‘Aeolus 1 data improved forecasts by an incredible 5 per cent’

Q. How did the Aeolus 1 satellite project come about?

A. The scientific project to study winds from space was given to the European Space Agency (ESA) in 1999. The idea was to put a laser in space and study the scattering pattern of laser pulses, which are dense and sharp light pulses, when they bumped into particles and air molecules. We mainly use ultraviolet pulses for this purpose generated by a UV Light detection and ranging (LiDAR) device. This gives us the movement of air molecules in space. With this data you can retrieve winds in clear air that are not connected to any patterns or features in the atmosphere. This was to be a science mission, and not an operational mission, and we wanted to see if we can build and demonstrate the technology to monitor and study winds. The satellite was launched after almost two decades.

Q. Why was it important to study winds through a satellite?

A. We launched the Aeolus 1 satellite in 2018 with the objective of retrieving clear air wind data. We wanted an observational system that could provide the vertical profiles of winds which was not available until that moment. Before that, what we were using as wind data was more to do with moving patterns in the atmosphere such as cloud patterns. In this, you take the images of cloud patterns at different times and try to gauge how the clouds are moving and get the data on wind from that. You can also retrieve wind data from humidity and temperature patterns in the atmosphere. However, these measurements are always related to certain phenomena and you had to make certain assumptions about the heights at which these were occurring, such as the stratification of the moving clouds. The dream of the wind community was to have a tool in space that can measure winds in clear air without any patterns of clouds or other phenomena.

Q. What is being measured by the Aeolus 1 satellite?

A. The satellite is not measuring full wind vectors but only the vertical direction of wind vectors. It was shown in studies before that this information is enormously valuable as we do not have the vertical profile of winds from ground-based instruments such as radiosondes (balloon mounted wind measuring instruments). These radiosondes are not uniformly spread around the world especially in tropical areas and in areas above the ocean and in polar regions. Wind information from these crucial regions was lacking before.

Q. Where has the data from Aeolus 1 been used and what has been the response to that?

A. The technology of Aeolus 1 had some issues and the quality of data was not as per our expectations. We were able to measure winds from the scattering of air molecules with a possible error margin of six to seven metres. For the winds that are scattered by small particles in the air the uncertainty was 3-4 m. Initially we were disappointed. Our data has been used by the European Centre for Medium-range Weather Forecasts (ECMWF) and the National Centre for Medium Range Weather Forecasts (NCMRWF) in India and despite the problems, our data was able to significantly improve the weather forecasts by 5 per cent. The weather agencies said that usually their improvements are incremental and on a much smaller scale and they were happy with the improvement brought about by Aeolus. These improvements were particularly in the tropical areas, oceans and the polar regions where there was a lack of wind information earlier. There have also been studies from the US where data from Aeolus 1 has improved the forecasts of hurricanes.

This was first published in the 1-15 July, 2024 print edition of Down To Earth