Differential Global Positioning System dGPS Research Articles

Accuracy Assessment of Open Source Digital Elevation Models

Digital Elevation Model is a three-dimensional representation of the earth's surface, which is essential for Geoscience and hydrological implementations. DEM can be created utilizing Photogrammetry techniques, radar interferometry, laser scanning and land surveying. There are some world agencies provide open source digital elevation models which are freely available for all users, such as the National Aeronautics and Space Administration (NASA), Japan Aerospace Exploration Agency’s (JAXA) and others. ALOS, SRTM and ASTER are satellite based DEMs which are open source products. The technologies that are used for obtaining raw data and the methods used for its processing and on the other hand the characteristics of natural land and land cover type, these and other factors are the cause of implied errors produced in the digital elevation model which can't be avoided. In this paper, ground control points observed by the differential global positioning system DGPS were used to compare the validation and performance of different satellite based digital elevation models. For validation, standard statistical tests were applied such as Mean Error (ME) and Root Mean Square Error (RMSE) which showed ALOS DEM had ME and RMSE are -1.262m and 1.988m, while SRTM DEM had ME of -0.782m with RMSE of 2.276m and ASTER DEM had 4.437m and 6.241m, respectively. These outcomes can be very helpful for analysts utilizing such models in different areas of work.

Structure from motion will revolutionize analyses of tidal wetland landscapes

Ecosystem services of tidal wetlands depend upon hydrology and vegetation, which in turn vary with elevation differences on the order of centimeters. Variability on such a fine scale is not captured in digital elevation models prepared from conventionally acquired LiDAR data products that generally have a spatial resolution of 0.5–1.0m and vertical uncertainties up to 15cm. Until recently, capturing critical fine scale features required laborious, hands-on field surveys that took days to collect data and time limitations usually required surveys to be restricted to selected areas of a wetland. Using Structure-from-motion (SfM) photogrammetry and a small unmanned aerial vehicle, precise three-dimensional point clouds, digital surface models (DSM) and color orthomosaics were produced for three salt marshes in Eastern Canada. Vertical and horizontal measurements from the SfM photogrammetry compared favorably to those taken with a Differential Global Positioning System DGPS). Average horizontal displacements of 1.0–2.9cm were found across the three salt marshes with an average elevation difference of 2.7cm (±1.7cm) in comparison to DGPS. Analysis of the relationship of elevation between points taken with the DGPS and extracted from the SfM DSM gave an R2 of 0.99. With a ground sampling distance of 2.3cm our SfM photogrammetry generated models captured variations in topography associated with geomorphic features such as creeks, ponds, channel edges, and logs not visible in the DSM prepared from LiDAR of the same sites. SfM photogrammetry enables mapping of important hydrological features, such as creeks carrying drainage from upland watersheds or connectivity of ponds on the wetland surface. The former are important for transport of contaminants or diadromous fish, and the latter is important for resident fish, water birds, and mosquito larvae. Using SfM to distinguish vegetation structure that may indicate vegetation composition will enable more informed analyses of elevational controls on plant distribution and better prediction of their fate with sea level rise.

Utilization of laser range finder and differential GPS for high‐resolution topographic measurement at Hacituğrul Tepe, Turkey

AbstractTopographic maps are fundamental for geoarchaeological field studies and archaeological excavations. However, traditional methods of topographic mapping, as well as modern high‐tech methods such as airborne laser scanning and photogrammetry of high‐resolution satellite images, are often cost‐ineffective for field studies in terms of time, money, and labor. We here propose a method to measure topography for archaeological sites and surrounding areas quickly and accurately, using a laser range finder (LRF) and differential global positioning system DGPS. Three‐dimensional coordinates of points on land surfaces are measured through the LRF, targeted from multiple measuring locations whose positions are acquired with the DGPS. The point data are then interpolated to produce a digital elevation model (DEM) using a geographic information system (GIS). High‐resolution DEMs can be obtained with this method, with horizontal and vertical accuracies on the order of 10 cm. We here demonstrate the method for measuring detailed topography of the Hacituğrul Tepe in central Turkey. Digital topography data incorporated in GIS can also be part of an archaeological database, providing opportunities for quantitative analyses of topography and archaeological materials. © 2009 Wiley Periodicals, Inc.