Laser remote sensing represents a powerful technique for investigating many aspects of the environment ranging from probing the upper regions of the atmosphere to measuring the depths of the oceans. It has also been show to be capable of mapping pollution and may be capable of monitoring crops for stress. Recent, advances in the technology may permit it to be miniaturized and used in new exciting ways.

The laser-induced fluorescence imaging system allows the recording of spectrally selected fluorescence images of the whole leaves or plants which is better and in contrast to the so far applied spot spectrofluorometer measurements. The fluorescence images of leaves of winter wheat (Soissons variety, Alsace) have been recorded at the four characteristic emission bands (440, 520, 690 and 740 nm) with a high resolution imaging device consisting of a frequency triplet or doubled Nd:YAG source for 355 nm or 532 nm excitation and of an intensified and gated CCD digitized camera. The effect of four different nitrogen treatments (0, 100, 140 and 180 kg/ha) on the fluorescence parameters (intensities F440, F520, F690, F740 and ratios F440/F520, F440/F690, F440/F740 and F690/F740) obtained by image processing has been analyzed by statistical treatment, in a randomized blocks experiment. The measurements have been carried out on two leaf storeys weekly gathered during two months (May and June 1996). For 355 nm excitation, a significant decrease of the fluorescence ratios F440/F690 and F440/F740 was observed for increasing nitrogen concentration: the blue and green mean fluorescence intensities remained much the same, while the red and far-red chlorophyll fluorescence emissions were enhanced by the fertilization. The fluorescence results are in excellent correlation with the crop yields.

Fluorescence imaging system (FIS) developed in our laboratories was used to study steady state fluorescence characteristics of plants subjected to chronic ozone stress. The imaging system consisted of four ultraviolet (UV) fluorescent lamps as an excitation source, an automated filter wheel with band pass filters, and a cooled charge coupled device (CCD) camera. Fluorescence images were captured at blue (F450), green (F550), red (F680), and far-red (F740) region of the spectrum centered at 450 nm, 550 nm, 680 nm, and 740 nm, respectively. Four different concentration schemes of tropospheric O₃ and CO₂ interactive environments were considered for this investigation. Soybean plants were grown full-season in 3 m diameter open-top chambers (OTCs) purged with the following gaseous treatments: charcoal filtered (CF) air; CF plus CO₂; nonfiltered (NF) air plus O₃; and NF plus O₃ plus CO₂. Cultivars 'Forrest' (O₃ sensitive) and 'Essex' (O₃ tolerant) were planted in each chamber treatment. The mean seasonal (7 h/day) CO₂ and O₃ concentrations monitored for these treatments were: 331 (mu) l/l CO₂ and 22 nl/l O₃; 472 (mu) l/l CO₂ and 21 nl/l O₃; 327 (mu) l/l CO₂ and 63 nl/l O₃; and 479 (mu) l/l CO₂ and 64 nl/l O₃, respectively. The most pronounced differences among the treatments were noted in the F450 and F550 images of leaves in both cultivars exposed to elevated O₃ with more pronounced irregular appearances (white spots) in the O₃ sensitive cultivar. Changes in cellular membrane integrity caused by chronic exposure to elevated O₃ may have attributed to the increase in F450 and F550 intensities observed on the leaves grown in the elevated O₃ environment. Significantly higher F680 and F740 fluorescence image intensities were observed in the elevated O₃ exposed leaves in the presence and in the absence of elevated CO₂ in both soybean cultivars. These observations suggested that elevated O₃ affected the photosynthetic efficiency of the plants even in the environment with elevated CO₂. The O₃ sensitive 'Forrest' was found to have higher fluorescence intensities in all four bands compared to those of the more O₃ tolerant 'Essex.' Although visible stress symptoms such as chlorosis, discoloration, or necrosis were not evident in the leaves used in this study, FIS demonstrated the capability of detecting the effects of chronic exposures to different air quality treatments. The OTC system air treatment environments in conjunction with FIS enhanced our understanding of the interactions between plant stresses and fluorescence responses. These findings with FIS represent a new approach in the studies of plant-pollutant interactions by providing a rapid nondestructive assessment.

