Azimuthal Variation of Hurricane Waves

(1)(1)

Problem: How do ocean waves in the vicinity of a hurricane vary in height, wavelength, propagation direction and composition?

Instrument: The NASA Scanning Radar Altimeter (SRA) measured waves from a NOAA aircraft during the 1998-2005 hurricane seasons.

Results and Observations: Hurricane Ivan was moving northwest (arrow) in the Gulf of Mexico on 9/14/04 when the 12 SRA directional wave spectra were measured. Waves in the right forward quadrant are highest (11.4 m) and longest (350 m) and travel in the downwind direction. In the left rear quadrant they are lowest (5.6 m). The waves are most complex in the right rear quadrant. To the left of track they propagate nearly perpendicular to the wind.

Figure 3: Significant wave height is the top number in each spectrum, bottom number is distance from the eye center. Thick radials indicate downwind vector. Outer solid circle is 200 m wavelength and inner is 300 m. Dashed circles are 150, 250 and 350 m (outer to inner). The central area shows m/s wind contours within ±1° lat/lon of the eye. Locations of the 12 SRA directional wave spectra are indicated by dots.

Impact Statement: Wave measurements are critical to verify and improve numerical models used by forecasters and disaster managers

Edward.Walsh@nasa.govEdward Walsh and Wayne Wright, Code 614.6-Instrumentation Sciences Branch

Charles.W.Wright@nasa.gov

WALLOPS UAV-BORNE SPECTRORADIOMETER INSTALLATION & OCEANIC TEST FLIGHT

Frank Hoge, Code 614.2-Ocean Sciences Branch

Problem: To develop a UAV-borne spectroradiometer for calibration and validation of satellite ocean color radiometers.

Need: Calibration and validation of satellite ocean color radiometers is rarely performed over wide areas of continental shelves where

(1) water masses are heavily laden with organic matter and particulates and (2)  atmospheric correction is generally more difficult. 

Instrument: A miniature computer rides above the spectroradiometer ocean-viewing optics package. The UAV platform is an Aerosonde/AAI Corporation unit.

Figure 1: Oceanic spectroradiometer and its data acquisition computer in the UAV  payload bay

Figure 2: UAV platform and integrated hyperspectral radiometer undergoing vibration testing on the taxiway prior to oceanic test flight.  A safety cage surrounds the exposed propeller.

frank.hoge@nasa.gov

Impact Statement: This new UAV-borne  technology would allow very frequent cal/val underflights of satellite ocean color sensors using highly calibrated radiometers flown at very low altitudes where atmospheric correction errors are significantly minimized. 

Results:

Figure 3: The graph shows typical high resolution spectroradiometer data taken over the Atlantic Ocean on the ~6 hour flight of the Wallops UAV-borne spectroradiometer

by a team of scientists, engineers, and technicians.

WALLOPS UAV-BORNE SPECTRORADIOMETER INSTALLATION & OCEANIC TEST FLIGHT cont.

frank.hoge@nasa.gov

The spectra were taken at different locations offshore of Wallops Island, Virginia.  

The black line represents data taken further offshore nearer the continental shelf.

It is brighter (higher amplitude) since there are fewer absorbing constituents further offshore.

More inshore, the yellow spectrum indicates that absorbing organic matter allows less light to escape from the water column and is thus darker (lower amplitude)

Most of the sunlight penetrates the ocean in the 400nm to 700nm wavelength regions and is absorbed and scattered by:

Phytoplanktonorganic matternon-living particulates. 

This color span (400-700nm) thus represents the region of most interest to researchers who study in-water phenomena.

About the Graph: