Our Mark 3 Bioacoustic Monitoring System systems were designed and built by Gordon Grigg and Andrew Taylor for the Western Australian Department of Environment and Conservation to monitor frog populations at sites near the WA/NT border to assess the impacts of the arrival of Cane Toads.

Three systems were deployed from November 2005 - May 2006 at locations in Gregory National Park (NT), Keep River National Park (NT) and north of Kununurra (WA). Systems have operated nominally through hostile environmental conditions - extreme heat & humidity and violent storms. Shade air temperature reach 44C at theses sites and effective ambient temperature are higher. All sites experienced flooding due to record cyclonic rainfall in early 2006 - one system became inoperative after being completely submerged.

Systems were mounted on a 2.5 metres galvanized steel pole sitting on a pegged base plate. Three stainless steel guy wires anchored the pole to star pickets. Welded brackets support system, battery and panel. The pole was constructed by ? Engineering at Katherine.

All sites had good solar exposure with trees and terrain blocking less than half the potential solar input. There were no interruptions to supply despite presumably overcast periods of several days at the peak of the wet.

These systems are based on a single board computer with a 200MHz StrongArm processor, 64 MB of ram and 128 MB Flash. These boards have low power consumption (1-2 watts) but run a general purpose operating system (Linux 2.4) and provide sufficient computational capability for real-time identification of frog calls.

A pair of microphone is mounted on the exterior of the computer enclosure with a stereo separation of 25cm. Mounting of the microphone elements flush on the flat surface of the enclosure increases microphone sensitivity by approximately 9db. A sleeve of PVC pipe mounted around the element and it is covered with synthetic fur to reduce wind noise and exclude insects. A large half-circle of PVC pipe is mounted above the microphone element to provide sunlight protection. In our field experience microphones, along with power supply, are the major points of vulnerability of bioacoustic monitoring systems. Microphones are necessarily exposed to the environment. The Knowles waterproof electret microphone elements have impressively robust specifications and the 2 microphones elements submerged in flood waters for some days were undamaged. Even with robust elements, it is essential that insects be excluded. They can disable microphones by filling cavities with frass or mud.

Frog identifications and system condition data is stored in the on board flash. An 80Gb 2.5" laptop disk is used to store sound. The disk is kept continuously spinning. A flash memory cache could allow the disk to be powered down for a large fraction of the time but as the reduction in power consumption was not essential and there was uncertainty about reliability, we opted for the simplest approach.

Digitization of sound is done with an iMic USB board The gain of the iMic was increased 12db by changing surface mount resistors R18 & R25 from 47k to 10k. The iMic is general suitable, inexpensive, compact and low power consumption but it introduces significant noise. This noise largely manifests as narrow spikes at precise 1khz intervals at -65-75db. This fortunately can be removed with little impact by post-processing with a 250hz comb filter.

Sound is sampled in 16 bit stereo at 16khz. It is losslessly compressed with the program shorten. Shorten runs quickly on the StrongArm processor which lacks and FPU and produces compression results in this context similar to other sound compression software we have tried.

A small PCB designed and built by David Johnson containing an efficient DC-DC converter supplies 5V power to the system.

System Components

Part	Supplier	Supplier Part#
Knowles MR-8406 waterproof microphone x2	Digikey	423-1016-ND
TS-7250 SBC with 64 MB RAM and 128 MB Flash + Real Time Clock	Technologic Systems	TTS-7250-64-128F + OP-BBRTC
Samsung 2.5" 80GB disk (MP0804H)	AusPC Market
Gigasave PH02B USB HDD enclosure	David Reid Electronics
Griffin iMic USB audio interface.	Magical Deals (ebay.com.au)
SL1I-12L Piezo Buzzer	Farnell	3921130
IP65 Sealed ABS Enclosure	Jaycar	HB-6130
BP Solar SX30 30 watt photovoltaic panels	Solar Online Australia
Concorde PVX-340T absorbed glass mat (AGM) 12 volt 38 Ahr battery	Solar Online Australia
Steca Solsum 5A Solar Regulator SSR5	Solar Online Australia
Bulgin waterproof 6-way plug&socket (PX0739/PX0739)	Farnell	314201/314298
Black PVC battery box	Solar Online Australia
Tycab AWC22603 4mm Twin Double Sheathed Cable (22 amp)	Solar Online Australia
Synthetic fur	Lincraft	AC336
flexible electrical conduit, PVC pipe, cable ties, silicone,6mm eye connectors	hardware store