Landsat monitoring of Chinese Da Xin an lin forest fire region

Landsat monitoring of Chinese Da Xin an lin forest fire region

Wang Xinmin, Hu Deyong, Dai changda,
Pan Xizhe, Wang Zhensheng
Remote Sensing Satellite Ground Station,
P.O. Box 2434 Beijing, China

Abstract
Landsat data was used to monitor Da Xin An Lin forest fire and also to study environment changes after the fire. The derived information and findings have been very useful to fire suppressing activities and the forestry department.

Introduction
From May 6 to June 2, 1987, huge forest fire occurred in Da Xin An Lin, North-East of China. We monitored the fire, using TM data. The interpretation results provided a timely grasp of the actual fire status over the whole area and were very useful in decision making for fire-suppressing activities. After the fire was just over, digital mosaics of the whole fire-affected are in different scales and a total fire-affected are of 1.26 million hectares was calculated. These materials and related TM data (prior to, during and after the fire period) provide valuable information for environmental change study and forest rehabilitation planning.

Band selection for forest fire monitoring
Conventionally bands 4, 3 and 2 are used in false color composite. Recently bands 4, 5 and 3 (or 1) are suggested to include the informative band 5<1-2>. Both these combinations do not fit the requirements for forest fire monitoring.

It is recognized that the fire temperature of the burning grassland and grass plot within the forest, as well, may reach some 500-6000C. For fallen leaves, branches, stubs and bushes, the temperature may be 100-2000C higher. In Da Xin An Lin the forest is dominated by timber, rich in turpentine and pine tar, the temperature may even exceed 10000C. Besides, along the path of forest fire cyclone wind, there is a low altitude high temperature zone. In its central part the temperature may reach as high as 12000C. For monitoring the surface temperature of the land or ocean (at around 3000K) AVHRR 4 and 5 or TM 6 is commonly used. For temperature range 1200-15000K, the blackbody peak emittance moves to 1.93-2.41. TM 7 (2.08-2.35u) is the best for this purpose.

Consequently TM 7, 4 and 3 in color rendition of red, green and blue sequence are used for color composite of the forest fire scenes. TM 7 reflects fire information of the forest and is nearly as informative as TM 5 in other respects. TM 4 is not sensitive to smoke and is used to reflect ground vegetation. This color combination provides image nearly in nature color and is well accepted by forestry departments.

TM processing and interpretation
TM data were routinely received and systematically corrected when landsat 5 passed Da Xin An Lin fire region. Interpretation results were immediately passed to the fire-suppressing authorities.

The night scene WRS 211/221 of May 13, 1987 covered the whole fire region at that time for the first time. It gave the actual fire status and accurate location of the fire fronts for both west and east wings and was used to correct AVHRR data to make fire status map. The AVHRR 212/221 night scene of May 20, 1987 showed the tendency of fire spreading to the Inner-Mongolian primeval forest region and helped to make emergent measures. The WRS 121/023 scene of May 23, which covered the east and central parts of the fire region, there were only two remaining small firing plots. One in the middle south would be blocked by swamp land between the valleys, while the other in the east was already surrounded by burned area. Consequently on May 25, the fire-suppressing authorities announced that the forest fire in the east and central parts were entirely under control.

WRS 122/023 scene of May 30, 1987 covered 90% or more of the all fire region. It showed that the Da Xin An Lin fire was basically under control except there might be some hidden burning plots with spreading smoke under the cloud in the west side. This inference was justified by WRS 123/023 scene of June 6, 1987.

After the fire was over a digital mosaic image of the whole fire-affected region (Fig.1) was made from TM WRS 121/023 (May 23), WRS 122/023 (May 30) and WRS 123/023 (June 6) scenes. Based on visual interpretation of several tens of window scenes, the degree of forest damage was classified and corresponding map (scale 1: 500,000) was made.

Fig 1 Mosaic image of the forest fire region in Da Xin An Lin

Environmental change monitoring
Da Xin An Lin fire occurred in a barren frigid zone at North latitude higher than 500. A large stretch of forest was destroyed and serious environmental changes ensued. We monitored these changes, using multi-temporal TM scenes prior to, during and after the fire. The scenes used are WRS 121/023 of June 5, 1986, June 13, 1989 and WRS 122/023 of Feb. 7, 1987, May 30, 1987, June 1, 1988 and Oct. 7 1988. A lot of 512X512 windows of areas suffering form different degrees of damage were chosen for investigation. The general conclusions are: in lightly damaged area the forest was basically recovered to its original state; in the moderately damaged area there was flourishing coverage of bushed and grasses and on its slope surviving trunks basically regenerated; in the heavily damaged area except grasses and bushes there was no living vegetation at all and its sunny slope there was sign of loss of soils.

For instance, there is a set of 512X512 windows around a small town named Xi Lin Ji. Before the fire, this area was heavily forested with some cutover spots. The town was entirely burned away in the fire, the forest was heavily damaged except for some small moderately damaged spots In the window scene of June 1, 1988 surviving forest in the moderate damaged area regenerated, while in the heavily damaged area, there were only few vegetation and grass coverage on the flat land along the roads. The heavily damaged area was already covered by grasses and bushed in Oct. 7,1988. Besides, there was sign of fire-affected timber collection in the upper right and low left of this area.

Another example is the set of windows around the Fresh Flower Mountain area. It had heavily, moderately and slightly damaged forest. Multi-temporal investigation showed that this area was dominated by larch. Within the past year, the light disaster area in the upper half of the window regenerated. No vegetation existed on the sunny slopes in the heavily damaged area. In addition, there was loss of soil. The shady slopes, however, were then covered by bushes and grasses. Along the river the flat farmland/marshland recovered.

References

Dai Changda, etc., Proc. Sino-French symposium on Remote Sensing Application, Press of surveying and mapping. 1988, pp. 19-27.
Charles Sheffield, P.E. and R.S., Vol. 51, No. 6. 1985, pp. 681-6.