Arnold F. Theisen

Plant stress detection by remote measurement of fluorescence

Chlorophyll fluorescence of mature lemon trees was measured with a Fraunhofer line discriminator (FLD). An increase in fluorescence was correlated with plant water stress as measured by stomatal resistance and twig water potential.

Fluorescence Changes in a Drying Maple Leaf Observed in the Visible and Near-Infrared

When the source of nutrients for a leaf are disrupted, the mechanisms for energy transfer, that are part of the photosynthetic process, undergo changes that alter the abortion and emission characteristics of the leaf. A series of fluorescence measurements made of a maple leaf as it dried, permit some of these changes to be observed. The emission peaks at approximately 690 nm and 740 nm are present throughout the measurements, although the intensity of the peaks vary. Additionally, a feature with an emission maximum at approximately 440 nm and an excitation maximum at approximately 330 nm appeared as the leaf dried and rave provide an alternate indication of stress. Removing a leaf from the tree accelerates changes that occur in vivo when a plant is under stress. These changes are not visually apparent; however, analysis of the data indicate the strong probability that they would be easily detected with a remote-sensing instrument such as the Fraunhofer luminescence detector (FLD).

Laboratory analysis and airborne detection of materials stimulated to luminesce by the sun

Abstract The Fraunhofer line discriminator (FLD) is an airborne electro-optical device used to image materials which have been stimulated to luminesce by the Sun. Such materials include uranium-bearing sandstone, sedimentary phosphate rock, marine oil seeps, and stressed vegetation. Prior to conducting an airborne survey, a fluorescence spectrometer may be used in the laboratory to determine the spectral region where samples of the target material exhibit maximum luminescence, and to select the optimum Fraunhofer line.

Use of laboratory spectrometry to predict the detection of phytoplankton luminescence by an airborne Fraunhofer line discriminator

Abstract The Fraunhofer line discriminator (FLD), an airborne electro-optical instrument designed to measure solar-stimulated luminescence, has a sensitivity approaching that of current laboratory fluorescence spectrometers. The feasibility of using an airborne FLD for detection of near-coastal and open-ocean phytoplankton was established by using a laboratory fluorescence spectrometer to measure the luminescence of phytoplankton and to determine the minimum concentration detectable with an FLD Laboratory measurements of the excitation spectra of 13 species of phytoplankton (six diatoms, five dinoflagellates and two chrysophytes) were obtained with the emission wavelength held constant at 656.3 nm and the excitation wavelength scanned from 320 to 640 nm. Integrated excitation intensities were normalized to a standard concentration of rhodamine wt dye and the resulting luminescence compared to the minimum detectable FLD level of 0.12 parts per billion (p.p.b.) rhodamine wt. Results demonstrated that all 13...

Use of the Fraunhofer Line Discriminator (FLD) for Remote Sensing of Materials Stimulated to Luminesce by the Sun

Luminescence has been little used as a remote sensing tool in mineral exploration because artificial excitation sources are relatively low powered. Their effective range is on the order of a meter for hand-carried ultraviolet lamps, a few tens-of-meters for cathode-ray systems, and a few hundred meters for laser systems. The work must be performed at night with hand-carried lamps and cathode-ray systems in order to avoid obscuring the low intensity luminescence by bright sunlight. Luminescence stimulated by laser sources may be measured in daylight, but the luminescence signal at visible and near-visible wavelengths must compete with reflected daylight and background luminescence stimulated by the Sun.