FORMA Vegetation T-Statistics (WRI/GFW/FORMA/vegetation_tstats)
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.
The images in this ImageCollection contain the “reversed rectified
t-statistics” used in calculating NTT, the vegetation color index derived
from MODIS NDVI that FORMA uses to measure browning. Using a sum reducer on
over various date ranges in this ImageCollection produces an “NTT” image.
The images are broken by “ecogroup”. Ecogroup geometries can be found
here.
| Name | Description |
|---|---|
| tstat_r | Reversed rectified, ie (max(0,-t_stat)), t-statistics. |
Providers | |
|---|---|
| World Resources Institute / Global Forest Watch (producer, licensor) | |
| Google Earth Engine (host) | |
| STAC Version | 0.6.0 |
| Keywords | FORMA, GFW, MODIS, WRI, daily, deforestation, forests, monitoring |
| License | proprietary |
| Temporal Extent | 12/31/2011, 4:00:00 PM - now |
| Type | image_collection |
| GSD | metersm |
| Asset schema | {"name":"year","description":"Year of the most recent data included in the dataset","type":"INT"},{"name":"biweekly","description":"The biweekly (every 16 days) period of the year","type":"INT"},{"name":"ecogroup_id","description":"ID of associated ecogroup. Ecogroup geometries and IDs are available in\nthe fusion table found [here](https://fusiontables.google.com/DataSource?docid=1sqNt2yENpQI5JqLpFONJ2ppnqL77G9XkzKM9VdyS#rows:id=1)\n","type":"STRING"} |