SNAKE RIVER, WYOMING, CROSSING WITH THE LEICA NA-3000 DIGITAL LEVEL

Abstract

A Leica NA-3000 digital level was used to carry a line of precise levelling across the Snake River where it courses a 40 m deep gorge in Grand Teton National Park, Wyoming. Two semi-permanent turning points were established 80 m apart across the river, a shaded instrument was set within 12 cm of the mid-point on a gravel bar in the river, and the height difference between the two turning points was measured 25 times in double-run mode. The standard deviation of a homogeneous set of 25 readings is ±0.10 mm. The standard deviation of all 52 readings is ±0.14 mm. Both results are acceptable in a 30 km-long levelling line otherwise surveyed to First Order, Second Class standards to monitor tectonic displacement across the Teton fault.