Satellite reflectance: Suspended sediments increase the radiance emergent from surface waters in the visible and near infrared (NIR) proportion of the electromagnetic spectrum. The Landsat TM and ETM+ visible and NIR bands, 1-4, are optical bands recording electromagnetic radiation of 0.45-0.52, 0.52-0.60, 0.63-0.69 and 0.76-0.90 Î¼m, respectively. Cloud-free pixels in the middle of the river width, counting the information only from water surface but not from land, were used to estimate SSL.
Since analysis was carried out for individual image with quite a small angular range, the atmospheric correction has a little effect on correlation analysis. Thus, the atmospheric correction was neglected. The analysis involved transformation of the raw Landsat TM and ETM+ digital numbers (DNs) to physical values of 1 radiance using in-flight sensor calibration parameters. Landsat data: Landsat scenes captured between 1988 and 2000, including 110 Thematic Mapper (TM) images and 21 Enhanced Thematic Mapper Plus (ETM+) images were used to estimate the patterns of suspended sediment load in the Mekong. The spatial resolution of TM and ETM+ data is 30 m (except for band 6 of the thermal infrared channel with 120 m). The images were acquired from the different seasons of the year from the Landsat archive from the United States Geological Survey (USGS) (http://glovis.usgs.gov). The three visible and near infrared bands were included in the analysis. These data were combined with in situ measurements for determination of statistical relationships between reflectance of different TM and ETM+ bands and SSL. The monitoring cases from 1988 to 2000 were used to illustrate the longitudinal profiles and the temporal change of SSL of the Mekong.
Last date updated on June, 2014