Scientific Rationale
Variability in biological and physical processes over a range of temporal and spatial scales is a basic characteristic of the marine realm (Mann and Lazier, 1996). Quantifying this variability is key to understanding, for example, population dynamics of commercially and ecologically important species, ocean/atmosphere interactions, and implications for possible global climatic change to these. Knowledge of such processes is limited in many instances because of a lack of appropriate data, often as a result of difficulties associated with sampling some marine environments.
Acoustic techniques
Acoustic techniques offer a number of powerful and versatile means for investigating the marine environment. They operate over long range, are non-invasive, and can facilitate sampling over large areas/volumes in short periods of time. Acoustics have, for example, provided valuable data on the abundance, distribution and behaviour of fish and invertebrates (MacLennan and Simmonds, 1992; Brierley and Watkins, 1996), on the structure and variability of the oceans, their underlying geology and, to a more limited extent, overlaying ice features (Clay and Medwin, 1977; Melling et al., 1995; Brierley et al., 1998).
Current limitations
Operational limitations of conventional research vessels have prevented acoustic investigation of some ocean environments, and have limited the precision and accuracy that may be associated with some acoustically derived measurements. Thus, whilst ship-borne acoustics are used routinely to study abundance, distribution and behaviour of Antarctic krill in the open ocean (Brierley et al., 1997), investigation of the species under sea ice - a habitat of major importance to it (Smetacek et al., 1990) - has seldom been undertaken. This is because of the physical barrier ice presents to towed instrument arrays and to sound, and because fundamentally, manoeuvring ships through ice disrupts the very environment one is attempting to study. Similar constraints have hampered large-scale investigations of Antarctic sea-ice structure and under-ice oceanography. Knowledge of sea-ice is vital because of the key role it plays in climate regulation (Johannessen et al., 1994).
Ship avoidance
Furthermore, whilst acoustic survey methods are used in the assessment of many of the worlds' commercially important pelagic species (for example Atlantic herring - Simmonds et al., 1997; krill - Everson and Miller, 1994), there are a number of caveats inherent to this approach. Noise from survey vessels, for example, can disturb animals such that they move away from the survey path, with the result that species densities observed from ships may underestimate actual values (Mitson, 1995). Acoustic surveys also tend to be blind to the upper few metres of the ocean, and so biomass there is undetected. The magnitude of these potentially significant source of bias is hard to quantify. Accurate assessment of fishery resources is, however, crucial if they are to be managed on a sustainable basis (Hilborn and Walters, 1992).
The role of AUV's
With the coming of age of Autonomous Underwater Vehicles (AUVs), it has at last become practical to investigate some previously impenetrable environments, such as under sea-ice and the near surface, and to address quantitatively issues such as vessel avoidance that were difficult to study with conventional marine research tools. USIPS is an integrated multidisciplinary programme which aims to capitalise on the unique capabilities of Autosub-1 (within present operational limits) to achieve such ends.
USIPS
A collaborative team from British Antarctic Survey (BAS) and Marine Laboratory Aberdeen (MLA) will mount a state-of-the-art scientific echo-sounder on Autosub-1 to address two key objectives:
- to investigate the physical and biological environment of the Antarctic Marginal Ice Zone (MIZ), and
- to assess the potential of AUVs for improving acoustic estimates of biomass.
The acoustic instrumentation required to achieve both these objectives is the same. This commonality, in conjunction with a shared requirement to gain a greater understanding of the limits of conventional acoustic surveys, a complementary skill base and a mutually beneficial sea-going schedule, underpins this collaboration between BAS and MLA.
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