Assessment of ERS-l SAR Data for Rice Crop Mapping and Monitoring
Supan Karnchanasutham, Dr. Apichart Pongsihadldchai
Office of Agricultural Economics, chatuchak, Bangkok 10900, Thailand
Chockchai Rodprom
National Research Council of Thailand, chatuchak, Bangkok 10900, Thailand
Abstract
The objective of the study is to evaluate the capabilities of BRS-l SAR data for monitoring of rice planting acreage and its growth. The study area was about lOO Km in Tha Muang district, Kanchanaburi province. The ERS-l PRI. acquired during 35 day repeat orbit were used in the study. These data were acquired on 20 August 1993, 29 October 1993 and 3 December 1993 respectively. The study area was divided into 10 test sites and each of which was randomly selected 6 sample areas for extensive measurements of rice plant parameters height, density, net weight, yield etc.) as wen as auxiliary infomtation (wind, rain, and growth stage etc.). A Global Positioning System (GPS) was used to locate and register test site boundaries and calculate the area of each test site. The BRS-l data were geometrically corrected to topographic map at scale 1 :50,000. The field boundaries of all of the surveyed test site were digitised and superimposed on the geometrically corrected data which is filtered by MAP filter method.
The result of the study revealed that it was very difficult to identify the rice crop if only single data was used. The rice planted area classified from date composite was found to be 20,253 hectares or about 27% of the total study area. The rice mapping accuracy was 78% while the overall accuracy was 79%. The very bright of backscattering coefficient (dB) was observed in August. This was due to the fact that the muddy broadcast rice was adopted in this area. The water level in the field for this type of planting method was very limited. The closer to the harvesting date of the rice crop is, the better classification of planted area would be obtained.
Introduction
Rice is the most important crop in Thailand in terms of acreage, number of, farmers and export earning. The ability to monitor and forecast its production is therefore vary crucial for short term policy determination.
One major problem in utilising satellite data for crop area estimation is due to the cloud covers of the areas on the imagery because the needed data is in the rainy season. The capability of ERS-1 satellite that can see through cloud or all-weather conditions will make the estimation of crop area possible. The combination of SAR and other satellite data such as TM and SPOT will be very useful for crop classification in the area where cloud is always present all year round.
2.0bjectives
To evaluate the capabilities of ERS-l SAR data for monitoring of rice
planting acreage and its growth in Kanchanabw-i province.
3.Equipment and data acquisition
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Topographic map at scalel:50,000
- Aerial photography at scale 1:15,000
- Global Positioning System (GPS)
- Field equipments i.e compass, frame, counter etc.
- LANDSAT TM CCT Path 130 Row 50 acquired on 17 IAN. 1994
- SPOT CCT acquired on 26 Feb.1994
4. Study area
An 10X10 square kilometers area located in Amphoe Tha Muang Kanchanaburi province, Thailand between latitude 99o 37 44.1 E -99o 43 17.22 E and :'~, longttude13o 50 58N -13o 56 5 N was as the study area. This area IS part of the Mae Klong irrigation Project of the Mae Klong river basin which is one of the largest river basins in Thailand.
