1. Australian Antarctic Data Centre
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4. SIC_1961_georectification

Description

The orthorectification of the QuickBird image (30 January 2006) was done as part of the Heard Island AAS2939 project (Lucieer et al. in Jan - June 2008). This QuickBird image was orthorectified and co-registered to the IKONOS Jan. 2004 image (metadata ID: SIC_266_267_georectification). All processing was done in ENVI 4.4 (https://esriaustralia.com.au/envi).

Quality

The processing used on this image was as follows:

Pansharpening
- Fuse or merge the high-resolution panchromatic band with the lower resolution multispectral bands to create a high-resolution multispectral image based on an image transform.
- Panchromatic band has to overlap with multispectral bands in wavelengths.
- Wavelet-based pansharpening is more correct from a spectral perspective than ENVIs pansharpening algorithms, such as HSV, Brovey, Gram-Schmidt, PCA, and CN.
- Wavelet Fusion is an ENVI extension available from the ITTVIS codebank https://esriaustralia.com.au/envi
- The original unprojected multispectral and panchromatic images were used for pansharpening.
- The input images are transformed into wavelet space. Their wavelet coefficients are combined. Then an inverse wavelet transform is applied to the combined wavelet coefficients to create the fused image.
- Fusion strength: the ratios used to blend together the wavelet coefficients of each image at each decomposition level. The settings used were:
- Image A: Multispectral image
- Image B: PAN image
- Map projection: Match Image B (PAN)
- Fusion strength: 50:50
- Additional options: defaults

- Output file name: include psdwt (pansharpened with discrete wavelet transform)

Orthorectification of the pansharpened image

Orthorectification parameters in ENVI:
- Orthorectification was done without GCPs as the match between the DEM and the QuickBird image was very good. Co-registration was applied after orthorectification to fine-tune the image rectification and to match the QuickBird image to the 2004 IKONOS image (metadata ID: "SIC_266_267_georectification").
- RPC model based on the *.rpb file from the panchromatic band - RADARSAT 2002 DEM was first re-projected in ArcGIS, so that it is in a geographical coordinate system (dem_gg.bsq).
- The DEM resampling was set to Cubic convolution because it is upsampled to a higher resolution and cubic convolution results in a smoother interpolation.
- The Geoid offset was set to the default of 0.0 as no accurate geoid offset was found on the Geoscience Australia website.
- The projection was set to UTM, Zone 43 South with a WGS-84 Datum.
- The pixel size was set to 0.6 m in both X and Y directions.

Image to image registration to IKONOS 2004 image

- Image-to-image registration was used to register the Jan 2006 QuickBird image to the IKONOS 2004 image (the base image). 101 manually selected GCPs (tie points) were selected between the images.
- Automatically selecting tie points was attempted, however all points generated were located in unreliable areas (e.g. Glacial or water surfaces) and had extremely high RMS error values, therefore these additional GCPs were not used.
- The 101 GCPs chosen had an RMS Error value of 26.67. However, as we applied a triangulation (rubber sheeting) transformation, this RMS value has no significant meaning and does not reflect the accuracy of the GCP selection.
- The image was warped using a triangulation method with nearest neighbour image resampling.
- Upon observation of the resulting registered image it became apparent that part of the coastline was excluded from the image during the triangulation transformation. Therefore 4 more GCPs were added to the existing points, resulting in a total of 105 GCPs. The new RMS error value was 26.47.
- The image was warped again using the same method.

Access

A PDF document providing further details is available for download from the provided URL.

Access to the image itself is limited owing to copyright issues. Contact the Australian Antarctic Data Centre for details and further information.

Temporal Coverages

• Start date: 2006-01-30 - Stop date: 2006-01-30

Spatial Coverages

Data Resolution

Science Keywords

• EARTH SCIENCE > SPECTRAL/ENGINEERING > VISIBLE WAVELENGTHS > VISIBLE IMAGERY

Use Constraints

This data set conforms to the CCBY Attribution License (http://creativecommons.org/licenses/by/4.0/).

Please follow instructions listed in the citation reference provided at http://data.aad.gov.au/aadc/metadata/citation.cfm?entry_id=SIC_1961_georectification when using these data.