Scott Braun: TRMM is the Tropical Rainfall Measuring Mission. It was launched in November of 1997, originally designed as a five-year mission, but we've gone now for fifteen years.

Fifteen years and thousands of storms later, TRMM has contributed to the advancement of scientific milestones. TRMM has advanced research in the areas of agriculture, disease tracking, precipitation physics, and natural hazards.

Scott: We get roughly three hourly rainfall estimates across much of the globe at fairly high resolution, and these rainfall estimates are used to monitor major rainfall events, and to look for events that might lead to significant flooding and even landslides, and there are a number of groups that have been using it as sort of an early warning system.

TRMM's unforeseen longevity has provided more robust information on weather and climate patterns that can only be seen after years of observations. This decade and a half of data lets scientists see variations in rainfall from year to year, how El Nino affects rain patterns worldwide, and the anatomy and lifecycle of major storms, like hurricanes.

Scott: It's also proven to be an extremely useful satellite for understanding hurricanes, partly because its orbit stays within the tropics, so you get much more frequent observations. And it's just provided a wealth of rainfall information over its relatively short time period that, in many ways, surpasses all of the information we have prior to that.

From giant storms to individual droplets: TRMM also provides scientists with data on the precise physics of falling rain drops.

Scott: TRMM has a unique set of instruments, including the first and only precipitation radar in space. It also has a microwave imager, which is an instrument that can give you the equivalent of an X-ray of a storm, whereas the radar is giving you more of a CAT scan of the storm. It provides extremely valuable information on the structure, rainfall structure, of storms, which tells us something about how the storm is responding to its environment, whether or not it might intensify or weaken in the upcoming hours.

Building on TRMM's success will be the Global Precipitation Measurement, or GPM, mission. Its two instruments are more advanced and more sensitive versions of TRMM's microwave imager and precipitation radar. GPM's orbit will also extend coverage beyond the tropics, and provide measurements of light to heavy rain and snow, expanding TRMM's legacy into the future.