TRMM Tropical Rainfall Measuring Mission

In early 2001, NASA began using its Tropical Rainfall Measuring Mission — TRMM — to help improve data from older weather satellites.

Because the TRMM satellite flies over a given location only once a day, it can’t by itself track storms as they develop — or be used to issue emergency alerts reliably. So TRMM scientists combine TRMM data with data from several older, less sophisticated satellites. Here’s Robert Adler of the Goddard Space Flight Center in Greenbelt, Maryland.

Robert Adler: When the two satellites cross over we collect that data. So we basically compare the very good estimats from TRMM and what might be slightly-poorer estimate, or in some cases, quite a bit poorer estimate, from the other satellites, and we adjust them, or calibrate them …

In this way, Adler and his colleagues produce a weather map with the accuracy of TRMM — every three hours. The map shows exactly where it’s raining over most of the globe. This information is useful in areas with few ground-based instruments — such as parts of Central and South America, Asia and Africa.

In the future, these maps should be very useful — for example, to help relief agencies prepare for possible storm damage — and reveal patterns of global drought.

Adler and his colleagues produce maps of exactly where its raining over most of the globe — from 50 degrees south latitude to 50 degrees north latitude.

Launched in 1998, TRMM was the first satellite to carry weather radar. Instruments on TRMM detect not just clouds and the heat given off by storms, they actually see where and how fast rain is falling. It’s similar to the ground-based radar used on TV weather reports.

Adler notes that these new maps can be used to monitor drought and floods over different time scales. It allows one to measure rainfall from one month to the next, from one year to the next or from decade to decade. It allows you to study El Nino, La Nina and tropical cyclones. These new data also allow scientists to track a single heavy rain event over a few hours or days.

Some researchers use the data to try to understand the interactions that are going on between the atmosphere and the land surface or ocean surface. Hydrologists can use it to predict how much water will come down a river as a result of rain runoff.

Excerpts from interview with Robert Adler:

Robert Adler: “But in addition to that, by combining this information from all the different satellites, you can track the heavy rain event over just a few hours or a few days. And I think for a lot of places that don’t have access, as I said, to those ground-based measurements, these space-born measurements will be a tremendous boon. And of course evaluating were you are from an agricultural standpoint. That’s very important to everybody.”

Robert Adler: “And I think it still has to be evaluated. But there’s no doubt that using some plan like this — where you have at least one very good satellite, and then use the other satellites that are already available. Often they’re up there for some other purpose, but the data is available, so we can use them and integrate them in this fashion — produces what I think a lot of us, from the scientific standpoint have been looking for for a long time …” The improved forecasts and better early-warning information would help everybody from local farmers to aid agencies, who would be better able to target relief efforts.

Adler is now trying to develop a “drought index.” A color coded map would be used to display where droughts are occuring. By comparing maps from hour to hour or day to day, one can determine when a drought has been curbed by rainfall or if a drought is likely to continue. This is useful information for international relief agencies to determine which areas will need help. It can also show where food production might be harmed by weather.

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