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The red edge band, around 700 nm, used to investigate the health of vegetation. Many people regard it as a simple, workable substitute for hyperspectral imagery in vegetation work.

Red edge is a feature of the German RapidEye constellation. It will also feature on DigitalGlobe's WorldView-2 next year and star on the South African satellite, Sumbandilasat.

Sumbandilasat was built in answer to a requirment for a high resolution multispectral micro-satellite. Sunspace, the University of Stellenbosch and the South African Department of Science and Technology were the key players in its construction. Its payload will deliver 6.25 metre spatial resolution and six spectral bands.

Russell Main and others presented a paper on at a recent conference in Australia. The paper examined work done on the use of red edge for detecting stress in strands of Eucalyptus Grandis.

Main says hyperspectral remote sensing has a number of disadvantages related to the low signal-to-noise ratios and data redundancy given the large number of contiguous bands.

He says that designing sensors for more specific applications could solve these problems. For instance, stress in vegetation can be adequately mapped with just two bands, provided they are narrow enough and centred on the correct frequency.

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