Key Techniques Of Remote Sensing Retrieval Of Vegetation Eco-water In Western Sichuan Plateau

The coupling of vegetation and hydrological cycle is the core issue of the international geosphere biosphere project"Biological Aspect of Hydrological Cycle",and it is also the research difficulty of ecological hydrology.In the research of ecological hydrology,vegetation eco-water(layer)is an important part of hydrological cycle.Vegetation eco-water includes the water storage of vegetation itself and the water storage of vegetation root soil vegetation atmosphere interface plays a key role in the process of material exchange and circulation.Scientific estimation of vegetation eco-water is of great scientific significance for fully understanding the transmission mechanism and law between vegetation soil atmosphere water.Remote sensing technology provides an important means for quantitative retrieval of vegetation eco-water at regional scale.However,it is difficult to accurately retrieve vegetation eco-water from a single remote sensing data source.How to coordinate multi-source remote sensing data and scientifically and effectively improve the estimation accuracy of vegetation eco-water is a key technical problem to be solved.Based on the National Natural Science Foundation of China(41671432)and the Sichuan Natural Resources Department Project(KJ-2020-05),the research area of Sichuan Plateau is rich in water resources.Based on the advantages of optical,SAR and Li DAR remote sensing,this paper quantitatively inverses and analyzes the vegetation eco-water under the stress of 5·12 Wenchuan earthquake in the Western Sichuan Plateau during the wet dry season,in order to enrich the quantitative study of vegetation eco-water and reveal the effect of vegetation ecological hydrology.The research contents and achievements are as follows:(1)Based on the Landsat optical remote sensing vegetation index,a new vegetation moisture content(FMC)inversion model is constructed,and the range projection ratio index(DPRI)is improved.The DPRI is retrieved from the re sampled broadband reflectance hyperspectral data.The FMC inversion model FMC_DPRIL was established by combining it with simple ratio vegetation index-FMC_DPRIL-SR,the model 10 fold cross validation coefficient(R²)=0.73,relative root mean square error(r RMSE)=12.19%.(2)An inversion method of water storage of implant is proposed by combining optical remote sensing,SAR and Li DAR.First,use FMC_DPRIL-SRinversion FMC;Secondly,microwave remote sensing was used to retrieve the biomass,which was divided into shrub,grass,grassland and woodland biomass.A random forest(RF)inversion model(R²=0.67,r RMSE=12.04%)of shrub and grass biomass based on S1 information index was constructed,which cooperated with lidar and alos Parsar,established RF forest height inversion model(R²=0.64,r RMSE=12.9%)and DBH RF inversion model(R²=0.61,r RMSE=13.91%),according to the results of forest height and DBH inversion,constructed a new forest biomass inversion model(R²=0.67,r RMSE=13.93%);finally,combined with vegetation water content and biomass,calculated the water storage of vegetation.(3)A new inversion model of root soil water storage(SEE-WP-RSM)was constructed.The WCM-PARSAR model was used to calculate the root soil moisture content,and the see method was used to calculate the root soil thickness.Then,the see-wp-rsm model was constructed based on the characteristics of root soil moisture content,root soil thickness and soil bulk density.Finally,the root soil water storage in the Western Sichuan Plateau during the dry period,wet period and before and after the Wenchuan earthquake was calculated by using the model.(4)Combined with DPRI?L and LST,a new vegetation index model under drought stress,was established based on TVDI_DPRIL-LST,the drought degree of Western Sichuan Plateau can be divided into six grades.An inversion method of vegetation eco-water based on optical remote sensing,SAR and Li DAR is proposed.Firstly,the inversion models of vegetation water storage and root soil water storage in typical experimental area of Western Sichuan Plateau are obtained.Secondly,the above models are used to retrieve vegetation water storage and root soil water storage in four periods of Western Sichuan Plateau.Then,the vegetation eco-water in four periods of Western Sichuan Plateau is calculated.The vegetation