The Acousonde uses the smallest and most convenient battery possible that can still support ultrasonic sampling rates in temperate waters. Unfortunately, batteries tend to perform poorly near freezing, so colder waters will push the Acousonde's small battery to the limits of its capability.

In early 2012 the Acousonde successfully gathered data at 232 kHz sample rate in Arctic conditions at temperatures well below 0°C, but with reliability limitations. Since then, new firmware has dramatically improved reliability near freezing. In early 2013 an Acousonde placed in a freezer (-12 to -17°C) recorded at 232 kHz sample rate for over 13 hours.

To increase power margin when sampling at very high rates in extreme cold, one can apply an external power source with the Acousonde.

Tagging studies that do not require suction-cup attachment or flotation, such as those with seals, may still be better served by the 3A, although the 3B could be used without its float and suction cups to provide a broader, shorter tag. This might be more appropriate depending on the species.

In either case, the likelihood of flow noise on a moving animal favors the default moderate-sensitivity low-power hydrophone and, if the optional high-frequency hydrophone is desired, aggressive high-passing (typically a gradual rolloff below 10 kHz) to prevent low-frequency noise from clipping the acoustics excessively.

The HF option allows recording up to 42 kHz bandwidth, with a very gradual rolloff above that; even at 100 kHz signals are attenuated only by 22 dB. In contrast, the low-power (LP) channel can only record up to 9.3 kHz bandwidth unless the anti-alias filter is defeated.

The HF option uses components with much lower noise than those of the LP channel. With nominal gains the HF channel's self noise expressed in dB re 1 µPa²/Hz is about 30 dB less than that of the LP channel. So, adding the HF option gives you the flexibility to obtain quieter recordings.

The HF channel uses more power and stores more data than the LP channel, so using the HF channel limits deployment life compared with the LP channel.

Optimizing the high-pass cutoff frequency for the HF channel involves several tradeoffs. The cutoff can be set as low as 20 Hz, which may be desirable in quiet environments when only slow tag speeds are anticipated, or if maximum recording bandwidth during periods of little movement is worth sacrificing data quality at higher speeds. On the other hand, if low frequencies on the HF channel are not relevant to the application, it may be safest to set the cutoff as high as 10 kHz.

A 10 kHz high-pass cutoff may also be appropriate if using the HF channel to study ambient ocean noise. With this cutoff, attenuation below 10 kHz roughly compensates for the typical increase in ambient noise with decreasing frequency. Configuring a high-pass filter for this purpose is sometimes called prewhitening.

If frequencies over 10 kHz are of less interest, a less expensive option would be to install a higher-sensitivity low-power hydrophone in place of the default low-power hydrophone (Option B003-CH).

That being said, the Acousonde does support both a low-power (LP) and an optional high-frequency (HF) channel. The two channels could be configured to cover different sound levels and frequency ranges. For example, a configuration with an insensitive LP channel and a sensitive broadband HF channel could satisfy a range of fixed recording needs, although it could be less suitable for animal-tag applications.

First, this is an archival tag, meaning that it must be physically recovered for you to retrieve its data.

Second, the Acousonde 3A includes no attachment, flotation, tracking, or retrieval equipment, meaning that you must supply all of these for the 3A. The Acousonde 3B, on the other hand, incorporates suction-cup attachment, flotation, retrieval strobe, and a receptacle for a third-party VHF retrieval transmitter.

Third, the Acousonde's usefulness may be seriously impacted by flow or attachment noise; if your application environment involves banging, creaking, vibration, or strong, poorly faired flow, your acoustic records may be contaminated with noise. Severe contamination can render your acoustic data useless.

The Acousonde 3B incorporates a strobe that can improve nighttime retrieval capability.

Note: serious ethical, legal and personal-safety issues accompany any attempt to attach tags to wild or protected animals. This short discussion of attachment alternatives is not intended to downplay the responsibilities and risks associated with this activity. You are responsible for obtaining the necessary permits and conducting your research with the utmost concern for your safety and the safety of your associates and subjects.

To make direction-finding easier, some field biologists specify a custom VHF pulse rate of 120 ppm (pulses per minute) and a custom pulse width of 25 ms (55 ppm and 20 ms are typical manufacturer defaults). Users must also specify a frequency band compatible with the VHF receiving equipment they plan to use.

To make direction-finding easier, some field biologists additionally specify a custom VHF pulse rate of 120 ppm (pulses per minute) and a custom pulse width of 25 ms (ATS transmitters typically default to 55 ppm and 20 ms). Users must also specify a frequency band compatible with the VHF receiving equipment they plan to use.

Seawater contact with steel bolts or eyebolts secured in the aluminum battery housing will cause galvanic corrosion. Eventually this corrosion may permanently fuse the two metals together. To avoid this, coat the threads before assembly with an anti-seize product such as Loctite Marine Grade Anti-Seize. Alternately, use an aluminum or nylon bolt.

Pivot arm. The pivot arm is made of PVC plastic machined to fit a US standard 1/2" schedule 40 PVC pipe coupling. The pivot arm outer diameter is 0.838 +.000/-.003" (21.3 +.000/-.076 mm).

Pivot arm length. The default length of the pivot arm is 1.25" (31.75 mm) but could be cut down to 0.75" (19.05 mm) if requested.

Pivot axis hardware. The pivot axis is a 10-32 x 1.75" long pan-head Phillips bolt made of 316 stainless steel with a matching elastic stop nut. To adjust pivot resistance requires a #2 Phillips screwdriver and a 3/8" or adjustable wrench.