Remote Sensing Monitoring Of Rice Planting Structure Changes In Jianghan Plain

Since the 1980 s,due to natural factors and socio-economic development,rice planting in the Jianghan Plain has undergone complex changes in both spatial distribution and type composition,which makes it extremely challenging to quickly and accurately acquire the complex rice planting structure in the region on a large scale and a long time scale.To solve this problem,the key lies in the accurate recognition of different types of rice remote sensing in different periods and the objective analysis of their temporal and spatial characteristics.In this paper,Jiangling County,known as a grain-producing County in Jianghan Plain,is taken as the research object.The remote sensing image data set of long time series is taken as the main information source.According to the characteristics of different types of rice gro wth and development,the visualization of rice type expression and the enhancement of rice information image characteristics are carried out by using remote sensing multi-characteristic index.Based on this,machine vision recognition technology was applied to classify and extract three types of rice in the study area from 1987 to 2018: early rice,middle rice(including rice-shrimp)and late rice.On this basis,the rice planting structure and its spatial and temporal variation characteristics in the region were analyzed and studied by means of geometric center of gravity displacement and spatial transfer matrix of crop distribution.The results show that:(1)By combining the RVI index of different rice types at maturity with NDVI index and LSWI index at transplanting stage and combining with the suitable RGB color matching scheme design,different rice types,such as double cropping rice,medium rice and shrimp rice,not only show unique image color characteristics,but also produce obvious color difference with easily mixed land.In HSV color space,machine vision color clustering is used to extract remote sensing information of rice.The overall classification accuracy and Kappa coefficient are 93.35% and 90.79% respectively,which are higher than those of rice recognition based on time series NDVI image classification.(2)Over the past 30 years,the rice planting structure in Jiangling County has shown obvious staged changes with 2008 as the node.In the first ten years(1987-1996),the total area of rice in the county increased slightly,and the rice planting structure consisted of two-cropping rice and one-season mid-season rice.In the following ten years(1996-2008),the rice planting area declined sharply until 2008,when the rice planting area dropped to the lowest level.At the same time,the rice planting structure in that year was very single,with only one-season rice.In the last 10 years(2008-2018),rice planting structure has become more and more complex,including not only traditional early and late rice and one season mid-season rice,but also more shrimp rice.The total area of rice has also increased significantly,which is mainly due to the significant increase in the area of local mid-season rice.In recent two years,its planting area is much larger than that in the 1980 s and 1990 s.From 1987 to 2018,the area of double-cropping rice in Jiangling County first increased,then began to decline year by year,until 2008,it was almost negligible.Since then,the area of double-cropping rice has increased,but still less than in the 1980 s and 1990 s.One-crop rice has always occupied the dominant position in the rice planting structure in Jiangling County,but its area change is based on 1996,showing a trend of decreasing first and then increasing gradually,and increasing significantly after 2008.In addition,the late rice planting in Jiangling County in recent two years,not only mostly from the early rice harvested after the formation of Ratooning rice,but also its area is smaller than the shrimp rice planting area.(3)The distribution of Mid-season Rice in Jiangling County is more balanced among villages and towns,and its area center of gravity is closest to the geographical center of Jiangling County.The spatial distribution of double-season rice in Jiangling County is quite different.The area center of gravity of double-season rice in Jiangling County is not only far from the geographical center of gravity of the county,but also gradually moves to the Northeast in 1987-2018,especially in late double-season rice.In the past 30 years,the net increment type transformation of double-cropping rice and one-cropping rice in Jiangling County basically occurred between them and other types of rice,but 2008 was a special year,the Double-cropping Rice Planting in Jiangling County basically disappeared,and most of them were transferred to one-cropping rice(4)From the qualitative analysis of the driving factors of the spatial and temporal changes of rice in Jiangling County,the most direct reason is the socio-economic factors.The adjustment of market economy and the transfer of rural population labor force directly affect the change of rice area.From the quantitative analysis of driving factors,the core factors affecting rice planting in Jiangling County before 2008 are cotton planting area,total agricultural output value and total power of agricultural machinery,but the core factors after 2008 are effective irrigation area,rural working population,vegetable and fruit area,drought and waterlogging harvesting area and total power of agricultural machinery.