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Geolocation by light: accuracy and precision affected by environmental factors

Lisovski, Simeon; Hewson, Chris M.; Klaassen, Raymond LU ; Korner-Nievergelt, Fraenzi; Willemoes Kristensen, Mikkel LU and Hahn, Steffen (2012) In Methods in Ecology and Evolution 3(3). p.603-612
Abstract
1. Geolocation by light allows for tracking animal movements, based on measurements of light intensity over time by a data-logging device (geolocator). Recent developments of ultra-light devices (<2 g) broadened the range of target species and boosted the number of studies using geolocators. However, an inherent problem of geolocators is that any factor or process that changes the natural light intensity pattern also affects the positions calculated from these light patterns. Although the most important factors have been identified, estimation of their effect on the accuracy and precision of positions estimated has been lacking but is very important for the analyses and interpretation of geolocator data. 2. The threshold method is... (More)
1. Geolocation by light allows for tracking animal movements, based on measurements of light intensity over time by a data-logging device (geolocator). Recent developments of ultra-light devices (<2 g) broadened the range of target species and boosted the number of studies using geolocators. However, an inherent problem of geolocators is that any factor or process that changes the natural light intensity pattern also affects the positions calculated from these light patterns. Although the most important factors have been identified, estimation of their effect on the accuracy and precision of positions estimated has been lacking but is very important for the analyses and interpretation of geolocator data. 2. The threshold method is mainly used to derive positions by defining sunrise and sunset times from the light intensity pattern for each recorded day. This method requires calibration: a predefined sun elevation angle for estimating latitude by fitting the recorded day/night lengths to theoretical values across latitudes. Therewith, almost constant shading can be corrected for by finding the appropriate sun elevation angle. 3. Weather, topography and vegetation are the most important factors that influence light intensities. We demonstrated their effect on the measurement of day/night length, time of solar midnight/noon and the resulting position estimates using light measurements from stationary geolocators at known places and from geolocators mounted on birds. Furthermore, we investigated the influence of different calibration methods on the accuracy of the latitudinal positions. 4. All three environmental factors can influence the light intensity pattern significantly. Weather and an animals behaviour result in increased noise in positioning, whereas topography and vegetation result in systematic shading and biased positions. Calibration can significantly shift the estimated latitudes and potentially increase the accuracy, but detailed knowledge about the particular confounding factors and the behaviour of the studied animal is crucial for the choice of the most appropriate calibration method. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
animal movement, calibration methods, geolocation, migration, tracking
in
Methods in Ecology and Evolution
volume
3
issue
3
pages
603 - 612
publisher
British Ecology Society / John Wiley & Sons, Inc.
external identifiers
  • wos:000304902500019
  • scopus:84861233421
ISSN
2041-210X
DOI
10.1111/j.2041-210X.2012.00185.x
language
English
LU publication?
yes
id
af22a7ee-b781-4725-897b-ab83d98e923c (old id 2896961)
date added to LUP
2012-07-24 11:01:13
date last changed
2017-11-19 03:56:43
@article{af22a7ee-b781-4725-897b-ab83d98e923c,
  abstract     = {1. Geolocation by light allows for tracking animal movements, based on measurements of light intensity over time by a data-logging device (geolocator). Recent developments of ultra-light devices (&lt;2 g) broadened the range of target species and boosted the number of studies using geolocators. However, an inherent problem of geolocators is that any factor or process that changes the natural light intensity pattern also affects the positions calculated from these light patterns. Although the most important factors have been identified, estimation of their effect on the accuracy and precision of positions estimated has been lacking but is very important for the analyses and interpretation of geolocator data. 2. The threshold method is mainly used to derive positions by defining sunrise and sunset times from the light intensity pattern for each recorded day. This method requires calibration: a predefined sun elevation angle for estimating latitude by fitting the recorded day/night lengths to theoretical values across latitudes. Therewith, almost constant shading can be corrected for by finding the appropriate sun elevation angle. 3. Weather, topography and vegetation are the most important factors that influence light intensities. We demonstrated their effect on the measurement of day/night length, time of solar midnight/noon and the resulting position estimates using light measurements from stationary geolocators at known places and from geolocators mounted on birds. Furthermore, we investigated the influence of different calibration methods on the accuracy of the latitudinal positions. 4. All three environmental factors can influence the light intensity pattern significantly. Weather and an animals behaviour result in increased noise in positioning, whereas topography and vegetation result in systematic shading and biased positions. Calibration can significantly shift the estimated latitudes and potentially increase the accuracy, but detailed knowledge about the particular confounding factors and the behaviour of the studied animal is crucial for the choice of the most appropriate calibration method.},
  author       = {Lisovski, Simeon and Hewson, Chris M. and Klaassen, Raymond and Korner-Nievergelt, Fraenzi and Willemoes Kristensen, Mikkel and Hahn, Steffen},
  issn         = {2041-210X},
  keyword      = {animal movement,calibration methods,geolocation,migration,tracking},
  language     = {eng},
  number       = {3},
  pages        = {603--612},
  publisher    = {British Ecology Society / John Wiley & Sons, Inc.},
  series       = {Methods in Ecology and Evolution},
  title        = {Geolocation by light: accuracy and precision affected by environmental factors},
  url          = {http://dx.doi.org/10.1111/j.2041-210X.2012.00185.x},
  volume       = {3},
  year         = {2012},
}