eco-water is the sum of the water storage of the vegetation itself and the water storage of the root soil.Finally,the response of the vegetation eco-water in the Western Sichuan Plateau to the seasonal changes and the 5·12 Wenchuan earthquake stress is analyzed.The results showed that:the change of water storage of different vegetation types in wet and dry seasons was evergreen forest,mixed forest,deciduous forest,shrub grass and grassland;the change of eco-water storage of different vegetation types in wet and dry seasons was grassland,evergreen forest,deciduous forest,shrub grass and mixed forest;The change of water storage of vegetation in different degree arid area of Western Sichuan Plateau is 2.494033623×10⁹Mg,and the change of water storage of evergreen forest is the largest,which is 2.071349492×10⁹Mg On the whole,the change of water storage of vegetation in dry season is higher than that in other drought grade areas;the ecological water of vegetation in different degree of drought area is 4.718495449×10¹⁰Mg;the change of eco-water of vegetation in dry season is larger than that in other drought grade areas;The water storage of different types of soil vegetation in the Western Sichuan Plateau is higher in the wet season,and vice versa in the dry season.The change of water storage of calcareous rudiment vegetation is larger in the wet-dry season(6.079806×10⁸Mg),followed by gley soil with high activity(4.73824×10⁸Mg)and dark gley soil(4.01387×10⁸Mg)The amount of water storage of calcareous rudiment is larger(1.405017×10¹⁰Mg),followed by dark gley soil(1.119915×10¹⁰Mg)and denatured rudiment(5.770063×10⁹Mg);the total water storage of vegetation is 6.639086803×10⁹Mg in dry season The results show that the total water storage of vegetation is9.133120426×10⁹Mg in wet season,2.494033623×10⁹Mg in wet-dry season,27.31%in wet-dry season.The total vegetation eco-water in dry season is 1.86658285×10¹¹Mg,the total vegetation eco-water was 2.33843239×10¹¹ Mg in wet season,the total vegetation eco-water change is 0.4718495449×10¹¹ Mg,the variation of total vegetation eco-water in wet and dry seasons accounted for 20.18%of the total vegetation eco-water in wet season;and 0.073810898×10⁸Mg in 5·12 Wenchuan earthquake,the total vegetation eco-water under earthquake stress is0.97868833×10⁸Mg.The main innovations of this paper are as follows(1)An inversion method of water storage of implant is proposed by combining optical remote sensing,SAR and lidar.Firstly,a new vegetation index DPRI is established by using Landsat information DPRI?L.Combined with simple ratio vegetation index(SR),a new multi vegetation index FMC inversion model is constructed FMC_DPRIL-SR.Secondly,the vegetation biomass is divided into shrub grass,grassland and woodland biomass by microwave remote sensing inversion,and the inversion model of shrub grass and grassland biomass is constructed based S1,and the woodland biomass inversion model based on lidar and ALOS PARSAR is proposed;finally,the water storage of vegetation body is calculated by combining biomass and vegetation water content.(2)A new inversion model of root soil water storage(SEE-WP-RSM)was constructed.Firstly,a new inversion model of soil moisture content of root system WCM-PARSAR is established;secondly,a new model of soil thickness inversion of root system-SEE model,is established;finally,the SEE-WP-RSM model is established by using soil moisture content,root soil thickness and other soil properties parameters.(3)An inversion method of vegetation eco-water is proposed by combining optical remote sensing,SAR and Li DAR.Firstly,the inversion models of vegetation water storage and root soil water storage in the typical experimental area of Western Sichuan Plateau are obtained;secondly,the above models are used to invert the vegetation water storage and root soil water storage in four periods of Western Sichuan Plateau;then the vegetation eco-water in four periods of Western Sichuan is calculated,and the vegetation ecological water is the sum of vegetation water storage and root soil water storage;finally,the model is applied to the inversion of vegetation water storage and root soil water storage in four periods of Western Sichuan Plateau.After that,the response of vegetation eco-water in Western Sichuan Plateau to seasonal changes and 5·12 Wenchuan earthquake stress was analyzed.