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Land Cover Productivity

BRS in conjunction with CSIRO and the Cooperative Research Centre for Greenhouse Accounting, has established an archive of satellite imagery that can be used to measure land and resource condition. The satellite data are compiled from the MODIS Terra satellite, which was launched in December 1999. One of the key datasets collected by Terra is the 250-metre, 16-day Normalised Difference Vegetation Index (NDVI), which is a commonly used index of vegetative production. An NDVI value of zero means no green vegetation and close to +1 (0.8 - 0.9) indicates the highest possible density of green leaves. NDVI data are used as a surrogate for both green cover and, when integrated over a growing season, of productivity.

Seasonal metrics have been estimated for the growing season April to March:

• Minimum NDVI gives an estimate of perennially green vegetation, bare ground and water.
• Mean NDVI estimates productivity over the season.
• Coefficient of variation gives a measure of the seasonal response eg higher responses are found in cultivated crops.
• Date of maximum NDVI can be used to separate summer and winter crops as well as irrigated and dryland crops.
• Percent anomaly shows the deviation from the average and can be used to assess seasonal productivity.

The data for the period 2000-2005 have been compiled in an online mapping tool.

These thresholds can also be used to identify land cover types, for example water has values of NDVI below 0 whilst woody vegetation usually has NDVI values in excess of 0.3.

Research is being undertaken on behalf of the Murray-Darling Basin Commission to investigate how MODIS NDVI data can be used to map annual land cover in the Riverine Plains of southern New South Wales and northern Victoria. The map below shows the location of the Riverine Plains study area.

Land cover is a description of the biophysical state of the land and a land use such as cropping may have different land covers throughout the year. For example, when ploughing takes place the land appears as bare soil. As the crop is sown and starts to germinate, it will appear as a green flush and rapidly increase in greenness to a peak, thereafter it may set seed and become browner. At some point, it will be harvested and again appear as a bare cover.

Key metrics are classified into seasonal responses (summer and winter) as well as seasonal and perennially green cover and these are then combined with a baseline land cover to establish a change in land cover. Preliminary results are shown below for the Berriquin irrigation district.