The ERS backscatter shows a significant drop in values for Classes I to VI during the fire-period. This is expected as the vegetation on the ground has been destroyed resulting in weak backscattering. The radar backscatter signals increase very substantially when the fire has stopped burning. The radar backscatter signal after fire is equal to or higher than the level before-fire. The strong backscatter is possibly due to the dead vegetation stands on inundated or moist ground, resulting in an efficient double-bounce scattering configuration for radar backscattering. The inundated ground is probably due to the brief period of rains during the delayed wet season in late November/December [4]. For JERS SAR, Class I (Burnt Forests), Class III (Cleared Dark Lands) and Class IV (Paddy Fields) have the same pattern of change in the radar backscatter signal but the increse in backscatter after fire is not as substantial when compared to the case of ERS. Having a longer wavelength, L-band microwave has stronger penetration depth that results in less sensitivity to the moisture conditions on the ground. Class II (Cleared Bright Lands), Class V (Peat Swamp Forests) and Class VI (Secondary Forests) have little change in their radar backscatter values throughout the three different periods. Class VIII shows an atypical backscattering pattern in the ERS images. Its backscatter increases strongly during fire and stay constant after fire. From the SPOT images, this class does not show any different features than Class II, i.e. land cleared by fires between the grids of irrigation channels. The reason for its bright appearance is not understood.
Figure 6: Radar Backscatter Signatures of JERS images over different period of time (1 – Before-fire, 2 – Fire-burning, 3 – After-fire)


Figure 7 : Radar Backscatter Signatures of ERS images over different period of time (1 – Before-fire, 2 – Fire-burning, 3 – After-fire)

Fig. 8 : SPOT image of the study area acquired on 06 Jun 1997	Fig. 9 :SPOT image of the same area acquired on 08 Sep 1997
Fig. 10 : SPOT image of the area acquired on 20 Nov 1997

Conclusions
The change in ERS and JERS SAR backscatter of several land cover classes during the fire events in 1997 has been studied. Typically, for C-band ERS SAR, the backscatter of the fire affected areas decreases during fire and increases shortly after the fires, when the land becomes moist due to the rains. However, for the L-band JERS SAR, the backscatter typically does not vary significantly during and shortly after the fire periods.

References

• S. C. Liew, O. K. Lim, L. K. Kwoh and H. Lim, "A study of the 1997 forest fires in South East Asia using SPOT quicklook mosaics", Proc. 1998 Int. Geosci. Remote Sensing Symp., Vol. 2, 879-881, 1998.
• S. C. Liew, L. K. Kwoh, K. Padmanabhan, O. K. Lim and H. Lim, "Delineating land/forest fire burnt scars with ERS interferometric synthetic aperture radar",. Geophysical Research Letters, 26(16), 2409-2412.
• S. C. Liew, L. K. Kwoh, K. Padmanabhan, O. K. Lim and H. Lim, "Monitoring vegetation cover changes in peat swamp area of Central Kalimantan using ERS interferometric synthetic aperture radar", Paper Presented at the International Conference and Workshop on Tropical Peat Swamps - Safeguarding a Global Natural Resource, 27-29 July 1999, Penang, Malaysia.
• S. Couturier, S. C. Liew, M. Nakayama and H. Lim, "Monitoring vegetation regeneration in fire-affected tropical forests using ERS/JERS synthetic aperture radar", Proc. 1999 Int. Geosci. Remote Sensing Symp.