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DRAFT – subject to revision
APPENDIX X. LABORATORY TEST OF BAT DETECTORS AND BAT DATALOGGERS’ ABILITY TO CAPTURE
ULTRASOINC SIGNALS
I. INTRODUCTION
During the evaluation of the data generated from the winter deployment, it became obvious that the
different devices did not record ultrasonic signals equally. Even a casual examination of a minute-byminute comparison of the number of files generated (and the number of calls recorded) reveals wide
discrepancies, not only between detectors and data loggers, but also between the detectors themselves.
We conducted a review of the literature relative to comparisons of bat detectors signal detecting ability
and discovered that this has been reported by others. Several investigators of the earlier bat detector
models reported that detectors had different sensitivities that can lead to differences in signal detection
cone, angular range of detection, and maximum detection distances (Downes 1982; Forbes and
Newhook 1990; Waters and Walsh 1994).
More recent evaluations of newer models of bat detectors are provided by Solick et al (2011) and Adams
et al (2012). Solick et al (2011) performed a side-by-side comparison of selected bat detectors (AnaBat’s
SD1, Wildlife Acoustics’ SM2, Pettersson’s D500x, and Binary Acoustics AR125) that confirmed different
devices generate different bat activity rates due to the differences in the devices’ microphone quality,
sensitivity settings, and information processing strategy.
Adams et al (2012) compared the detection of echolocation calls (both synthetic and free-flying bats)
among five commonly used bat detectors (AnaBat SD2, Avisoft UltraSound Gate, Batcorder 2, Batlogger,
and Wildlife Acoustic’s SM2BAT). In general, signal detection was most affected by the frequency
dominating the signal and the distance from the source. The effect of angle was less apparent.
Given the discrepancy we observed in the signal detecting ability among devices used in our field
deployments, we decided to verify this phenomenon by testing the signal detecting abilities of the
detectors and data loggers under laboratory (controlled) conditions.
II. OBJECTIVE
The intent of this study was to document the ultrasonic signal detecting abilities of the devices
evaluated in this study under controlled conditions through the use of known ultrasonic frequencies, at
known amplitudes, and at various angles to the microphone. The devices tested were: SM2Bat+ bat
detector, D500x bat detector, AnaBat Roost Logger, and the Bat Logger II. (See the main report for a
description of these devices.)
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III. MATERIALS & METHODS
Dave Plummer (Electronics Technician) and Ted Etter (Electronics Engineer) performed the laboratory
test (discussed below) at the Missoula Technology & Development Center.
In order to test each device under identical conditions we created a circuit and software for generating
and controlling ultrasound signals. In the remainder of this report, we refer to this equipment as the
Ultrasonic Signal Source Equipment (Fig. 1 and 2). The frequencies that we used in the test ranged from
approximately 25kHz to 80kHz in 5kHz increments.
The materials used in perform the laboratory test are discussed in section III.A; the method used to test
the devices is presented in section III.B.
A. Materials
Ultrasonic Signal Source Equipment
For the transducer of the Ultrasonic Signal Source, we chose the SensComp’s Series 600 model.
Characterizing its output amplitude over the range of frequencies being generated was the first task.
This was done so that similar signal amplitudes could be produced over a range of frequencies. The
transducer was biased with 200VDC and signals of specific frequencies and amplitudes were capacitively
introduced from a function generator (BK Precision 4070A). The ultrasonic signal was received on
another Series 600 transducer also biased at 200VDC. Both the introduced signal from the function
generator and the received signal were observed with an oscilloscope (Tektronix MSO 3014) (Fig. 2).
The separation between the transducers for this test was 24 inches. The resulting frequency response
curve compared well with that provided by the manufacturer. Based on that data, we determined gains
for specific frequencies that would result in nearly equal output amplitudes for all of the frequencies.
Fig. 1. Illustration of the components involved in the Detector/Logger test.
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Fig. 2. Circuit board for the Ultrasonic Signal Source
(top). Function generator and oscilloscope used to
generate and view ultrasonic signals of specific
frequencies and amplitudes (bottom).
