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

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Presentation on theme: "Bat detectors John Errington MSc(Physics) and Jonathan Pounder BSc(Enviromental Studies)"— Presentation transcript:

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

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? 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 Bat call is picked up by sensor Audible sound out from speaker or phones

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

8 Heterodyne detectors

9 Detector types : Frequency division Benefits: o Suitable (but limited) for recording calls for later analysis. o No chance of missing a bat because they don’t need tuning. Disadvantages: o Sound quality is not very pleasant unless a more upmarket “AR” type is used. o Creates artificial harmonics that can distort a sonogram. o 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: o Slow down call. This helps you hear changes during the call. o Very pleasant to listen to. o Very good for recording and analysis. Disadvantages : o Can miss bat calls while playing back sounds. o Rather expensive and can be fragile Sound clip: TE compilation, daub, pip, noctule

12 TE detectors

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

14 Real time ultrasonic recording Benefits: o Can record entire frequency range o Can record continuously unattended o Can play back original sound o Ideal for bat call analysis and as an aid to species identification. Drawbacks: o Very expensive o Sometimes not very robust o 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 bat detector – to – sound recorder – to – computer audio Data stored usually as.wav or.mp3 USB Mic or Line in

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 Bat detector sensors Piezo transducer High voltage Capacitance Microphones Small Electret Miniature Electret – hearing aid types Micro-electrical- mechanical system (MEMS) transducers Very sensitive, robust, cheap very 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 and flatter frequency response. Extremely robust.

22 Sensors in use Type of sensorManufacturer / Model Piezo SensorBelfry, Magenta 2 & 3 Capacitance MicAvisoft, BATech, Petterson D1000X Electret CSE, Ciel, BATBOX Magenta 4 & 5 Mini Electret Maplin kit (no longer available) Used a tiny hearing aid microphone MEMS Mic BATON Multiple sensorsPetterson D100 (2 piezo 1 electret)

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 Out in the field This is where the bat detector is to be used, each design having its own benefits and disadvantages. Areas to consider: 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 o Weight in hand o Supports & straps o Add-ons – particularly when recording for later analysis o 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: o Low light levels o Ease of use with cold hands or gloves

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


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