Visualization of Water Levels from JERS-1 SAR Images Using Strong Scatters- Phitsanulok, Thailand
Figure 3. Full resolution images of the small rectangle area shown in Figure 2(a)
Figure 4 shows the upper-right-quarter of the SAR image observed in May 1998. Both the SAR image and the corresponding scatterers' map are brighter everywhere when compared to those of January, as previously mentioned.
Figure 4. SAR image and scatterers' map obtained from data observed in May,1998
Figure 5 shows the full resolution images of the area shown in Figure 3 (also arked in figure 4(a)). There is no corresponding VNIR data. In this case, the river appears more clearly and slightly wider against the bright background in the SAR image, although we cannot easily see the entire water level picture. On the other hand, we cannot easily distinguish the river from the surrounding area in the scatterers' map because scatterers are everywhere and rivers do not particularly stand out in such situations. However, we can easily grab the entire picture of water level rises from the isolated scatterers' map.
Figure 5. Full resolution images from the data observed in May,1998.
Figure 6 shows the scatterers' maps from November 27, 1997 to August 18, 1998. Those maps roughly indicate the water levels during this period. Examine the lower left quarter of the images. The number of bright fine features slightly increases from November to January and February. But these features increase significantly in May, indicating that the rainy season has begun. In July, the background becomes brighter and some very dark areas appear, indicating that the water gathers to lower places. In August, most of the bright fine features are gone. We interpret this to mean that water levels in narrow channels are lower than that in July, although it is still raining.
5. Conclusion
We can roughly estimate water levels in narrow channels and wet areas of Thai rice-growing areas from JERS-1 SAR images using isolated strong scatterers' maps. Although original SAR images may be better for examining water levels on a pixel-by-pixel basis in certain conditions, the isolated scatterers' map is superior for grabbing the entire water level picture at one time. We expect that the regional scale estimate for water levels could easily be obtained using these isolated scatterers' maps.