Controller Circuit description
The Ultrasonic Signal Source Equipment’s controller circuit is centered on a Microchip PIC18F2523. This
microcontroller’s main functions are to: 1) create pulses by controlling the signal from the function
generator, 2) enable the appropriate amplitude gain of the signal at each frequency, 3) provide DC
voltage to control the frequency output of the function generator. These functions allow the
microcontroller to set the duration, amplitude, and frequency of an ultrasound signal. Sequences of ten
pulses at each of the 12 frequencies (i.e., 25, 30, 35 … 80 kHz) are generated by software.
Once the 25kHz to 80kHz sine wave signal from the function generator is brought onto the circuit board
it must pass through a switch, controlled by the microcontroller, before passing through an amplifier
and out to the transducer. To set the duration of each pulse an analog switch is software controlled to
gate the function generator’s output through to the remainder of the signal’s circuit path. Pulses of
ultrasound frequency sine waves, and periods of no signal, are controlled by the software.
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After passing through the switch the ultrasound signal’s amplitude is adjusted by an operational
amplifier before it goes out to the transducer (Fig. 3). The microcontroller uses a multiplexer to set the
gain of the amplifier by switching in different values of feedback resistors, depending upon the
frequency being generated. The switch, amplifier, and multiplexer are sourced with plus and minus
15VDC, from a CUI Inc PYB30-Q24-T515-U power supply, to drive the transducer.
Fig. 3. Transducer – front (left) and back (right).
The microcontroller has built in pulse-width modulation (PWM) modules, one of which is used to control
the frequency output of the function generator, which has a voltage controlled frequency sweep
capability. A control signal of zero to five volts was used to sweep the output of the function generator
from ~25kHz to ~80kHz. The signal-averaged duty cycle of the PWM signal determines the output
frequency of the function generator.
A 12V 80Ah AGM battery was used to power the circuitry. The 200VDC bias voltage for the transducer
was generated using a pre-existing circuit designed for another project.
To allow for the duration of pulses and the time between them to be changed, we incorporated a series
of switches. A pushbutton tied to one of the microcontroller’s inputs was used to start the sequence of
pulses
Software Flow Description
The software program that operates the Ultrasonic Signal Source Equipment cycles in an idle loop,
flashing an LED to indicate the microcontroller’s operation, until the pushbutton start switch is closed.
While the program is producing ultrasound signals the LED does not flash.
Once the start switch has closed, the software scans the switch setting that sets the pulse width and
time between pulses. Throughout the test the duration of the pulses was set at 16mS and the time
between pulses was 50mS.
The microcontroller outputs a PWM signal which causes the function generator to produce a 25kHz sine
wave. The gain of the operational amplifier is then set by the microcontroller using outputs to the
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multiplexer. After a two second pause the microcontroller allows ten pulses to pass from the function
generator, through the analog switch and the operational amplifier, to the ultrasound transducer. After
another two second pause, a half second long pulse at the same frequency is output, and then a one
second pause (Fig. 4). The purpose for this long pulse was to behave as a separator between pulse
sequences of different frequencies.
The processes (described above) then repeats, with the only differences being that the PWM signal
changes to cause the function generator to increase its frequency output by approximately 5kHz, and
the gain will change to maintain a relatively constant transducer output amplitude for the new
frequency.
The software continues to produce ten 16mS pulses and a half second pulse, at each 5kHz step
frequency, until stopping after producing output at 80kHz. The software then returns to an idle loop,
flashing the LED and scanning for a pushbutton closure.
Frequency Sensitivity Test Timeline
Start Button
10 Pulses @ 30kHz
10 Pulses @ 25kHz
30kHz Tone
25kHz Tone
2S
2S .5S
3S
2S .5S
10 Pulses @ 35kHz
10 Pulses @ 80kHz
80kHz Tone
3S
2S .5S
Time Axis
Fig. 4. Timeline of events of one test at a given amplitude.
We changed the microcontroller’s software for the testing of the Bat Logger II. We used the switches to
direct the code to the proper subroutine for the single frequency being tested. The pulse and interval
durations were set in code, and were maintained at 16mS and 50mS respectively.
Device Configuration
The devices were configured as follows:
SM2Bat+: Sample Rate= 384000; Channels- Mono-L; File Format- WAC0; Gain left- +0.0 dB; Gain
right- +0.0 dB. Schedule (advanced): Time set to just before midnight prior to each test, then
test initiated after device indicated it was recording.
D500x: f=500; PRE=OFF; LEN=1.0; Input Gain=45; Trig Lev=80; Interval=0.
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AnaBat Roost Logger: Set to sample continuously; battery capacity entered as 1300AH.
