The first Mark 4 Bioacoustic Monitoring System pictured was built for the New South Wales Department of Environment and Conservation to monitor Ground Parrots at Barren Grounds in SE NSW. The second Mark 4 system pictured is a development system deployed in sub-tropical rainforest on the outskirts of Brisbane. The antenna underneath the panel provides an Internet connection via a wireless (802.11b) link.

The Mark 4 systems use essentially the same electronics as our Mark 3 systems. There are 2 significant changes.

A 1GB USB flash is used to cache sound allowing the hard disk to be powered down for a large fraction of the day with consequent significant power savings. The USB interface to the hard disk does not allow the disk's power state to be controlled. The disk is powered by from a separate 5V line (on the custom power PCB) which is switched on and off via a digital GPIO line on the StrongArm board.

The system with the wireless link copies sound, when possible, directly from the flash cache to a remote server. Its hard disk is not used during normal operation .

The microphone is the other innovation in the Mark 4 systems. These use 2 waterproof Knowles WP-3502 electret microphone capsules embedded in epoxy. The Barren Grounds systems is horn-loaded with an ad hoc (prototype) construction of (circular) PVC pipe. The PVC horn is 485mm long, 150mm wide and 155mm high. The central partition between the two microphone elements is 335mm long and 14mm wide

The horn frequency response curve is an advantage, Wind, vehicle and aircraft noise falls largely below the low frequency horn cutoff reducing the risk of these causing the signal to exceed ADC limits and clipping resulting. The directional sensitivity in the horizontal plane of the horn is similar useful. It reduces the chance of a source immediately below (or above), for example an orthopteran on the ground below, causing clipping.

An external covering of Lincraft synthetic fur over plastic mesh protects the elements and reduces wind noise. The doormat material above provides sun&rain protection and reduces rain noise.

An iMic USB audio interface is enclosed in the microphone. External USB connection is via several metres of data cable terminated in a Bulgin 6-way waterproof plug (PX0739)

A simpler and less effective horn loading system without wind shield is employed on our Queensland development system.