Behind the creation of the Solar BAR: An iconic acoustic project meets an incredibly dedicated team

Nicole Bray from Frontier Labs

Solar BAR at Gluepot Reserve, South Australia

What does Australia sound like?

That’s the question posed by the Australian Acoustic Observatory (A2O) – an ambitious open-source project that aims to give everyone the ability to listen in on hundreds of ecosystems across the Australian continent continuously for five years.

The project relies on 360 super-sensitive acoustic recorders specially designed and manufactured by Frontier Labs for the project. The recorders can be found in a variety of climate extremes – from the dense wet rainforests of Cape York to the red centre and down along the freezing Tasmanian coastline.

To celebrate and appreciate the work that went in to designing these unique recorders, we’re taking a closer look at five key design decisions that make the Solar BAR such a groundbreaking bioacoustic research tool.

Design Challenge 1: High quality open access data

The Australian Acoustic Observatory is an open-access project, meaning anyone with an internet connection should be able to download and listen to the files. However, 360 acoustic sensors recording 24/7 for 5 years makes for a lot of data! 17,520,000 hours or 2000 years of audio to be precise. With mind-boggling amounts of data to record, data compression was an important requirement of the project from the start.

Michael Maggs, Frontier Labs’ lead engineer, explained the difference between ‘good’ and ‘bad’ compression and why the Solar BAR uses lossless .FLAC files to capture a larger and more complete sample of the natural world.

“Everything we stream on Spotify or Netflix, for example, uses lossy compression to increase streaming speed. Those compression methods are based on psycho-acoustic models of human hearing – we know what frequencies we can afford to cut out without compromising quality.

This is not true of bioacoustics. When you’re trying to capture calls from another species entirely, you cannot cut out any audio information as it may be vital to identifying what type of animal made that noise, even if we humans can’t hear it.

When you look at the spectrogram of the audio, it’s then you realise you can see more frequencies than you can hear, including the tiny details that would otherwise be discarded by a lossy algorithm.

An example of two ways data can be lost if lossy file types are used to record sound

Finding a compression algorithm that was not only lossless but also universally compatible was critical to the overall aims of the Australian Acoustic Observatory. FLAC works perfectly. The algorithm itself is scalable, so we could fine tune the best balance between processing power, battery life and file size.”

Tidy files, happy scientists

Neatly organising two centuries worth of data is not a job anyone wants to get stuck with, hence why the Solar BAR recorder has a metadata stamping feature built in.

Each recording file is stamped with its GPS location and the date and time of the recording. This is crucial for a big data project like the AAO as it ensures every piece of data can be placed in time and space, allowing scientists to generate more insight from the raw data as well as keeping the files nicely organised!

Design challenge 2: Creating sophisticated technology that’s easy to use

As Steve Jobs famously observed, “Simple is harder than complex. You have to work hard to get your thinking clean to make it simple.”

“A lot goes on behind the scenes to make a complex device seem simple and we’ve definitely taken more than a few cues from Apple” admits Michael.

“We often say “make it more iPhoney” when our design starts to get too complex, or “would our parents be able to use this without any training?”

With hundreds of ecologists, scientists and researchers from all over Australia independently maintaining the AAO data collection sites, designing the Solar BAR for maximum user friendliness was a key consideration.

“There’s a lot of settings that you change on the device while you are in the field, which can be a lifesaver, but at the same time, all you need to do to make it work is turn it on, close the lid and walk away.”

Reducing human error

The Solar BARs are designed to be left alone for extended periods of time, but even these super endurance recorders will reach maximum data storage  eventually. With 4 SD card slots available, the recording time is limited only by the maximum capacity of the SD cards used. For example, using four 512GB cards would enable 18 months of continuous listening. The Australian Acoustic Observatory uses two 512GB cards in each recorder – teams go out to change SD cards approximately every 6 months so they can start processing the data faster.

It is this cross-over point that is most likely to be problematic for the project as it introduces the potential for human error.

The waterproof seal around the rim of the box is one of the most important features of the Solar BAR. If scientists don’t seal the box properly after changing over the SD cards, it can result in moisture damage.

