Acousonde™ Applications Questions

Updated July 2017

Application environment

Will it work reliably in my application environment?
Power is the key element in understanding how reliably the Acousonde will work in your field environment.

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.

Application configurations

Will the default configuration provide what I need?
By default, the Acousonde comes with a single "Low-Power" hydrophone of moderate sensitivity (nominally -187 dB re 1 V/µPa) filtered through an adjustable anti-alias device with moderate self-noise (about 70 dB re 1 µPa2/Hz when 20 dB of user-selected gain is applied). This configuration provides sampling-rate flexibility and will capture most sounds against a background of moderate ambient noise. It is not ideal for measuring a quiet ambient noise background, nor for monitoring extremely strong sounds.
What should I order for use as an animal tag?
After the Acousonde 3B's introduction in 2011 it quickly became preferred over the 3A for tagging cetaceans. The 3B includes both flotation and suction-cup attachment in a unified hydrodynamic design, while the 3A requires third-party attachment and flotation.

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.

Do I need the optional high-frequency (HF) hydrophone?
The two reasons you might need the HF option are frequency bandwidth and self-noise.

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.

What's the best frequency at which to fix the HF channel high-pass filter?
When you specify the high-frequency (HF) option, you'll need to choose the permanent cutoff frequency for the HF channel's fixed high-pass filter. The HF channel uses much more gain than the low-power (LP) channel, so strong signals are more likely to overload the channel and ruin data quality. Strong acoustic signals — especially those due to flow or mechanical noise near the recorder — are typically at low frequencies. So, attenuating low frequencies before digitizing the acoustic signal can help preserve data quality on the HF 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.

What should I order for quiet recording?
If you are not expecting severe low-frequency noise from flow or other sources, and would like the quietest and widest-band recordings possible, use the high-frequency channel option (Option B003-HF) combined with a 20-Hz high-pass frequency. As the unit will still include the low-power hydrophone channel, you retain the flexibility to choose less-sensitive recording at deployment time.

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).

What should I order to handle loud sounds?
If exceptionally strong sounds must be handled, we recommend a custom low-power (LP) hydrophone that clips at about 201 dB re 1 μPa 0-pk (Option B003-CH). But, the LP channel cannot record bandwidths greater than 9.3 kHz; recording strong sounds with a wider bandwidth would require a custom-desensitized high-frequency option (Option B003-HF).
What's the best configuration for all applications?
There is no one-size-fits-all configuration. A unit optimized for broadband, quiet recordings may clip excessively when used as an animal tag. A unit optimized to record strong sounds without clipping may miss weak sounds. A unit optimized to suppress flow noise will also suppress other low-frequency sounds, such as vessel noise, that may be of interest.

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.

Marine wildlife

Will it work for my species?
Only you, as the biologist, can assess whether the Acousonde's configuration satisfies the requirements of working with your species. Three key characteristics of the Acousonde, however, will affect its applicability.

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.

If it requires recovery, how do I recover it?
For some species, such as blue whales, recovery presents a major obstacle. First, you must be certain the tag and attachment assembly will float! Second, you must have a way of knowing where the tag is after it leaves the subject. The typical approach is to incorporate a separate VHF transmitter in the tag assembly. VHF wildlife transmitters can be detected from distances of 20 miles or more, provided your receiver can be located at higher elevation (a building, hillside, or aircraft) and in an area of low electromagnetic noise (the bridge of a research vessel may not qualify). However, while a VHF transmitter or something like it is a necessity to find the tag when it is within a few miles of you, it does not help you if the tag is out of range. Long-distance tracking requires a satellite transmitter; note that adding satellite-tracking capability to the Acousonde will require extensive custom development.

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

How do I attach acoustic recording tags to my subject?
That's up to you. The A-series Acousonde (Model B003A) is designed to be as broadly useful as possible. You can attach it with suction cups, crossbow, or glue; however, as the expert with your species, you must develop the most suitable attachment approach. Model B003A comes with no attachment gear. Model B003B, on the other hand, incorporates a low-profile suction-cup attachment system.

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.

How long can an attachment last on an animal?
The duration of attachment depends on the attachment technique. To date, attachment methods have included suction cups (whales), glue (seals), tethers (manatees) and surgical implantation (sharks). These techniques have yielded attachment lifetimes from a few minutes to several weeks. To our knowledge nobody has used the Acousonde with a dorsal-fin saddle.
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Differences between the Acousonde 3A and the Acousonde 3B

Do the 3A and the 3B differ electronically?
Yes. The 3B includes an ambient light sensor and a retrieval strobe. The light sensor serves primarily to restrict flashing of the strobe to nighttime; however, it is also tied to the auxiliary sampling system so that the 3B can record ambient light level. Another difference is that the 3B only provides 2 MicroSD storage-card slots, while the 3A provides 4 (in most cases battery limitations and the large capacities of modern MicroSD cards renders this difference moot). Finally, the 3B omits some extra components and debugging ports that the 3A supports for non-wildlife applications.
Do the 3A and the 3B differ acoustically?
Yes. While the 3A and the 3B offer identical hydrophone configurations, the high-frequency hydrophone option will respond more uniformly in the 3A than in the 3B. Limited space in the 3B requires the hydrophones to be placed adjacent to the pressure housing for the battery. This shouldn't be an issue for the lower frequencies monitored by the low-power hydrophone, but the presence of an air body near the high-frequency hydrophone may significantly affect its directionality.

