THE INFLUENCE OF CHLOROPHYLL PIGMENT UPON UPWELLING SPECTRAL RADIANCES FROM THE NORTH-ATLANTIC OCEAN - AN ACTIVE PASSIVE CORRELATION SPECTROSCOPY STUDY

Active-passive correlation spectroscopy (APCS) methods have been applied to airborne upwelled radiances and 532 nm pulsed laser-induced phytoplankton chlorophyll pigment fluorescence obtained during the North Atlantic Spring Bloom Experiment (NABE) of the Joint Global Ocean Flux Study (JGOFS). The active-passive spectral data obtained during a transect between Ireland and Iceland over 300 km cloud-free portion of the JGOFS 20-degrees-W longitude line have been subjected to two-band radiance-ratio analyses. The chlorophyll pigment was found to significantly influence the upwelled radiances over considerable portions of the observed 380-740 nm color spectrum. Satisfactory recovery of chlorophyll pigment concentrated in North Atlantic case 1 waters was obtained over a broad region of the blue-green spectrum (approximately 430-530 nm) when ratioed with bands of the green-yellow spectrum (approximately 540-585 nm). The data confirm that the 420/550 nm band combination out-performs 443/550 nm for chlorophyll concentrations greater than or similar to 1.5 mg m-3 however, the results indicate that further improvement could be realized using the 490 nm band in combination with either the 555 or 565 nm bands. Chlorophyll pigment was found to be recoverable using the 652/685 nm chlorophyll absorption/fluorescence radiance ratio. Other findings include satisfactory chlorophyll recovery using the 415 nm band ratioed with bands in the 562-584 nm spectral region, suggesting that these waters were bloom dominated with a relatively low concentration of dissolved organic matter (DOM). This latter finding agrees with low DOM fluorescence values found using an auxiliary 355 nm laser excitation source. To illustrate these experimental findings, radiance-ratio spectral correlation matrices are presented together with corresponding along-track active/passive cross-sectional profiles.