AN ANALYSIS OF CHLOROPHYLL FLUORESCENCE ALGORITHMS FOR THE MODERATE RESOLUTION IMAGING SPECTROMETER (MODIS)

Next-generation ocean color sensors will include channels to measure p assive chlorophyll fluorescence as well as traditional channels that u se radiance ratios to estimate chlorophyll concentration. Because the chlorophyll fluorescence signal is small, these sensors have significa ntly higher signal to noise ratios in the channels used to measure flu orescence. Small changes in sensor performance, atmospheric transmissi vity, and fluorescence efficiency could potentially result in signific ant changes in the performance of the fluorescence algorithms. We perf orm a sensitivity analysis on the present MODIS algorithms and derive the minimum chlorophyll concentrations that can be observed for variou s combinations of sensor performance, atmospheric conditions, and phyt oplankton physiology. We show that the present sensor specifications w ill allow us to observe fluorescence at chlorophyll concentrations as low as 0.5 mg/m3 at the full resolution of the sensor (nominally 1 km( 2) at nadir) under optimum viewing conditions. Although band position changes over a +/-4 nm range affect the absolute reading of individual bands by less than 2%, the impact on the total performance of the flu orescence algorithm can be greater than 70%. (C) Elsevier Science Inc. , 1996.