While the MADA website does not discuss the use of satellite images for irrigation management the potential exists as indicated by research conducted in Japan, (CRISP Session Code: AGS-02, Paper 173, Yoshinari Oguro, Chisato Imamoto, Yuzo Suga, Shoji Takeuchi, MONITORING OF RICE FIELD BY LANDSAT-7 ETM+ AND LANDSAT-5 TM DATA). To explore this idea further we can analyze Landsat and ASTER datasets.

The large area covered by Lansat images (over 300,000 km²) means that scenes of interest to the Tropical Rain Forest Information Center at Michigan State University may extend over large tracts of land used for agriculture as indicated in the following browse images (TRFIC/BRSRI).

The Cropping Cycle These browse images indicate the progression of vegetative growth from July 2000 to February 2001. In July we can see that some vegetation covers the land before the growing season. By September the land has been prepared and flooded. Closer inspection might tell us if transplanting has been completed. By November the crop seems fully grown, but the colors do not tell us if ripening has started, or if the crop is affected by insects and/or fungal diseases. By February the crop has been long harvested and the straw has been burned off. Note that these images sell for US$600. The author bought a Landsat-7 image, not shown here, for March 2001, costing $50 from BSRSI. This appears to be a false-color image in which the infrared band 4 has been used to exaggerate the greens colors of plants, here mainly the tropical forest, since the rice crop has been harvested.

Vegetation Indices

Many techniques have been developed to analyze vegetation, most of which rely on mathematical formulas that compare or combine the Landsat and ASTER bands. The Normalized Difference Vegetation Index is commonly used as shown in the following images and described in detail by Terrill Ray of the California Institute of Technology (FAQ on Vegetation Indices).

The first image shows the NDVI using Landsat. The red area in the north along the coast is the location of the paddy fields, red now because of the bare soil that is visible. The straight lines indicate irrigation canals. The band of green crossing the image marks the second growth forest located on a dome of granite covered by resistant rocks of Cambrian age. The smaller patches of red are small fields and orchards and urban areas. Yellow areas represent vegetation that is mature or stressed because of lack of rainfall.

The next image shows the NDVI using the red and near-infared bands from an ASTER dataset dated February 2, 2002, about 11 months later than the first image. The condition of the vegetation may be slightly different, but what is remarkable is the greater detail in the ASTER image, which has a resolution of 15 meters compared to 30 meters for Landsat. The average family holding is 5 hectares (about 225 x 225 meters). In a fully zoomed image this size of holding would be represented by about 7x7 Landsat pixels or 15x15 ASTER pixels. (In practice the holdings comprise smaller scattered parcels.) While both Landsat and ASTER datasets appear to have sufficient resolution for managing irrigation facilities, the ASTER image shows the smaller canals while Landsat does not. The greater detail might be useful in assisting Water Users Associations to resolve differences concerning water rights. (Some striping is visible in the ASTER image, resulting from characteristics of the sensor. This would normally be removed by filtering or by a technique based on Fourier analysis).

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