seawifs highlights october 2001 seawifs views hurricane michelle stirring up the ocean this is a...
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SeaWiFS Highlights
October 2001
SeaWiFS Views Hurricane Michelle Stirring Up the Ocean
This is a before–after pair of SeaWiFS images which shows how a hurricane can stir bottom sediments into the water column.
The first image was collected on October 24, 2001, and the second image was collected on November 5, 2001 just after Hurricane Michelle had passed through the area. (The center of the hurricane is still visible in the upper left corner of the November 5 image.)
The most noticeable change is in the Gulf of Batabano between the western end of Cuba and the Isle of Youth. On October 24th, the water was clear enough to reveal features on the ocean floor. After the hurricane passed, the water became milky and opaque—hiding our view of the bottom.
Similar increases in turbidity can be seen farther east in the Gulf of Ana Maria, around the Florida Keys, and over Great Bahama Bank just at the edge of the hurricane.
POC: 970.2/Gene Feldman
SeaWiFS Views Hurricane Michelle Stirring Up the Ocean
Before: Oct. 24, 2001
After: Nov. 5, 2001
The historical CZCS archive has been revised using compatible algorithms for the modern era. This figure shows the results of this revision. The DAAC CZCS (presently available) is shown top left, new reanalyzed CZCS Algorithm Improvement (AI – modernized algorithms) is top right, a blended-reanalyzed CZCS where CZCS is merged with in situ data is shown at bottom left, and SeaWiFS (bottom right) is shown for comparison. The reanalysis exhibits remarkable similarityin spatial structure. These methods have been accepted in Applied Optics:” The NOAA-NASACZCS Reanalysis Effort”, by W.W. Gregg, M.E. Conkright, J.E. O’Reilly, F.S. Patt, M. Wang, J.A. Yoder, and N. Casey-McCabe. POC: 971/Watson Gregg
Surface Emissivity at Millimeter WavelengthsCurrent retrievals for snow cover typically use satellite microwave radiometry at frequencies 37 GHz. Higher frequencies—e.g. from SSM/T-2 or AMSU-B (at 90-183 GHz)—are seldom used because of significant atmospheric contributions. We have recently developed a new method to remove atmospheric contributions, principally from water vapor, when the atmosphere is relatively dry.
The results are illustrated in the accompanying figure, where data from the Millimeter-wave Imaging Radiometer (MIR) at 89 and 150 GHz (upper panels) are compared with 0.87 m reflectance and normalized difference snow index (NDSI) data (lower panels) from the MODIS Airborne Simulator (MAS). These data were collected on an ER-2 aircraft on February 12, 1997 over a section of the Midwest. The flight included areas in the Dakotas with over 60 cm of snow (the red areas in the 0.87 m reflectance and NDSI plots).
The figures illustrate that with the new atmospheric correction, the emissivity at 89 and 150 GHz is closely related to snow cover. Both the 0.87 m reflectance and NDSI are high and the 89 and 150 GHz emissivities are relatively low in the snow covered region. This suggests millimeter-wave scattering by snow is occurring on the ground.
The flight leg from southwest to northeast, passing Duluth and entering the Lake Superior, is of particular interest. The emissivity at both 89 and 150 GHz over the lake is high (0.9), suggesting the lake near Duluth (indicated by the arrow A) is frozen. The southern area is marked with high 0.87 m reflectance and NDSI, as well as low emissivity at 89 and 150 GHz; this is the expected radiative signature of snow-covered lake ice. The northern area is marked with high NDSI, low 0.87 m reflectance along with high emissivity at both MIR channels; this suggests that an area of bare lake ice is present. The entire flight over the snow-covered land surface shows emissivity variations at millimeter wavelengths that are likely closely related to the contrasting land use and vegetation classifications for specific locations.
POC: 975/James R. [email protected]