Field test of two single-frequency GPS receivers

The U.S. Geological Survey's Cascades Volcano Observatory (CVO) has been testing low-cost, low-power Global Positioning System (GPS) receivers for use in the monitoring of restless volcanoes. Field tests of two single-frequency (L1 only) receivers, the Ashtech SCA-12S and the Leica SR261 show that these units can measure positions precisely enough to meet our monitoring needs. For line lengths up to 10 kilometers, I have found repeatibilities to be less than a centimeter for horizontal coordinates. Hourly data using broadcast orbits was processed using manufacturer and Bernese software. Repeatibilities were similar for both data sets.