Method For Burned Forest Area Identification And Vegetation Restoration Using Satellite Data

Fire is one of the major disturbance affecting the stability of forest ecosystem.Studing on the post-fire vegetation recovery can provide a powerful scientific reference for sustainable development of forest ecosystem.Based on GF-1 WFV and Landsat TM/ETM+ time-series data,burned areas in northeast forest region and southwest forest region where fire occured frenquently have been selected as experimental areas for the method of burned forest area identification and vegetation restoration monitoring by using remote sensing technique.This article mainly included the following three aspects.On one hand,separation index M value has been selected to evaluate the ability to separate burned area by using selected vegetation index such as normalized difference vegetation index(NDVI),enhanced vegetation index(EVI),global environment monitoring vegetation index(GEMI),burned area index(BAI)and normalized burn ration(NBR).Then the best suitable vegetation index for GF-1 WFV and Landsat 8 data was studied for burned area identification.On the other hand,GF-1 WFV data has been selected to research the spectral changes of post-fire vegetation at different disaster degrees.Three typical vegetation indices such as NDVI,EVI and GEMI which can characterize vegetation restoration were used to study the vegetation monthly recovery law in different disaster degree during the first two years after the fire.Combined with the altitude,latitude and climatic conditions of burned area,influence factors of vegetation monthly changes were analyzed.Furthermore,burned area of the Great Xing'an Mountain "5·6" largest fire has been selected for the studing of yearly vegetation recovery.Based on Landsat TM/ETM+ time-series data,two vegetation restoration models-stand regrowth index(SRI)and relative regrowth index(RRI)have been used to study annual changes of vegetation regeneration in different damage degrees during 30 years after the fire.Meanwhile,main factors which affecting vegetation growth have been analysed.The main conclusions of this paper were as follows:(1)NBR based on the reflectance of near infrared and short wave infrared band has the same ability with BAI,it can separate the burned area well.The ability of NDVI is inferior to that.EVI and GEMI has poor ability to separate fire zone.For Landsat8 data with short-wave infrared band,using NBR to identify the burned area has a better effect,overall accuracy of recognition was 88.33%,and the Kappa coefficient was 0.73.However,for GF-1 WFV data which only has visible band and near infrared band,BAI has better recognition effect.The overall recognition accuracy reached 91.00%,Kappa coefficient was 0.78.(2)After burning,vegetation no longer exhibited the typical spectral characteristics of normal vegetation,Its spectral characteristics were similar to that of dry dead vegetation and dry soil.In blue,green and red bands,spectral reflectance of burned vegetation was higher than that of normal vegetation,it didn't have the peak and valley in the reflection and the more serious it burned,the greater the reflectivity increased.In near infrared band,spectral reflectance of burned vegetation decreased,no longer had the "red edge" phenomenon which occurred in normal vegetation,and the spectral reflectance values were lower than that of normal vegetation.(3)In vegetation growth process,seasonal rhythms of vegetation in different damage degrees were basically same as those of the normal vegetation.They all had growing season and non-growing season.Otherwise,NDVI,EVI and GEMI value of the burned area were alwalys lower than those of normal vegetation.In addition,the more severely affected areas were,the lower the vegetation index was over post-fire two years which observed by GF-1 WFV per month.(4)Peak value occurred time of vegetation index at different damage vegetations in Yajiang County was 1 to 2 months later than that in the study area of Manning County,which was related to its high altitude,high latitude and climatic characteristics.(5)From SRI,vegetation in light burned area could recover to the pre-fire vegetation state in the third year after the fire.For the moderate burned area,it needed 6 years to return to the state of pre-fire vegetation.However,vegetation in severe fire area took 14 years to restore to the pre-fire vegetation state.(6)From RRI,It took 8 years for light burned area to restore to the same state as the post-fire normal vegetation.For the moderate burned area,it closed to the state of post-fire normal vegetation after 13 years,this was basically same as the recovery time of severe burned area.