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Bat detectors

Bat detectors. John Errington MSc(Physics) and Jonathan Pounder BSc(Enviromental Studies). John Errington. Lecturer in Electronics and IT at University of Northumbria (retd) 30 years interest in bat detector design Webmaster for Durham Bat Group www.durhambats.org.uk. Jonathan Pounder.

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Bat detectors

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  1. Bat detectors John Errington MSc(Physics) and Jonathan Pounder BSc(Enviromental Studies)

  2. John Errington • Lecturer in Electronics and IT at University of Northumbria (retd) • 30 years interest in bat detector design • Webmaster for Durham Bat Group • www.durhambats.org.uk

  3. Jonathan Pounder • Lecturer in Environmental Conservation at Houghall College • Environmental Consultant • Licensed Bat Worker with Durham Bat Group

  4. What does a bat sound like? Audible sound out from speaker or phones Bat call is picked up by sensor The bat detector takes signals from a special microphone, converts them to match the human hearing range, and outputs them to a speaker or headphones

  5. Microphone or “sensor” Detector electronics in box – needs a battery Loudspeaker, headphones or earpiece

  6. Types of bat detector • Heterodyne • Frequency division (FD) • Time expansion (TE) • Digital Signal Processing (DSP) • Real time ultrasound recording

  7. Benefits: Usually quite sensitive Pleasant sound. Tuning can be an aid to identification Disadvantages: Can be mis-tuned, leading to false identifications. Can miss bats you're not tuned to. Not suitable for call recording and analysis. Heterodyning changes harmonic relationships in the call. Detector types: heterodyne Sound clip: common pip

  8. Heterodyne detectors

  9. Detector types : Frequency division • Benefits: • Suitable (but limited) for recording calls for later analysis. • No chance of missing a bat because they don’t need tuning. • Disadvantages: • Sound quality is not very pleasant unless a more upmarket “AR” type is used. • Creates artificial harmonics that can distort a sonogram. • Can lack sensitivity • Sound clip: Belfry bat detector • Sound clip: Daubentons bat with BATON)

  10. FD and dual-mode detectors

  11. Detector types: Time expansion • Benefits: • Slow down call. This helps you hear changes during the call. • Very pleasant to listen to. • Very good for recording and analysis. • Disadvantages : • Can miss bat calls while playing back sounds. • Rather expensive and can be fragile • Sound clip: TE compilation, daub, pip, noctule

  12. TE detectors

  13. Detector types: DSP • Benefits: • Better audio representation of bat call • More accurate for recording and analysis • Problems: • Not presently available in a portable detector • Need to use high quality components (e.g. sensors) to justify added complexity DSP FComp F Div AR

  14. Real time ultrasonic recording • Benefits: • Can record entire frequency range • Can record continuously unattended • Can play back original sound • Ideal for bat call analysis and as an aid to species identification. • Drawbacks: • Very expensive • Sometimes not very robust • Don’t provide audio output

  15. Recording ultrasound bat calls An ultrasound receiver picks up bat calls and transfers them to a computer or field recorder via the USB interface Software running on the computer receives the data, supports analysis and storage of data, and can produce sound output to headphones (like a bat detector)

  16. Ultrasound recording: Avisoft

  17. Bat call recording on a budget

  18. Recording bat calls Data stored usually as .wav or .mp3 USB audio Mic or Line in bat detector – to – sound recorder – to – computer

  19. Bat call analysis • Sound recording and editing software • e.g. AUDACITY (Freeware) • Call analysis software: • Freeware: • WaveSurfer, SoundRuler • Commercial software: • Avisoft “SASlab”, £2000 • Batbox “Batscan” £30 • Petterson “Batsound” £300 • SonoBat (TE only) $320 Bat calls are stored on computer - usually as .wav or .mp3 files

  20. The end result: a sonogram

  21. Piezo transducer High voltage Capacitance Microphones Small Electret Miniature Electret – hearing aid types Micro-electrical- mechanical system (MEMS) transducers Bat detector sensors • Very sensitive, robust, cheapvery limited bandwidth • Wideband, flat response, good sensitivity, expensive, not robust, need high voltage supply • Sensitive, robust, cheap, best at lower frequencies • Generally less sensitive than larger mic’s, and more expensive, but better high frequency response. • Similar to miniature electrets but with much higher bandwidth andflatterfrequency response. Extremely robust.

  22. Sensors in use

  23. MEMS microphones A MEMS microphone combines a capacitance microphone micromachined on silicon as shown here,with all of the electronics (drive circuit, amplifier, etc) needed to make it work

  24. This is where the bat detector is to be used, each design having its own benefits and disadvantages. Areas to consider: Out in the field • Weatherproof: • Rain • Cold Weather • Robust design: • Knocks bangs and bumps • Dropping the detector • – impact resistant These are now considered in most of the modern designs

  25. Design and Use • The design in relation to fitting it into the hand and operating it. • This includes • Weight in hand • Supports & straps • Add-ons – particularly when recording for later analysis • Ease to change a battery quickly • Knobs and dials • Can sometimes be the deciding factor in identifying bats in the field quickly. Factors to consider: • Low light levels • Ease of use with cold hands or gloves

  26. Associated Equipment • Little extras come in very useful • Spare Batteries (ensure they are the right type) • Earphones – allow you to focus your attention on what you’re hearing particularly with background noise (road or river) • Head torch • MP3 player • Thermometer

  27. Safety, theft and concealability • Particularly in urban areas - • Keep them out of sight • If in doubt - Make sure someone knows where you are and when you will be back.

  28. Best buys

  29. More information • For more information about bat detectors, how they work, reviews etc. visit our website • www.durhambats.org.uk

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