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Investigating Coral Reef Ecosystems in Support of NASA’s Earth Science Program
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Airborne Missions

Airborn Mission: Hawaii

 

 

March 2005 AVIRIS Mission: Hawaii

On March 1, 2005, AVIRIS was flown on the Twin Otter over Kaneohe Bay on the windward coast of Oahu, Hawaii.  This project was in collaboration with Dr. Eric Hochberg, Hawaii Institute of Marine Biology, University of Hawaii.  The location of the Hawaii Institute of Marine Biology (HIMB) on Coconut Island at the southern end of the bay affords very easy access to the Kaneohe reef system, which is among the most-studied in the world.  Kaneohe Bay exhibits a wide range of reef communities, including dense coral thickets, algal turfs, encrusting calcareous algae, filamentous macroalgal beds, extensive carbonate sand deposits, and regions of heavy terrigenous sediment imputs.  Water depth averages ~1.5 m on the bay’s barrier reef flat, ~13 m in its lagoon, and ranges from 1 m to the deep ocean on the fore reef slope.  Optical water type for the bay ranges from clear oceanic case 1 over the outer fore reef to turbid case 2 near stream outflows in the lagoon. 

Kanehoe Bay
Kanehoe Bay, Hawaii. March 1, 2005.

Eric and his team conducted field optical measurements concurrent to the AVIRIS overflights using two instrument packages.  The first instrument is a diver-operated portable fiber optic spectrometer (Ocean Optics USB2000 in an underwater housing).  Using this spectrometer, they measured spectral reflectance at the sea surface and sea floor.  Measured over different albedos (i.e., bright and dark seafloor plus water column), sea surface reflectance can be used for empirical atmospheric radiative transfer effect corrections, effectively calibrating the AVIRIS imagery to Earth-surface reflectance.  Seafloor reflectance measurements will be used to test the efficacy of water column radiative transfer corrections.  The second instrument package consisted of a WETLabs ac-s (spectral beam absorption and attenuation meter) and a WETLabs ECO-VSF-3 (three angle, three wavelength backscattering sensor).  This package was deployed concurrently with the AVIRIS overflight, thus measuring water column inherent optical properties occurring at the time of image acquisition.  Given these data, coupled with water depth derived from SHOALS lidar data (acquired 2000), we intend to remove water column radiative transfer effects from the AVIRIS imagery, thus generating an image of seafloor spectral reflectance.  We will classify this image using a library of ~30,000 reflectance spectra measured in situ on reefs throughout the world.

 

 

FACTOIDS

Kaneohe Bay, Oahu:
  • March 1, 2005
  • 8 Flightlines
  • Altitude ~4 km
  • Pixel Size ~3 m

 

Research funded by NASA’s Ocean Biology and Biogeochemistry Program
and NASA’s Interdisciplinary Research in Earth Science Program