Volume 9, Number 3 • May/June 2001

SBIR Leads to Plant Fluorescence Sensor

Growers and foresters alike have yet another source for improving the health of their crops due to the work of a Billerica, Massachusetts, company funded through the Small Business Innovation Research (SBIR) Program at NASA Stennis Space Center. Aerodyne Research, Inc. has successfully developed the Plant Fluorescence Sensor (PFS), a real-time sensor that passively monitors plant health by remotely sensing plant responses related to the fundamental process of photosynthesis.

As NASA’s lead center for the commercialization of remote sensing technologies, the NASA Earth System Science Office (ESSO) at Stennis incorporates the technology of remote sensing into its efforts. One focal area of research is the pre-visual sensing of unhealthy, or stressed, plants. Aerodyne’s development of the PFS through the SBIR Program is in response to one of the ESSO’s challenges.

Aerodyne designed and built the PFS as a robust sensor of sunlight-excited chlorophyll fluorescence. It provides for the real-time, in situ remote sensing of photosynthetic activity in plants. This sensor, which operates as a Fraunhofer line discriminator, detects light at the cores of the lines comprising the atmospheric oxygen A-band and B-band, centered at 760 nanometers (nm) and 688 nm respectively. Fraunhofer lines identify the spectral regions where little or no solar radiation reaches the surface of Earth, providing an area free of solar background interference. These bands also correspond to wavelengths in the red and far-red chlorophyll fluorescence bands. The intensity and spectral band shape of chlorophyll fluorescence in green plants has been linked to the physiological status of plants, thus providing a good indicator of general plant health.

The measurement of chlorophyll fluorescence emission has generally been performed with active stimulation in laboratory settings. However, the passive measurement of in situ solar-stimulated plant fluorescence has proven to be a more difficult task because the intensity of plant fluorescence, under the best of circumstances, is several hundred times less than that of sunlight.

The PFS does not use an interferometer or spectrometer. Rather, it is designed to pass the light collected from the fluorescing plants through a cell containing oxygen at low pressure. The oxygen absorbs the energy and subsequently re-emits photons that are detected by a photomultiplier tube. Since the oxygen in the cell absorbs light at exactly the wavelengths that are absorbed by the oxygen in the atmosphere, the residual response to sunlight is minimal. The induced fluorescence signal provides an immediate, absolute measurement of plant fluorescence intensity in the narrow bands in which the sensor responds.

A real-time sensor that passively monitors plant health can improve the health of plants by monitoring their photosynthetic activity. Photo provided by NASA Stennis Space Center.

Aerodyne has built and tested three experimental prototypes using off-the-shelf components. The PFS’s core components are relatively inexpensive, have few moving parts and are based on established technologies, thus increasing their reliability. The company has successfully conducted numerous field tests using the patented PFS on a variety of crops, including hydroponic bean gardens, sorghum plots, cotton plots and greenhouse-grown Laurel oak seedlings. These tests indicated that the PFS is capable of pre-visual detection of plant stress resulting from water and nitrogen deficiencies as well as other applied stresses.

Aerodyne Research sees a market for the Plant Fluorescence Sensor as a passive remote monitor of plant health. Applications include site-specific agriculture, hydroponic growing environments, crop condition assessment, damage assessments due to a variety of stressors, forestry and ecological monitoring—including carbot sequestration and soil remediation. Expectations are that passive remote sensing of plant fluorescence will be proven as a reliable and readily available tool for the early detection of plant stress, thereby allowing for corrective measures and the realization of substantial improvement in yield.

This unique remote sensing product falls at the very center of the NASA Earth Sciences Enterprise (ESE) and is directly representative of the Memorandum of Understanding between NASA and the U.S. Department of Agriculture for joint applications research and technology in agriculture, forestry and other natural resources management. This technology also supports the ESE commitment to the U.S. Global Change Research Program.

Aerodyne Research has provided research and development (R&D) services since 1970 to commercial and government clients working to solve national and international problems. The R&D staff is organized into six technology centers that address a wide range of topics requiring expertise in the physical and engineering sciences.

Aerodyne has elected to retain title to this invention, which has been credited to Dr. Paul Kebabian.

For more information about the Plant Fluorescence Sensor, contact Dr. Herman Scott at Aerodyne Research, 978/663-9500, ext. 267, or log on to Aerodyne’s Web site at http://www.aerodyne.com.