ACE2: The New Global Digital Elevation Model
Detailed accurate Digital Elevation Model (DEM) data have historically not been available on other than a regional scale, and often have uncertainties in both vertical and horizontal precision.
- PDF / 1,379,754 Bytes
- 7 Pages / 547.087 x 737.008 pts Page_size
- 88 Downloads / 244 Views
ACE2: The New Global Digital Elevation Model P.A.M. Berry, R.G. Smith, and J. Benveniste
Abstract Detailed accurate Digital Elevation Model (DEM) data have historically not been available on other than a regional scale, and often have uncertainties in both vertical and horizontal precision. This paper presents the results of a global assessment of the unique Shuttle Radar Topographic Mission (SRTM) DEM using more than 100 million height datapoints derived from ERS1, ERS2, Topex, EnviSat and Jason-1 radar altimeter data, retracked using an expert system approach. This paper outlines the retracking approach taken to derive heights from the altimeter waveforms and describes the methodology for fusion of these data with the SRTM dataset, correcting errors in the SRTM heights and providing accurate measurements beyond the SRTM latitude limit, to produce a full global DEM. Of particular interest, the unique ability of radar altimeters to provide very precise vertical measurements has allowed the correction of vertical offsets to better than 1 m within ACE2, and has also allowed identification of horizontal misplacements. As part of this development, a detailed quality matrix is being generated, to give users information both on the data source of each pixel, and an assessment of the vertical precision of the measurement. It is this detailed global assessment of quality that makes the ACE2 development both unique and of special value for a range of geodetic applications. The first full release of ACE2 is scheduled for later in 2008.
P.A.M. Berry () E.A.P.R.S. Lab, Gateway House, De Montfort University, Leicester LE19BH, UK e-mail: [email protected]
30.1 Introduction The ACE (Altimeter Corrected Elevations) Global Digital Elevation Model (GDEM) was created by fusing altimeter derived heights (produced using a system of multiple retrackers) with ground truth available from a range of publicly available datasets to create an enhanced GDEM (Berry, 2000; Berry et al., 2000; Hilton et al., 2003). However, this was curtailed in spatial resolution to 30
(about 1 km at the equator) by the level of detail available in the ground truth, and the spatial distribution of the altimeter tracks from the ERS1 Geodetic Mission, which have an average across-track spacing of 4 km and an along-track sampling of about 350 m. The release of the SRTM dataset derived using interferometric SAR (Hensley et al., 2000) presents a 3
dataset up to a latitude limit of 60◦ N and 54◦ S. This dataset represents a very substantial improvement in the quality and spatial resolution of the publicly available DEM data, with a global vertical accuracy estimate of ± 16 m (ibid). However, as both global and regional evaluations with ground truth have shown, there are regional differences in the estimate of accuracy of this dataset (Denker, 2004; Brown et al., 2005; Hall et al. 2005; Smith and Sandwell, 2003); crucially, these quality assessments are limited by the availability of ground truth. It was therefore decided to carry out a global assessment of the SR
Data Loading...
