Reflected GPS signals can probe winds deep inside storms like 2017’s Hurricane Harvey, improving forecasts.
NASA Goddard MODIS Rapid Response Team
By Paul Voosen
SAN FRANCISCO, CALIFORNIA—Earlier today, after a successful rocket launch from India, the beginnings of a new satellite constellation for Earth observation took place. An existing flotilla of more than 80 microsatellites owned by the startup Spire Global, based here, captures signals that have traversed the atmosphere from GPS satellites to measure key properties such as temperature and humidity. Now, two new microsatellites from the same company will collect GPS signals after they bounce off land or ocean to probe conditions at the surface.
Unlike the microwaves used by traditional weather satellites, the long wavelengths of GPS can peer through clouds and heavy rain to measure the winds of hurricanes and other storms. The reflected signal can also reveal sea ice cover and, critically, soil moisture, which can indicate drought and guide storm forecasts. “We’re trying to produce data that will be used for the long term,” says Dallas Masters, Spire’s director of Earth observations, who announced the launch this week at a meeting of the American Geophysical Union here.
Over the past few years, a constellation of eight NASA microsatellites, called the Cyclone Global Navigation Satellite System (CYGNSS), has proved that harvesting GPS reflections can work from space, providing measures of hurricane wind speed that could measurably improve hurricane forecasts. The mission has also proved adept at gauging soil moisture, to the point that half of its science team now focuses on the topic.
No operational satellites now supply soil moisture measurements for weather forecasting. The National Oceanic and Atmospheric Administration (NOAA) explored the possibility of adopting CYGNSS data for its forecasts, but the agency’s technical requirements were an obstacle, says Chris Ruf, CYGNSS’s principal investigator and an atmospheric scientist at the University of Michigan in Ann Arbor. It appears that Spire, which has hired several CYGNSS engineers, might get there first, Ruf says. “You know what they say is the sincerest form of flattery?” he says. “I just hope they don’t screw it up.”
The new Spire microsatellites, which hitched a ride as a secondary payload on an Indian rocket carrying a radar-imaging satellite, resemble small 5-kilogram monoliths. Spire will launch a second version of the reflection satellite into polar orbit next year, and it hopes to eventually send more than three dozen into orbit.
Spire is one of a handful of companies seeking to carve out a niche in providing satellite data to private users, government agencies, and scientists, with an eye especially on improving weather forecasts. Both NASA and NOAA are now studying data from the company’s existing satellites as part of pilot projects; Masters hopes the next phase of the NOAA pilot will expand to include GPS reflection data.
There’s much that could be done with wind and soil-moisture data from such a fleet of satellites, says Eric Maloney, an atmospheric scientist at Colorado State University in Fort Collins. Scientists could greatly improve their estimates of how winds help fuel the Madden-Julian oscillation, a large cluster of storms that periodically forms in the Indian Ocean and marches around the equator, influencing global weather. Spire’s adoption of GPS reflection technology “reflects the enormous promise of this technology for a variety of earth science applications,” Maloney adds.
Spire and similar companies continue to face thorny questions about their business model, however, especially if the government is to rely on their data. Typically, federal scientific data must be made free for the public to use—but such sharing could undermine companies’ existence. Scientists are meeting next week at the National Academy of Sciences in Washington, D.C., to discuss the problem, Ruf says, which is far from solved.
Source: Science Mag