Rapid Assessment of Vegetation Condition after Wildfire (RAVG) Canopy Cover Percent Change (Image Service)

The USDA Forest Service Rapid Assessment of Vegetation Condition after Wildfire (RAVG) program produces geospatial data and maps of post-fire vegetation condition using standardized change detection methods based on Landsat or similar multispectral satellite imagery. RAVG data products characterize vegetation condition within a fire perimeter, and include estimates of percent change in basal area (BA), percent change in canopy cover (CC), and a standardized composite burn index (CBI). Standard thematic products include 7-class percent change in basal area (BA-7), 5-class percent change in canopy cover (CC-5), and 4-class CBI (CBI-4). Contingent upon the availability of suitable imagery, RAVG products are prepared for all wildland fires reported within the conterminous United States (CONUS) that include at least 1000 acres of forested National Forest System (NFS) land (500 acres for Regions 8 and 9 as of 2016). Data for individual fires are typically made available within 45 days after fire containment ("initial assessments"). Late-season fires, however, may be deferred until the following spring or summer ("extended assessments"). National mosaics of each thematic product are prepared annually. The associated burned area perimeters are available via the Enterprise Data Warehouse (EDW, see https://data.fs.usda.gov/geodata/edw/datasets.php). Assessment type (initial or extended assessment) for each fire is included as an attribute in the perimeter dataset.美国农业部林务局（USDA Forest Service）开展的火灾后植被状况快速评估（Rapid Assessment of Vegetation Condition after Wildfire, RAVG）项目，采用基于陆地卫星（Landsat）或同类多光谱卫星影像的标准化变化检测方法，生成过火后植被状况的地理空间数据与专题地图。RAVG的数据产品可表征火场边界内的植被状况，包含断面积（basal area, BA）变化百分比、冠层覆盖度（canopy cover, CC）变化百分比以及标准化综合燃烧指数（composite burn index, CBI）的估算值。标准专题产品包括7级断面积变化百分比（BA-7）、5级冠层覆盖度变化百分比（CC-5）以及4级综合燃烧指数（CBI-4）。依据适宜卫星影像的可获取情况，RAVG产品覆盖美国本土（conterminous United States, CONUS）内上报的所有野火事件，且此类野火需包含至少1000英亩的国家森林系统（National Forest System, NFS）用地；2016年起，第8、9大区的该类用地阈值调整为500英亩。单场野火的数据通常会在火灾封控后45天内对外发布，即"初始评估"产品；但季末发生的野火可能会延迟至次年春季或夏季发布，即"延期评估"产品。各专题产品的全国镶嵌图按年度编制完成。相关的过火面积边界可通过企业数据仓库（Enterprise Data Warehouse, EDW，详见https://data.fs.usda.gov/geodata/edw/datasets.php）获取。每场野火的评估类型（初始或延期评估）已作为属性字段纳入该边界数据集中。