CEPS Research
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CEPS Research |
| Remote sensing techniques are being used in this project to
investigate changes in forests. The results will lead to better understanding
of large-scale forest structure, an important goal of global change
research.
Why Are Forests Important? Forests cover about a third of the Earth's land surface, and they effect the exchange of gases and energy between the atmosphere and the surface.
About 80% of the global biomass is contained in forests, and this forms the central
component of the stocks and acquisition of carbon in the biosphere. The growth and
distribution of forests has a critical impact on atmospheric carbon dioxide
concentrations, a central issue in global change research. Measuring the size and complexity of forest canopies
over large areas would enable scientists to better understand these environmental processes. Remote Sensing Remote sensing techniques are being used in this study to observe forest canopy structure on a regional scale. The forests being studied here are located at the Smithsonian Environmental Research Center (SERC), located near Washington D.C. in Maryland. Remote sensing data from satellites and an airborne system are being used to extend the local view of stand structure to make predictions about changes in canopy structure and stand biomass at the regional scale.Sensors such as the Landsat Thematic Mapper (TM) have shown great promise for these applications. This study is making use of the archive of Landsat TM data at Center for Earth and Planetary Studies which include 19 scenes dated 1982-1997. Landsat Thematic Mapper images, at 30m resolution, indicate radiance at seven visible and infrared wavelengths. (figure 1). This study is also using data from a new type of sensor, an airborne laser altimeter, to directly measure important aspects of forest structure. NASA's SLICER (Scanning Lidar Imager of Canopies by Echo Retrieval) is a laser sounding device that directly measures the vertical distribution of canopy surface area. The SLICER remote sensing system measures the round-trip travel time of a pulse of laser light to determine the distance to the reflecting surface. This system can be used for precise measurement of the vertical structure of canopies and the estimation of biomass. We are using SLICER profiles covering an area centered on the forest-atmosphere research tower located at SERC (figure 2). Scientific Results The Landsat and SLICER data have been co-registered. Landsat reflectance data have been compared to measurements of canopy height from the laser instrument. Comparing TM reflectance and canopy height measured by SLICER is demonstrating that the laser instrument provides similar data to field measurements. The estimates has been tested by comparing Landsat reflectance to Lidar measurements of canopy height. These preliminary results were reported at the spring 1999 meeting of the American Geophysical Union. Click here to read the report.Future Work The long-term results from this study may include predictive equations relating canopy state and Landsat data to canopy structure estimates, and an analysis of the relationship between spectral measurements and forest biomass values. The relationships between biomass and reflectance will be statistically compared to that seen with the laser data, testing their regional scale validity. These results may provide methods of estimating biomass and other canopy parameters at regional scales, an essential part of understanding global change processes.People Working On This Project: |
| Figure Captions: |
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| Figure 1. Landsat Thematic Mapper image of the Washington
D.C. area. The Chesapeake Bay is clearly visible. The yellow dot represents the location
of figure 2.
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| Figure 2. Landsat Thematic Mapper image of the Smithsonian
Environmental Research Center site in Maryland. The ground data for this study were
collected within the forest stands visible here on the edge of the Chesapeake Bay. White lines
indicate flight tracks of the airborne laser instrument.
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| Figure 3. Photograph of the ground site that was measured by SLICER profiles. The tower in the image is used by SERC for forest-atmosphere
research.
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| Updated:
March 19, 1999 (jh) ©1994-2002 National Air and Space Museum |
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