Effects of habitat feature, antenna position, movement, and fix interval on GPS radio collar performance in Mount Fuji, central Japan

Abstract

The location performance of a global positioning system (GPS) collar was assessed for different habitats and geographical areas. We tested the effects of habitat features, antenna position, movement, and fix interval on location performance around Mount Fuji, a single peak surrounded by wide and flat areas. Fix rate decreased from 100% in open flat areas to 53% under sloped dense canopy. The openness (the actual available sky, i.e., the percentage of a radio collar exposed to the sky when part of the collar is blocked due to terrain and vegetation) and canopy closure affected location accuracy and most other performance parameters. All nine habitat features except for available sky (theoretical, due to terrain) influenced location time. Any combination of obstructions between collar and satellite decreased the available number of satellites, the fix rate, increased the location time, and resulted in poorer location (higher DOP, lower 3-D proportion, or greater location error). A horizontal antenna yielded poorer location performance than a vertical one in the forest but not in the open area.Location performance always decreased when moving in forest rather than in open areas. Location performance changed with fix interval. Sixty-minute intervals resulted in a longer location time and a lower DOP than 10-min intervals. Vegetation affected location performance more than topography in the Mount Fuji area. Factors that cause a longer location time will shorten battery life. We suggest that location frequency and duration employed for field research should be decided by considering the aim of the study and the effects of habitat features, animal activity, and fix interval on GPS performance and battery longevity. The strengthened effect of canopy closure during windy weather should be considered for forest-dwelling animals.

Resolving issues of imprecise and habitat-biased locations in ecological analyses using GPS telemetry data

“…Excluding canopy effects, terrain complexity alone may result in an 8 per cent or less reduction in fix rates and 10-13 m measurement error on average (D'Eon et al 2002;Cain et al 2005). Collar orientation alone tends to have a negligible effect on GPS errors in open areas, but can reduce fix rates up to 80 per cent and location precision as much as 17 m under dense canopy cover (Heard et al 2008;Jiang et al 2008). Cain et al (2005) observed that reducing the frequency with which locations were collected, from every 15 -30 min to every 6-13 h, reduced fix rates up to 8 per cent without affecting location precision.…”

“…An interaction between movement and forest cover was observed by Jiang et al (2008) using devices affixed to a vehicle moving approximately 10 kph. Jiang et al (2008) documented reductions in both fix rates and the proportion of fixes in a three-dimensional mode when moving through forest but not through open areas.…”

Home range sizes and space use of African elephants (Loxodonta africana) in the Southern Kenya and Northern Tanzania borderland landscape

“…Dataset that had GPS errors like missing coordinates were removed from the dataset before analysis. The causes of GPS errors are: Temporal malfunction of the GPS collars (Gala, 2014), canopy cover (Jiang et al, 2008;Sager-Fradkin et al, 2007;Heard et al, 2008), topography (terrain and slope; Hebblewhite et al, 2007;Frair et al, 2004) and collar orientation (Sager-Fradkin et al, 2007;Heard et al, 2008;Moen et al, 1996;Frair et al, 2010). The data available for analysis after screening ranged between 58 and 92% (Table 2), which is within acceptable range to characterize wildlife movement patterns and make sound inference (Frair et al, 2010).…”

Screening GPS telemetry data for locations having unacceptable error

“…These problems are caused by variations in canopy closure across a landscape, by rugged topography, by changes in collar orientation with respect to GPS satellites, by fix interval, and by behavior of collared animals (Belant, 2009;Cain et al, 2005;D'Eon and Delparte, 2005;D'Eon et al, 2002;Jiang et al, 2008;Lewis et al, 2007;Mattisson et al, 2010). Missed fixes pose major problems but one can identify them from the null, default, or illogical values representing them in the data.…”