Looking at vegetation through remote sensing

April 06, 2000

Scientists have found some unique ways to use remote-sensing data in analyzing and modeling vegetation. The latest remote sensing research in the field of geography will be presented April4-8 at the Association of American Geographers Meeting at the David L. Lawrence Convention Center in Pittsburgh, Pa.

University of Kansas geographer Mark Jakubauskas is using a technique called harmonic analysis to study changes in vegetation during a growing season, and from one year to the next. A series of satellite images measures the greenness of the vegetation every two weeks. As plants green up, mature, and then brown down or senesce measurements of the greenness over time forms a wavelike pattern. This wave can be mathematically analyzed to create two new measurements. One being the amplitude, which is the measure of the height of the wave and the second, is the phase, which is the time of year at which peak greenness occurs.

Using the measurements from these waves, Jakubauskas can determine the type and growth pattern of vegetation. Changes in the amplitude of the wave from one year to the next can signal a loss of vegetation (desertification) or regrowth of vegetation (regeneration after a forest fire). Changes in phase can indicate changes in crop types, or year-to-year variation in crop growth and maturity.

Next, Jakubauskas will be applying harmonic analysis to a ten-year series of satellite images to study land use and land cover changes in the western Great Plains. The changes identified by the harmonic analysis may detect an early warning signal of climate change.

Old Dominion University geographer Tom Allen identifies changes in forest cover in the spruce-fir zone of Great Smoky Mountains National Park by using digital satellite data. Allen is using a modified technique on Landsat's Thematic Mapper instrument data to investigate the decline of the Fraser fir (Abies fraseri) forest when the balsam woolly adelgid (Adelges piceae) pest was introduced to the Great Smoky Mountains in the late 1970's.

The balsam woolly adelgid took a bite out of the Fraser fir population and using this technique, Allen is able to see the rebounding of the forest. This method combines brightness, greenness, and wetness measurements in order to provide more detailed information such as the type and location of regrowth patterns in the spruce-fir forests.

Canopy and structural changes such as thinning, extensive canopy mortality, and differential regeneration of the canopy and lower canopy species can be distinguished using this technique. "The rugged topography of Great Smoky Mountains National Park, the complex patterns of fir mortality and regeneration, and the unique habitat and aesthetic value of spruce-fir forests make this an excellent opportunity to advance forest monitoring approaches using remote sensing," says Allen.

In the future, Allen would like to see this method applied to analysis of coastal zones, floodplain areas, and to survey other forest threats such as hemlock wooly aphid and beech bark disease.

NASA/Goddard Space Flight Center

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