PARENT SESSION
Oral Session #71: Remote Sensing and GIS.
Presiding: J.D. Allan
Wednesday, August 7. 1:00 PM to 4:45 PM. Palo Verde Room, Radisson.

Prospects for remotely measuring the 3-D distribution of canopy PAR absorbence.

KNOX, ROBERT^*,1, ¹ NASA's Goddard Space Flight Center, Greenbelt, MD

ABSTRACT- A sensor that vertically resolved ratios of red-to-near-infrared reflectance could map 3-dimensional distributions of photosynthetic surfaces and absorbence of photosynthetically active radiation (PAR). Spectral vegetation indexes already play a central role in Earth System Science and research on global change. Although some vertical information can be reconstructed by combining data collected at different viewing angles, current multispectral imagers are limited to collecting data in 2-D pixels. Lidars collect time-tagged information along the viewing axis, and some imaging lidars develop 3-D representations of plant canopies. Atmospheric lidars commonly employ information from multiple laser wavelengths near particular narrow absorption lines to measure concentrations of gases. In vivo the spectral features of chlorophyll are rather broad and overlap with signals from prominent atmospheric constituents. Only at the 'red edge' reflectance transition of chlorophyll do plant canopies provide a unique spectral feature sharp enough for differential absorption lidar (DIAL) measurements. Recent advances in laser and detector technologies have let us to construct a prototype vegetation lidar operating at 660 nm and 780 nm wavelengths. Airborne or field instruments using this technique could measure and map volumetric distributions of canopy chlorophyll. From Earth orbit, an imaging lidar of this type could estimate how global production is allocated among plant strata, as well as help calibrate out view angle, illumination angle, and atmospheric effects on multispectral vegetation data from other sensors.

KEY WORDS: lidar, vegetation, chlorophyll