NASA Multisensor Aircraft Campaigns for the Study of Forest Ecosystems

This special issue of Remote Sensing of Environment is dedicated to results from research carried out under two NASA-sponsored Multisensor Aircraft Campaigns (MACs) focused on forest ecosystems: the FED (Forest Ecosystems Dynamics) study, which focused on a research site near Howland, Maine (Levine et al., 1993) and the OTTER (Oregon Transect Terrestrial Ecosystems Research) study, which examined the vegetation gradient in western Oregon (Peterson and Waring, 1993). NASA supports a variety of aircraft-based remote sensing instruments directed toward exploring possible future space-based observatories for terrestrial research. In recent years, NASA has actively pursued study sites where numerous investigators coordinate their research objectives and activities, and supporting aircraft flights are concentrated in Multisensor Aircraft Campaigns. This approach not only makes for more efficient use of aircraft hours, but it also fosters cross-collaboration of research activities between scientists of diverse interests and expertise. The research carried out under the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) and the Geological Remote Sensing Field Experiment (GRSFE) are two of the better known examples of NASA MAC activities. The OTTER and FED MAC activities were developed at approximately the same time and were carried out during the growing seasons of 1989 and 1990. In both cases, the objectives were to study forest ecosystems to better understand the contribution that remotely sensed observations can provide in ecosystems research. The real contrast between the studies, other than being on opposite coasts of the United States, is that the FED MAC was dedicated to a single research site in northern Maine, whereas OTTER explored the variation of ecosystems that occurs longitudinally across a severe moisture gradient in western Oregon. As a result, studies at each of the six OTTER research sites were less intensive that those which were carried out at the single FED MAC site. The contrast in observed ecosystems and methodology encouraged NASA to support both forest ecosystem studies simultaneously. The apparent imbalance in this issue, between presentations from the FED MAC (10) and the OTTER MAC (4), is explained by the coincident publication of a special issue of Ecological Applications dedicated to the OTTER studies (Peterson and Waring, 1993). The diversity of research encouraged by MAC studies is well demonstrated in these reports. Not only are all portions of the electromagnetic (EM) spectrum considered, but the scales of analysis extend from plant cells to the 200 km Oregon Transect. For the newcomer to remote sensing research, the range of subjects discussed here may seem chaotic and overwhelming. The context for this diversity is found in the primary objective of NASA aircraft missions-assessment of advanced remote sensing concepts. Theoretical understanding of electromagnetic energy/matter interactions suggests that there is considerable information contained in EM measurements which is not exploited by existing spaceborne sensor systems. However, there are sufficient imponderables in the theoretical knowledge of terrestrial EM interactions such that collection of empirical observations is warranted. The current compliment of NASA aircraft experimental sensor systems covers a considerable range of advanced remote sensing system concepts. The AVIRIS (Airborne Visible Infrared Imaging Spectrometer) and ASAS (Advanced Solid-state Array Spectroradiometer) are both directed toward more fully exploiting the spectral reflectance properties of terrestrial materials in the solar irradiance portion of the spectrum. AVIRIS is primarily directed