In order to study phenomena happening in the sea-bottom sediments, capsules have been conceived in the past which bear instruments and which were attached to a cable along which they were transferred down to the sea-bottom. After arriving there, the capsule took a sediment sample which was then mounted up to the ocean surface.
It has further been proposed to use for this purpose a submarine vehicle with or without an operator on board, this vehicle being guided down to the site where the samples were to be taken. Unfortunately, these two methods can be applied down to a restricted ocean depth only and are not suited for a long-term investigation. Moreover, these methods do not allow to implant measuring instruments inside the sediment.
The document IEEE Journal of Oceanic Engineering, vol. OE-10, No. 1, January 1985, pages 38 to 49, suggests to use free penetrators which fall by gravity to the sea-bottom and penetrate into the sediments for collecting measuring data therefrom. These data are then transmitted to the ocean surface through an ultrasound transmission channel. According to this paper, it seems possible to define in advance the penetration depth of the penetrator into a given sea-bottom sediment. A drawback of such a penetrator is constituted by the fact that it remains definitively in the sediment and that its instrumentation cannot be retrieved at the end of the investigation phase. This drawback is particularly cumbersome if the penetrator does not reach its correct measuring position after its gravity descent, be it that it has not reached the desired site, or that it entered incorrectly, for example obliquely.