Thursday, July 24, 2014

NASA's Hurricane Severe Storm Sentinel (HS3) mission: The HIRAD instrument

This is an artist's concept of aircraft with HIRAD scanning a tropical cyclone. 

Credit: NASA

The Hurricane Imaging Radiometer, known as HIRAD, will fly aboard one of two unmanned (UAV) Global Hawk aircraft during NASA's Hurricane Severe Storm Sentinel (HS3) mission from Wallops beginning August 26 through September 29.

One of the NASA Global Hawks will cover the storm environment and the other will analyze inner-storm conditions.

HIRAD will fly aboard the inner-storm Global Hawk and will be positioned at the bottom, rear section of the aircraft.

"HIRAD's purpose is to map out where the strongest winds are in a hurricane. During its first deployment in 2010 for the GRIP airborne campaignHIRAD had two interesting hurricane cases, Earl and Karl," said Daniel J. Cecil, the principal investigator for the HIRAD instrument at NASA's Marshall Space Flight Center, Huntsville, Alabama.

"We have made improvements to the instrument since then, and are looking forward to the next good case, out over water, avoiding land of course!"

What is NASA's HS3 mission?
NASA's HS3 mission is a collaborative effort that brings together several NASA centers with federal and university partners to investigate the processes that underlie hurricane formation and intensity change in the Atlantic Ocean basin.

What is HIRAD?
HIRAD is a passive microwave radiometer that was developed at NASA Marshall.

A radiometer is an instrument used to measure the power of electromagnetic radiation.

Because HIRADis a passive microwave radiometer it detects microwave radiation naturally emitted by Earth.

The radiation HIRAD detects is then used to infer wind speed at the surface of an ocean.

The antenna on HIRAD makes measurements of microwaves emitted by the ocean surface that are increased by the storm. As winds move across the surface of the sea they generate white, frothy foam.

This sea foam causes the ocean surface to emit increasingly large amounts of microwave radiation, similar in frequency or wavelength, but much lower intensity, to that generated within a typical home microwave oven.

HIRAD measures that microwave energy and, in doing so, allows scientists to deduce how powerfully the wind is blowing.

With HIRAD's unique capabilities, the two-dimensional structure of the surface wind speed field can be much more accurately determined than current operational capabilities allow.

What information does HIRAD provide?
HIRAD provides unique observations of sea surface wind speed, temperature and rain. The data HIRAD gathers will advance understanding and predictability of hurricane intensity.

HIRAD's data will also help better determine maximum wind speed and structure of the vortex (spinning center). The region of strongest winds are also much better observed with HIRAD than current capabilities.

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