Authors / CoAuthors
Dowling, T. | Gallant, J. | Read, A.
Abstract
The 1 Second DSM Version 1.0 is a gridded digital surface model representing the radar reflective surface (bare earth, vegetation and built structures) as observed by the Shuttle Radar Topographic Mission in February 2000. It was derived primarily from the 1 second SRTM version 2 provided by DIGO, supported by the Geodata 9 Second DEM in void areas and the SRTM surface water database. Stripes and voids have been removed from the 1 second SRTM data to provide an enhanced and complete digital surface model for Australia and near-shore islands. The grid spacing is 1 second in longitude and latitude (approximately 30 metres).
Product Type
dataset
eCat Id
68614
Contact for the resource
Custodian
Point of contact
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia
Keywords
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- DEM topographic
- ( Theme )
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- DEM
- ( Theme )
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- data
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- AU
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Topology
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- Published_Internal
Publication Date
2009-01-01T00:00:00
Creation Date
Security Constraints
Legal Constraints
Status
Purpose
Maintenance Information
asNeeded
Topic Category
elevation
Series Information
Lineage
The 1 second DSM was derived primarily from the SRTM 1 second data by de-striping and void filling. Source data used to create the 1 Second DSM Version 1.0 were: 1. SRTM 1 second Version 2 data (Slater et al., 2006), supplied by DIGO as 813 1 x 1 degree tiles. The data was produced by NASA from radar data collected by the Shuttle Radar Topographic Mission in February 2000. 2. Geodata 9 Second DEM Version 3 (Geoscience Australia, 2008) used to fill voids. 3. SRTM Water Body Data (SWBD) shapefile accompanying the SRTM data (Slater et al., 2006). This defines the coastline and larger inland waterbodies for the SRTM DEM. De-striping The SRTM data contains striping artefacts oriented approximately northeast-southwest and northwest-southeast that vary in amplitude from about 0.2 m to nearly 4 m. The wavelength of the striping is approximately 800 m. The stripes were detected in the elevation data using a 2-dimensional Fast Fourier Transform. The peaks in the spectra were visually identified and manually delineated using a software tool designed specifically for this purpose. Striping was found to occur everywhere except where the relief was high enough to obscure the striping. The spectral analysis was performed on sub-tiles to account for spatial variation in the intensity and direction of striping. The Fourier transform was applied to overlapping sub-tiles covering 1536 x 1536 cells (0.43 x 0.43 degrees). The central 1024 x 1024 cells were retained, each comprising one sixteenth of a 1 x 1 degree tile (900 x 900 cells) with a 62-cell overlap on each edge to provide smooth transitions between the sub-tiles. Void filling Voids (areas without data) occur in the SRTM data due to low radar reflectance (typically open water or dry sandy soils) or topographic shadowing in high relief areas. The Delta Surface Fill Method (Grohman et al., 2006) was adapted for this task, using the Geodata 9 second DEM as the source of infill data. The 9 second data was refined to 1 second resolution using ANUDEM 5.2 without drainage enforcement. The Delta Surface Fill Method calculates height differences between the SRTM and the infill data to create a "delta" surface with voids where the SRTM has no values, then interpolates across the voids. The void is then replaced by the infill DEM adjusted by the interpolated delta surface, resulting in an exact match of heights at the edges of each void. Two changes to the Delta Surface Fill Method were made: the interpolation of the delta surface was achieved with natural neighbour interpolation (Sibson, 1981; implemented in ArcGIS 9.3) rather than inverse distance weighted interpolation; and a mean plane inside larger voids was not used. Water bodies Water bodies that were flat in the original 1 second data were modified by the de-striping process, so were re-flattened after the striping was removed. The SRTM Water Body Data was converted to a grid at 1 second resolution then adjusted to match the extent of equal-height pixels in the original SRTM 1 second data. Grid cells within that water mask were set to the original SRTM height. Edit rules for land surrounding water bodies The SRTM edit rules set all land adjacent to water at least 1 m above the water level to ensure containment of the water (Slater et al., 2006). Following de-striping, void filling and flattening of water, the heights of all grid cells adjacent to water was set to at least 1 cm above the water surface. The smaller offset (1 cm rather than 1 m) could be used because the cleaned digital surface model is in floating point format rather than the integer format of the original SRTM. Some small islands within water bodies are represented as voids within the SRTM due to the edit rules. These voids are filled as part of the void filling process, and their elevations are set to a minimum of 1 cm above the surrounding water surface across the entire void fill.
Parent Information
Extents
[-44, -10, 113, 154]
Reference System
Spatial Resolution
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