| Poyang Lake Wetland is a typical lake wetland in China.There are more than 50 kinds of national protected birds inhabited here or as migration transit sites,and it is one of the important grain producing areas in southern China,which play an important role in maintaining regional ecological balance and in maintaining and protecting international biodiversity.But in recent years,many problems happened in Poyang Hu region such as vegetation degradation,species habitat destruction,lake shrinkage,water quality deterioration,etc.The development of remote sensing technology provides massive data for the survey of wetland resources,which facilitated large-scale monitoring and research work on wetlands.The classification and change monitoring of Poyang Lake wetland can help to understand the temporal and spatial evolution and regularity of Poyang Lake wetland objectively and grasp the distribution and change characteristics of wetland resources,and provide basis for wetland protection and scientific decision-making.This article takes the aera around Poyang Lake as the research area.Remote sensing image data such as Landsat series satellite data,GF-1-WFV data and HJ satellite data and other auxiliary data are used.Based on the analysis of wetland characteristics of Poyang Lake,extracting wetlands such as sand,water,grassland and bare beach in the main lake area of Poyang Lake by Support Vector Machine classification,and constructing classification rules of Poyang Lake ring lake area to distinguish paddy Field,water Body,sandy land,forest land and construction land,for classifying the typical wetlands in the study area.Then the distribution and area changes of the wetlands in the main lake area in different seasons were monitored and analyzed,and the distribution and area transfer of paddy fields in the study area over 40 years were monitored and analyzed.Through research and analysis,the following conclusions are drawn:(1)Due to the differences of spectral channel setting,atmospheric correction parameters setting and geometric position of image points among Landsat8-OLI,GF1-WFV and HJ-CCD satellite image sensors,the reflection spectrum of imaging data at the same coordinate point have similar trend,but the reflection values are not completely consistent.The HJ image reflectivity is higher overall,and the recognition of ground boundary is blurred.The Landsat8 image has low reflectance in the near-infrared region and is sensitive to water and vegetation.The meticulous ground objects can be recognized in the GF1 images,but the number of bands is limited.Landsat image should be the main image in the study,and HJ image and GF1 image should be used to supplement the missing phase;(2)In the study area,the natural waters and reservoirs and ponds have different reflectances in the visible range,and the near-infrared band approaches zero.The reflectivity of grassland and forest land varies greatly in season in near-infrared band,and the maximum difference is about 0.25 and 0.2 respectively.Due to different farming methods,the rice fields have significant spectral differences between no rice period and planting period,which are similar to those of other wetlands in the same period;(3)The POA of sand,water,grassland and bare beach wetlands extracted by support vector machine is over 98%,with the PPA and PUA of water body and Caozhou are over 98%,so the distinguishing effect is good.Using the DT classification rules to distinguish the water bodies,forest land,paddy fields,sandy land and construction land in the surrounding lake area with POA higher than 95%,and the Kappa coefficient is more than 0.93,and the PPA of paddy fields is over 94%;(4)Affected by the climate,topography and human factors of the study area,the distribution and area of wetlands in the main lake area vary greatly.From May to September,the water area of the lake area is above 2300 km2,and the highest water area accounts for more than 94% of the total area.During the dry season of Poyang Lake,the area of Caozhou remained above 1200 km2,mainly distributed on both sides of the river into the lake delta and the lake channel.Grassland and sand have the fastest growth rate after the water area shrinks in October;(5)The paddy field area of Poyang Lake has remained above 5000 km2 for more than 40 years and fluctuated around 6000 km2.In the past 15 years,the fluctuation trend has weakened and the area has approached 6000 km2.Urban expansion occupies large areas of paddy fields,and the distribution of forest landsbut was fragmented.From 1989 to 1995 and from 2008 to 2013,other types were transferred to paddy fields with 1673.90 km2 and 1482 km2 respectively.From 2013 to 2018,the paddy field decreased by 446.27 km2 and the unchanged area exceeded 5200 km2.Human development and utilization of Poyang Lake resources is one of the main reason for the continuous change of paddy fields. |
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