Gathering the global atmospheric data that go into weather forecasts has long been the job of big, costly, government-run satellites. But the launch of a Russian Soyuz rocket scheduled for 14 July could signal
a shift toward a different model, in which
some of the data come from swarms of
small private satellites.
The rocket’s payload of dozens of
CubeSats—the shoebox-sized satellites that
have upended the aerospace industry with
their low cost and fast path to the launch
pad—includes 11 tiny weather satellites,
eight from Glasgow, U.K.–based Spire
Global, and three from GeoOptics, based in
Pasadena, California. With those spacecraft
expanding in-orbit constellations, the companies plan to compete in a forthcoming pilot program, in which the National Oceanic
and Atmospheric Administration (NOAA)
will buy weather data from them to supplement information from multibillion-dollar,
publicly funded satellites.
“It’s been a long battle,” says GeoOptics
CEO Conrad Lautenbacher. “People are
starting to figure out that it’s not just some-
thing that’s the purview of the government
and several large contractors.”
The upstart companies rely on a tech-
nique known as GPS radio occultation, or
GPS-RO, which takes advantage of the net-
works of navigation satellites launched in
recent decades. Each of the small private
satellites carries a receiver that listens for
the continuous radio chirps emanating from
GPS satellites in more distant orbits. When
one of those transmitters drops below the
horizon, the signal passes through Earth’s
atmosphere and is bent, like light refract-
ing in water. That delays when a CubeSat
receives the signal, and the interval can be
used to infer temperature, pressure, and hu-
midity at different heights until the signal
is lost near the surface. Planetary scientists
pioneered the technique in the 1960s to
probe the atmospheres of Venus and Mars.
For Earth, every new satellite launched in
the GPS networks of the United States, Eu-
rope, Russia, and China adds more oppor-
tunities to take observational slices through
the atmosphere. Like the readings that
conventional weather satellites take from
above, the GPS-RO data can be fed into
numerical weather prediction models. But
GPS-RO data have superior vertical resolu-
tion, says Sean Healy, a scientist at the Eu-
ropean Centre for Medium-Range Weather
Forecasts (ECMWF) in Reading, U.K.
Moreover, because the measurements are
based on a timing delay—measured by standard atomic clocks—they are not biased by
the quirks of the satellite that made them.
That opens the way to using GPS-RO to
identify and correct errors in more problematic data sources, like weather balloons.
With a few more years of data gathering,
GPS-RO could even become the standard
for tracking global climate change. “We’ll be
able to monitor the Earth’s mean temperature,” says Bill Schreiner, a geodesist at the
National Center for Atmospheric Research
in Boulder, Colorado, and the director of
the Constellation Observing System for
Meteorology, Ionosphere, and Climate
(COSMIC), a system of six GPS-RO satellites
launched in 2006.
COSMIC, a joint project of the United
States and Taiwan, showed the value of
GPS-RO data. But the system is now down
to just one of its 70-kilogram satellites, and
the launch of the first stage of a $450 million replacement network, COSMIC-2, has
been delayed until April 2018. Europe operates several GPS-RO satellites, and 2 weeks
ago, China’s FY-3C satellite began sharing
GPS-RO data with world weather agencies.
But overall, the number of radio occultation
profiles fed daily into the ECMWF forecasting model has fallen from nearly 3000 a few
years ago to 2000, Healy says. The center
wants at least 20,000 daily profiles, and
more would be better, he notes.
Private companies began to smell a
market, and Spire has established itself as
the team to beat, with 32 of its 5-kilogram
CubeSats, called Lemurs, already in orbit.
The company began with a $100,000 crowdfunding campaign, but now has $80 million
CubeSat networks hasten shift
to commercial weather data
Two companies hope to sell atmospheric data to NOAA
Spire’s tiny weather satellites, called Lemurs, use a
delay in GPS signals to measure the atmosphere.
By Eric Hand
orbit emits constant
in low-Earth orbit
measures delay in
GPS signal bent because of
atmospheric temperature, pressure,
Over the horizon
Small GPS radio occultation (GPS-RO) satellites can probe the atmosphere by measuring a delay in radio signals.