Terrain mapping by reflectorless laser rangefinding systems for inner zone gravity terrain corrections

Abstract

Reflectorless laser rangefmding technology has the ability to generate reflections from many types of materials and angles of incidence without a comer reflector . These laser “guns” have built in inclinometers and compasses which when combined with the laser for distance measurements result in three dimensional mapping, a hand held total station. Although the angle and distance resolution is much poorer than that for total stations, for short (hundred meters) distances the mapping is more than adequate for terrain mapping for gravity terrain corrections. The nearby terrain model is usually estimated visually perhaps with an inclinometer and an optical rangefmder at best, but not digitally and with poor repeatability. The inaccuracy of present inner terrain correction methods can be detrimental to many surveys, and especially for microGal surveys. The combination of digital gravity meters, Global Positioning System locations and the laser gun terrain models result in a totally digital, quantitative gravity surveying system with greater ultimate accuracy. Field procedures and custom software have been developed and combined with a Laser Atlanta Optics Advantage rangefmder for gravity terrain corrections. Examples of surveys in the Dallas, Texas area, in canyons near Sodaville, Nevada, and at an operating mine in northern Nevada are presented. The terrain corrections from laser mapping when compared to corrections from 1:24,000 forty meter USGS and high resolution photogrammetric DTM models, show significant differences. The results demonstrate that the reflectorless laser rangefmder with inclinometer and compass can provide digital, quantitative terrain models for better terrain correction accuracy more efficiently and economically than previously possible and that real time gravity surveying is possible.