Tony M Jan 6, 2017:

@ Daryo You have exactly highlighted the key issue here — and it's not dissimilar to that of using sonar arrays.

However, there are vital clues in the context already given that clarify 2 of your points at least. 'Drop' here I'm sure only means 'lowered on a cable etc.) — I don't think we'd used the word 'drop' in a technical context to mean 'left on sea-bed'; also, it does specifically say that the vessel is "drifting along transects" — so NOT "from a non-moving ship"

The whole point, here, I believe, is that they are trying to perform an accurate survey (note using a grid of transects, i.e. very specific positioning) BUT there is no way to know precisely where the CAMERA is at any moment; however, they can know where the VESSEL is (GPS, etc.); hence if the camera's position relative to the ship can be deduced, then its absolute position can be too. This is often done, for example, by measuring the inclination of the suspension device and extrapolating from that based on depth, with allowance for bending of the suspension etc. according the vessel's movement.

Daryo Jan 5, 2017:

what I could find so far ... there is an opposition between "towed" and "dropped" underwater cameras

the "dropping" could mean "let the camera sink straight down" from a non-moving ship while staying attached to a cable
BUT
it could also mean to literally drop the camera on the seabed and leave it there!

More context needed ...

Tony M Dec 28, 2016:

Note: It seems many people here may not have truly appreciated the specific, unusual linguistic point here in the source term.

'drop camera is (AFAIK) a relatively unusual term, and I'm pretty sure it has a quite specific meaning.

Obviosuly it is going to be an udnerwater / submersible camera — the source text doens't say that, because in the context, it is clearly implicit, and IMHO does not therefore need to be addressed in translation.

However, the 'drop' is something else — note that they are talking about accurate positioning, and I think that is the key point here.

If you just dangle your camera over the side of your boat on a wire, even if you know where the vessel is, you will not be able to tell precisely where the actual camera is. There needs to be some specific mechanism for knowing its position — for example, by fixing it on a rigid mast below the vessel, or by using a system of detectors to measure the deflection of the suspension cable.

I'm pretty sure this is the significance of 'drop' here, and that it does need conveying in some way in the translation. Sadly, I suspect only greater context will make it possible to know exactly. Ask customer?

florence metzger Dec 27, 2016:

drop camera
un quadrillage de la zone a été effectué par drop-camera (Figure 11). Plus de 460 points de contrôles repartis le long de radiales perpendiculaires au trait de côte ont été réalisés (Figure 16). Ces relevés géoréferencés servent dans un premier temps au traitement informatique des photographies aériennes, ainsi qu’à la réactualisation des données cartographiques plus anciennes.
Parallèlement, l’acquisition de ces séquences vidéo a également permis d’identifier un certain nombre d’éléments de caractérisation du milieu (e.g. présence d’espèces, description de l’herbier à posidonie, épiphytisme, nature du substrat).