Robert D. Watson

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.

Spectral reflectance and photometric properties of selected rocks

Abstract Studies of the spectral reflectance and photometric properties of selected rocks at the USGS Mill Creek, Oklahoma, remote sensing test site demonstrate that discrimination of rock types is possible through reflection measurements, but that the discrimination is complicated by surface conditions, such as weathering and lichen growth. Comparisons between fresh-broken, weathered, and lichen-covered granite show that whereas both degree of weathering and amount of lichen cover change the reflectance quality of the granite, lichen cover also considerably changes the photometric properties of the granite. Measurements of the spectral reflectance normal to the surface of both limestone and dolomite show limestone to be more reflective than dolomite in the wavelength range from 380 to 1550 nanometers. The reflectance difference decreases at view angles greater than 40° owing to the difference in the photometric properties of dolomite and limestone.

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.