bread and butter” procedures.     

DETERMINATION OF TAPE TEMPERATURES ON THE MEASUREMENT OF THE WANKIE AND SABI GEODETIC BASES,SOUTHERN RHODESIA (1953)

Abstract

The Wankie Geodetic Base was measured in May 1953 and the re-measurement of the Sabi Geodetic Base was also completed during the month following. For these measurements the standard “Macca” equipment was used, the gear being lent to the Southern Rhodesia Government by the Directorate of Colonial Surveys. As it was anticipated that both measurements would be made under hotter and more sunny conditions than normally prevail in England, the Directorate of Colonial Surveys suggested that the opportunity be taken of carrying out further tests in the determination of temperatures by the “resistance thermometer” as described by Messrs. Clark and Johnson of the National Physical Laboratory in their paper on the “Measurement of Temperature of Geodetic Surveying Tapes. Accordingly, through the good officesof the Director of the National Physical Laboratory, the apparatus comprising the resistance theremometer was made available for use on these two base measurements.     

The use of atmospheric dispersion in optical distance measurement

The development of lasers, new electro-optic light modulation methods, and improved electronic techniques have made possible significant improvements in the range and accuracy of optical distance measurements, thus providing not only improved geodetic tools but also useful techniques for the study of other geophysical, meteorological, and astronomical problems. One of the main limitations, at present, to the accuracy of geodetic measurements is the uncertainty in the average propagation velocity of the radiation due to inhomogeneity of the atmosphere. Accuracies of a few parts in ten million or even better now appear feasible, however, through the use of the dispersion method, in which simultaneous measurements of optical path length at two widely separated wavelengths are used to determine the average refractive index over the path and hence the true geodetic distance. The design of a new instrument based on this method, which utilizes wavelengths of6328 ? and3681 ? and3 GHz polarization modulation of the light, is summarized. Preliminary measurements over a5.3 km path with this instrument have demonstrated a sensitivity of3×10 ⁻⁹ in detecting changes in optical path length for either wavelength using1-second averaging, and a standard deviation of3×10 ⁻⁷ in corrected length. The principal remaining sources of error are summarized, as is progress in other laboratories using the dispersion method or other approaches to the problem of refractivity correction.     

Mt. Pinatubo Volcano/Typhoon Yunya

Abstract

Lineaments have proved to have greater control over groundwater but their depth persistence and their control over groundwater flow have remain unexplored for many years. In the present study an attempt has been made to unearth the depth persistence of lineaments by integrating data collected from resistivity soundings. The lineaments are interpreted from IRS 1A imagery and revealed NE‐SW, NNW‐SSE, NNE‐SSW, N‐S, E‐W and NW‐SE orientations. The integration of resistivity data shows that N‐S and NW‐SE trending lineaments have depth persistence and also have greater control over groundwater movement.     

SILTING AND ISLAND GROWTH IN THE ZAMBEZI NEAR LIVINGSTONE

Abstract

The Northern Rhodesia Survey Department recently carried out a series of measurements of certain cross-sections of the Zambezi in the vicinity of Livingstone. The stretch of river over which the above were made is that known as the Regatta Course and extends between the top of Loando or Long Island downstream to the mouth of the Maramba River. This stretch is about three and a half miles southwest of Livingstone and two to four miles upstream from the Victoria Falls.     

THE YEAR 1934 IN SARAWAK

Abstract

General.— The year 1934 has seen on the survey side an active continuation of trig. and cadastral surveys and on the land side standardization of procedure and routine. Good progress has been made in both branches. The surplus of revenue over expenditure, noted last year for almost the first time, has been very considerably increased, being of the order of eighty-two thousand dollars.     

