An inexpensive and effective basis for monitoring rice areas using GIS and remote sensing

To ensure orderly, planned rice production, and to meet environmental constraints on the location of rice in the landscape, there is a need to locate and measure the area of rice plantings by paddock and by farm. Traditionally, rice areas have been estimated from manual measurements taken from aerial photography: overall, an expensive and time-consuming approach. In a pilot study covering 5 seasons on an area of 6 by 6.25 km containing 160 paddocks in 22 farms, we have found that it is possible to locate rice areas accurately, to determine their size, and to classify the vigour of the crop. Information is transferred into a geographic information system from classified satellite imagery using Landsat Thematic Mapper bands 3, 4, and 5 and then processed with a simple rule to distinguish rice rapidly from other crops. Furthermore, the classification categorises rice within each paddock into 3 statistically distinct groups of poor, medium, or good crop vigour. Total rice area and area of each rice class are computed for each rice paddock. Paddock data are combined to give corresponding values for each farm and for the entire study area. This information could be useful for forecasting rice yields in the current season and for the management of paddocks for more uniform and higher yields in subsequent seasons. The procedures used require inexpensive software and are largely automated since they include unsupervised clustering. The need for special skills is thereby minimised, making the transfer of the technology to interested parties quite straightforward. Over the 5 seasons, all paddocks growing rice were correctly identified and only 2 non-rice paddocks wrongly identified as growing rice.