OC3522Summer 2001 OC Remote Sensing of the Atmosphere and Ocean - Summer 2001 Ocean Color
L t ( ) = L w ( ) + L G ( ) + L 0 ( ) ) + L A ( )+ L r ( )
L t = L 0 0 + L rayleigh +L aerosal L 0 0 = radiance leaving surface = L reflectance & L water
Surface Reflectance Specular (mirror-like) ii rr Diffuse ii L G ( ) = glint radiance L W ( ) = water-leaving radiance
Sunglint Examples ftp://daac.gsfc.nasa.gov/data/czcs/oss_hires/97.tiff
L A ( ) = scattering due to aerosols (Mie) + molecular Raleigh scattering At a given wavelength; e.g. 70nm, L w = 0 Then L t ( ) = L r ( ) + L a ( ) ; measure L t ( ) ; estimate L a ( ); left with L r ( )
Bio Optical properties Suspended and dissolved substance Dominant compounds Chlorophyll dissolved organic compounds decayed organic matter “yellow substance” Maul, 1985
A ratio of the reflectance in one band to that in another can be used to determine chlorophyll concentrations Blue -443nm Yellow -550nm point near 500nm
Water Types Case I water Satellite Oceanography, Robinson (1983)
Case II waters: Suspended sediments
Case II waters: Gelbstoff (yellow substance)
( L w ( ) SeaWiFS Channels increased concentration decreased concentration Compute the chlorophyll in the water
( L w ( ): CASE I waters The bio-optical algoritms for L w ( ): in water or upwelled radiance L w ( ) backscatter coeff./ absorbtion coeff. blue green red
SeaWiFS Channels increased concentration decreased concentration
Case 2-Glebstoff Case 1
Are the differences detectable?
Again for the general solution… To derive ocean properties, we want the path radiance to have a small and removable contribution: Three sources: scatter by clouds (non-removable) scatter by molecules (calculable as Rayleigh scatter) scatter by aerosol particles (implied from red/NIR channels) Then the surface radiance, L 0 ( ), can be derived from measurements of L t ( ) L 0 ( ) = L G ( ) + L W ( ) so if sunglint can be avoided by geometry, L 0 ( ) = L W ( ) (containing information about ocean constituents)
Previous Ocean Color instruments: Coastal Zone Color Scanner (CZCS) on Nimbus-7 Ocean Color and Temperature Scanner (OCTS) on ADEOS 412 nm Channels 443 nm Channels
SeaWiFS on SeaStar (Sea-viewing Wide Field-of-view Sensor)
SeaWiFS channels: Band Center Wavelength (nm) Bandwidth Band Center Wavelength (nm) Bandwidth
BLUEGREEN
Shelf waters stirred by Hurricane Floyd Sept July 27, 2001 Seawifs
Jan 1986 June 1986
Feb 1983 Apr 1986