Paul Roe and David Tucker from QUT checking a Solar BAR to collect new data recordings

Even a leaf or small twig being caught in the seal can allow room for extra moisture to build up inside, causing corrosion and potentially leading to a short-circuit. To mitigate this risk as much as possible, all the electronics are coated in a waterproof acrylic coating and there is dedicated space inside the recorder box for desiccant sachets, which absorb any condensation build up. These sachets must be swapped over periodically as well to ensure optimal performance.

Finally, making sure the recorders are easy to install required some clever design too. The Solar BARs are mounted off the ground on a star picket for easy placement in the chosen location (no need to look for a tree!) and were designed so they could be mounted and installed by one just person. There is a specially designed base plate with an angle gauge to lock the device at the angle that will catch the most light and an arm to attach it to the pole. The connection between plate and arm is deliberately off-centre so that the weight of the battery is distributed evenly, making it possible to hold the device steady in one hand. Even the placement of the holes used to bolt the Solar BAR onto the star picket was carefully considered. Different star pickets have different spaces between holes, so the attachment arm has a sliding notch to accommodate different sizes.

Although the backing plate looks lop-sided, it is deliberately designed like this to counter the weight of the battery when mounting the Solar BAR to the picket
Handy features to make life easy for scientists

Design Challenge 3: Field experience vs lab assumptions

Using feedback from ecologists working in the field was critical to perfecting the overall design. The prototype for the Solar BAR had a solar panel that connected to the recording box via a cable, until a throw-away comment by well-respected bioacoustic expert Ted Pederson changed that approach.

“Rats like to chew cables,” observed Ted. Not only that but branches fall and natural disasters are becoming more frequent. With the need to deploy the devices for extended periods of time, the exposed cable was a weakness the project couldn’t afford.

The resulting all-in-one design, with the solar panel attached to the lid of the box, is much more robust and also much easier to handle in the field, further improving the simplicity of the design.

Design Challenge 4: Continuous power for continuous recording

The solar panel is the most obvious design feature of the Solar BAR, and for good reason – it allows the device to work indefinitely without the need to swap out the battery. However, there is much more to the power source for this recorder than meets the eye.

Eliminating electrical noise

The electrical noise generated by power flowing between the solar panel, the battery charger (also known as the voltage converter) and the battery itself can be picked up by the sensitive microphone and amplifiers. This creates lots of unwanted noise that is difficult if not impossible to filter out on the recordings.

This diagram shows how electrical noise can affect a recording if special care isn’t taken to design it out of the system

After experimenting with various solutions, the Frontier Labs team decided to design their own battery charger instead, tinkering with all three components until no interference was detectable in the recordings.

Size vs Weight

Choosing the right size solar panel and battery for the job can be tricky too. Most of the deployment locations for the Australian Acoustic Observatory are in remote areas. Setting them up in these hard-to-get-to places usually requires scientists to carry them in on foot for several kilometres.

You don’t want to have to carry out an oversized battery or solar panel if you don’t need to, but neither do you want options that are too small and run out of power in the middle of your deployment.

In the end, the AAO team and the Frontier Labs team decided upon the 10W solar panel with a 7.2 amp hour lead acid battery combination, which has worked well.

Design Challenge 5: Fit for purpose and within budget

A tight budget meant design decisions were carefully considered to reduce the need for more expensive components.

With 90 sites and almost as many varying climates, it was never going to be affordable to make the devices run exclusively on lithium batteries, which cost 10 times the price of a comparable lead acid battery and need to be custom made for the device.

Most A2O sites have adequate sunlight, so 80% of them use the lead battery solution. However, the Solar BAR is made to run on both lead and lithium batteries if needed, freeing up options should lithium be required.

2000 years of data is just the beginning

With data now beginning to pour in after the first year of recording, it is clear that the Solar BARs have been deployed successfully.

New and innovative ways of monitoring wildlife have already been made possible thanks to the project. Hoot Detective, a citizen science initiative that asks the public to identify owl calls, had thousands of people actively listening to the data collected.

The Solar BAR, with its ability to continuously record, has opened up new possibilities in the bioacoustics field. Australian innovation has again captured the attention of the world, with scientists in the Americas and Europe keen to use these ultra-long deployment recorders for their own studies.

If you’re curious about using a Solar BAR in your own work, or would like to join the project, head over to the Frontier Labs website for more information.