| The upper reaches of Heihe river is located the middle section of Qilian mountains,which belongs to the arid and semi-arid area.Vegetation types such grassland,shrubs,forests,and meadow are diversity.They play an important role in ecological services,special in the water conservation in the Hexi corridor region.Monitoring the vegetation variation in the middle section of Qilian mountains can lay foundation for the protecting ecological environment in the region.Measuring and analyzing vegetation spectral reflectance are the precondition of monitoring vegetation dynamic changes in large scale by remote sensing technology.In this study,first,the spectral reflectance of plant population in growth period were measured by ASD FieldSpec 3 in 2016.At the same time,physiological and ecological parameters of vegetation(i.e.,leaf area,leaf area index,leaf chlorophyll content and biomass)were measured regularly.Then the relationships between the physiological and ecological parameters and the spectral reflectance are analyzed.And then,according to the relationships,the spatial distribution of physiological and ecological parameters are estimated by the images of GF1.The main results are as follows:(1)Elymus nutans Griseb,Potentilla fruticosa,and Caragana jubata are selected as the research objects and the canopy reflectance of the three species in different phenological periods are measured.In addition,we also measured the canopy reflectance of four species of alpine meadow.The result show that canopy reflectance of the same species in different phenological phase has same trend in the whole spectral range except for the near infrared spectrum,but obvious differences in the near infrared band.In the visible band,the order of canopy reflectance about four subalpine meadow species are in the order of Polygonum viviparum > Elymus nutans Griseb> Foeniculum vulgare > Potentilla anserina > Carex Evergold.However,in near infrared and mid infrared bands,the canopy reflectance of 4 vegetations four plant species is different.For two kinds of shrub species(i.e.,Potentilla fruticose and Caragana jubata),the canopy reflectance of Potentilla fruticosa in the range of 350~2500 nm is higher than that of Caragana jubata.The canopy reflectance of the two shrubs species reaches the maximum in the filling period in the range of 760~1350 nm.The difference between the spectral reflectance of different surface features is more obvious,especially for the vegetation and non-vegetation.(2)The vegetation indexes are calculated based on measured spectral reflectance of Elymus nutans Griseb,Potentilla fruticosa and Caragana jubata.We develop relationships between different vegetation index and LAI and leaf SPAD values in different phenological periods,being prediction models of LAI and leaf SPAD values in different phenological periods.The results show that there is the optimum phenological period to estimate the LAI and SPAD for a certain species.LAI and leaf SPAD values of Elymus nutans Griseb are best predicted in the heading and the filling period.However,the optimum predicting periods of Potentilla fruticosa and Caragana jubata for LAI are the leaf expansion period and the germination period,for leaf SPAD values the filling period.Biomass of vegetation were measured in the middle growth period of 2016.We use vegetation indexes DVI and SR705 to estimate biomass of shrub and grassland were DVI,SR705,but coefficients of determination are low,and the root mean square errors(RMSE)are big.That expresses predicting models are not good.The predicting models considering soil moisture are also not good due to low coefficients of determination and the high root mean square error(RMSE).(3)Selecting GF-1 images as data sources,we can estimate distribution of vegetation indexes.According to relationship between vegetation indexes derived from the field measurement and the physiological and ecological parameters,we can obtain distributions of physiological and ecological parameters based on GF-1 image data. |
PDF Full Text Request