Bat Logger II: Sensitivity potentiometer in middle position. Data logger scaling: 0.0119 = 0.0;
0.35897 = 15.0.
Laboratory Environment
We conducted the lab test in the photography studio at the Forest Service’s Missoula Technology and
Development Center. The studio has foam acoustic panels on much of its wall surfaces. In order to
further isolate the devices being tested, we placed the devices in a four sided (three sides and a ceiling)
interview booth lined with acoustic foam panels. The device under test (DUT) was placed on a stand in
front of the rear wall of the booth. We placed the ultrasonic signal source at the same elevation as, and
four and a half feet in front of, the DUT (Fig 5).
The ultrasound signal control circuitry, instruments, power supplies, computer, and technician were
located on the other side of one of the walls of the interview booth. Approximately five feet of long
twisted pair wires made the connections for the transducer’s power, drive signal, and their returns.
B. Methods
Test of the devices’ ultrasonic signal detecting ability
With the exception of the Bat Logger II, we tested all the devices in the same manner. We placed a
single device in the booth directly facing the transducer (zero degrees orientation), powered up ready to
record (Fig. 5). Since the SM2Bat+ and D500x both have external microphones, they were aligned on
their long axis (i.e., microphone in front/handle behind) for this orientation.
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Fig. 5. Lab setup for testing of ultrasonic sensitivity of the device.
We set the output of the function generator for 2 Volts peak-to-peak (Vpp). This was used to generate
the highest amplitude ultrasonic signals. The start pushbutton on the ultrasound signal controller was
used to initiate a subroutine in the program on the microcontroller. The circuitry then generated ten
pulses at 25kHz followed by a half second continuous tone of the same frequency. After a pause the
same was done at 30khz, then 35 kHz, and so on until 80kHz, at which point the software exits the
subroutine and goes into an idle loop. This constituted one test segment, and the DUT was accessed,
the file(s) downloaded and stored to a directory (e.g. P_2Vpp_0deg). (Note: Only one test segment was
run for each device.)
To generate the next amplitude, we set the output of the function generator to 600mVpp and another
test segment was run, then the same was done for 200mVpp. We then rotated the DUT 45 degrees to
one side and another three segment runs were conducted. (For the devices with external microphones,
the microphones were rotated.) Then the DUT was rotated another 45 degrees, thereby positioning it 90
degrees to the signal source, and another three segment runs conclude the testing for a given device.
This resulted in nine test segment runs for each device. (See Table 1 for an example of how test were
performed.)
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Table 1. Method used to test devices’ ultrasonic signal detecting ability (sensitivity) at various
frequencies and wave amplitudes (intensities). Ten ultrasonic signals of known
frequency and intensity were pulsed to all devices at various angles of incidences. The
number of signals (pulses) that the tested device actually detected was verified.
Transducer at a 0o angle* from Device A**.
Signal intensity:
Voltage used to generate wave amplitude
(Volts peak-to-peak)
Ultrasonic
High
Medium
Low
Frequency
Amplitude
Amplitude
Amplitude
(kHZ)
(2 Vpp)
(0.6 Vpp)
(0.2 Vpp)
25
10 pulses
10 pulses
10 pulses
30
10 pulses
10 pulses
10 pulses
35
10 pulses
10 pulses
10 pulses
↓
↓
↓
↓
80
10 pulses
10 pulses
10 pulses
*Angles of incidences were 0, 45, and 90 degrees.
**All 4 devices were tested.
We suspended the external microphones for the SM2Bat+ and the D550x in a rubber band ‘cradle’ in
order to isolate them from interference. (Also, it should be noted that the SM2bat+ was the only device
that had an omnidirectional microphone.)
The Bat Logger II counts ultrasound events and outputs a voltage based on that count to an Onset HOBO
data logger. That voltage is scaled to an Activity Level number representing the number of events
recorded. (See a more detailed discussion of the Bat Logger II in the main report [section XXXX]) The
three other devices are able to represent the frequencies recorded, but the Bat Logger II does not. In
order to determine its sensitivity at different frequencies the software on the Ultrasound Signal Source
Equipment’s signal controller was modified to output ten pulses at a given frequency based on switch
settings.
