Assessment of tilt capability for spaceborne global ocean color sensors

The importance of tilt capability for sun glint avoidance for future global ocean color missions was analyzed. The analyses focused on Sea-viewing Wide Field-of-view Sensor (SeaWiFS) mission, because its radiometric, orbital, and sensor characteristics are well defined. The analyses concentrated on two major questions: 1) does tilting to avoid sun glint increase or decrease the total ocean coverage, and 2) at high latitudes far from the region of maximum sun glint, should the sensor be tilted or untilted? For ocean coverage maximization, if the sensitivity of ocean color algorithms to sun glint is of the same order as the error in the atmospheric correction algorithms, then a tilted sensor produces nearly 20 percent better coverage than an untilted one after 2 d in the absence of clouds, and 12 percent after 4 d including clouds. Thus, the tilt capability can improve the ocean coverage of future ocean color missions. At high latitudes differences in transmitted water-leaving radiance between tilted and untilted sensors were well within the algorithm errors. Furthermore, sun glint radiances exceeding the algorithm errors occurred at high wind speeds as far as 70" from the solar declination, suggesting that sensors should remain in the tilted mode up to this limit.