Permitting information

What are the precise dimensions and weight of the Acousonde 3A?
The Model B003A cylindrical Acousonde ("Acousonde 3A") with a battery cap and A-size lithium battery but WITHOUT flotation, attachment, or recovery gear, weighs 262 g (in air) in a volume of 172 cc (this compares to 212 g and 135 cc for the Model B002B Bioacoustic Probe). The "torpedo" shape is 3.2 cm in diameter and 22.1 cm long (compared with 3.2 cm and 19.3 cm for the Bioacoustic Probe). It is negatively bouyant; in seawater the tag weighs approximately 86 g (compared with 74 g for the Bioacoustic Probe). Of course, flotation, attachment and recovery gear will add to the size and weight of your total package. Please also see the Acousonde 3A PDF brochure.
What are the precise dimensions and weight of the Acousonde 3B?
The Model B003B Acousonde ("Acousonde 3B") with battery cap, A-size lithium battery, flotation, quad suction cup attachment, retrieval strobe, and (separately-procured) VHF transmitter, weighs at most 360 g in air (substituting a single suction cup for the four separate suction cups may add as much as 31 g in air, but only 3 g when submerged in seawater). The 3B hydrodynamic shape is 4.2 cm high (including uncompressed suction cups), 7.9 cm wide at its widest point, and 22.4 cm long (not counting the VHF transmitter or the retrieval strobe that protrudes an additional 1.7 cm from the end of the attached float). The 3B is positively buoyant, with a buoyancy in seawater no less than 50 g. The downloads area provides a detailed diagram of the Acousonde 3B as well as a one-page PDF brochure with specifications.

General attachment/deployment guidelines

What VHF transmitter is recommended for the Acousonde 3A?
The Acousonde 3A comes with no flotation, attachment, or retrieval gear. This third-party equipment, not the size or shape of the Acousonde 3A itself, will drive the choice of VHF transmitter. Please correspond with your source of this gear regarding a VHF transmitter.

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.

What VHF transmitter is recommended for the Acousonde 3B?
The Acousonde 3B float provides a receptacle 17.85 mm (0.703") in diameter by 50.8 mm (2.00") deep designed for an Advanced Telemetry Systems (ATS) model F1835B bottle-shape implant transmitter, modified at the ATS factory with a stiff antenna as used in their backmount transmitters. Note that ATS transmitter dimensions and weight can vary from batch to batch, so if you order from ATS, please insist that the above diameter is the "absolute maximum" diameter, and specify that the transmitter weight, including antenna, must not exceed 26 g in air.

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.

What does the Acousonde 3A mechanically provide to secure attachment or retrieval gear?
Model B003A includes a cylindrical battery cap with a 10-24 threaded screw-hole at the center; this can be used to secure eyebolts with 10-24 threads (for tethers) or to attach flotation. A urethane "key" protruding from the Acousonde's surface can be used to prevent screw-on flotation from rotating unintentionally. Attachment systems such as suction cups must be secured either to the flotation (not included) or to the urethane body of the Acousonde itself. This has been done in the past with gear as simple as cable ties and electrical tape.

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.

What are the best locations for securing the Acousonde 3A?
Attachments must avoid stress to sensitive components. The three most fragile components are the main (low-power) hydrophone, the high-frequency hydrophone (if that option is present), and the pressure transducer. The photograph in the Acousonde 3A PDF brochure identifies the locations of these components. The two recommended regions for attachment strapping are (a) the battery housing and (b) the bank of flash memory cards situated between the two hydrophones.
I want to launch the Acousonde onto a target. Can it handle the impact?
Unknown. The Acousonde 3A shares its basic mechanical design with its predecessor, the Bioacoustic Probe, and that earlier instrument took abuse well. However until recently no customer has ever asked about high-speed impact tolerance, so it was not part of the Acousonde's design criteria. To recommend the Acousonde for use in these applications, we would need to perform potentially destructive testing that would probably indicate a need for additional development. Given the expense of this testing and development, demand will determine our ability to support high-speed impact applications.

3B deployment grip

How do I mate the 3B's deployment grip with my deployment gear?
The 3B deployment grip (model DG3B) consists of a stainless-steel endoskeleton overmolded with silicone shaped to conform with the Acousonde 3B's surface. The endoskeleton may be adjusted in the field for tighter or looser grip with gentle bending, while the pivot resistance may be adjusted by means of a screwdriver and wrench. Specifications:

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.

Understanding acoustic recording tags

Why can't acoustic recording tags telemeter their data in real time?
The Acousonde samples acoustic data at rates up to 232 or possibly even 464 kilohertz. To be useful, it must gather hours of recordings, potentially adding up to several gigabytes of data. There is no way to transmit this vast amount of data by satellite or radio, especially from a low-power device that spends most of its time submerged. However, if a tag designer knows up front exactly what sort of signal is of interest, the tag may be designed with special-purpose hardware and/or software to detect, characterize, and count occurrences of that signal. In this case telemetry may be possible since the acoustic data will be heavily preprocessed and compressed on board the tag.
How does the Acousonde differ from other acoustic tags?
The Acousonde, strictly speaking, is not an "acoustic tag." For decades, the fish-biology community has used the term "acoustic tag" to refer to active "pinger" tags that produce ultrasonic pulses. These pulses allow researchers with detection equipment to follow the tagged subject. The Acousonde, on the other hand, passively acquires acoustic data. It does not transmit ultrasonic pulses. We advocate calling passive-acoustic tags such as the Acousonde "bioacoustic tags" or "acoustic recording tags" to reduce confusion.
OK, how does the Acousonde differ from other BIOacoustic tags?
The two key differences between the Acousonde and many other acoustically-related tags are: (1) the Acousonde is designed to allow application by small, tight-budget biology teams without requiring extensive training or the presence of an engineering specialist; and (2) the Acousonde is a broadband acoustic recorder. It digitizes and records full acoustic waveforms, and does not include any detection or compression hardware such as pulse detection (although such capabilities may be implemented in future firmware releases). As such it is substantially more complex and requires more processing power, a larger battery, and greater data capacity than a pulse detector.