The Bat Logger II was powered up, then using Onset HOBOware Pro software the integrated data logger
was launched with a 10 second sampling interval. Promptly after launch, the Ultrasound Signal Source
Equipment’s program was initiated, generating 10 pulses at 25kHz after a five second pause. The data
logger (of the Bat Logger II) was then downloaded when more than 10 seconds had passed since
launching, ensuring that the count acquired by the Bat Logger II had been sampled by its data logger
(Fig. 6).
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Bat Logger II Frequency Sensitivity Test Timeline
Bat Logger II Power Up
HOBO Launch
Ultrasound Signal Source Equipment Start
10 Pulses at Freq. X
HOBO Sample
HOBO Readout
5 Seconds
10 Seconds
Time Axis
Fig. 6. Timeline of events during test of Bat Logger II at one frequency.
After a change in switch settings on the controller circuit, the logger was then launched again, testing
the Bat Logger II’s ability to log pulses at 30kHz. This was repeated at 5kHz intervals up to 80kHz. The
same intensity and orientation changes were made as had been done with the other devices. This
resulted in 108 files.
We manually reviewed the WAVE files of the SM2Bat+ and D500x devices using Cornell University’s Lab
of Ornithology sound analysis software, Raven Lite 1.0. We reviewed the AnaBat Roost Logger files on
AnalookW software. The Bat Logger II device is designed to use Onset’s HOBOware Pro software for
reporting ultrasonic activity.
We recorded (counted) the number of pulses (as observed on the sound analysis software) at each
frequency, intensity, and orientation.
IV. RESULTS
The results of the laboratory test of the signal detecting ability of the devices are summarized below.
More detailed data and graphs are presented at the end of the Appendix.
Bat Detectors
The graphs presented Figure 1 show how the two bat detectors were able to record/log signals pulsed
over the range of frequencies (i.e., 25, 30, 35 … 80 kHz), at different ultrasound intensities (i.e., high,
medium, and low), and at different orientations (angle of incidences between the device and the signal
source).
At high signal intensities, the omnidirectional microphone of the SM2Bat+ detected signals in all
directions (except the 80 kHz signals delivered at a 90o angle).
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The D500x has a directional microphone and detected high intensity signals at 0o and 45o, but detected
no signals delivered at right angles. Also, the D500x consistently missed the first 3 of the 10 signals
delivered, regardless of angle or intensity.
Neither detector performed well at capturing low intensity signals (200mVpp). Neither detector picked
up any low intensity signals delivered at 90o. The D500x detected no low intensity signals emitted at
45o.
Signals of medium intensity yielded intermediate detecting abilities from both detectors.
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SM2Bat+ (by Wildlife Acoustics)
D500x (by Pettersson Elektronik)
Fig. 1. Signal detecting ability of the 2 bat detectors (left: SM2Bat+; right: D500x) of
signals with varying: frequencies, angles of incidences, and intensities. (More graphs and
data of the lab results are provided at the end of this Appendix.)
Bat Data Loggers
As discussed in the main report (see section <<XXX>>), the Bat Logger II device records activity in
“levels” or “steps”. Since we delivered 10 pulses to the device, the Bat Logger II should have been able
to detect (and log) signals at either the 3rd step (5-10 pulses) or 4th step (10-20 pulses).
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Figure 2 shows the results of the two data loggers’ signal detecting abilities. The data loggers were able
to detected many high intensity frequencies when the device and transducer were in direct alignment
(i.e., 0o angle of incidence). Increasing the angle of incidence or decreasing the signals’ intensity
dramatically lessens both data loggers’ signal detection. This results in almost all low intensity signals
going undetected, especially if the signals were at an angle to the device.
AnaBat Roost Logger (by Titley Scientific)
Bat Logger II (by Messina)
Fig. 2. Signal detecting ability of the 2 bat data loggers (left: Roost Logger; right: Bat
Logger II) of signals with varying: frequencies, angles of incidences, and intensities.
(More graphs and data of the results are provided at the end of this Appendix.)
Detectors verses Data Loggers
Figure 3 shows how all of the devices compared against one another. A top down viewing of the matrix
highlights how the devices’ signal detecting abilities compare relative to the intensity of the signals. A
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horizontal view (i.e., across) focuses on the devices’ differing detecting abilities due to the angle of
incidence.