TWO NOTES ON SHORT TERTIARY BASES

Abstract

During recent years a light apparatus has been made up in the Survey of India to provide a basis for minor triangulation. The idea originated with the writer when executing rough triangulation under war conditions, when the need was felt for checking work which had become liable to development of considerable error. The terrain was not such as to allow the measurement of an ordinary base of such a length as half a mile; nor were other facilities present. Accordingly a length of 200 feet was marked out, with the help of a 100-foot steel tape, on a fairly smooth site on rolling ground; and its subtended angle at a distance of about 1500 feet was measured carefully with numerous repetItIons. This 1500-foot length was in turn extended in a similar way to a 3-mile side of the triangulation. No great accuracy was looked for, but enough to rule out the possibility of gross mistake in the irregular triangulation.     

THE GEODIMETER: AN INSTRUMENT FOR THE ACCURATE MEASUREMENT OF DISTANCES BY HIGH-FREQUENCY LIGHT VARIATIONS

Abstract

During the last few years a method of measuring accurately the lengths of lines of moderate length by means of high-frequency variations in the intensity of light emitted by a special transmitter, which promises to have many important applications in triangulation and precise traversing, has been devised by Mr. E. Bergstrand, of the Geographical Survey of Sweden. In principle, the method has certain resemblances to the apparatus invented and used by Fizeau for measuring the velocity of light, Bergstrand's instrument having been designed in the first place for the measurement of the same constant. In Fizeau's apparatus, it will be remembered, a ray of light was directed through the cogs of a revolving toothed wheel towards a distant mirror, and, when the wheel reached a certain angular velocity, the ray reflected from the mirror was intercepted by the cogs, so that an observer stationed on the same side of the wheel as the light source no longer saw the reflection of the light in the mirror. The angular velocity of the wheel being known or observed, the time taken for the cogs to obliterate the reflected image could be calculated, and twice the distance to the mirror divided by this time gave the velocity of light. In the Bergstrand apparatus, which is called the “geodimeter”, light pulses of known frequency and varying intensity are directed to the end station of the line whose distance is required, and, after reflection by a mirror at that station, are received back in a special receiving apparatus alongside the transmitter. Here they are converted into small electric currents, which, when the required distance is a certain function of the wave length of the transmitted and reflected pulses, can be made to give zero deflection on a sensitive galvanometer. In this way, the distance to be measured can be determined in terms of the wave length of the pulses. Experiments so far carried out with this apparatus have been successful up to distances of about 36 kilometres. Even with the latest model, however, as we shall see later, it is necessary to know the approximate distance to within 1½ km.     

Harveys and Walking Maps

Abstract

Geographical information is connected to everyday life in many ways. Web cartography has made geospatial data more available to the public. In the next few years, the average age of the population will be over 51 years, with more than 15% of the population over the age of 65 years. The fact that the senior population is increasing suggests that online mapping and map viewer design should be aware of the senior population’s visual restrictions, as well as restrictions of other potential map users, including colour-vision-impaired users. This paper describes the senior population’s visual restrictions that can be compared with colour-vision-impaired users and provides guidelines with regard to online mapping and map viewer design for this growing segment of the elderly population.     

Population Enumeration on a Grid Square Basis: The Census of Scotland,a Test Case

Abstract

After examination of the existing Census organisation, the problems of making full use of the data are investigated, in particular the disparity of units on the ground, changes over time, and variations in the nature of the published information. Proposals are made and explained for the adoption of a grid square enumeration system, which in this case is tested by application to an urban and a rural area. The problem of conflict between grid square and local authority boundary is examined. The more general usefulness of a grid square enumeration system is demonstrated in relation to comparability of data, mechanisation of processing and graphic output, and the data bank concept. Further testing by means of a sample census is being currently undertaken.     

LATITUDE,LONGITUDE AND AZIMUTH FROM TWO STARS

Abstract

The article discusses an observation consisting of pointings made to two stars on opposite sides of the meridian, the altitude in each case being set equal to the star's declination.     

