Six-satellite system for weather forecast proposed

Plan to overcome hitches in current mechanism

 India may have a constellation of six micro-satellites circling the Earth in a low-earth orbit to collect accurate climatic data for better weather forecasting in the future, if the Union Government approves the proposal of a former ISRO official.

forecast: An artistic representation of the Constellation Observing System for Meteorology, Ionospphere and Climate system.

Conceptualised in the line of the six-year old US-Taiwan COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate) system, the Indian constellation of six microsatellites, each wei­g­hing 50 kg, would collect vertical profile on temperature, pr­e­ssure and humidity, which can be fed into forecasting models.

“The proposal is to have half-a-dozen satellites in low-earth orbit (about 700 km) altitude, each of which will have 30 observations in a day, resulting in close to 200 daily observations. The entire project cost should be around Rs 50 crore,” D Narayana Rao, former director of Indian Space Research Organisation's National Atmospheric Research Laboratory in Tirupathi told Deccan Herald on the sidelines of 99th session of the Indian Science Congress.

Rao presented his proposal at a session chaired by Shailesh Nayak, secretary in the Union Ministry of Earth Sciences, who would ultimately have to approve it when Rao would put up a formal proposal. “It is emerging idea for accurate observations but we have to look at other aspects before going ahead,” Nayak said.

The proposed Indian constellation is in the same line as COSMIC that measures key attributes of atmosphere using radio occultation, a method first developed in the late 1960s to study atmospheres on other planets by two US institutions,  Jet Propulsion Laboratory and Stanford University. Radio occultation works when micro­satellites track radio-signals emitted by 24 GPS satellites and measures their bending angle just above the horizon.

Temperature, pressure, and moisture affect the density of the atmosphere. When radio signals from the higher-orbiting GPS satellites pass through the atmosphere, the signals' paths are bent and their progress is slowed. The rate of these changes depends on the atmosphere's density along the path, which can be measured using the GPS-RO satellites, each of which will carry dual-frequency GPS receivers.

But COSMIC does not provide enough data about the tropics, where Indian interest lies. The proposed constellation can fulfil the requirement.

Currently, weather data are collected by 35 predominantly land-based weather stations, virtually leaving out the entire Indian Ocean. The existing practice of using radio-sonde balloons has its own limitation that can be overcome using the constellation. The proposed weather forecasting system, however, would not be a part of the Rs 350-crore National Monsoon Mission that will come up before the Union Cabinet for a green signal later this month.

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