upwel ling spectral irradiance did not follow the expected pattern of exponential 

 decrease with depth. As the instrument approached the coral, the spectral 

 distribution of the upwelling irradiance showed a decrease in the blue and 

 green regions of the spectrum but an increase at wavelengths greater than 

 589 nm. Particularly striking was an increase in the far red at 694 nm (fig. 

 3). The total integrated quanta in each scan follows the rule for conservation 

 of energy and decreases with depth. The increase in the signal between 589 and 

 671 nm results from reflectance of the yellow brown coral, which begins to 

 "dominate" the spectral irradiance signature. The far red signal may be 

 interpreted as an emission of red light due to algal fluorescence, as has been 

 seen in oceanographic measurements of spectral irradiance (R. C. Smith, C. R. 

 Booth, and P. Dustan, unpub. obs.). The intensity of the signal increases as 

 the instrument approaches the coral (depth approx. 4.4 m), suggesting that the 

 fluorescence may emanate from the zooxanthel lae in the tissues of the coral. 

 These findings complicate the calculation of an energy absorption budget for 

 the coral, since the organism is simultaneously absorbing and emitting light 

 and each process is functioning with its own wavelength dependency. However, 

 the results suggest that we may have uncovered a measurable parameter that may 

 one day be used to probe the photophysiology of corals and the bio-optics of 

 coral reef ecosystems. 



Researchers are beginning to realize that the fluorescence signature of an 

 alga contains information about the plant's photosynthetic apparatus, including 

 information on its potential for primary productivity (Kiefer, 1973; Vincent, 

 1979; Harris, 1980; Abbott, et al . , 1982). The data on corals are particularly 

 exciting, since they suggest that the spectral signals may contain information 

 on the physiological state of corals and their zooanthellae in addition to 

 possible estimates of primary production. This suggests that there is much to 

 learn about the optics of corals and their associated zooxanthel lae using the 

 passive techniques of bio-optics. 



REMOTE SENSING 



Coral reefs cover areas of the ocean that are remote and difficult to work 

 in for extended periods of time. They are also vast in their coverage of the 

 world's tropical oceans and may play a significant role in the carbonate balance 

 of the seas. If the optical signal emanating from the reef can be understood 

 sufficiently to provide interpretation from an orbiting spacecraft, estimates 

 of coral reef primary productivity and possibly calcification could be made on 

 a global scale. The importance of this cannot be underestimated when one 

 considers man's impact on the coral reef ecosystems that are presently in close 

 proximity to centers of human habitation. 



Our research expedition to Florida in 1982 gathered data to test the 

 hypothesis that coral reefs may be resolvable in spacecraft imagery (Landsat) 

 (P. Dustan, C. R. Booth, and A. R. Hibbs, unpub. data). We obtained measurements 

 of upwelling spectral irradiance from a variety of habitats in the shallow 

 coral reef ecosystem of John Pennekamp Coral Reef State Park, including grass 

 flats, coral colonies, and sand. We then simulated the spectral sensitivity of 

 the Multispectral Scanner (MSS) onboard Landsat 3 so that the optical signal we 

 recorded could be compared to the signal recorded by a Landsat MSS sensor. The 

 equation for the simulation then "converts" the spectroradiometer signal into 



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