Optical calibration, bathymetry, water column correction and bottom typing of shallow marine areas, using passive remote sensing imageries
Busy? 4SM in 10 lines
4SM gallery: direct access to various aspects of 4SM
see also 4SM advantages
see also 4SM illustrations
see also 4SM flowchart
see also 4SM study cases

1 - NO NEED for field data, nor for atmospheric correction
2 - this is demonstrated in this website, using a variety of hyper/multi spectral data
Requirements are
1 - homogeneous water body and atmosphere
2 - some coverage of optically deep water
3 - some coverage of dry land
Problems are
1 - the precision on estimated depth is found wanting, because the noise-equivalent change in radiance  of accessible data is too high for shallow water column correction work 
2 - radiance data should be preprocessed by the provider at level 1 in order to improve S/N ratio
3 - exponential decay: the deeper/darker the bottom, the poorer the performances
I keep digging
until suitable data
become available

Physical model of simplified RTE in 4SM BPL and Soil Line at Negril, Jamaica BPL and Soil Line at Clipperton Island
Physical model of simplified RTE in NOAA's RLN method Regression of computed depths: NOAA's RLN mode vs 4SM's PAN mode The calibration plot in 4SM
Ikonos at Lee Stocking Island, Bahamas