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1 second SRTM Derived Hydrological Digital Elevation Model (DEM-H) version 1.0

Note: This metadata describes the dataset in accordance with the ANZLIC (Australia New Zealand Land Information Council) Core Metadata Guidelines Version 2.


Dataset citation

ANZLIC unique identifier: ANZCW0703014615

Title: 1 second SRTM Derived Hydrological Digital Elevation Model (DEM-H) version 1.0


Custodian

Custodian: Geoscience Australia

Jurisdiction: Australia


Description

Abstract:

The 1 second SRTM derived DEM-H Version 1.0 is a 1 arc second (~30m) gridded digital elevation model (DEM). The DEM-H captures flow paths based on SRTM elevations and mapped stream lines, and supports delineation of catchments and related hydrological attributes. The dataset was derived from the 1 second smoothed Digital Elevation Model (DEM-S; ANZCW0703014016) by enforcing hydrological connectivity with the ANUDEM software, using selected AusHydro V1.6 (February 2010) 1:250,000 scale watercourse lines (ANZCW0503900101) and lines derived from DEM-S to define the watercourses. The drainage enforcement has produced a consistent representation of hydrological connectivity with some elevation artefacts resulting from the drainage enforcement. A full description of the methods is in preparation (Dowling et al., in prep).

This product is the last of the series derived from the 1 second SRTM (DSM, DEM, DEM-S and DEM-H) and provides a DEM suitable for use in hydrological analysis such as catchment definition and flow routing.

ANZLIC search words:

  • ECOLOGY Landscape Mapping
  • LAND Topography Models
  • PHOTOGRAPHY AND IMAGERY Remote Sensing
  • WATER Hydrology

Spatial domain:

locality map

Geographic extent name: AUSTRALIA EXCLUDING EXTERNAL TERRITORIES - AUS - Australia - Australia

Geographic extent polygon: 113 -10, 154 -10, 154 -44, 113 -44, 113 -10,

Note: The format for each Geographic extent name is: Name - Identifier - Category - Jurisdiction (as appropriate) See GEN Register

Geographic bounding box:
North bounding latitude: -10 °
South bounding latitude: -44 °
East bounding longitude: 154 °
West bounding longitude: 113 °

Data currency

Beginning date: 2000-02-11

Ending date: 2000-02-22


Dataset status

Progress: In Progress

Maintenance and update frequency: Not Known


Access

Stored data format:
DIGITAL - ArcGIS-grid ArcInfo grid Geographic WGS84
Available format type:
DIGITAL - ArcGIS-grid ArcInfo grid Geographic WGS84

Access constraints:

These datasets are available freely, with the user being required to agree to the disclaimer at the time of order before the order can be processed. Creative Commons Attribution Australia Licence means data can be shared (copied, distributed, transmitted) or adapted provided you acknowledge the author or licensee. Consult the Creative Commons website for more information. http://creativecommons.org.au

Free Data Download

Data quality

Lineage:

Drainage enforcement

The 1 second Hydrological Digital Elevation Model (DEM-H) was derived from the 1 second Smoothed Digital Elevation Model (DEM-S) using the ANUDEM software (Hutchinson, 1988, 1989, 2009), version 5.2.5, dated 1 December 2010. This version of ANUDEM was modified to work effectively on the SRTM data, as briefly described in Hutchinson et al. (2009). ANUDEM uses a spline interpolation method that smooths the surface, enforces continuous descent along supplied drainage lines and removes sinks consistent with the accuracy of the source elevation data (DEM-S).

The 1:250,000 scale stream line data used to produce the GEODATA 9 second DEM Version 3 was chosen as the source of drainage line data as it was the only available source of cleaned and correctly oriented drainage lines and it covered the entire continent. This 1:250,000 scale data, with a spatial accuracy of about 200 metres, was significantly coarser than the 1 second DEM-S that is accurate to 50 metres or better. In low relief landscapes the spatial error of the 1:250,000 stream lines is not a significant problem but in steeper areas the spatial offsets result in drainage lines being incised into hillslopes rather than valley floors. To prevent this, the mapped stream lines were used only where slope in DEM-S was less than 10 degrees. The excised segments were replaced with infilling stream lines derived from DEM-S using a version of the AT search algorithm (Ehlschlaeger, 1989; known primarily as its implementation in GRASS as r.watershed) method that constructs flow lines through depressions without first filling the depressions to the outlet level.

The ANUDEM software cannot process the entire continent, or entire drainage basins at the 1 second resolution in a single pass. Drainage enforcement was therefore performed separately for each 1?1 degree tile using ? degree overlaps on each side. The resulting 2?2 degree tiles were trimmed to a 100 cell overlap, mosaicked with adjacent trimmed tiles then clipped to the 1?1 degree tile.

The mosaicking process does not guarantee the preservation of continuous descent along drainage lines so a final descent enforcement step was applied using the CheckStreamDescent program written for that purpose. CheckStreamDescent processes all tiles as a single data set so continuous descent of all stream lines to their termination points was ensured.

