| The surface albedo refers to the ratio of the solar radiation reflected from the earth's surface to the total solar radiation incident on the earth's surface.It reflects the net radiation energy reaching the earth's surface and the energy distribution between the earth's surface and the atmosphere.It is also an important parameter for the study of climate models and disaster monitoring.An important parameter.In recent years,as the global climate has gradually warmed,the ecological environment has been destroyed,natural disasters have occurred frequently,and the surface albedo has become the research hotspot as the first parameter in the land surface process.Guizhou Province,as the center of southwest karst area,has strong karst development and wide carbonate exposed area.According to different lithological distribution,three typical karst zones,pure-karst,semi-karst and non-karst,are formed,which are typical vulnerable areas of ecological environment.All along,the ecological and environmental problems in Guizhou Province have aroused widespread concern from the government and all sectors of society.Measures,vegetation as an important part of the ecological environment,under the influence of this natural environment and human factors,vegetation types and vegetation phenological changes are very susceptible.Surface albedo is very sensitive to changes in vegetation,and the size of surface albedo is also affected by factors such as vegetation type.Therefore,exploring the response characteristics of vegetation changes and surface albedo is of great significance to the improvement of ecological environment and climate monitoring in karst areas.In this paper,MODIS MCD43A3 surface albedo data,MODIS MCD12Q1 vegetation type data,MODIS MOD13A1 vegetation index data,surface observation data of Puding flux observation station and Landsat data are used as the main research data sources.Based on different karst zoning conditions,the relationship between vegetation type,vegetation phenology change process and surface albedo in the karst area from 2009 to 2017 was analyzed from the large-scale range with Guizhou Province as the study area.The spatial and temporal distribution characteristics of land use types and the characteristics of albedo changes were analyzed from three small-scale ranges with typical peaks,forest peaks and topography in Huishui County,Pingtang County and Luodian County.The conclusion is as follows:1)The MODIS surface albedo data products are compared and analyzed based on the ground measurement data of the Puding flux observation station and the medium-high resolution Landsat remote sensing images.The results show that the MODIS surface albedo products can be applied to karst areas and can reflect karst Changes in regional albedo.2)According to the analysis of MODIS vegetation type data,surface albedo data and the distribution of different karst areas,the vegetation types changed little in space-time distribution from 2009 to 2017.The area distribution of different vegetation types was forest land > cultivated vegetation > grassland > other,while different vegetation types had obvious distribution differences in different karst areas.The distribution of forest land area size The distribution of grassland area is pure-karst > non karst > semi-karst,while the distribution of cultivated vegetation area is pure-karst > semi-karst > non karst.At the same time,the surface albedo of different vegetation types in different karst areas also has obvious differences,which is shown as cultivated vegetation > grassland > other > forest land.3)According to the reconstructed NDVI time series data,the threshold method is used to extract the vegetation phenology indicators,and the analysis shows that the vegetation phenology shows a gradual advance from east to west at the beginning of the growth season,and a gradual backward trend from west to east at the end of the growth season,and the length of the season It gradually increased from west to east.The beginning of the growing season is mainly concentrated on the 74 th to 120 th day of Julian day,the end of the growing season is mainly concentrated on the 330 th to 346 th day of Julian day,and the length of the vegetation growing season is more than 252 days;combined with the surface albedo Analysis of the change trend shows that there is a certain linear relationship between the change of vegetation phenology and the change of surface albedo.The effect of vegetation phenology on surface albedo is as follows: length of growing season> end of growing season> early of growing season.4)Different vegetation types have different inter-annual changes in vegetation phenology.At the early of the vegetation growth season,the woodland,grassland and cultivated vegetation all show an early trend.There is an early trend,and all vegetation types are delayed in the length of the growing season.5)From 2009 to 2017,the land use has undergone a strong mutual transformation.Among them,the area of forest land,construction land and water body shows an increasing trend,and the grassland and cultivated land are in a decreasing trend;while the surface albedo of different land use types has a certain difference.For the trend of construction land> cultivated land> grassland> forest land> water body,the characteristics of the surface albedo change in different karst landforms are consistent with the overall change trend.In general,the surface albedo will not only be affected by natural and human factors It will also be affected by changes in land-use types and different landform features. |
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