Bat detectors
Bats are special because they are so good at hiding.
Most bat species are small, they are active when it is dark and
they use ultrasound for navigation and communication.
Therefore, detectors are needed that can record ultrasound and can be used for
either active or passive monitoring.
There are good bat detectors available, but I wanted a more flexible and powerful
detector that can be extended in functionality when needed. My requirement list was
something like this when I started to develop my own detector:
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The software should be open and free for all kind of usage, even commercial use
if someone want to include parts of it in products that are sold for money.
-
Hardware should be as cheap as possible and easily available where they are
selling electronic things.
The core part should be a small computer that can run the operating
system Linux.
-
There must be support for high quality ultrasonic microphones for professional use,
but also a possibility to have entry level alternatives for beginners.
This resulted in a Do-It-Yourself, DIY, bat detector based on three main parts:
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Computer:
Raspberry Pi is a small computer that is powerful enough and has a
lot of features that makes it good to use for a bat detector.
The base price for it is 35$, but it will cost somewhere between 50 and 100$
depending on taxes and model.
-
Microphone:
Ultrasonic microphones with USB connections are supported.
The detector automatically identifies microphones from Pettersson and Dodotronic.
For entry level options there are sound cards available that runs at a sampling
rate of 192 kHz.
That will be enough for the most common bat species and sound up to about 90 kHz
can be recorded.
But then you have to find a suitable microphone element and build that part
yourself.
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Software:
This is the part that I develop myself. Mainly based on my own needs and
what I think is fun to develop.
The rest is probably things you already have. Power supply for the
Raspberry Pi computer is the same as the USB power sources used for mobile
phones.
The user interface for the detector is a web page that can run in a web
browser in your computer or mobile phone.
Recorded files can be stored on USB memory sticks, or internally in the
detector for later download to a computer.
Then there are extra options like
USB GPS receivers for time and position and
USB 4G modems for internet access.
There are two main things that makes other bat detector alternatives better.
One is power consumption and the Raspberry Pi needs up to 5 Watt of power
where many other detectors can run for weeks on standard batteries.
A slightly bigger Powerbank can be used for single night sessions and will
last for about 12 hours.
If power is available you can use a mobile phone charger and run it permanently.
The other problem is that you must know a little about computers and how to run
commands from a terminal window when installing the software.
If you don't have that knowledge you must ask for help, but I think that there
are many people who will be happy and found it interesting to set up a
Raspberry Pi for bat monitoring if you ask them.
The WURB detector
The WURB detector has been developed since 2017 and I have tried different
option for configuration and control.
In 2020 I started a complete redesign of the software and the version called
"CloudedBats_WURB_2020" is more or less like I want it to be.
There are users in a couple of countries and there are nearly no issues
reported that are related to reliability and stability.
For my personal use I have four of them for field work, and some more for
development and test.
The field work detectors are all equipped with Pettersson u384 microphones and
are configured like this:
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One WURB detector is for active monitoring. Audio feedback is activated and I
use a technique called pitch shifting for that.
It is like frequency division but the sound quality is not destroyed,
the frequencies are just divided by a factor between 10 and 50.
Recordings can be triggered either manually or automatically when sound is
detected.
If a GPS receiver is attached each file will have the correct position in the
file name that makes is useful for transect monitoring.
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Then I have two detectors with powerbanks for deployment over night.
The GPS receiver can be removed after deployment since the position will
not change. If they are within a WiFi network they can be controlled
remotely and recorded files can be download while they are running and
are recording new files. I also have some 4G modems that can be used at remote
places to set up communication tunnels (similar to VPN) for remote access and
file download from anywhere where internet is available.
This is really handy because the
detectors can then be controlled and checked that they was correctly setup,
and you don't have to wait to the day after to start analyzing the recorded
files.
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The last one is a permanent station at home where the WURB detector is
connected and powered by using Power-over-Ethernet, PoE. It is then open
to the internet and anyone can log in as a read-only user and download
files by using SFTP. It was deployed in may 2021 and except for some problems
with thunderstorms it has been running for about 7 months at the moment
(and there are bat activities even when there is snow and the temperature
is below zero degC).
There is a user manual for the WURB detector here:
CloudedBats-WURB-2020, User manual - basic usage
.
A more detailed description and installation instructions can be found in the
source code repository at GitHub:
CloudedBats-WURB-2020
.
The Pathfinder detector
Pathfinder is an experimental detector for active monitoring only. The plan is to
have stereo sound and also night vision by using infrared light.
The stereo part is already working and I'm working on the night vision part.
Maybe there will be a prototype available during 2022.
The AudioMoth detector
This is another kind of open source detectors developed by a team at
Open Acoustic Devices.
They use an interesting concept by also implementing open hardware.
The AudioMoth detector is a good complement to my style of bat detector,
they can be setup to run over longer time periods and the price tag is low.
That means if you need many detectors for a survey, or want to introduce
new people to bats, then AudioMoth definitely is an option.
My plan is to also support for sound files recorded by the AudioMoth detectors
when developing the post processing parts. There are some limitation when
recording files by using that kind of minimalistic/low power processor that
can easily be handled in a post processing step.
Read more about the AudioMoth project here:
OpenAcousticDevices - AudioMoth
