The new generation of Electronic Click Detector (ECD): the development and field trials data

The use of envelope detection methods to reduce the bandwidth of an echolocation click into the audio-band is not a new concept. However, the increasing popularity of portable digital recorders with excellent signal to noise performance needs such signal processing if ultrasonic transient data needs to be captured. Similarly, this approach allows high frequency information to be recorded onto video recorder sound tracks providing the advantage of synchronised sound with images for behavioural studies. This paper describes the development of a new generation of ECD with improved performance and includes cetacean echolocation data recorded using this equipment in two independent studies

Development of a simplified ray path model for estimating the range and depth of vocalising marine mammals

A simplified ray path model has been developed to simulate various source, receiver geometries. The difference in the arrival time of the multi-path signals (surface and seabed reflections) were calculated and compared with those measured on recorded data obtained during sea trials. A number of assumption have been made in initial models including a constant sound velocity-depth profile and the treatment of the surface and seabed as a simple reflecting surfaces. Initial results have shown a number of examples with a reasonable correlation between estimated position of a submerged cetacean and the associated surface observations. Examples of multiple (positioning) solutions were however found, these are in the main thought to be due to imprecision in the knowledge of the hydrophone and water depth and inaccuracies in the initial timing measurements. The use of correlation techniques and stand-alone depth measurement devices is therefore proposed for future measurements and analysis using this technique. It is felt that within constraints, this technique provides valuable additional information regarding cetacean behaviour in the wild and can be used on recorded data sets to validate observer records. The addition of more complex time measurement techniques and better ray path modelling will hopefully provide a useful analysis tool in the study of cetaceans

An experimental technique for tracking dolphins in the vicinity of a trawl net

The system described in this paper provides a means of tracking one or more echolocating cetaceans (dolphins, porpoises and whales) in three-dimensional space. The aim of the research is to enable the behaviour of cetaceans to be observed passively in the wild in the vicinity of a large trawl net and to evaluate the effectiveness of deterrents intended to prevent the by-catch of these animals