Google Earth Engine——WRI/GFW/FORMA/thresholds该数据集包含阈值，当越过该阈值时，会产生FORMA警报。

NOTE from WRI: WRI decided to stop updating FORMA alerts. The goal was to simplify the Global Forest Watch user experience and reduce redundancy. We found that Terra-i and GLAD were more frequently used. Moreover, using GLAD as a standard, found that Terra-i outperformed FORMA globally.

FORMA alerts are detected using a combination of two MODIS products: NDVI (Normalized Difference Vegetation Index) and FIRMS (Fires Information for Resource Management System). NDVI updates are processed every 16 days, while fire updates are processed daily. Models are developed individually for each ecogroup to relate the two inputs to the area of clearing, using the Hansen annual tree cover loss data to train the model. The minimum threshold to qualify as an alert is 25% of the pixel cleared, though thresholds vary by ecogroup to minimize false positives. Here is an example script for a quick introduction to the FORMA datasets.

This image contains the thresholds at which, when crossed, a FORMA alert is produced. The values are equal to max(25,40%*RegionalMax), where RegionalMax is the historical maximum clearing for a pixel in this ecogroup. Ecogroup geometries can be found here.

WRI的注意：WRI决定停止更新FORMA警报。其目的是简化全球森林观测的用户体验，减少冗余。我们发现，Terra-i和GLAD的使用频率更高。此外，以GLAD为标准，发现Terra-i在全球的表现优于FORMA。

FORMA警报是使用两个MODIS产品的组合来检测的。NDVI（归一化植被指数）和FIRMS（资源管理系统的火灾信息）。NDVI更新每16天处理一次，而火灾更新则每天处理一次。为每个生态组单独开发模型，将这两个输入与清理区域联系起来，使用汉森年度树木覆盖损失数据来训练模型。有资格成为警报的最低阈值是25%的像素被清除，尽管阈值因生态组而异，以尽量减少假阳性。下面是一个快速介绍FORMA数据集的脚本示例。

该图像包含阈值，当越过该阈值时，会产生FORMA警报。这些值等于max(25,40%*RegionalMax)，其中RegionalMax是这个生态组中一个像素的历史最大清除量。生态组的几何图形可以在这里找到。

Dataset Availability

2012-01-01T00:00:00 - 2016-01-01T00:00:00

Dataset Provider

World Resources Institute / Global Forest Watch

Collection Snippet

Copied

ee.Image("WRI/GFW/FORMA/thresholds")

Resolution

250 meters

Bands Table

引用：

The FORMA datasets are available without restriction on use or distribution. WRI does request that the user give proper attribution and identify WRI and GFW, where applicable, as the source of the data.

代码：

var dataset = ee.Image('WRI/GFW/FORMA/thresholds');
var thresholds = dataset.select('delta_bound');
var visParams = {
  min: 0.0,
  max: 50.0,
};
Map.setCenter(25.73, -7.61, 2);
Map.addLayer(thresholds, visParams, 'Thresholds for FORMA alerts');