Remote sensing solutions aid fire damage assessment

August 31, 2007

Innovative new digital imagery technology is being used to help timber growers and timber insurers launch fast and effective salvage operations in the wake of devastating forest fires.

Remote fire infared imaging

Left: Fire damaged compartment as seen with the human eye with the normal rainbow of colours. Centre: Near-infrared image of the same compartment ... chlorophyll in the leaves of healthy, growing trees reflects near-infrared wavelengths and appears red on the image. Right: This image combines near-infrared and red imagery which makes it possible to derive an NDVI, or crop index which represents in exaggerated colours the health of the compartment.

 

"South Africa has never experienced the kind of devastation that we've had this year," says Pierre Bekker of Safire Insurance Company. "We have had to make some quick decisions about where timber can be salvaged, and the longer we take to assess a burnt area, the less time the farmer has for salvaging."

Where swift responses are needed for areas larger than 300 ha, Safire and grower companies have turned to Pietermaritzburg-based Land Resources International (LRI), which uses LREye Imagery. A series of ortho-rectified aerial digital images are taken to correctly map timber compartments and then to assess the extent of •re damage in each compartment.

LREye Imagery is multispectral, simultaneously providing four bands of data (red, green, blue and near-infrared). The images can be used to provide a traditional colour image, or they can be manipulated to supply a range of different information. The near-infrared images are particularly valuable for revealing the stress levels in trees still standing in the fire-affected areas, which helps with assessing whether there is likely to be recovery or whether those trees should be targeted for salvage harvesting.

Mondi Business Paper is another company using LREye Imagery to provide information for more effective forest management. "You don't always see things on the ground – for example heavy weed infestation in the middle of the compartment – so we use LREye Imagery as a management tool to help us focus our energy on problematic areas," commented Mondi's Mark Norris-Rogers.

There are many applications for the technology. For instance it has been used by Mondi and Sappi to assess Sirex woodwasp infestation. According to Andrew Coleman, Technical Director of LRI, the near-infrared imagery can detect the early stress stages of Sirex-affected trees before the symptoms of stress are detectable by a forester on the ground.

LRI is currently using the technology to assist farmers, foresters and environmentalists throughout southern Africa.

How LREye Imagery near-infrared technology works

The part of the light spectrum visible to the human eye is the normal rainbow of colours we see every day. Other parts of the spectrum (such as near-infrared wavelengths) are invisible to the human eye, but may be recorded by electronic sensors sensitive to these wavelengths.

Living plant material contains a unique spectral identity which can be qualitatively analysed with near-infrared technology. In the case of forestry compartments, chlorophyll in the leaves of green, healthy, growing trees reflects a high level of near-infrared wavelengths, and appears red on processed imagery. Conversely, stressed or diseased trees re•ect little near-infrared light, and dead trees re•ect none. In this way, near-infrared imagery is an extremely useful tool for identifying and delineating healthy and damaged or stressed trees.

By combining near-infrared and red imagery, users are able to derive an NDVI, or crop index, which represents geographically in exaggerated colour indices the health of forest compartment data.

Published in July/August 2007

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