Authors / CoAuthors
Unknown
Abstract
The 1 second SRTM derived DEM Version 1.0 is a 1 arc second (~30m) gridded digital elevation model (DEM). The DEM represents ground surface topography, and excludes vegetation features. The dataset was derived from the 1 second Digital Surface Model (DSM; ANZCW0103013355) by automatically removing vegetation offsets identified using several vegetation maps and directly from the DSM. This product provides substantial improvements in the quality and consistency of the data relative to the original SRTM data, but is not free from artefacts. Man-made structures such as urban areas and power line towers have not been treated. The removal of vegetation effects has produced satisfactory results over most of the continent and areas with defects are identified in the quality assessment layers distributed with the data and described in the User Guide (Geoscience Australia and CSIRO Land & Water, 2009). A full description of the methods is in progress (Read et al., in prep; Gallant et al., in prep). Smoothed and drainage enforced versions are under development, and are expected to be released in 2011.
Product Type
dataset
eCat Id
77227
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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- GIS Dataset
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2013-08-21T00:00:00
Creation Date
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Maintenance Information
asNeeded
Topic Category
geoscientificInformation
Series Information
Lineage
Source data 1. SRTM 1 second Version 2 data (Slater et al., 2006), supplied by Defence Imagery and Geospatial Organisation (DIGO) as 813 1 x 1 degree tiles. Data was produced by NASA from radar data collected by the Shuttle Radar Topography 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 DEM and DSM. 4. Vegetation masks and water masks applied to the DEM to remove vegetation. DSM processing This DEM was based on the 1 second SRTM-derived Digital Surface Model (DSM) that was itself derived from the 1 second Shuttle Radar Topographic Mission data. The DSM was produced by removing stripes, filling voids and re-flattening water bodies. Further details are provided in the DSM metadata (ANZCW0703013336). The vegetation removal used the DSM without voids filled so that vegetation height estimates would not be affected by interpolated heights and so that voids adjacent to vegetated areas could be filled using bare-earth elevations. Vegetation offset removal The processing of vegetation offsets to produce the DEM relies on Landsat-based mapping of woody vegetation to define where the offsets are likely to occur. The mapped extents of woody vegetation were adjusted using an edge-matching process to better represent the extents of areas affected by vegetation offsets in the SRTM DSM. Vegetation was processed across approximately 40% of Australia as shown in the vegetation mask ancillary dataset and in the User Guide (Geoscience Australia and CSIRO Land & Water, 2009). Vegetation offset processing involves detecting vegetation patches, measuring the height offset around the edges, interpolating the height offset across the vegetated areas and subtracting the offset from the DSM. The heights of the offsets are estimated by measuring height differences across the boundaries of the vegetation patches. The method provides good estimates of the offsets in flat landscapes with well-mapped vegetation boundaries. The effect of sloping terrain is accounted for in the estimation of the offsets, but the results are less reliable in hilly terrain. Estimates of the offsets can also be very poor where the mapped vegetation extents do not match the extents of vegetation offsets as seen by the SRTM instrument. The estimation of the vegetation offsets can also be under or over-estimated if vegetation and topographic patterns coincide, such as trees on hilltops or dune ridges, or in inset floodplains or swamps. The height offsets at vegetation edges are interpolated within vegetation patches to estimate the effects within the patches. The best results tend to be in small patches such as remnant tree patches. In continuously forested areas with few edges for estimating the offsets the heights are likely to be less reliable, and there is no information at all on variations of the height offset within continuous forests. The removal of vegetation has been quite effective overall but there are many areas that contain either untreated or incompletely treated vegetation effects. The methods will be fully described in Read, et al. (in prep) and Gallant, et al. (in prep). Please consult the User Guide (Geoscience Australia and CSIRO Land & Water, 2009) for the rest of the lineage and metadata information.
Parent Information
Extents
[-44.0, -10.0, 113.0, 154.0]
Reference System
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