As a final step, the ocean areas were set to `no data?. Other water bodies have not been altered after drainage enforcement and most water bodies include a drainage line through them reflecting the connectors in the AusHydro data. Note that this is in contrast to the finishing of the DSM, DEM and DEM-S that all contain flattened water bodies and used the SRTM edit rules to ensure that land adjacent to water bodies is at a higher elevation than the water.

Positional accuracy:

The positional accuracy of watercourses in flatter areas is the same as for the 1:250,000 stream line data, about 200 m. For other features the horizontal positional error is generally the same as for the raw SRTM 1 second data, with 90% of tested locations within 7.2 m for Australia. See Rodriguez et al. (2006) for more information.

Attribute accuracy:

The primary purpose of a hydrological DEM is to support hydrological analysis related to connectivity of flow paths and hydrological properties of catchments and stream lines. The combination of ANUDEM and the CheckStreamDescent analysis ensures that DEM-H V1.0 correctly represents flow pathways as defined by the AusHydro 1:250,000 mapping, modified by the infill streams defined from DEM-S.

Flow paths where there are no mapped streams reflect the surface topography as represented in DEM-S so will be affected by errors in that DEM. In particular, areas where removal of vegetation offsets (to produce the DEM) was ineffective will exhibit incorrect flow pathways.

Drainage enforcement modifies elevations and surface form significantly in some areas and applications that are concerned with landforms and elevations where drainage connectivity is not a critical factor should use DEM-S in preference to DEM-H.

The elevation error for DEM-H is difficult to characterise. In general it will be similar to the raw SRTM 1 second data, with 90% of tested heights within 9.8 m for Australia (Rodriguez et al., 2006) but significant changes to elevation have occurred due to the smoothing and drainage enforcement processes. As noted in the Quality Assessment section above, errors as large as 200 m occur in some areas.

Further information on known errors is provided in the User Guide (Geoscience Australia and CSIRO Land and Water, 2011).

Logical Consistency:

The DEM-H represents heights of the land surface modified to ensure that elevations decrease continuously in the downstream direction along drainage lines. Smaller sinks have been cleared as part of the process but a large number of sinks remain where indicated by the elevation data. Most of these are genuine topographic depressions but some are due to data errors.

There are no voids and there are no discontinuities due to tile boundaries.

Completeness:

The DEM-H covers all of continental Australia and near coastal islands land areas including all islands defined by the available SRTM 1 second elevation and SRTM Water Body Data datasets.

The following tiles containing fragments of mainland or pieces of islands were not supplied at 1 second resolution and are therefore missing from the DEM-H: (e.g. E112 S26; E113 S29; E118 S20; E120 S35; E121 S35; E123 S16; E124 S15; E125 S14; E132 S11; E133 S11; E134 S35; E141 S10; E142 S10; E143 S10; E146 S17; E150 S22; E152 S24)

Note that the coordinates are of the southwestern corner of the tile.


Contact information

Contact organisation: Commonwealth of Australia (Geoscience Australia) (GA)
Contact position: Manager Client Services
Mail address: Cnr Jerrabomberra Ave and Hindmarsh Dr
Mail address: GPO Box 378
Locality: Canberra
State: ACT
Country: Australia
Postcode: 2601
Telephone: 02 6249 9966
Facsimile: 02 6249 9960
Electronic mail address: sales@ga.gov.au

Metadata information

Metadata date: 2011-12-08


Additional metadata

Metadata reference XHTML: http://www.ga.gov.au/meta/ANZCW0703014615.html

Metadata reference XML: http://www.ga.gov.au/meta/ANZCW0703014615.xml

Overview of quality assessment

Differences in height between DEM-S and DEM-H were examined to identify areas where defects were created by the drainage enforcement process. Some large elevation differences, up to 290 m, were due to valid drainage enforcements in canyons. Other significant differences are related to various problems including:

? Excessive height reductions on steep slopes due to multiple parallel infill stream lines eg 152.295 Degrees E, 30.943 DegreesS.

? Excessive smoothing (lowering of hilltops and raising of lower slopes) in some areas (eg the eastern peaks of the Stirling Range, WA, around 118.28?E 34.36?S, with hilltops lowered by around 200 m).

? Drainage enforcements to the level of open-cut mines traversed by mapped stream lines resulting in deep incisions extending long distances downstream of the mines, with the worst instance being from the coal mines in Latrobe Valley, Victoria, to the outlet of the Gippsland Lakes, to an elevation of about 60 m for about 180 km.

? A few extraneous infill stream lines in inland areas creating long stream lines where none were mapped (eg in tile e129s25)

? Errors in the 1:250,000 stream lines (eg 148.29?E, 35.35?S)

Note that only the last two issues (extraneous infill lines and stream line errors) affect the hydrological quality of DEM-H; the other problems create incorrect elevations but the hydrological connectivity is correctly represented.

DEM-H Ancillary data layers

Flow direction grids along watercourses has been included in 1 km tiles.

Authors:Wilson, N. Tickle, P.K. Gallant, J. Downling, T. Read, A.
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