Appropriateness of the linear correction method for GPS positional fixes in wildlife studies

This paper describes the results of tests performed to evaluate linear corr ection of GPS measurements as an alternative to differential correction of GPS positional fixes. Differential correction requires information which is not provided by the existing animal-borne GPS systems for smaller mammals. Therefore, linear correction, by means of a second GPS rover, has been sug gested as an alternative to differential correction. To test the accuracy o f linearly corrected measurements, we compared the position estimates of ra w, linearly corrected and differentially corrected GPS positional fixes wit h the true (known) geodetic position. The tests indicate that the accuracy of linear correction is highly unstable and is related to differences in th e satellite constellation used by the GPS receivers. Linear correction is c onsequently strongly discouraged. If differential correction is not possibl e, we recommend the use of raw GPS measurements, of which the error is well known and more predictable.