Originally Posted by Peter-1959
I can't find good information on how they are searching, what sort of sensory equipment.
I presume you have looked at the information provided by BEA on the search equipment:
Sea Search Operations
If you follow the links there, you will find the specs for the sonar on the Orion towed vehicle. If you dig deep, the specs for the REMUS AUVs from Waitt Institute are here:
AUV Specifications | Search for Amelia though I don't see mention of the sonar frequency and range. Specs for the sonar on the Geomar vehicle are here:
IFM-GEOMAR: The AUV Abyss where it mentions the frequency but not the range.
The search is being conducted with side-scan sonar. The sonars operate with frequencies in the span of 50-250kHz, depending on the required trade-off of range and resolution. The typical ranges used are about 300-500m either side of track, and the achievable resolution allows detection of an object about the size of a 55 gallon oil drum.
There are laserlight camera's these days, which can be operated till 6000m or more, mounted on a ROV. Certain laserlight wavelengths will give distinguishable reflections on metal surfaces, and meanwhile penetrate deep enough through low density organic sediment layers.
Laser scanning cameras have the advantage of reducing the common-volume scattering (water volume that is common the both the path from the light source to the target, and from the target to the camera), and thus the fog effect of underwater photography. That can greatly increase the optical range above the 10-20m typical of conventional photography in the deep ocean. A quick scan of the literature shows that ranges of 4-6 attenuation lengths are achievable, limited by forward scattering, which is not eliminated. See for example:
http://jaffeweb.ucsd.edu/files/bathy...m%20L-bath.pdf
Attenuation length (distance in which intensity drops by 1/e) in the deep ocean does not exceed 50m:
http://www.nestor.noa.gr/2nd/files/247_252_bradner.pdf Typical AL in the deep ocean is probably less than half that. That puts the range of a laser scanner at a maximum of 6*50=300m, but more typically 4*25 = 100m. That does not compete well with sonar for a wide area search for large objects that are likely sitting proud on the seafloor.
I'm not sure about your point regarding wavelength. The range of wavelengths is quite narrow, in the blue-green range, for which attenuation in seawater is reasonably low. Red, infrared and UV are strongly absorbed.
Do you know of some equipment with specifications that exceed the above numbers?