NASA GPM: Contributing to Earth observations from space

The NASA NPOL radar station (left) and D3R Radar station (right) precipitation radars deployed south of Waterloo, Iowa, for the Iowa Flood Studies ground measurement campaign. 

Credit: NASA/Matt Schwaller

The Global Precipitation Measurement (GPM) Core Observatory, launched on Feb. 27 from Tanegashima Space Center in Japan, will help advance our understanding of Earth's water and energy cycles, improve the forecasting of extreme events that cause natural disasters, and extend current capabilities of using satellite precipitation information to directly benefit society.

The GPM mission will provide unprecedented data on rain and snowfall. The science instruments on the GPM Core Observatory will provide data that will yield the greatest clarity on rain and snow yet gathered from orbiting spacecraft.

With GPM, scientists will gather vast amounts of precipitation data on a global scale. But, how do they know how to interpret the data? How do scientists know the data is correct?

This is where ground validation contributes to the mission. Using instruments that complement and correlate with those on the spacecraft, scientists on the ground gather similar precipitation data.

These data are directly compared with that from satellites to improve the models relying on the satellite data.

Walt Petersen, GPM ground validation scientist from NASA's Wallops Flight Facility at Wallops Island, Va., said, "GPM ground validation is a) the process by which we identify uncertainties in satellite-based precipitation products compared to ground observations"

"b) how we improve satellite-based methods of estimating precipitation by better understanding precipitation physics."

"c) how this physics relates to what the instruments 'see,' and d) assess the utility of GPM products in monitoring the global water cycle, flood and weather prediction, and e) al this adds to and aids our understanding of climate change."

This is an artist's depiction of NASA's Global Precipitation Measurement mission's Core Observatory. 

Credit: NASA

The GPM program uses remote campaigns and a Precipitation Science Research Facility at Wallops to supplement and correlate the data gathered by Earth-orbiting satellites.

"Ground validation is central to understanding the quality of GPM precipitation products, how the products can be improved, and evaluating the utility of the measurements in a variety of earth system science applications," Petersen said.

The remote campaigns, using instrumented aircraft and ground-based instruments, allow scientists to monitor precipitation under a variety of conditions and geographic regions.

Petersen said, "The Wallops Precipitation Research Facility collects multi-frequency dual-polarimetric radar observations of precipitation rates, types, sizes and shapes through the depth of the troposphere."

"We collect high quality, concentrated rain gauge network measurements of area-mean rainfall, and use networks of imaging instrumentation to observe the number and distributions of the size, shape and type of precipitation particles falling to ground."

"Collectively, these measurements enable us to describe precipitation physical properties over scales ranging from that of an individual rain drop or snowflake to that of the Delmarva and Chesapeake Bay regions."

With ground validation, scientist will be able to gauge the quality of Earth observations from space using GPM and improve combined space- and ground-based data products used to understand global precipitation.