2009 Mapping Amazonian forest type, age, and secondary forest biomass accumlation rates from Landsat time series and GLAS

For the first time, scientists have been able to measure entirely from space the rates of carbon accumulation (sequestration) in the biomass of tropical forests that regrow where agriculture has been abandoned, and to automatically monitor tropical forest regrowth. In an area of Rondônia, Brazil, the authors combined maps of forest age with estimates of forest biomass that were based on data from the Geoscience Laser Altimeter System (GLAS) (http://nsidc.org/data/icesat/index.html). The estimated rate of biomass accumulation agreed well with estimates based on labor-intensive ground studies in the area. GLAS is the first publically available lidar data from space.  Lidar technology uses lasers to measure forest height. GLAS is on board NASA’s Ice, Cloud and land Elevation Satellite (ICESat). The scientists also estimated the biomass of and mapped different types of old-growth tropical forest, including not only the lowland evergreen forests that typically come to mind, but also swamp forests and drier forest types. Forest biomass is related to the amount of carbon that forests store.

 

To map forest age, the authors developed a new automated method to track land-cover change with long time series of Landsat imagery. The method detects when forest begins to regrow on previously deforested lands, and it tracks the regrowing forests through time. The novel method avoids many of the time-consuming steps that are normally required to interpret this type of satellite imagery. The method also can find secondary forest that is up to about 30 years old. Such older secondary forest is often difficult to impossible to distinguish from old-growth forest if only one image date is used. The new method holds promise for automating the tracking of tropical deforestation and forest regrowth over large areas. More work is needed to develop and test the method, however, so that it can be used in mountainous tropical landscapes.

 

In addition, the study is the first example in the scientific literature on land-cover change to use Google Earth for validating land-cover maps.  The study uses Google Earth to validate the maps of tropical forest type and age. 

 

Dating back to the 1972, Landsat data form the longest and most consistent record of tropical forests available (http://landsat.usgs.gov/). The Landsat series of satellites are operated by the US Geological Survey and built by NASA (http://ldcm.nasa.gov/), but some of the Landsat imagery was also provided by Brazil’s National Institute for Space Studies, which operates a Landsat image receiving station (http://www.dgi.inpe.br/CDSR/). The authors of the study include scientists from the US Forest Service International Institute of Tropical Forestry, Colorado State University (http://welcome.warnercnr.colostate.edu/), and the University of California, Santa Barbara (http://www.geog.ucsb.edu/).  The work was a contribution to Landsat Science Team Research and the Landsat Data Continuity Mission (LDCM).

 

Helmer, E. H., M. A. Lefsky and D. A. Roberts. 2009. Biomass accumulation rates of Amazonian secondary forest and biomass of old-growth forests from Landsat time series and the Geoscience Laser Altimeter System.  Journal of Applied Remote Sensing Vol. 3:033505. (http://spiedl.aip.org/dbt/dbt.jsp?KEY=JARSC4)