REMOTE-SENSING OF OCEAN COLOR - A METHODOLOGY FOR DEALING WITH BROAD SPECTRAL BANDS AND SIGNIFICANT OUT-OF-BAND RESPONSE

A methodology for delineating the influence of finite spectral bandwid ths and significant out-of-band response of sensors for remote sensing of ocean color is developed and applied to the Sea-viewing Wide-Field -of-view Sensor (SeaWiFS). The basis of the method is the application of the sensor's spectral-response functions to the individual componen ts of the top-of-the-atmosphere (TOA) radiance rather than the TOA rad iance itself. For engineering purposes, this approach allows one to as sess easily (and quantitatively) the potential of a particular sensor design for meeting the system-sensor plus algorithms-performance requi rements. In the case of the SeaWiFS, two significant conclusions are r eached. First, it is found that the out-of-band effects on the water-l eaving radiance component of the TOA radiance are of the order of a fe w percent compared with a sensor with narrow spectral response. This i mplies that verification that the SeaWiFS system-sensor plus algorithm s-meets the goal of providing the water-leaving radiance in the blue i n clear ocean water to within 5% will require measurements of the wate r-leaving radiance over the entire visible spectrum as opposed to just narrow-band (10-20-nm) measurements in the blue. Second, it is found that the atmospheric correction of the SeaWiFS can be degraded by the influence of water-vapor absorption in the shoulders of the atmospheri c-correction bands in the near infrared. This absorption causes an app arent spectral variation of the aerosol component between these two ba nds that will be uncharacteristic of the actual aerosol present, leadi ng to an error in correction. This effect is dependent on the water-va por content of the atmosphere. At typical water-vapor concentrations t he error is larger for aerosols with a weak spectral variation in refl ectance than for those that display a strong spectral variation. If th e water-vapor content is known, a simple procedure is provided to remo ve the degradation of the atmospheric correction. Uncertainty in the w ater-vapor content will limit the accuracy of the SeaWiFS correction a lgorithm. (C) 1995 Optical Society of America