Low Intensity Signals
(200 mVpp)
Angle of Incidence (0o/ 45o/ 90o)
High Intensity Signals
(2 Vpp)
Signal Intensity (High/Medium/Low)
Medium Intensity Signals
(600mVpp)
Fig. 3. Comparison of all devices showing frequencies detected at various intensities (top down view) and
different angle of incidences (across view). SM2 = SM2Bat+; RL1 = Anabat Roost Logger; BL II = Bat Logger
II.
V. DISCUSSION/CONCLUSION
Discussion
As mentioned in the Introduction (section I), we observed that the number of files that each device
generated (during the winter 2013 deployment) were markedly different. To further investigate this we
performed this laboratory test to document the devices’ signal detecting abilities by delivering synthetic,
known ultrasonic frequencies to the devices at varying angle of incidences and intensities. For this
laboratory test, we used the same settings that the devices had during the field deployment.
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The two detectors showed distinct differences in their ability to capture the ultrasound signals directed
at them (Fig. 1). In large part this is likely due to differences in microphone type and differences in
device configuration.
A notable observation regarding the D500X was that it consistently recorded only the trailing seven
pulses, completely missing the initial three. Based upon the settings used each detector showed that at
the highest intensity sound level, and when aligned (i.e., zero degrees) to the sound source, both were
able to record all frequencies tested. At moderate signal intensities (600mVpp), the D500x recorded at
all frequencies, whereas the SM2Bat+ stopped recording frequencies higher than 65kHz. The SM2Bat+’s
omnidirectional microphone clearly shows an advantage at off axis recording. The D500X showed that
off axis and at middle intensity level it would record lower frequencies. Throughout the test, of the two
detectors tested, the SM2Bat+ showed the best ability to record a broad range of frequencies.
Both detectors only sparsely detected low intensity signals. It is noteworthy that neither detector
captured low intensity signals that were at right angles of the device.
The two data loggers tested also showed obvious differences (Fig. 2). The AnaBat Roost Logger logged
all high intensity frequencies (except 25kHz) when aligned (0o angle) to the device. At medium and
lower intensities and off axis its range of frequencies narrowed and centered around 40kHz. The Bat
Logger II microphone apparently has resonance issues around both 30kHz and 50kHz, since no pulses
were logged at these frequencies. Although no pulses higher than 60kHz were logged, it did show
reception of a broader range of frequencies than the AnaBat Roost Logger at lower intensities and off
axis.
Conclusion
Based on these data, it is clear that in the field each device will have different results based on call
intensity and orientation of the microphone relative to the bat. The obvious implication of the data is
that different bat detector brands should not be expected to perform similarly and bat data loggers do
not mimic bat detectors. As such, any detector or data logger based surveys must make an effort to
standardize the brand of the device used. Switching devices and/or using non-standardized equipment
(especially in a large scale sampling effort) will likely result in widely differing results of bat activity.
(Also see conclusions in Waters and Walsh 1994:219.)
This laboratory study illustrates that the different devices have strengths and weakness that the
individual user must carefully consider in order to use these tools for gathering reliable, valid bat activity
data.
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VI. LITERATURE CITED
Adams, A.M., M.K. Jantzen, R.M. Hamilton, and M.B. Fenton. 2012. Do you hear what I hear?
Implications of detector selection for acoustic monitoring of bats. Methods in Ecol. & Evol.
3:992-998.
Downes, C.M. 1982. A comparison of sensitivities of three bat detectors. J. Mammal. 62: 343-345.
Forbes, B. and W. M. Newhook. 1990. A comparison of the performances of three models of bat
detectors. Jour. Mammal. 71:108–110
Solick, D., C. Nations., and J. Gruver. 2011. Activity rates and call quality by different bat detectors.
Western EcoSystems Technology (WEST), Inc. Power Point presentation made at the 41st
Annual Symposium of the North American Society for Bat Research (NASBR), Toronto, Ontario.
26-29 October 2011. Presentation obtained from Solick (dsolick@west-inc.com) in Sept. 2013.
Waters, D. A. and A. L. Walsh. 1994. The influence of bat detector brand on the quantitative estimation
of bat activity. Bioacoustics 5:205–221.
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SUMMARY OF DATA
CHARTS & TABLES
OF
LABRATORY TEST OF BAT DETECTORS AND BAT DATALOGGERS’
ABILITY TO CAPTURE ULTRASOINC SIGNALS
See  Lab Test – Charts & Tables
Appendix X, page 16
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