Scientists at the Earth Science Office at the NASA Marshall Space Flight Center in Huntsville, Ala., are testing an airborne system that could drastically change the way hurricanes are forecast.
The Hurricane Imaging Radiometer (HIRAD) flies on a Global Hawk unmanned vehicle to gauge the intensity of a hurricane out over the ocean. There are differences with this system and conventional hurricane forecast tools that could make HIRAD a game changer for forecasters and emergency managers.
The HIRAD measures the wind speed and rain intensity of a hurricane out over the ocean. What’s different from the conventional measurement is that HIRAD can measure a larger swath of area without the need to fly a manned aircraft directly through the storm.
The instrument that’s being used now and has been used for the last 15 or more years measures a “pencil thin” swath straight down from the aircraft and required some luck to get over the strongest part of the storm. HIRAD looks side to side, and it can take measurements in about a kilometer-wide (0.62 mile) swath. The Global Hawk can also fly at altitudes above 60,000 feet, enabling it to fly over a storm and not just through it.
It can also stay out for as long as 31 hours, which is nearly four times more than the conventional aircraft, allowing it to gather more information and provide additional details. This allows for monitoring of the storm sooner rather than waiting for it to get close to land.
The measurements are taken in different frequency bands to give estimates of wind speed and rain rate, according to Dan Cecil, atmospheric scientist at the Global Hydrology and Climate Center at the National Space Science and Technology Center in Huntsville.
“The rain will interfere with the signal and that’s why we need to measure it in a few different frequencies,” Cecil said. “The basic measurement is as the wind stirs up the ocean and makes the surface rougher, the radiation coming from it will have a different signal and the instrument is measuring that signal and relaying what kind of wind speed must be necessary to generate that.”
The result is a better idea of the storm’s intensity in real time and, the hope is, a better forecast and response.
“Part of the problem is there is a lot of uncertainty in the ‘now cast,’ just determining how strong the hurricane is right now,” Cecil said. “Having the wide swath measurement below the aircraft helps narrow down how strong the hurricane is right now and that gives us a better starting point and that’s going to translate into: What’s the forecast from here.’
The Global Hawk will fly in August and September during the Atlantic hurricane season and again next year. After that, scientists hope it becomes a regular part of forecasting.