Articles in the Geodesy Category

Nov 2005 | Comments Off on Signal propagation through the troposphere
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Space environmental effects on satellite communication can be considered as related to space segment, ground segment and on the signals propagating through the earth’s lower and upper atmosphere. The atmospheric structure has significant influence on signal propagation. This has definite influence on the data processing methodologies. The specific applications with which are concerned here are …

Oct 2005 | Comments Off on CLASSROOM GEODESY
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The Coordinates Class room espouse readers to graticules of Mathematics and Physics that epitomize the Geospatial Information Technology. A chain of structured presentations related to interdisciplinary principles that define Geodesy, GPS, GIS, Geospatial data management and Image processing are to be en suite in this section in each issue of the Coordinates. Initially the chain …

Oct 2005 | Comments Off on International Terrestrial Reference Frame (ITRF)
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The International Terrestrial Reference Frame (ITRF) “yy” is a realization of the International Terrestrial Reference System (ITRS), where the “yy” represents the year of the solutions. Since its fi rst realization in 1988, there have been many variations and additions in use of data types and changes in computational strategy.
International Earth …

Sep 2005 | Comments Off on The old Indian Datum
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Under the new Map Policy, it seems that India has decided to retain the old Indian Datum, which has been identified by “Everest”, for DSMs. The following geodetic definition issues and “specifi cations” are worth commenting:
Vintage – 1880s.
Name – On a recent enquiry, four SOI experts provided four different names. However, it cannot be “Everest”.
Spheroid …

Sep 2005 | Comments Off on Malaysia precise geoid (MyGEOID)
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GPS infrastructures that have been established in Malaysia are mainly served as a ground control stations for cadastral and mapping purposes. Another element that has not been utilised is the height component due to its low accuracy. Conventional levelling is still the preferred method by the land surveyors to determine the stations orthometric height (H) with a proven accuracy. Therefore, Department of Survey and Mapping Malaysia (DSMM) has embarked the Airborne Gravity Survey, with one of the objectives is to compute the local precise geoid for Malaysia within centimeter level of accuracy. With the availability of the precise geoid, the “missing” element of GPS system is solved.

Aug 2005 | Comments Off on Classroom Geodesy
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In continuation of the discussion about the ellipsoid and geoid in the earlier interaction through the Classroom feature, let us define the reference coordinate systems. Consider a vertical axis oriented towards the north pole as Z axis. The X axis is oriented towards the First point of Aries ?. The Y axis completes a right …

Aug 2005 | Comments Off on Mumbai Floods: Another wake-up call

Maharashtra was the first state in the country to have a disaster management plan. It all started with the Latur Earthquake of 1993. As a part of response programme, the Maharashtra Emergency Earthquake Rehabilitation Project (MEERP) was launched the same year. This later led to the exercise of preparing a State Disaster Management Plan. The World Bank, United Nations Development Program (UNDP) as well as several bilateral donor agencies supported the initiative.

Aug 2005 | Comments Off on Mumbai floods: How GPS-GIS can help
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The 26th July 2005 floods in Mumbai, which caused widespread destruction, deaths and damage to property and infrastructure, have once again highlighted the importance of disaster mitigation and management using modern technology. Monitoring natural disasters like floods, earthquakes, volcanic eruptions, landslides, avalanches, cyclones, etc., with the ultimate aim of predicting them, and managing the rescue and rehabilitation operations during and after such calamities, have been discussed in various forums in the past. The devastating Latur earthquake of 1993, the Bhuj earthquake of 2001, the Orissa cyclone, and the recent tsunami after the Sumatra earthquake, which caused extensive damage in terms of human lives and property, have drawn the attention of the Indian scientific community to the immediate need of monitoring and managing such disasters in our country in the most effective, efficient and economic manner. Traditionally, maps are being used for this purpose, as an effective tool, since ancient times. However, with the introduction of computeraided techniques in map-making, and the space technology in surveying and mapping, the utility of geodetic and map data for this important activity has increased many-fold. However, a well-coordinated programme for optimum utilization of these important technological tools, resulting in efficient management of the disasters, still remains an elusive dream of administrators, scientists and technologists.

Aug 2005 | Comments Off on When ellipsoidal heights will do the job, then why not use them!
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In Today’s world, with GPS, we can survey ellipsoidal heights (h) with 5-10 cm accuracy for geodetic control points on land and differential heights (?h) between well defi ned topographic features with relative accuracy of 1: 1Million or better. In few specific cases, this type of accuracy may require specially designed GPS surveys. In navigational mode, an instantaneous positional accuracy of about ± 5 m is easily possible. As these heights are the direct product of the GPS survey(s) and thus defi ned with respect to the ellipsoid, which is a time-invariant zero reference surface, they can be used without any reference to the geoid or Mean Sea Level (MSL). If we recall, in the classical surveys, e.g., triangulations and/or traverses, the vertical angles used to provide the “?h” and thus there will not be any need to convert them to orthometric heights.

Jul 2005 | Comments Off on Classroom Geodesy
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IV MURALI KRISHNA Professor and Head, Centre for Spatial Information Technology, Jawaharlal Nehru Technological University, Hyderabad
iyyanki@icorg.org

Geodesy is science of the measurement and mapping of the earth’s surface. Satellite Geodesy in an orderly intensive manner started with the launch of the first artificial satellite SPUTNIK in October 1957. By the year 1964, many basic geodetic problems …