3. Data Reception and Processing in Hit
At a moment, HIT has two antenna systems, a 7.3 meters Transportable Ground Station (TGS) antenna and a 13 meters antenna, the latter was just established in March this year. Currently SeaWiFS and MODIS are received by the 7.3 meters antenna and Landsat-7/ETM+ and SPOT-1,2, and 4 are received by the 13 meters antenna. In addition, NOAA/AVHRR is received by a 1.2 meters antenna system.
Landsat-7/ETM+ data are processed soon after reception in the 13 meters antenna system. As the products, Raw, Level-0, Level-0R, Level-1R and Level-1G are archived. The format of Level-1R is HDF only and those for Level-1G are HDF, FAST and GeoTIFF. SPOT-1, 2 and 4 data are also processed in the 13meter antenna system and Level-1B with CAP format is archived as the SPOT data product. For NOAA/AVHRR, raw AVHRR data are converted to NOAA/NESDIS Level-1B format. For SeaWiFS and MODIS, all data are archived in HDF format.
4. Some Preliminary Results
We preliminary evaluated the spectral information by AVHRR, SeaWiFS, MODIS, and ETM+ data. AVHRR, SeaWiFS, and MODIS data were acquired on the same day (Aug. 4, 2000). ETM+ was acquired on July 22, 2000, almost same season as that for the formers. Figure 1 shows AVHRR false-color composite image, in which red and blue are assigned to band-1 and green for band-2. As there are only two bands for visible and near-infrared regions, there is no other way to enhance spectral information except NDVI, which will be discussed later.
On the other hand, as SeaWiFS has total eight bands in the same wavelength regions, there might be various band combinations to enhance spectral information in land areas as well as in water areas. Figure 2 shows an example for such an enhanced false-color composite image. In Figure 2, red is assigned to the enhanced image by the computation of (B6-B1)/(B6+B1), where B1 and B6 are data values for band-1 and band-6 respectively. This image enhances the difference of reflectance in band-1 (blue-color region) and band-6 (red-color region). The other two color components, green and blue, are assigned to band-8 (near-infrared) and band-4 (green-color region) respectively. Therefore the color image in Figure 2 includes all information from blue, green, red and near-infrared regions. The result clearly indicates the differences between forested land covers and urban/agricultural land covers, while in AVHRR image these differences are not identified so clearly.
Figure 3 shows an example of MODIS false-color composite image acquired on the same day as AVHRR and SeaWiFS. The color assignment is that red is assigned to band-6, green to band-2, and blue to band-1. Band-6, 2 and 1 correspond to band-5, 4 and 3 of ETM+ respectively. Figure 4 shows the false-color of ETM+ in the color assignment similar to MODIS, namely red is assigned to band-5, green to band-4 and blue to band-3. Both images indicate similar color tones for similar land covers. This result suggests that there might be a possibility to use both data as a complement data set as described in section 2.
Figure 5 shows an enhanced color image using principal component analysis (P.C.A.) for eight bands data only in water areas. The colors are assigned to the first three principal components, red to PC-1, green to PC-2 and blue to PC-3. The image clearly shows the differences in water quality between the water in Pacific Ocean and the water in coastal regions or Seto Inland Sea. Figure 6 shows the color image for sea surface temperature (SST) derived from AVHRR on the same day. It is clearly seen from both images that the boundary for two different water quality in Figure 5 corresponds to the boundary for two different temperature regions in Figure 6, namely between inner or coastal water areas with lower temperature and the warm ocean current (Kuroshio) with higher temperature. This result suggests that the combined use of visible information from SeaWiFS and thermal information from AVHRR is very effective for monitoring sea surface environmental conditions.
Figure 7 and 8 show the comparison of NDVI images derived from AVHRR and SeaWiFS data respectively. As described in section 2, there might be a possibility to improve NDVI parameter by using SeaWiFS band-6 as a visible band. The comparison of Figure 7 and 8 supports this improvement. In Figure 7 it is rather difficult to discriminate the differences between forested land covers and agricultural land covers (see Kyushu region in Figure 7). On the other hand, in Figure 8, it is very easy to discriminate these differences. The observation seasons of both images are summer and rice is planted in almost agricultural areas and it is almost a peak condition for rice-growth in this season. Therefore, the result of Figure 7 and 8 clearly supports that NDVI derived from SeaWiFS is more effective than that by AVHRR for monitoring vegetative conditions.
