Table 1.
Summary statistics for 68th and 95th percentiles of spatial errors (and their latitudinal and longitudinal components) associated with each Argos Location Class (LC) for Kalman-filtered Argos telemetry data, collected from bearded seals (N = 6) and ringed seals (N = 10) between 19th July 2011 and 18th April 2013 along the west coast of Svalbard.
Fig 1.
Raw Kalman filtered Argos tracks (black) and GPS tracks (red) for the focal A) bearded seal and B) ringed seal.
Dots highlight instrumentation site (blue) and the final location (yellow).
Fig 2.
Spatial errors of the best modelled Argos location estimates relative to the true (GPS) position for the focal A) bearded seal and B) ringed seal using three different location error correction methods.
* denotes use of the original error structure provided the most accurate modelled locations. Red dotted lines signify the 95% percentile of the empirical cumulative distribution function (right side axis) for each suite of errors. Generally, 95% of all errors were less than 4.2 km from the true position, with modelled locations being most accurate for the ringed seal.
Fig 3.
Optimal state-space modelled (SSM) Argos location data (black) overlaid with GPS locations (red) for the focal A) bearded seal and B) ringed seal.
* denotes optimal model was constructed using the error structures derived from data in [10]. Modelled location and GPS point estimates are shown as black and red dots, respectively. For each tripEstimation model, the underlying time-spent along the full path estimate is shown in purple (obscured in the bearded seal plot in favour of displaying point estimates). Black boxes highlight areas of departure by each model from the true path. Modelled location estimates for the bearded seal fitted well with GPS locations with the exception of two areas, at the very northerly edge of its trajectory, and just south of Prins Karls Forland. Note the sparse numbers of GPS location estimates for the ringed seal, particularly during transit movements between fjords. Although there were ~50% fewer Argos location estimates for the ringed seal, all models reconstructed some aspects of these transit movements despite showing a number of erroneous land locations. The exception was the tripEstimation modelled data, presumably due to the effects of incorporating a land mask during the modelling process.
Table 2.
Root Mean Square Error (RMSE) estimates (km) between modelled Argos locations and the true (GPS) position at varying sensitivities for three commonly-used location error correction models freely-available within the R statistical framework; crawl [14], bsam [17] and tripEstimation [31].