Green vegetation when excited by specific wavelengths of light dissipates a portion of the absorbed energy as light emissions in the form of fluorescence. Fluorescence emissions from vegetation occur in five primary regions of the spectrum, namely; ultraviolet (UV), blue, green, red, and far-red (FR). Many investigators have demonstrated relationships between these fluorescence intensities and ratios of these intensities to various forms of plant stress. The observed fluorescence from plant constituents varies with concentration and location within the leaf due to the interactions of diffused fluorescence with the optical properties (i.e. absorption and transmission characteristics) of neighboring compounds. Recently there has been considerable debate as to the extent UV excitation sources penetrate the leaf and to what regions of the leaf can the majority of these in vivo fluorescence emissions be attributed. The deeper a compound is located within the leaf the lower the probability that fluorescence emissions will be received from this compound due to decreases in the quanta of excitation energy and increases in the probability that the fluorescence emission will be reabsorbed. These studies demonstrated that a portion of the fluorescence excitation radiation at 280 nm (4.5 W/m² at the leafs surface) was transmitted through both field grown corn (Zea mays L.) and soybean (Glycine max Merr.). Furthermore, UV transmittance increased toward longer wavelengths leading to an increased quanta UV light exciting a higher percentage of compounds located throughout the mesophyll and bundle sheath layers of the leaf. Significant amounts of fluorescence were observed in the green and far-red bands at the abaxial (bottom) surface of the leaf with adaxial (top) surface excitation, while fluorescence emissions in the UV, blue, and red bands were to a large extend reabsorbed. Leaf transmittance is relatively high in the green and far-red regions of the spectrum giving rise to these emissions at the bottom surface. In addition, both UV and blue fluorescence emissions were observed from the leaf epidermis and quantified to 15% of the blue band fluorescence and up to 30% of the UV band fluorescence emanating from the intact leaf.

A fluorescence imaging system and chlorophyll fluorescence emissions were used to evaluate whether EDU, N-[2-(2-oxo-1- imidazolidinyl) ethyl]-N'-phenylurea, provided protection against ultraviolet-B (UV-B) irradiation (290 - 320 nm) in cucumber (Cucumis sativus L.) leaves. Plants were grown in growth chambers illuminated for 14 h per day with 400 W high pressure sodium and metal halide lamps. Photosynthetically active radiation (PAR) for 1 hr at the beginning and end of each cycle was provided at 270 micrometers ol m^-2 s^-1 PAR; during the other 12 hr of the photoperiod, the plants received 840 micrometers ol m^-2 s^-1 PAR. Beginning on the twelfth day, the plants were exposed to UV-B radiation (0.2 & 18.0 kJ m^-2d^-1) for 2 days at 8 h per day centered in the photoperiod. Rapidly acquired (less than 1 s), high spatial resolution (less than 1 mm²) images were obtained for whole adaxial leaf surfaces using a fluorescence imaging system. The steady-state fluorescence images were acquired in four spectral regions: blue (F450 nm), green (F550 nm), red (F680 nm), and far-red (F740 nm). Fluorescence emission spectra for leaf pigments extracted in dimethyl sulfoxide (DMSO) were obtained by excitation at 280 and 380 nm (280EX 300 - 530 nm; 380EX 400 - 800 nm). Both UV-B and EDU induced stress responses in cucumber leaves that altered the fluorescence emissions obtained from extracts. In the fluorescence images only UV-B induced stress responses were observed but this damage was detected before it was visually apparent. There was no evidence that EDU afforded protection against UV-B irradiation. Use of fluorescence imaging may provide an early stress detection capability for helping to assess damage to the photosynthetic apparatus of plants.

The objective of this study was to describe the excitation- emission spectra of seed pubescence, pollen and spores, and senesced plant materials that could be carried in the air column. Reference samples were a mature green-colored corn leaf, green-, yellow- and brown-colored soybean leaves, cellulose, commercial grade cotton batting and a soil. Spectral luminescence signatures were collected over the 300 to 800 nanometer region using a scanning spectrofluorometer. The excitation-emission spectra were broadband emission centroids in the 400-nm to 600-nm spectrum. Emission maxima were associated with the 440-nm, 470-nm and 370-nm excitation bands and the 455-nm to 590-nm emission bands. The coma of milkweed, silkvine, cotton (raw), cottonwood seeds and yellow- colored pollen and spores were highly fluorescent. The pappus of thistles, dandelion and goat's beard seeds and newly senesced grass leaves and glumes had moderate to high fluorescence. Dark brown-colored mushroom spores and weathered, senesced plant materials had low fluorescence. The emission spectra resembled that of regent, microcrystalline cellulose although impurities incorporated within the plant materials altered their emission intensities from that of cellulose. Moderate to low emissions were from tan- to dark brown-colored materials, whereas the white-colored or light, tan-colored materials had high emissions.

