An approach to monitor pine caterpillar
using TM imagery
Dai Changda, Lei Liping,
Hu Deyong, Wang Jiesheng
Remote Sensing Satellite Ground Station
Chinese Academy of Sciences
P.O. Box 8701
Beijing, China
Abstract
This paper deals with an approach to monitor pine caterpillar damage by using TM image. Through numerical analysis of samples, a set of TM data image processing methods were developed accordingly. Calculating and classifying the normalized perpendicular vegetation index and greenness change index provided an effective measure to detect insect damage of forest. A damage map with three levels varying from severe, light and unaffected was mode out. The area of each level and its attribute percentage were counted based on pixels and had satisfied accuracy comparing to the field investigating results. This map showed comprehensively the caterpillar damage status and could meet the requirement of practical utilization.
Introduction
In recent years the pine caterpillar spreads widely and rapidly in China and causes damage to the forest not less than the forest fire. We have carried out an experimental study on monitoring caterpillar by the TM data with an aim to get timely precise pest information which is important in taking action against the pests.
Study site and TM data
The study site is a state-owned Gushan forest farm in Chuzhou county, Anhui province, located in the lower middle reaches of Yangzi river. In that area valleys were cultivated for growing rice, wheat, rape and other crops. The hill slopes were afforested dominantly with Masson pine trees after 1950. Now the man-make pine forest has grown up, but caterpillar becomes a problem. In the spring of 1988 more than half of the forest suffered different disaster of pest damage. After treatment, the over sintering caterpillar were under controlling the spring of 1989. Two WRS 123/28 scenes of TM data of April 23, 1988 and April 26, 1989 were chosen. Comparison can, therefore, be made not only among different field locations for 1988, but also between the same field locations of 1988 and 1989.
Image processing and information extraction
Caterpillars Consume pine needles, causing reduction of leaf are and changing thermal status in the plant. This will decrease brightness of TM4 and increase that of TM 3,5 and 7, . But these changes are influenced by many interfering factors caused by complicated ground objects and atmospheric conditions. The following processing stapes are taken to enhance our required information.
- Statistical Analysis of Image
The statistical analysis of the study site windows for 1988 and 1989 TM data shows: the mean brightness of all bands except TM4 and the minimum brightness for all bands are higher in 1988 while ratio of TM4 and mean brightness of TM4 are higher in 1989. This indicates the reduction of biomass in 1988 by caterpillars.
- Rationing and Smoothing of Data
Spectral analysis of forest areas in different pest-affected levels and non-forest ground objects such as residential area, cultivated field, water body, etc., shows that they are very complicated in spectral characteristics and dispersed widely in brightness. TO eliminate the interference from these non-forest ground object, ratioing of TM4 to TM3 was carried out and followed by 5X5 template smoothing.. These processing provides a means to differentiate the pine forest by the complicated background.
