Tuesday, February 21, 2012

Continental reference image

Late last year Geoscience Australia released the Australian Geographic Reference Image (AGRI), a national mosaic which provides a spatially correct reference image at a 2.5 metre resolution. Base imagery comes from Japan's Advanced Land Observing Satellite (ALOS) and was captured between 2007 and 2010. In total 9,560 corrected scenes were used to generate AGRI. This product is available under Australian Creative Commons 2.5 licence and is supplied by Geoscience Australia on demand for a fee of $250.

AGRI was developed to address the need for a higher resolution reference image, of known accuracy, over the entire Australian continent. There are many potential uses for AGRI, but in particular it is a valuable resource for both users and providers of satellite imagery over Australia. A problem common to all remote sensing is the need to accurately locate observations to the ground (through a process called 'geo-referencing' or, because satellite observations often form images, 'image rectification’ and in some cases 'orthorectification') - to ensure that observations taken at different times and from different satellites and instruments can be compared, and are accurate and consistent.

The most reliable approach is to register all images to a single, controlled image base – a reference image. Geoscience Australia has used this approach since 2002, rectifying images from satellites to the national Landsat panchromatic mosaic. However, the Landsat panchromatic mosaic has an accuracy of no more than fifteen metres so, is not suitable for use with higher resolution imagery available from more recent Earth observation satellites. AGRI is a timely addition and will ensure consistent positional accuracy of high resolution imagery captured all over Australia.

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