As a result, the annual discharge from the drainage system has increased from 0.15 billion m3 to 0.45 billion m3 on average, i.e. one-tenth of the total inlet water. The average TDS of the drainage water has increased from less than 1 g/L to 2 g/L, four times that of inlet water. Soil salinity has been gradually controlled. The average grain yield has increased from 1,005 kg/ha before 1960 to 6,450 kg/ha after 1996. It is obvious that the artificial drainage system plays an important role in this achievement. However, on average, 70% of the inlet salt, computed by the administration office using a simple salt balance method, is left inside the system every year. Assuming the salt is distributed evenly throughout the irrigated area, the amount of accumulation would be about 3,100 kg/ha/yr, which could lead to a severe salinity problem.3.?Materials and Methods3.1. Data SourceTo depict the history of past spatial and temporal changes in soil salinity in HID, archive remote sensing images were used. LANDSAT was chosen as the major source as it is the world’s longest continuously acquired collection of space-based land remote sensing data. Similar data from IRS (Indian Remote Sensing satellite) and CBERS (China-Brazil Earth Resources Satellite) were used when needed to compensate for the absence of qualified LANDSAT images.Images acquired in seven specific years (1973, 1977, 1988, 1991, 1996, 2001, 2006) were selected for this study. For each year, images acquired in March, June and selleck chemical August were used. The images acquired during March, when the land is not yet vegetated and salt surface features are enhanced due to the freeze-thaw process, were used to delineate salt-affected areas. Images acquired in June and August were used to delineate the cropped (irrigated) area, as June corresponds to the mature season for summer crops and August for autumn crops, i.e. when the leaf area reaches its maximum. Images acquired at adjacent dates were used as substitutes if no qualified image was available due to bad weather or sensor failures. Table 1 lists the data used in this study.Table 1.The images used in this study.To link changes in salinity with land and water management practices, data on annual irrigation depth, annual drainage depth, annual rainfall and monthly averaged groundwater table d
Images from satellite synthetic aperture radar (SAR) of the ocean surface have been shown to routinely reveal the sea-surface roughness signatures of marine meteorological phenomena [1, 2]. This is because the near-surface wind rapidly generates short surface waves (here, we are referring to the order of magnitude 1 to 10 centimeter wavelengths) that roughen the surface. The characteristic wavelength of the SARs referenced above is also order of magnitude 1 to 10 centimeters.