Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

open soon after dawn and transpire water vapor throughout the daylight period. During stress periods, stomates may close for part
of the day, generally near mid-day. Under prolonged stress conditions, stomatal closure shifts to earlier times during the day; stomates
may close by mid-morning and remain closed until the following morning - or remain closed entirely. Under these conditions
the relationship between canopy greenness (e.g., measured with a vegetation index or by spectral mixture analysis) and
photosynthetic fixation of carbon is lost and the remotely sensed vegetation metric is a poor predictor of gas exchange. Prediction
of stomatal regulation and exchange of water and trace gases is critical for ecosystem and climate models to correctly estimate
budgets of these gases and understand or predict other processes like gross and net ecosystem primary production. Plant gas
exchange has been extensively studied by physiologists at the leaf and whole plant level and by biometeorologists at somewhat
larger scales. While these energy driven processes follow a predictable if somewhat asymmetric diurnal cycle dependent on soil
water availability and the constraints imposed by the solar energy budget, they are nonetheless difficult to measure at the tree and
stand levels using conventional methods. Ecologists have long been interested in the potential of remote sensing for monitoring
physiological changes using multi-temporal images. Much of this research has focused on day-to-day changes in water use, especially
for agricultural applications. Ustin et al. showed seasonal changes in canopy water content in chaparral shrub could be estimated
using optical methods. Vanderbilt et al. followed asymmetric diurnal changes in the reflectance of a walnut orchard, but
could not attribute specific reflectance changes to specific changes in canopy architecture or physiology. Forests and shrub lands
in California experience prolonged periods of drought, sometimes extending six months without precipitation. The conifer and
evergreen chaparral communities common to the foothill region around the central valley of California retain their foliage
throughout the summer and have low transpiration rates despite high net radiation and temperature conditions. In contrast, grasslands
and drought resistant deciduous species in the same habitat are seasonally dormant in summer. Because of differences in
the mechanisms of drought tolerance, rooting depth and physiology between different plant communities in the region, it is likely
that they display differences in diurnal water relations. The presence of diverse plant communities provides an opportunity to
investigate possible diurnal landscape patterns in water relations that could be observed by an airborne hyperspectral scanner. This
investigation of AVIRIS data collected over forest and shrub land represents the continuation of a prior investigation involving
spectral mixture analysis of diurnal effects in the same AVIRIS data set.
Derived from text
Diurnal Variations; Vegetation; Moisture Content; Gas Exchange; Remote Sensing; Spectral Reflectance
20000064577 Colorado Univ., Cooperative Inst. for Research in Environmental Sciences, Boulder, CO USA
A Method to Access Absolute fIPAR fo Vegetation in Spatially Complex Ecosystems
Wessman, Carol A., Colorado Univ., USA; Nel, Elizabeth M., Colorado Univ., USA; Bateson, C. Ann, Colorado Univ., USA;
Asner, Gregory P., Colorado Univ., USA; Summaries of the Seventh JPL Airborne Earth Science Workshop January 12-16, 1998;
Dec. 19, 1998; Volume 1, pp. 409-416; See also 20000064520
Contract(s)/Grant(s): NAGW-2662; No Copyright; Avail: CASI; A02, Hardcopy; A04, Microfiche
Arid and semi-arid lands compose a large fraction of the earth’s terrestrial vegetation, and thereby contribute significantly
to global atmospheric-biospheric interactions. The thorny shrubs and small trees in these semi-arid shrub lands have counterparts
throughout much of the world’s tropical and subtropical zones and have captured substantial areas of the world’s former grasslands.
The objective of our field and remotely sensed measurements in the semi-arid shrublands of Texas is to monitor interannual
variability and directional change in landscape structure, ecosystem processes and atmosphere-biosphere exchanges. to understand
the role ecosystems play in controlling the composition of the atmosphere, it is necessary to quantify processes such as photosynthesis
and primary production, decomposition and soil carbon storage, and trace gas exchanges. Photosynthesis is the link
whereby surface-atmosphere exchanges such as the radiation balance and exchange of heat, moisture, and gas can be inferred.
It also describes the efficiency of carbon dioxide exchange and is directly related to the primary production of vegetation. Our
efforts in this paper focus on the indirect, quantification of photosynthesis, and thereby carbon flux and net primary production,
via remote sensing and direct measurements of intercepted photosynthetically active radiation (IPAR).
Derived from text
Vegetation; Ecosystems; Arid Lands; Remote Sensing; Photosynthesis; Canopies (Vegetation)
20000064578 Geological Survey, Reston, VA USA
Mapping Chestnut Oak Forest Associated with Silicified Hydrothermally Altered Rocks in teh Carolina Slate Belt Using
Airborne Visible/Infrared Imaging Spectrometer (AViris) Data
Rowan, Lawrence C., Geological Survey, USA; Crowley, James K., Geological Survey, USA; Schmidt, Robert G., Geological
Survey, USA; Mars, John C., Geological Survey, USA; Ager, Cathy M., Geological Survey, USA; Summaries of the Seventh JPL
Airborne Earth Science Workshop January 12-16, 1998; Dec. 19, 1998; Volume 1, pp. 353-354; In English; See also
20000064520; No Copyright; Abstract Only; Available from CASI only as part of the entire parent document
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