| Rice is a kind of thermophilic crop,which is very sensitive to temperature variation.When rice suffers from persistent low temperature and insufficient sunshine or from short-term extreme low temperature during growing season,it will cause chilling injury.This is one of the main meteorological disasters faced by paddy rice.The middle and lower reaches of the Yangtze River is one of the main rice planting areas in China.In spring and autumn,affected by the cold air from the north,the middle and lower reaches of the Yangtze River are prone to "Late Spring Cold" in spring,resulting in rotten seeds and seedlings of early rice,and "Cold Dew Wind" in autumn,affecting the heading and fruiting of late rice.These are two main chilling injuries affecting the growth of paddy rice in southern China.Previous studies mainly focused on chilling injury of rice in Northeast China.The application of remote sensing technology to the monitoring of chilling injury in the middle and lower reaches of the Yangtze River is even less.To fill this research gap,this thesis carried out a research on chilling injury monitoring of paddy rice based on remote sensing technology over the middle and lower reaches of the Yangtze River.The tolerance of rice to low temperature is different at different growth stages,so the key technology to achieve remote sensing monitoring of rice chilling injury is to get full coverage daily average temperature,extract rice planting area and identify the key growth period of rice.In this paper,Hunan,Hubei,Jiangxi,Anhui and Jiangsu provinces were selected as study areas.Based on MODIS land surface temperature dataset,vegetation index calculated from MODIS land surface reflectance data,DEM dataset and air temperature dataset measured at meteorological station,six daily average air temperature estimation methods were designed by combining two different quality screening methods(high-quality screening and effective value screening)and three regression models(simple linear,multiple linear and random forest).The combination with the highest accuracy(effective value screening plus random forest regression)was select for daily average temperature estimation,and the full coverage daily mean temperature data of the study area from 2005 to 2018 was obtained after fusing and interpolation;Based on MODIS land surface reflectance dataset,the vegetation index,normalized flood index and MODIS land use data were used to extract the area of rice planatation and to identify its key growth period in the study area from 2005 to 2018.Combined with the standard of rice chilling injury,I assessed the extent of rice chilling injury in spring and autumn in the study area,estimated the affected areas and degree were estimated and validated monitoring results using statistical yearbook and literature.This thesis conducted the monitoring of the extent of the rice cold damage disaster in the study area from 2005 to 2018,made the estimation of the affected area and the disaster level,and analyzed the temporal and spatial distribution characteristics of the rice chilling injury.The results showed that the chilling injury of early rice in the study area was the most severe in 2010,82.58%of the area was affected,and the affected area in Hunan Province was the largest,reaching 1354 thousand hectares.In 2006,30.63% of the early rice was affected by chilling injury,and Hunan Province had the largest affected area of 384 thousand hectares.In autumn,the two chilling injury processes of rice in 2006 and 2011 were more obvious.In 2006,344 thousand hectares of rice were affected,and Jiangxi Province was the most affected area,accounting for 15.60% of its planting area.In 2011,a total of 335 thousand hectares of rice were affected,and Jiangxi Province also had the largest affected area,187 thousand hectares,accounting for 9.16% of the province’s rice planting area.From 2005 to 2018,the chilling damage of rice in spring and autumn was mainly mild. |
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