Successful Creation of Regular Patterns in Variant Maps from Bat Echolocation
Calls
Heim DM
1
, Heim O
2,3
, Zeng PA
1,4
and Zheng J
1,4*
1
Key Laboratory of Yunnan Software Engineering, Yunnan University, Kunming, Yunnan 650091, China
2
Leibniz Institute for Zoo and Wildlife Research, D-10315 Berlin, Germany
3
Animal Ecology, Institute of Biochemistry and Biology, University of Potsdam, D-14469 Potsdam, Germany
4
School of Software, Yunnan University, Kunming, Yunnan, 650091, China
*
Corresponding author: Zheng J, Professor, Yunnan University, Information Security, China, Tel: +8613108839090; E-mail: conjugatelogic@yahoo.com
Received date: August 27, 2016; Accepted date: September 12, 2016; Published date: September 20, 2016
Copyright: © 2016 Heim DM, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and source are credited
Abstract
We report the creation of variant maps based on bat echolocation call recordings. The maps show regular
patterns while characteristic features change when bat call recording properties change. By focusing on specific
visual features, we found a set of projection parameters which allowed us to classify the variant maps into two
distinct groups. These results are promising indicators that variant maps can be used as basis for new echolocation
call classification algorithms.
Keywords: Echolocation; Algorithms; Morphometry; Fourier
analysis; Quaternions
Introduction
e identication of echolocation calls is essential to the research
and conservation of bat species [1]. However, automatic classication
algorithms have not yet been proven capable of providing 100% correct
classications or getting closes enough to this ideal performance [2].
Since our approach of using variant maps [3] shows already promising
results, we are condent it will continue adding valuable contributions
to the eld of automatic bat call identication.
Automated bat echolocation call identification algorithms were
developed since the late 1990s [4-7]. At that time, multivariate
discriminant function analysis or neural networks were used for the
classification of the calls. Since then, other methods have been applied,
e.g. algorithms of pattern recognition [8], support vector machines [9],
hierarchical ensembles of neural networks [9,10], geometric
morphometry [11], machine learning [12], CART [13] and random
forest classification [14]. For a critical analysis of the performance of
the applied methods we refer to Russo and Voigt [2] and the references
therein.
Using variant maps for the classification of bat echolocation calls
diers completely from these conventional techniques.
e main dierence is the pre-processing step, where the recordings
are transformed into variant maps. is step oers the possibility to
analyse the bat call recordings from a completely dierent point of
view. It provides additional degrees of freedom which allow a further
optimization of the identification process, e.g. by supplementing the
information obtained from a Fourier analysis of the bat calls.
Our method to transform the bat call recordings is based on
measures proposed by Zheng and Maeder [15] and Zheng [16] in the
1990s to partition special phase spaces in binary image analysis. ese
methods were extended in the 2010s [3,17] and successfully used to
classify quantum interactions [18,19], dierently encrypted messages
[20] and non-coding DNA [21-23].
Similar to these works, we transform the bat call recordings using
variant measures to obtain variant maps. Each recording contains
several calls of one bat species.
We used calls of four aerial-hawking
bat species in this study. Recordings were made on fields with three
different crop types far away from woody vegetation.
e
with each recording.
to extract usable
information from bat echolocation recordings created.
Transformation
e processed bat echolocation calls were recorded with a sampling
rate of 500 kHz and saved as “raw” 16 bit audio files. In the following,
we describe in four steps (A-D) how we transformed these files into
variant maps.
Step A: From analogue to digital audio
In a recording of data length N, the amplitude of the bat
echolocation calls is stored in N samples. Each sample corresponds to a
floating point number of 16 bits. For simplicity, we transformed the
floating point numbers to integer numbers of 16 bits.
Step B: From digital audio to quaternions
Next, we transform the integer sequence into a sequence of four
meta states {
┴
, +, −, } which resemble the quaternions {Bottom, Plus,
Minus, Top}. For this step we select the i-th sample A
i
and its next
neighbor A
i+1
and define the dierence ΔA=A
i+1
–A
i
and local average
L=(A
i
+A
i+1
)/2. Additionally we require the maximum A
max
and
minimum A
min
of the current sequence to define a middle value
V=(A
min
+A
max
)/2 and we define a tolerance T. Using these values we
transform the integer sequence A
1
...A
N
into a sequence of quaternions
B
1
...B
N
by using the rules:
if ∆A<T and L>V: B
i
=
Biological Systems: Open Access
Heim et al., Biol Syst Open Access 2016, 5:2
DOI: 10.4172/2329-6577.1000166
Review Article OMICS International
Biol Syst Open Access, an open access journal
ISSN:2329-6577
Volume 5 • Issue 2 • 1000166
┴
┴
created
maps have a regular structure, but characteristic features vary strongly
ese
results show that variant maps can be used