Four dates of Landsat Thematic Mapper data from 1993, April 9, July 30, August 15, and September 16, were used to assess temporal and spatial patterns of lake area and dimensions of suspended sediment concentration in Tuttle Creek Reservoir, Kansas. In 1993, excessive precipitation in the Big Blue River Basin, and throughout much of the Upper Middle West, led to widespread flooding. Rains produced substantial erosion, sediment movement down the stream network, and a runoff volume that filled Tuttle Creek Reservoir, a U.S. Army Corps of Engineers flood control structure. The April 9 data are from before the flood, the July 30 data are from the time of maximum pool size and use of the emergency spillway, and the August and September data document the declining pool sizes. Three separate analyses were performed on each of the four dates of Thematic Mapper data. One set of analyses involved applying an existing physical model that uses at-satellite reflectance for TM Band 3 to estimate variations in suspended sediment, turbidity, and Secchi depth throughout the reservoir. Maps of estimated parameters of water quality for the four individual dates were compared and analyzed to document spatial and temporal changes. The second research method involved unsupervised classification (ERDAS ISODATA algorithm) of the data from the Tuttle Creek Reservoir. Water areas were grouped into coherent classes for further spatial analysis using a two-step or layered classification procedure for each date. The third analysis used a GIS overlay technique to compare the area of the water surface for each of the four dates with the flood pool as marked on U.S.G.S. 7-1/2 minute quadrangles. Comparisons document the major change in lake area between April and July, the high levels of suspended sediment in mid-summer, and the decline in pool size and concentrations of suspended sediment by mid-September. The study illustrates the advantages of using remote sensing to assist in documenting a relatively short-term environmental hazard. This study also demonstrates the value of Landsat Thematic Mapper data for use in mapping geographic variations in water area and quality in conjunction with a major flood event. 相似文献
正1 Introduction The Lop Nor playa,located in the eastern end of the Tarim Basin,capped with a thick salt crust covering an area of approximately 5,500 km2(Ma 2007)that closely resembles a"Great Ear"in satellite images.Understanding the formation of the salt crust can provide important 相似文献
In the absence of a sufficiently dense network of climate stations covering all topographic regions of the Indus River basin and delivering high quality data over the last 30 years or more, daily precipitation data were obtained from the National Centers for Environmental Prediction-Department of the Enviornment (NCEP-DOE) Reanalysis 2 dataset for the period 1979 to 2011. The daily precipitation data were transformed into time series of frequency of extreme precipitation events of 1-day and 10-day durations defined in terms of 90th and 99th percentile threshold exceedances. The non-parametric Mann-Kendall trend test was applied to determine whether statistically significant changes in precipitation extremes occurred over time, in due consideration of autocorrelation in the data.
Extreme precipitation showed a high spatial variability, with the highest daily and 10-day precipitation totals, and thus highest 90th and 99th percentiles, in the southeastern lowlands at the foot of the Himalayas and the lowest in the Karakorum. Significantly decreasing trends in extreme precipitation were observed in the western part of the Indus River basin; significantly increasing trends were mainly detected in the very high mountainous regions in the east (Transhimalaya and Himalayas) and in the north (Hindu Kush and Karakorum) of the Indus basin. High precipitation rates are not common in the arid climate of these high mountainous regions. Future flood management plans need to consider the increasing trends in extreme precipitation events in these areas. 相似文献