Chelonia Limited

  Cetacean Monitoring Systems

 

T-PODs ceased production in 2008 and have been superceded by C-PODs. However, many T-PODs are still being deployed. The T-PODs consists of:

  • a hydrophone
  • an analogue processor
  • a digital timing/logging system and
  • analysis software that filters the data for cetacean clicks automatically, after it has been transferred to a PC.

T-PODs log the times and duration, to 10 microseconds resolution, of clicks resembling the echo-location clicks produced by the target species. The dedicated software on the PC then identifies and classifies trains of clicks within the logged data. This process of click train recognition filters out non-cetacean clicks and gives reliable data on the presence of the animals and some indication of their behaviour.

Clicks resembling those produced by cetaceans arise from various sources, but not in the semi-regular sequences called 'trains' that are produced by all echo-locating cetaceans. The process of 'train detection' is the key to the high quality of the output of T-PODs. Without automated detection of trains, the task of 'manually' analysing click data is vast.

In order to select clicks resembling the echolocation clicks of cetaceans, the T-POD compares the output of a pair of bandpass filters, one of which is set to the frequency (pitch) of the clicks of the species of interest. There are 16 frequency bands available, centred from 9 kHz to 170 kHz. In every minute, the T-POD runs six successive scans of 9.3 seconds each so that clicks at different frequencies can be collected. For each of these scans the user can define the target and reference frequencies and the effective maximum bandwidth of click that will be logged.

Bandwidth in this context means how pure or tonal a click is. Cetacean clicks are more tonal than most impulsive sounds in the sea, but brief tonal sounds do also come from rain, boat sonars, propellers, moving sand, and various other sources. The software (TPOD.exe) analyses the data on a PC to find click trains and identify those trains that are characteristic of dolphins and porpoises.