Since the second half of the 1980s several efforts started to establish the laser induced vegetation fluorescence as remote sensing tool to detect the growth and/or stress status of plants. The most extended European project, the EUREKA project LASFLEUR (1989 - 1994), demonstrated the technical feasibility and the significance of the sensed data. Exciting leaves with strong light pulses anywhere in the UV-A region of the electromagnetic spectrum stimulates a broad fluorescence emission from 400 to 750 nm. This emission is separated in two main components, the 'blue-green' (400 - 600 nm) and the red fluorescence region (680 - 750 nm). The blue-green band is originated by polyphenolic compounds of the cell walls, NADPH of the photosynthetic apparatus and possibly by several other plant pigments, except chlorophyll, which is the only emitter of the fluorescence at two bands in the red and in the NIR respectively. On the basis of the photon flux in these channels and with additional information, derived from e.g. the elastic back scattered signal, the time duration of back scatter and fluorescence signal, environmental light conditions, etc. a large set of vegetation parameters could be determined. During several demonstration campaigns status parameters as e.g. the chlorophyll concentration, photosynthetical activity and canopy structure were investigated. Additionally stress conditions as e.g. drought-, UV-stress and infection with different kinds of fungi were examined as well as the differentiation of plant types as e.g. mono-and dicotyledons. Extrapolating the knowledge of the EUREKA project leads to two different main applications. First with an advanced airborne remote sensing system monitoring of the vegetation status and stress conditions may be possible independently of other remote sensing techniques or the data may be used as input parameter for e.g. passive radiometer images. The second application will be a miniaturized sensor for agricultural machines giving direct access to plant parameter and hence the possibility for individual plant treatment as e.g. determining the growth state, fertilization or weed protection.

Fluorescence of crop residues at the end of the growing season may provide an indicator of the past crop's vegetative condition. Different levels of nitrogen (N) fertilization were applied to field grown corn and wheat at Beltsville, Maryland. The N fertilizer treatments produce a range of physiological conditions, pigment concentrations, biomass levels, and grain yields that resulted in varying growth and stress conditions in the living crops. After normal harvesting procedures the crop residues remained. The fluorescence spectral characteristics of the plant residues from crops grown under different levels of N nutrition were analyzed. The blue-green fluorescence response of in-vitro residue biomass of the N treated field corn had different magnitudes. A blue-green- yellow algorithm, (460/525)*600 nm, gave the best separations between prior corn growth conditions at different N fertilization levels. Relationships between total dry biomass, the grain yield, and fluorescence properties in the 400 - 670 nm region of the spectrum were found in both corn and wheat residues. The wheat residue was analyzed to evaluate the constituents responsible for fluorescence. A ratio of the blue-green, 450/550 nm, images gave the best separation among wheat residues at different N fertilization levels. Fluorescence of extracts from wheat residues showed inverse fluorescence intensities as a function of N treatments compared to that of the intact wheat residue or ground residue samples. The extracts also had an additional fluorescence emission peak in the red, 670 nm. Single band fluorescence intensity in corn and wheat residues is due mostly to the quantity of the material on the soil surface. Ratios of fluorescence bands varied as a result of the growth conditions created by the N treatments and are thought to be indicative of the varying concentrations of the plant residues fluorescing constituents. Estimates of the amount and cost effectiveness of N fertilizers to satisfy optimal plant growth condition for specific areas of the field for the next growing season may be useful indicators for crop management. Analysis of plant constituent qualities and quantities of dead crop materials during the harvesting practice or after harvest could be useful indicators of the previous crop's conditions. These measures could be used as a tool in determining precision farming management practices for site specific areas in a field.

The design and performance of a short-pulse (1.5 ns), high- energy (90 mJ/pulse) nonlinear cavity-dumped, frequency- doubled, solid-state intracavity Raman laser is presented. The laser described is utilized as the transmitter in a high- resolution surf-zone marine imaging lidar system.

