COMPARING DUNE HEIGHT MEASUREMENT METHODOLOGIES TOTAL STATION VERSUS DGPS

Transporting traditional surveying equipment such as a total station, can be strenuous for monitoring vertical growth of dunes at Great Sand Dunes National Park and Preserve. For years this method has been used to monitor vertical movement of the popular dunes in the park, some requiring the completion of a six mile hike with a 40-lb total station pack. This research compares the use of a lighter, more portable handheld Trimble GeoXH dGPS to a Nikon DTM-520 Total Station in measuring the vertical height of large dunes. Mapping grade dGPS units are known for their submeter horizontal accuracy, but lack the same dependability with measuring absolute vertical accuracy. The relative elevations they measure however, may be useful for measuring dune heights in the park. To further understand the relative vertical accuracy of the dGPS before assessing dunes, a series of measurements were used to monitor elevation drift in a fixed position over one hour in both cloudy and clear conditions. Results varied greatly based on atmospheric conditions, giving way to a better understanding of dGPS vertical accuracy in diverse weather situations. Following the fixed elevation tests, a multitude of dune heights were evaluated by collecting elevation data along the crests and bases using both the Nikon Total Station and Trimble dGPS. At the same site in which the total station’s reflective rod was used to measure elevation, the dGPS was also employed to collect approximately 10 generic points to record elevation as well. The manual elevation measurements from base to crest taken with the total station and dGPS were further analyzed using GIS software and Lidar DEM Models. It was conclusive after taking the difference of the values recorded by the total station and dGPS that 10 out of the 11 dGPS measurements recorded were within one meter of the total station measurements despite variances in weather. Thus, the use of a handheld dGPS unit may be a sufficient and more portable option for measuring and tracking vertical dune migration at Great Sand Dunes National Park and Preserve.