AN EVALUATION OF INEXPENSIVE HANDHELD GLOBAL POSITIONING SYSTEMS FOR POSITION AND VELOCITY ESTIMATES

摘要

Inexpensive handheld Global Positioning Systems (GPSs) provide researchers with opportunities to acquire position and velocity measurements for Lagrangian movements. The reduction in cost (O($100)), size (～cell phone), and weight (O(70 g)) of handheld systems have the cost of decreased accuracy. Two different handheld GPSs and three different position-correcting techniques are evaluated to determine their practicality in field applications. The handheld GPSs are placed on a metal plate to prevent multi-pathing, which is the main source of position error caused by reflected satellite signals in calculating position. Assuming the stationary position and velocity estimates represent the corresponding GPS errors, a stationary evaluation of each handheld GPS and position-correcting technique was performed, resulting in position errors on the order of 2 m and velocity errors on the order of 0.5 m/s. Performing a spectral analysis on the position and velocity errors provides the lower limit of velocities (0(3 m/s)) that can be estimated with confidence for frequencies ＜ 0.05 Hz using any of the techniques. One technique, a more costly (O($ 14000) for base station and third-party post-processing software) method, is shown to be capable of generating highly accurate position (errors of 0(0.10 m)) and velocity measurements (errors of O(1 cm/s)). The feasibility of this method for a nearshore drifter deployment is described with drifter velocities correlating to in situ velocities within the error of the instrument for the alongshore (0.02 m/s).