Eight briefcase-size NASA satellites flying in a row may be key to improving forecasts of a hurricane’s wind speed, detecting whether it will make landfall as a Category 1 or a Category 5, according to a release of NASA’s Jet Propulsion Laboratory on Monday.
NASA’s Cyclone Global Navigation Satellite System fleet, launched in 2016, was designed to show whether the GPS signals used for navigation by phones can be used to measure winds deep within a hurricane or typhoon, Xinhua reported.
The answer appears to be a resounding “yes,” said JPL.
Weather forecasting models have gotten much better at predicting the future track of a hurricane or typhoon, but they have not improved at predicting its maximum wind speed, which scientists call intensity.
“To predict intensity, you have to measure wind speed right in the middle of the storm and, until CYGNSS, there hasn’t been a way to do it other than flying Hurricane Hunter planes,” said CYGNSS Principal Investigator Christopher Ruf of the University of Michigan in Ann Arbor.
The new CYGNSS data proved to be an excellent match with Hurricane Hunter data collected at the same time during 2017’s hurricanes Maria, Irma and Jose, according to JPL.
The eight small satellites, orbiting with only a 12-minute gap between each one, collected more data on each storm than could be gathered during a Hurricane Hunter flight, according to JPL.
To see what’s in the atmosphere, many Earth-observing satellites send out electromagnetic signals with wavelengths that are just fractions of an inch long. To these short-wavelength signals, a drop of drizzle, speck of dust or any other airborne particle is an impenetrable obstacle.
Even though the wavelengths are longer than these tiny particles, they are close enough in size that signals bounce off particles like a billiard ball colliding with another ball. By “reading” these scattered signals, researchers can discern the shape and location of clouds and other obstacles that the signals ran into.
In other words, short wavelengths let researchers see a storm but not see through it.
CYGNSS, on the other hand, uses GPS signals. Their wavelength is 7.5 inches (19 centimeters) long — far longer than either the short wavelengths most satellite instruments use or any raindrop ever measured.
At that wavelength, Ruf said, “You don’t see a raindrop at all. You just go right through it.” That enables CYGNSS to see through a hurricane and measure the winds at the ocean surface.
GPS satellites, operated by the US Air Force, are in a much higher orbit than the CYGNSS fleet. As a GPS satellite flies over a tropical cyclone, its signals pass unimpeded through the storm and bounce off the ocean surface.
In their lower orbit, CYGNSS’s downward-looking GPS receivers are able to intercept signals returning upward. Distortions in these bounced signals show how rough the sea is, enabling researchers to calculate the wind speed that caused the roughness.