An Example of the Coastal Zone Color Scanner 

 Atmospheric Correction Algorithm Capability 



A number of observers utilizing CZCS data have been confused by the 

 fact that structure in the water that can be seen quite clearly on one day. 

 may not be so clearly identifiable on images taken on successive days. One 

 problem is that when the area in question is directly, or nearly directly, 

 below the subsatellite track, the sensor is viewing the area through the 

 minimum atmosphere. The same area may be visible several days after, but 

 the atmospheric attenuation will increase as the path length increases since 

 the scanner canscanout to 40 degrees either side of the spacecraft nadir. In 

 some cases, scenes are not selected for Level II processing because of an 

 apparent lack of information in the Level I data. The Level I image on this 

 page is the only Level I image shown in this atlas; however. Level I images 

 constitute the major archive from which scenes are selected for Level II 

 processing. Potential investigators should understand the characteristics 

 of the Level I data. 



The technique for processing the Level I data to remove the atmospheric 

 effect has been described extensively by Gordon (1978 and 1981a), and 

 Gordon ei al. (1979), and is used by NASA in the production of all of the 

 Level II imagery. The Level I image shown on this page appears to contain 

 very little ocean content information along the East Coast, which is 

 obscured by a light aerosol band extending from the area of the mouth of 

 Chesapeake Bay, over Cape Cod, and into the Gulf of Maine. This scene 

 would probably have not been selected for Level II processing except that 

 there was a ship operating in the area outside of the light aerosol bank 

 along the East Coast during the validation phase of the CZCS program, 

 and it was desirable to produce the Level II for that area of the image that 

 appeared to be clear. The Level II image (opposite page), presented in the 

 conventional Level II format, shows the amount of detail that can be 

 extracted from the Level I data after application of the atmospheric 

 algorithm. Very little evidence of the light aerosol bank is seen at all, and 

 considerable structures are seen in the water in both pigment and diffuse 

 attenuation coefficient imagery. This case should be kept in mind before 

 rejecting any of the Level I imagery for conversion to Level II when the 

 scene is of great interest and yet appears to show little detail in Level I. 

 Unless the Level I data is saturated, in which case no correction will be 

 successful, there is the potential of extracting information such as that 

 shown in this remarkable case. 



References 



Gordon, H, R.. 1978; Removal of atmospheric effects from satellite imagery of the oceans 



Applied Optus. 17. 1631-1636. 

 • 1981a; A preliminary assessment of the Nimbus-7 CZCS atmospheric correction 



algorithm in a horizontally inhomogcneous atmosphere. In Oceanography from Space, 



edited by J. F. R, Gower, Plenum Press, New York. 257-266. 

 Gordon, H. R., J. L. Mueller, and R. C. Wrigley, 1979; Atmospheric correction of 



Nimbus-7 Coastal Zone Color Scanner imagery. Presented at IFAORS Workshop on 



Inierpreiaitun of Remotely Sensed Data. Williamsburg, VA. May 23-25 (also in 



Remote Sensing of Oceans and Atmospheres, edited by A. Deepak Academic Press 



New York. 1980). 



i 



7 



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