The Development And Application Of The Monitoring Method Of Lake Ice Based On MODIS Images

As the third pole of the earth and the main components of the third pole,the Qinghai-Tibet plateau has a unique geological and geographical-ecological environment,the adjacent to the area of climate,vegetation,etc.Under the background of global warming,the geographical environment change of qinghai-tibet plateau has become a common concern of scholars.The qinghai-tibet plateau has many lakes and is affected by high altitude.The temperature of the lake area is lower than freezing in the cold season,thus forming the lake ice periodically.Lake ice phenology as an important part of lake ice and one of the elements of cryosphere,strong responses of a local and global climate change,and the long time sequence can be used as the climate change research of alternative materials.Based on Terra MODIS data and Landsat TM/ETM+/OLI images,on the analysis of the Lake,the Lake Ice features related to the reflectivity of differences in visible light,infrared spectrum,based on the combination of normalized difference snow Index(NDSI)to build a new remote sensing identification algorithms-Lake Ice Index(LII),and the qinghai-tibet plateau lakes,lake ice in remote sensing automatic monitoring and lake ice phenology characteristics analysis,research shows that:(1)The maximum difference between lake ice and water reflectivity is located in the red band,and the lake ice index based on NDSI and red band can effectively expand the spectral difference between lake ice and lake water.In terms of namtso freeze-melting period,the lake ice index method than other lake ice monitoring method has better monitoring effect,its most big mistake like yuan area do not exceed 3.5% of the total area of the lake,but the method of thin ice monitoring ability are relatively weak;In different periods of lake ice,using the index of the lake ice lake ice data extraction accuracy exists obvious difference,appear frozen period is better than that of melting period and freeze the worst characteristics,including the existence of ice on the lake is the main cause of this difference.In all the sample lakes,the difference between the lake ice ratio and the "truth value" of remote sensing monitoring is less than 5%,which indicates that the LII index constructed in this paper has good applicability and can be used for rapid monitoring of lake ice.(2)The frozen-ablation process pattern of the Qinghai-Tibet plateau lakes(area > 100 km2)can be classified into 3 categories,respectively,namely,the frozen-ablation process intact-stable type(such as qinghai lake),intact-unstable type(such as the wuling lake)and incomplete type(such as pegu fault).The Qinghai-Tibet plateau lakes,lake ice started to freeze and full freeze concentrated on November and December of each year,the freezing process lasts about 20 d;lake ice began to melt and melt completely in April and May,with an average duration of about 22 d.Lake completely freezing period lasts about an average of 119 d.Lake ice began to freeze,completely freeze,stage started melting and melt completely although there are large differences in space,but still showed some regularity,namely lake lake ice started to freeze and completely freeze in northern Qinghai-Tibet plateau and the Hoh Xil area as the center to postpone gradually,the lake ice began to melt and completely melt period and the former show the opposite trend.Lakes in the ice period duration obvious spatial differences,frozen duration and ablation duration without apparent regularity,whereas lakes freeze completely showed more obvious spatial distribution,namely big the Hoh Xil and northern the Qinghai-Tibet plateau as the center to the plateau edge gradually reduced.(3)During 2001-2016,the Qinghai-Tibet plateau lakes,lake ice started to freeze delay per year on average about 0.23 d,the lake ice freeze completely delay per year on average about 0.10 d,the number of lakes occurred early accounts for about 38% of the total number of lakes,the lakes are different degree of delay happened;On average,lake and lake ice began to thaw at an average of 0.42 d per year,with the delayed lake accounting for 63 percent of the total lake and 37 percent of the early lakes.The average total ablation period of lake and lake ice is about 0.35 d per year,and the delayed lake accounts for 48.3% of the total number of lakes,and 51.7% of the total lake.According to the instruction from the lake ice phenology characteristics of climate change,found that the Qinghai-Tibet plateau in the autumn and winter in 2001-2016,the average in a warming trend at the same time,also showed obvious space difference,the southern plateau lakes around,as well as the Hoh Xil nature reserve in the northeast,showed a trend of a warming climate,near the center of the Hoh Xil nature reserve in northwest plateau region,presents the tendency of a cold climate.During the spring and early summer season,the average of the Qinghai-Tibet plateau in a cooling posture,among them,the southern Qinghai-Tibet plateau and the east of the plateau at the Hoh Xil lake,Ulan Ul lake,Tu Cu and Gereng Cu,present a warming trend,in other parts of the plateau,especially at the center of the Hoh Xil nature reserve zone and represented in northwest plateau region,presents a cooling trend.