ABSTRACT

Autonomous landers are an important tool for research in the world's oceans beneath the sea surface They have the advantage of relatively low cost and the ability to remain on site for extended periods of time from a few hours to years A single ship can carry and service a fleet of more than ten landers providing spatial and temporal coverage on a scale not achievable by any other means The basic design features of landers and scientific results of studies of deep sea fishes are discussed

INTRODUCTION

In the age of space technology with communications, navigation and earth surveillance satellites circling the earth, we have become very accustomed to the ability to communicate rapidly and produce instantaneous synoptic pictures of the atmosphere, sea surface and land masses on a worldwide basis The marine sciences have benefited greatly from the ability to visualise oceanic fronts, gyres and areas of primary productivity For studies beneath the sea surface, however, the only way of making observations IS through the use of in situ instruments High frequency radio waves cannot penetrate the surface of the ocean and optical remote sensing methods only penetrate to less than one or two metres beneath the surface Whilst low frequency echosounders and sonars can map the sea floor at abyssal depths, high resolution studies require a towed body close to the sea floor Any other measurements or observations of processes on the deep sea floor, whether physical, chemical or biological require the presence of man-made instruments placed on the seafloor

Manned submersibles can spend only relatively short time periods (< 8h) on the seafloor and need good surface weather conditions in which to operate Equipment lowered on wires from ships can also only be left there for a limited time period Remotely operated vehicles (ROVs) require a tether with a power supply, so also suffer from the problem of requiring the continuous presence of a mother ship The only way of making continuous observations on the sea floor over extended Time periods is through the use of autonomous platforms The most successful type of autonomous platform is the deep ocean lander which are also known as "free-fall" or "pop up" vehicles Such a system is ballasted to fall to the sea floor at a modest velocity, typically < 1 m s 1 to ensure a soft landing Timing devices then activate on-board equipment The mission is terminated by release of ballast either using a timing device or by acoustic command from the surface The vehicle then ascends by virtue of its own buoyancy, whereupon it is retrieved by a surface ship "Lander", by analogy with interplanatory space probes, has come to be used as the generic term for this kind of device (Priede & Bagley, 2000)

LANDERS

Landers have evolved from oceanographic instrumentation moorings such as current meter and thermistor arrays which use the essential elements of a lander i e sub-surface buoyancy, ballast and a ballast release deuce Most early workers used programmable time releases

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