Macquarie Island Quickbird Image (15 March 2005) orthorectification
Quickbird image of Macquarie Island acquired on 15 March 2005. The image has been orthorectified, i.e. all geometric distortions caused by the earth curvature and relief displacement have been corrected. Twenty six ground control points spread out over the image were identified, based on survey cont...
| Other Authors: | , , , , |
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| Format: | Dataset |
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Australian Antarctic Data Centre
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| Online Access: | https://researchdata.ands.org.au/macquarie-island-quickbird-2005-orthorectification/701347 https://data.aad.gov.au/metadata/records/Macquarie_Quickbird_15Mar2005 http://nla.gov.au/nla.party-617536 |
| Summary: | Quickbird image of Macquarie Island acquired on 15 March 2005. The image has been orthorectified, i.e. all geometric distortions caused by the earth curvature and relief displacement have been corrected. Twenty six ground control points spread out over the image were identified, based on survey control marks and corresponding pixels in the Panchromatic band of the Quickbird image. This was done in collaboration with Henk Brolsma, Australian Antarctic Data Centre. The image was transformed based on the Quickbird RPC coefficients (sensor platform parameters) and the ground control points. The 5m AIRSAR DEM acquired by NASA (metadata record - Macquarie Island AIRSAR DEM (Digital Elevation Model / Entry ID: macca_dem_gis ) was used to correct the image for topographic relief distortions. The DEM was resampled with the bilinear resampling algorithm; the image was resampled with the nearest neighbour algorithm to retain the original pixel values. The horizontal accuracy is estimated to be within 5m or 2 pixels, but in places this may be greater. Coordinate system: WGS84 datum UTM zone 57S projection. The orthorectification was done by Dr Arko Lucieer, Centre for Spatial Information Science (CenSIS), School of Geography and Environmental Studies, University of Tasmania using ENVI 4.3 and the new image was exported to a GeoTIFF and a JPEG2000 (lossless compression) image. Quickbird imagery consists of four multi-spectral bands: Blue, Green, Red, Near-Infrared at 2.4m resolution (pixel size). Quickbird also acquires a panchromatic image (grey scale) at 0.6m resolution. Two colour composites have been included: 1. Visible bands (RGB = band 3, 2, 1) corresponding to the way the human visual system sees colours and very similar to an aerial photograph. 2. False colour composite (RGB = band 4, 3, 2). This colour composite includes the Near-Infrared band (band 4) to highlight vegetation in red. Cholorphyll in vegetation causes a high reflectance of NIR wavelength energy which shows up as bright red in the image. Vegetation that has been grazed or dies back looses its red colour. Two image formats have been included: 1. GeoTIFF (.tif and .tfw). This image is uncompressed and can be opened in ArcView 3.x or ArcMap without loading an extension. 2. JPEG2000. This image format is highly compressed without loosing image quality. This image is exactly the same as the GeoTIFF but has a smaller file size. JPEG2000 can be opened in ArcView with the ECW extension from ERMapper. In the file names: ms=multispectral (2.4m) ps=pansharpened (0.6m) orc=orthorectified vis=visible colour composite (RGB, 8-bit: 0-255) fc=false colour composite (NIR,R,G 8-bit: 0-255) All images without fc or vis in the filename have four bands and have a 16-bit data type (0 - 65535). Quickbird collects image data in 11-bit (0-2048), so in order to display these images the image values need to be stretched. For GIS use Arko recommends using the fc and vis files, because they have been stretched already. Keep in mind that ArcGIS has to build image pyramids and image statistics before display. In 2012 lakes, creeks, escarpments and ridges were digitised from the orthorectifed image. For details about the digitising and access to the resulting dataset, refer to the metadata record 'Macquarie Island - Digitising topographic features', Entry ID: Macquarie_Island_quickbird_digitising. |
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