Press Release

New NASA field campaign sees the forest for the satellite

By SpaceRef Editor
August 2, 2001
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Something different is “growing” in the Harvard Forest in central Massachusetts. Researchers and their instruments have spread throughout the forest in an effort to check the accuracy of land maps generated from NASA satellite data. These maps provide valuable information about the Earth’s land surface and different types of ecological communities.

Scientists are gathering at the Harvard Forest Long Term Ecological Research (LTER) site in Petersham, Mass., through August 8 to further improve land maps created from MODIS (Moderate Resolution Imaging Spectrometer) and MISR (Multi-angle Imaging Spectro-Radiometer) sensors aboard NASA’s Terra satellite.

The intensive campaign includes field, tower and aircraft measurements and involves two teams from Boston University (BU), the University of Arizona, and NASA’s Jet Propulsion Laboratory under the umbrella of the MODIS Land Team, and the “BigFoot project.” These teams are being hosted by Harvard Forest LTER through collaboration with Steve Wofsy, Professor of Atmospheric and Environmental Chemistry, Harvard University.

The BigFoot project, funded by NASA, works in collaboration with the MODIS Land Team to analyze the landscape features of areas centered around existing “flux towers,” or towers with sensors that collect data on the relationship between ecological communities, climate and the atmosphere.

Based on field campaigns, the MODIS Land Team and the BigFoot project will use different methods to gather and create datasets of the land that will then be developed into maps. Field data, Landsat satellite imagery and various geophysical statistics and models of ecosystem processes are all combined to create new maps. These new maps will then be correlated to the resolution (500m and 1km) of the MODIS and MISR data maps for comparison. By doing so, not only can various land and air methods be checked against each other to see which are most accurate, but the satellite maps themselves can be checked against other methods of gathering the same information.

During this campaign, the science teams will take detailed measurements of the temperate broadleaf ecological community at the Harvard Forest from the land and by air. The data will be compiled, integrated and then compared with MODIS and MISR.

“These land and aircraft measurements will be combined to produce a high resolution product which can then be compared with a corresponding MODIS product,” said Jeff Morisette, MODIS Land Team Validation Coordinator. “Both the field data and the satellites produce the same end product. They’re trying to get the same information but are using different modes of getting there. Comparing the two helps us understand the uncertainty in the satellite-derived products.”

The Harvard Forest LTER site is one of the initial 24 NASA Earth Observing System Land Validation Core Sites. These sites provide an infrastructure to support in situ measurements and build on existing programs of long-term measurements. The sites provide points on land where satellite, aircraft and ground data collection can all be synchronized and compared. Also, they are areas for which scientists can readily access in situ data coupled with EOS imagery and data-rich maps.

Currently, two Boston University teams are working in the Harvard Forest to develop the Leaf Area Index / Fraction of Photosynthetically Active Radiation (LAI/FPAR) vegetation maps from MODIS and MISR and Albedo/BRDF (Bidirectional Reflectance Distribution Function) maps from MODIS.

The LAI shows how much vegetation exists in an area as compared to the total ground area. The amount of greenness indicates photosynthesis that occurs in plants (from absorbed sunlight) and the amount of carbon they take in from the atmosphere. Also, FPAR measures the proportion of available solar radiation that a canopy absorbs. Albedo is the fraction of solar radiation that is reflected by the land/plant surface back into the atmosphere. With respect to the land surface, it quantifies the amount of energy that is absorbed by the biosphere, or the part of the Earth where life exists. BRDF describes how reflected light is affected by the angle at which the sun’s rays hit an object.

In addition to the work by BU, other teams and the “BigFoot” project, the “FLUXNET Project,” a NASA and Department of Energy validation activity, is also utilizing the Harvard Forest.

As part of the AmeriFlux network, FLUXNET provides researchers access to high quality measurements of carbon dioxide, water vapor and energy fluxes and more. The collection of data from many worldwide terrestrial ecosystems (including managed systems) are contributing to research on understanding how carbon, water, and nutrient cycles of terrestrial ecosystems respond to environmental and climatic disturbances, especially through the development and validation of ecosystem models and the validation of remotely-sensed products.

The Earth Observing System is the centerpiece of NASA’s Earth Science Enterprise. It consists of a science component and a data system that supports a coordinated series of polar-orbiting and low inclination satellites for long-term global observations of the land surface, biosphere, solid Earth, atmosphere and oceans.

For information about the MODIS Land Team, BigFoot, FLUXNET, and Harvard Forest, see:

For more information about the Harvard Forest Validation Campaign, see:

SpaceRef staff editor.