Articles in the Geodesy Category

Aug 2005 | Comments Off on Mumbai floods: How GPS-GIS can help

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!

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

IV MURALI KRISHNA Professor and Head, Centre for Spatial Information Technology, Jawaharlal Nehru Technological University, Hyderabad

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 …