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 ETM_2, smoothed most of the deep lagoon is optically deep in the Green band ... |  ETM_1, smoothed ... but not in the Blue band |
 The hydrologic properties are clearly NOT homogeneous, as illustrated by inconsistant dark bottoms for lagoon floor. We know that the lagoon floor in the atolls is draped with very bright fine grained coral debris |  The computed depth can only be very faulty for the lagoon floor Swell features at sea surface badly affect the results |
 | Optical water type OII+.15 for the clearest waters for wavelengths at 477, 577, 661 and 835 nm definitively not clear oceanic water, in spite of fairly good communications with open ocean basically the same water type as for the SPOT XS image: ==> we seem to get confirmation here that ETM Green band must be set ~=577 nm (instead of mid-waveband at 560 nm) ==> bottom detection by green band is less for Landsat ETM sensor at ~577 nm than for SPOT XS sensor at 550 nm. This is sad. |
