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Satellite image indicating suitability of vegetation for locusts
Satellite images of vegetation greenness are used to identify areas where ground vegetation in locust habitat areas has responded to rainfall and might provide suitable conditions for locust survival, breeding and potential population increase. Current vegetation index imagery is available within two weeks of the satellite observation period and is used to make decisions as to where locust surveys will be carried out.
The condition of vegetation is assessed directly during survey by recording the presence and amount of green leaf material on a scale from green shooting to completely dry, for several ground vegetation components (perennial grasses, ephemeral grasses and forbs).
The image below shows the relative greenness of vegetation in broad locust habitat areas for the 14-day period beginning on 23 August 2008. It shows green pasture and crop vegetation in parts of eastern NSW, Victoria and southern South Australia.
Source: Department of Land Information - Government of Western Australia (Satellite Remote Sensing Services)
NB: the APLC has responsibility for control of locusts in areas inside the red line.
The image above shows where vegetation is green using the Normalised Difference Vegetation Index (NDVI) obtained by satellite remote-sensing. The NDVI values are calculated using measurements from the Advanced Very-High Resolution Radiometer (AVHRR) on board the US National Oceanic and Atmospheric Administration (NOAA) polar-orbiting meteorological satellites. The radiometer measures the reflectance of solar radiation from the land surface in several different wavelength bands. Because green vegetation, soil and water reflect light in different wavelengths and in different amounts it is possible to use reflectance values to calculate a ratio of reflectance in different frequency bands (NDVI) to identify the density and vigour of green vegetation.
In arid and semi-arid areas of Australia, open plain landscapes with a sparse covering of grasses and forbs are important habitats for locust breeding, especially when these plants produce new growth following rain. Landscapes such as forest/scrub, dunes and rocky areas, are largely unsuitable for locust breeding and have been masked out in grey to emphasise the condition of predominantly grassy vegetation in locust habitats. The image provided above is re-scaled to show current NDVI values as a proportion of the historic range in records for the same locations. It has the effect of emphasising growth in response to rainfall in sparsely vegetated landscapes relative to much larger NDVI values for dense vegetation (such as coastal forests or crops).