Half Moon Lake regolith-landform map and GIS datasets

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

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Dataset citation

ANZLIC unique identifier: ANZCW0703003779

Title: Half Moon Lake regolith-landform map and GIS datasets

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Custodian

Custodian: Cooperative Research Centre for Landscape Environments and Mineral Exploration

Jurisdiction: Australia

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Description

Abstract:

Provides regional framework study of regolith and associated landforms over the Gawler region (centred around

Half Moon Lake in central South Australia). Datasets are all contained in a GIS - these include regolith-landform

units, enhanced Landsat TM imagery, site descriptions and photo links, enhanced DEMs and erosional scarps.

ANZLIC search words:

GEOSCIENCES Geology Maps
GEOSCIENCES Geomorphology Maps

Spatial domain:

locality map

Geographic extent polygon: 133.09943 -29.74063, 133.89898 -29.74063, 133.89898 -30.49619, 133.09943 -30.49619, 133.09943 -29.74063,

Geographic bounding box:: North bounding latitude: -29.74063 °; South bounding latitude: -30.49619 °; East bounding longitude: 133.89898 °; West bounding longitude: 133.09943 °

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Data currency

Beginning date: 1997-06-01

Ending date: 1998-06-01

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Dataset status

Progress: Complete

Maintenance and update frequency: Not Known

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Access

Stored data format:: DIGITAL - ArcGIS-coverage ArcInfo coverage Geographic GDA94; NONDIGITAL - Map Printed map

Available format type:: DIGITAL - ArcGIS-coverage ArcInfo coverage Geographic GDA94; NONDIGITAL - Map Printed map; DIGITAL - shp ArcView shape file ArcView Geographic GDA94

Access constraints:

Maps and associated GIS datasets are available through the CRC for Landscape Environment and Mineral Exploration

at the Geoscience Australia.

Order Product

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Data quality

Lineage:

Regolith-landform polygons were compiled from airphotos, satellite and geophysical imagery. The airphotos

were principally used to map the landforms. Compositional information within these landform units was then

interpreted from gamma-ray and enhanced Landsat TM imagery at the same scale as the aerial photographs.

The compilation sheet at 1:80 000 scale was scanned, cleaned and attributed using ArcInfo GIS software.

Site data was entered in Geoscience Australia's regolith database (RTMAP) database and then extracted to make a point

attribute file in ArcInfo. The regolith characteristics of over 120 sites were recorded, and referenced using a

Garmin GPS with a +/- 70 m location accuracy.

Image datasets were all enhanced in ERmapper:-

Landsat TM:

The Landsat TM image was derived from path and row 101/81 and was enhanced to highlight regolith materials

by a technique called Directed Principal Component Analysis (DPCA). For more information on this technique,

see the 'more metadata' section. The result is an image which displays the clay derived band as red, iron oxide

in green and silica in blue (see report for more detailed descriptions).

Atmospheric backscatter particularly in the shorter wavelengths, higher frequency bands (eg. 1, 2, 3 and 4)

was removed using a technique called "dark pixel subtraction". See the 'more metadata' for more information on

this technique.

Digital elevation model (DEM)

The DEM was compiled by AUSLIG, AGSO, the Australian Heritage Commission and the Australian National

University. It has a grid spacing of 9 second (in longitude and latitude) that equates to a 250m grid size.

Positional accuracy:

GPS +/- 70 metres for site observations and sample collection. Regolith compiled using 1:80 000 aerial photographs, Landsat TM (30 m pixels) and gamma-ray spectrometry imagery (400 to 1.5km line spacing). Geo-rectification of the Landsat TM imagery was accurate to 1.5 - 3 pixels (90 metres). Polygons based a gamma-ray responses will have a lower positional accuracy depending on the flightline spacing of the survey (generally expected to be -/+ 150-500 metres)

Attribute accuracy:

Map units compiled with 1:80 000 air photos, Landsat TM (30 m accuracy) and gamma-ray spectrometry (100 - 200 m accuracy). Landsat TM enhancement involved PCA and band ratios to map clays, iron oxides and silica (high reflective materials. Linear stretched K , Th, U and total bands were used to interpret the gamma-ray spectrometry datasets. These images were calibrated by field observations. The enhanced images related to regolith associations. Therefore the regolith units relate to similar material associations but are not neccessarly accurate for specific regolith materials.

Logical Consistency:

Several logical consistency tests were done including;

1. a visual check of maps at the final draft stage, and

2. a topological consistency check.

The topological consistency check involved the detection of errors in the spatial data structure (eg. all

polygons are closed, nodes are formed on the intersection of lines and that there is only one label for

each polygon, all points, lines and polygon are topologically related).

Completeness:

The map is a reconnaissance product and is based on two week field work. Although uniformly complete

in terms of attribute data described for each polygon - the quality of datasets used in the map compilation

varied across the study area. The upper righthand corner was based on detailed photo interpretation and

image calibration. The rest of the map was largely based on the interpretation of remotely sensed datasets

including gamma-ray spectrometry and enhanced Landsat TM imagery with ground truthing.

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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

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Metadata information

Metadata date: 2013-03-08

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Additional metadata

Metadata reference XHTML: http://www.ga.gov.au/meta/ANZCW0703003779.html

Metadata reference XML: http://www.ga.gov.au/meta/ANZCW0703003779.xml

The regolith-landform unit attributes and site information are stored in Geoscience Australia's regolith database (RTMAP).

The polygon attributes include all descriptions shown on the hard copy regolith maps as well as some addditional information.

The site attributes include a description of the regolith and landform types and, in many places, scanned photographs of the regolith at that location. Scanned photographs are hot-linked into the Arcview GIS as TIFF files.

DPCA method:

The DPCA is used to separate clays in the imagery by deriving principal components from ratio of bands 4/3 and 5/7. Ratio band 4/3 enhances vegetation and ratio 5/7 enhances a mixed response of vegetation and clay. The DPCA operating on these ratio bands is able to separate the vegetation from the clay response. The result is a 'clay' band, which is derived from the second principal component. Part two involves creating a 5/4 band ratio that highlights ferruginous materials and the addition of bands 1 and 7 that highlights silica rich materials (eg. quartz lags).

Dark pixel subtraction:

Dark pixel subtraction uses 'black bodies' in the image (eg. shadow) to measure the radiance due to atmospheric scattering. The dark pixel value is then subtracted from each of the Landsat TM bands.

Authors:Wilford, J. Craig, M.A.

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