U.S.-Japanese precipitation spacecraft will improve global cyclone tracking
A new climate-study spacecraft just entering environmental test here is expected to sharpen weather-forecasting models in ways that would have given forecasters a better handle on the back-to-back storms that slammed the U.S. Mid-Atlantic coast this fall.
The Global Precipitation Measurement (GPM) mission, a U.S.-Japanese follow-on to the Tropical Rainfall Measurement Mission (TRMM) launched 15 years ago byand the precursor to the Japanese Aerospace Exploration Agency ( ), will give unprecedented detail in its measurements of rainfall, snowfall and temperatures inside storms like Hurricane Sandy and the Nor'easter that followed it into New York Harbor and the New Jersey shore.
That, in turn, should allow meteorologists to tweak their computer models for better predictions of the track and intensity of violent storms. As has been the case with other weather-science instruments, there may be a future operational role for the sorts of data GPM will generate.
“If we demonstrate over the coming years after this thing is launched that, man, this thing is really helping in improving our ability to forecast snowstorms, that may bring to light a real need to have that type of system in an operational capacity,” says J. Marshall Shepherd, an atmospheric scientist at the University of Georgia who is president-elect of the American Meteorological Society. “From a hardware standpoint, ideally we'd really like to have these active radar-type systems in a geosynchronous satellite system.”
Before taking his academic appointment, Shepherd was deputy project scientist for the GPM mission. The spacecraft, which entered thermal vacuum testing here Nov. 13, carries two Japanese-built synthetic aperture radars (see photo) collectively dubbed the Dual Frequency Precipitation Radar (DPR). The radars will scan down through the atmosphere in Ka- and Ku-band frequencies (35.5 GHz and 13.6 GHz, respectively) to provide better three-dimensional data on precipitation structures, including very light rainfall and snow. The precursor TRMM spacecraft carries a single Ku-band radar in a 35-deg., 350-km (220-mi.) orbit.
The newer spacecraft also carries an advanced radiometer—the GPM Microwave Imager (GMI)—that passively measures energy from falling precipitation in 13 frequency channels. Set for launch in 2014 on a Japanese H-IIA rocket to a 65-deg. orbit at 407 km altitude, the spacecraft—formally known as the GPM Core Observatory—will allow scientists to calibrate radiometer data from as many as eight other present and planned satellites in a variety of orbits. The GPM constellation's deluge of data will yield precipitation measurements over 90% of the Earth's surface updated every 3 hr.
In the short term, forecasters will be able to predict the track of a storm approaching landfall, and measure temperature phenomena in the storm-eye wall called heat towers that signal changes in its intensity, according to Gail Skofronick Jackson, GPM deputy project scientist. The more heat towers—essentially thunderstorms riding from the cyclone's eye—that appear, the more intense the storm will become.
Over time, that kind of information will allow forecasters to improve the models they use, says Skofronick Jackson. It also will let scientists studying climate change calibrate satellite-radiometer data collected as early as the 1970s to find long-term trends in precipitation patterns, she says.
JAXA andengineers here are overseeing the environmental test sequence on the 3,200-kg (7,055-lb.) spacecraft. If all goes as planned, it should be ready to launch in February 2014, according to Art Azarbarzin, GPM project manager here.
However, that is being carried as an internal launch date, with a 50% confidence level, he says. NASA has promised Congress it will be able to launch the spacecraft by June 2014, an 11-month slip that was forced by the devastating earthquake that hit Japan in March 2011, damaging test facilities at JAXA's Tsukuba City site north of Tokyo, just as the two large Japanese radars were being tested. Debris from test-chamber walls contaminated the clean test environment, Azarbarzin says, and the loss of power prevented maintenance of proper temperature and humidity levels. As a result, the DPR had to be cleaned and retested before it could be shipped to Goddard for integration into the satellite.
The spacecraft also suffered from normal development delays in Japan and the U.S., including a problem perfecting the coating on the reflector for the GMI that Goddard engineers solved with a new vendor.
NASA's portion of the mission is capped at $932.8 million, including reserves. In addition to JAXA, other agencies participating in the effort by sharing their radiometer data are French space agency CNES and the Indian Space Research Organization, with their joint Meghatropiques mission; the U.S.; Europe's Eumetsat and the U.S. through its Defense Meteorological Satellite Program.
Nine U.S. and international satellites will soon be united by the GPM mission, a partnership co-led by NASA and JAXA. To watch an animation of the constellation in action, check out the digital edition of AW&ST on leading tablets and smartphones, or go to AviationWeek.com/video