By Dr. Prem Shankar Goel, Former Secretary, Ministry of Earth Sciences, India

Way back in 1975, when we were writing requirements for INSAT-1 satellite, Prof Yashpal, then Director Space Application Centre, said that Very High-Resolution Radiometer (VHRR) would be the essential component, in spite of the complexity it introduces to the configuration of the satellite, like one sided solar panel, and a solar pressure compensatory Sail and Boom. It also introduced the requirement of very high stability of the platform so that the cloud velocity could be computed to an accuracy of 3 meters per second. Since then, one or more VHRRs have always been in orbit inside INSAT satellites.

Today, meteorology is no more a synoptic view of a few weather parameters like clouds, wind velocity and temperatures at a few locations, but an outcome of high-resolution atmosphere and ocean coupled numerical models. This needs high-resolution (temporal and three-dimensional) data on land as well as the ocean. Weather is a chaotic system; hence, a small error in initial conditions leads to very quick divergence and hence inaccuracy in the weather forecast. The only way to collect this data worldwide, not limited by national boundaries, including over oceans, is via satellites. Further, it is not just the atmosphere data, but also the ocean data like surface winds, ocean temperature, etc. However, we need ground-based data primarily for the calibration of sensors in the satellite. Doppler Weather Radars play a very important role though, but they cannot be deployed in the ocean. WMO is one of the most cooperative frameworks in the world for sharing data, hence every country does not have to have satellite observations throughout the globe.

India has mastered the forecast methodology of cyclone intensity and its route, reducing the loss of life by three orders of magnitude. While thousands of people used to lose their lives, the number is now in the single digits. Further, we are able to map the floods in near real time and provide advisories to rescue teams.

India has a very comprehensive space segment for collecting weather and ocean data, like INSAT satellites, not only accommodating multichannel VHRRs but also wind profilers and microwave sounders, etc. We also have ocean observation satellites in Lower Earth Orbit (LEO). Indian scatterometry data is used worldwide for ocean state assessment. As we see a tremendous improvement in computing capability, already in petaflops, and the emergence of quantum computers in future, it would be possible to run global numerical models with a resolution of about a kilometre. Such high-resolution data for the whole globe can only be obtained through satellites. Needless to say, numerical weather modelling is one of the most intense computing problems. The more we improve the model, the more computing power will be needed.

Be it a short-term forecast, nowcast or long-term forecast of the Indian Monsoon, satellite data is an essential component of weather forecasts and weather services.

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