Correction of elevation-induced errors in locations of the ARGOS satellite-tracking system

Satellite tracking is an effective way to track moving objects over long distances, and has recently been used to show the migration routes and ecology of birds. Satellite tracking data has been useful for conservation of several bird species, and therefore accurate location data are required for such work. The ARGOS satellite-tracking system requires that the elevation of a platform transmitter terminal (PTT) be estimated before a location is calculated. Extreme errors can occur if the estimated elevation is incorrect. The authors have developed two correction methods for elevation induced errors that use the estimated locations on the assumption of zero-meter elevation. First, they attached an atmospheric pressure sensor to the PTT. The true elevation of the PTT can be calculated from the atmospheric pressure data transmitted via the satellite of the ARGOS system. The elevation-induced errors can be corrected by the geometrical calculations using the data of the estimated location, spurious location, assumed elevation (0 m) and true elevation. Second, they use a global digital elevation model (DEM) GTOPO30 with a horizontal grid spacing of 30 are seconds that is offered by USGS (U. S. Geological Survey). The elevation of PTT is estimated at the location reported from the ARGOS system by use of DEM. The elevation-induced errors are reduced by the same calculation as the first method. Next, the elevation of PTT is estimated at the corrected location. Iterating these calculations, the true elevation and location can be calculated.