C-POD specification

Working depth:

0 to 100 m and probably more. We welcome any offers of destructive testing.

Autonomous operation time:

Up to a theoretical maximum of 4 months for the standard version using 8 alkaline D-cells. Sea trials in the deployment area are required in order to determine more realistic limits.

Housing:

Polypropylene. Contains the transducers, electronics and battery pack.

Dimensions:

Length: 535 mm. Diameter: 90 mm

Weight:

Standard version: 1.7 kg without batteries, 2.9 kg with 8 alkaline D-cell batteries.

Buoyancy:

Approximately 0.5 kg

Mooring lines:

18 mm polypropylene line attached just above the centre of the housing to minimise tilt in a current. A security line can be attached to the lid.

Hydrophone:

20 kHz to 150 kHz, omni-directional hydrophone in a large-diameter housing to reduce surface noise. The transducer design avoids strong resonances and the transducer element mounting design gives high resistance to impact damage.

Memory:

Removable high density Secure Digital (SD) memory card.

Batteries:

Standard battery packs hold 8 alkaline D-cells. The battery housing is sprung to reduce battery damage from end impacts.

Detection range:

Measurements on T-POD detection of harbour porpoise, Phocoena phocoena (Tougaard et al) showed detections in shallow water out to approximately 300 metres from the POD, with a detection function equivalent to 100% detection within approximately a 70 to 100 metre radius. The C-POD is likely to be similar.

Dolphins: with louder clicks have a greater range and Philpott et al in Ireland showed detections to approximately 1200 metres of bottlenose dolphins (Tursiops truncatus), moving along the coast of the Shannon Estuary. The C-POD is likely to give a greater detection range and have many fewer undetected groups, as this occurred when the dolphin clicks were too broadband for the T-POD to log.

Standardisation:

Absolute sensitivity to 130 kHz pulses < ±2 dB relative to a standard yet to be defined.
Radial variation < ±2 dB relative to the mean sensitivity.

Deep water version:

Pressure-resistant transducer housing and non-buoyant aluminium case.

Detection method:

Digital time domain waveform analysis, using duration, intensity, bandwidth, frequency and envelope criteria to select possible cetacean clicks in the range 20-150 kHz.

Detection parameters:

Centre frequency, frequency trend, duration, intensity (8 bit), bandwidth, envelope slope are logged for each click.

Ambient noise:

The C-POD intensity measurement is standardised to allow continuous assessment, when cetaceans are detected, of the minimum intensity of clicks that are detectable at that time. This new method will allow assessment of the actual effect of ambient noise on click detectability, which is difficult or impossible to obtain from standard measures of noise as they lack crucial information on short-term temporal variations.

Attitude sensing:

The angle-from-vertical is recorded each minute, enabling the user to ensure that the C-POD has been correctly deployed in a vertical position. The sensor can be set to a pre-selected range to prevent logging until the C-POD is deployed. This allows the C-PODs to be set up and transported some time before deployment, saving power and memory.

Temperature sensing:

Temperature is recorded each minute.