Naturally it is harder to deploy a telescope at greater depths. But then the downward-travelling cosmic ray background is reduced considerably. By moving a telescope from a depth of 1000m to a depth of 5000m the sensitivity to discover a source is improved by almost two orders of magnitude. Furthermore bioluminescence, another major source of background, also decreases with depth.
In addition, physicists believe that it is advantageous to have phototubes looking not only downwards but upwards i.e. toward the remaining background of downward-travelling cosmic rays. This is possible because the sedimentation is minimal since the nearest rivers are the Po and the Nile. Furthermore, looking up is the only way to detect neutrinos in the hundreds of TeV range because at these energies the Earth absorbs the ones that could move upwards.
With no deep-sea remotely operated vehicle being available, the NESTOR collaboration opted for a design with dry power/signal connections and a tight clustering of the phototubes. The basic element is a titanium hexagonal star, 32 m in diameter, with two 15-inch phototubes, back to back, on each apex. A titanium sphere at the centre of the hexagon houses the digitizing electronics and transmits the signals to the shore station via an electro optical umbilical cable. Such hexagonal floors can be stacked vertically in a tower-like arrangement.
 In March 2003 the first hexagonal floor of a neutrino telescope
in the Mediterranean Sea began taking data.
(Credit NESTOR collaboration).
| In January 2002, the first multidisciplinary deep-sea laboratory with real-time data transmission to the shore was deployed (Credit NESTOR collaboration).
In January 2002 the first multidisciplinary deep-sea laboratory with real time data transmission to the shore was deployed, located only 10 miles away (SEA TECHNOLOGY, July 2003, Vol 44, No7). And then in March 2003 the first hexagonal floor of a neutrino telescope in the Mediterranean Sea began taking data (ASTROPARTICLE PHYSICS VOL 23,377-392, 2005, NUCLEAR INSTRUMENTS AND METHODS A, 552 (2005) 420-439).
Near future plans are to deploy a tower of four floors connected to the shore and also deploy four autonomous strings at distances of 300 m around the tower and thus form a sparse square kilometre-size detector designed to investigate emission of TeV energy neutrinos in coincidence with gamma ray bursts.
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