The objective of the study is to develop an algorithm of the bottom index for monitoring and sureying coral reels using the aerial multispectral imageries collected by the Compact Airborne Spectrographic Imager (casi) which spectral and spatial resolution are very high. Four kinds of bottom indices such as the bottom index, the brightness index, the bottom type index and the band ratio index were applied to the casi data to extract coral reefs at the off Kuroshima Island, Okinawa. To select the most suitable wavelength range for extracting coral reef area from the casi imageries, all combinations of the spectral bards were applied to each index. The selected spectral bands for the four bottom indices were the combination of two bands, band 39 (700 nm) and band 36 (680 nm), band 39 (700 nm) and band 27 (610 nm), band 39 (700 nm) and band 13 (500 nm), band 13 (500 nm) and band 27 (610 nm), and band 27 (610 nm) and band 24 (587 nm). For the bottom index, the combination of the band 39 (700 nm) and band 36 (680 nm) showed the most significant similarities with the ground truth survey by the professional divers.