The Utility of Day‐and‐Night Observation and Cloud‐Penetration Capability of ERS‐1 SAR Data for Detection of Wetlands

Abstract

The sensitivity of microwave sensors to changes in the complex dielectric constant of soil/water mix with change in water content has been used in several studies for soil moisture estimation and in the detection of wetlands. In the study, reported here, an attempt has been made to delineate various categories of wetlands, namely ‘bils’ (acquaculture ponds), lakes/ponds, creeks, and mangroves through visual interpretation of ERS‐1 SAR images acquired on 29th April, 1993 over part of Sundarban delta, abutting Bay of Bengal. An overall accuracy of 91.2% with respect to delineation of wetlands has been achieved. Further, the cloud penetration and day‐and‐night observation capability of ERS‐1 SAR, though well known, is also illustrated.     

The geopotential to (14, 14) from a combination of satellite and gravimetric data

A set of2261 5°×5° mean anomalies were used alone and with satellite determined harmonic coefficients of the Smithsonian' Institution to determine the geopotential expansion to various degrees. The basic adjustment was carried out by comparing a terrestrial anomaly to an anomaly determined from an assumed set of coefficients. The (14, 14) solution was found to agree within ±3 m of a detailed geoid in the United States computed using1°×1° anomalies for an inner area and satellite determined anomalies in an outer area. Additional comparisons were made to the input anomaly field to consider the accuracy of various harmonic coefficient solutions. A by-product of this investigation was a new γ_E=978.0463 gals in the Potsdam system or978.0326 gals in an absolute system if −13.7 mgals is taken as the Potsdam correction. Combining this value of γ_E withf=1/298.25, KM=3.9860122·10 ²² cm ³ /sec ² , the consistent equatorial radius was found to be6378143 m.     

DETERMINATION OF TIME AND LATITUDE BY THE EQUAL ALTITUDE METHOD WITH THE THEODOLITE

Abstract

The following investigation originated in some experiments that were made to discover the best way of using the Wild Universal Theodolite for astronomical observations. The special features of this instrument can be best realized if they are classified as advantages and disadvantages.     

THE ADJUSTMENT OF A FIRST-ORDER LEVELLING NETWORK

Abstract

In the E.S.R. January and April numbers of 1955, Vol. xiii, Nos. 95 and 96, Mr. Hsuan-Loh Su described the “Adjustment of a Level Net by Successive Approximations and by Electrical Analogy”. It does not seem to be as generally known as it should be that the rigid least square solution can be greatly simplified by utilizing the electrical analogy and solving by Kirchhoff's method. The method as detailed below has been in use for over 40 years.     

Cartography in Advertising

Abstract

This short paper attempts to pursue an analytical account of the cartography in present day advertising. Particular reference is made to the printed advertisements in newspapers, brochures and periodicals available in Britain.     

A Mathematical Approach to the Storage of Digitised Contours

Abstract

The increasing use of digitised data, especially contours, is creating problems of storage in the smaller computers. Efforts made to make digitised contour information more compact for use in a data bank are described which can produce savings in storage requirements of up to 85 per cent.     

Earth observations during space shuttle mission STS‐34: 18–23 October 1989

Abstract

Although high‐resolution microwave synthetic aperture radar (SAR) sensors possess all‐weather capability for mapping soil moisture from spaceborne platforms, continuous temporal and spatial monitoring of this important hydrological parameter has been relatively limited. However, the recent launch of operational SAR sensors aboard various satellites have made possible synoptic soil moisture monitoring a reality. Such systems operate over a wide range of frequencies, look angles, and polarization combinations, and thus show synergistic advantages when combined for estimating soil moisture patterns. Two soil moisture inversion algorithms have been developed using as inputs radar backscattering data at L, S, and C bands in the microwave frequency range. These models have been tested using radar image simulation with speckle added. It is observed that the neural network algorithm yields superior results in mapping actual soil moisture patterns over the linear statistical inversion technique, although both models show comparable errors in soil moisture estimation. We infer that using statistical estimation errors alone for comparison purposes may lead to erroneous conclusions regarding the advantages of one soil moisture inversion algorithm over another.