Imaging lidar, in which light detection and ranging is implemented with sufficient spatial resolution to resolve the size and shape of an object, has demonstrated impressive performance for detecting and classifying underwater targets. During 1996 the U.S. Navy deployed its first imaging lidar system with Naval Air Reserve Squadron HSL-94. This paper reviews the Magic Lantern^R system and discusses new technology and trends for future systems.

The mid-infrared airborne CO₂ laser spectrometer (MIRACO₂LAS) was developed by CSIRO Division of Exploration and Mining to investigate the potential role of high spectral resolution thermal infrared (TIR) remote sensing for improved remote sensing of minerals, especially those silicate minerals that do not have diagnostic features at shorter wavelengths, such as quartz, feldspars, pyroxenes and garnets. Other objectives include testing and validating methods used to separate the mineralogically significant emissivity from temperature effects in passive TIR systems, as MIRACO₂LAS reflectance data are unaffected by surface temperature effects. MIRACO₂LAS uses a CO₂ laser, which scans through 100 wavelengths between 9.1 and 11.2 micrometers, as a light source for 'active' remote sensing. The laser system is sufficiently rapidly tuned to allow the airborne system to operate in a line profile mode, producing contiguous ground reflectance spectra for a footprint (or pixel) diameter of 2 meters. Typical airborne data are presented, demonstrating successful identification of a number of minerals. A laboratory carbon-dioxide laser spectrometer system has also been developed to validate the MIRACO₂LAS spectral signatures and to construct reference spectral libraries of pure minerals and other materials. Besides the compositional influence on the reflectance spectra, physical parameters, such as grain size and grain shape, are shown to affect the reflectance spectra. Plant materials, many of which depart significantly from blackbody behavior for different leaf orientations and arrangements, are also investigated.

Remote sensing is becoming an increasingly important tool for the effective direction of oil spill countermeasures. Cleanup personnel have recognized that remote sensing can increase spill cleanup efficiency. It has long been recognized that there is no one sensor which is capable of detecting oil and related petroleum products in all environments and spill scenarios. There are sensors which possess a wide field-of- view and can therefore be used to map the overall extent of the spill. These sensors, however lack the capability to positively identify oil and related products, especially along complicated beach and shoreline environments where several substrates are present. The laser-based sensors under development by the Emergencies Science Division of Environment Canada are designed to fill specific roles in oil spill response. The scanning laser environmental airborne fluorosensor (SLEAF) is being developed to detect and map oil and related petroleum products in complex marine and shoreline environments where other non-specific sensors experience difficulty. The role of the SLEAF would be to confirm or reject suspected oil contamination sites that have been targeted by the non-specific sensors. This confirmation will release response crews from the time-consuming task of physically inspecting each site, and direct crews to sites that require remediation. The laser ultrasonic remote sensing of oil thickness (LURSOT) sensor will provide an absolute measurement of oil thickness from an airborne platform. There are presently no sensors available, either airborne or in the laboratory which can provide an absolute measurement of oil thickness. This information is necessary for the effective direction of spill countermeasures such as dispersant application and in-situ burning. This paper describes the development of laser-based airborne oil spill remote sensing instrumentation at Environment Canada and identifies the anticipated benefits of the use of this technology to the oil spill response community.

Specular reflections of light, or glints, on the ocean surface can be used to determine surface-roughness statistics. For example, the angular distribution of glints is related to the surface slope distribution. Such statistics are needed for interpreting data from various remote sensors and for studying the physics of the air-sea interface. Laser-glint techniques are convenient because they do not inherently depend on the ambient light conditions, the instruments can be made reasonably compact, and they do not disturb the surface. We deployed a first-generation laser-glint instrument package in the Pacific Ocean near the Oregon coast, during September 1995. This system used laser wavelengths of 633 nm and 830 nm, and was only operable at night. Measurements from this instrument have helped to verify the Cox-Munk model for slope statistics and to quantify the dependence of sea-surface mean- square slope on the air-sea temperature difference. The next- generation laser-glint instrument will use infrared laser light at 10.6 micrometers to enable daytime operation, which previously has not been accomplished with a laser-glint sensor.

A tunable thermal-infrared carbon-dioxide laser reflectance sensor operating in the 9-11 micrometer region of electromagnetic spectrum is being used to study plant physiological changes due to stresses. The system is capable of gathering information at various wavelengths, incident angles, and linear polarization combinations. Preliminary reflectance measurements of two different plant types demonstrate the possible potential of this system to characterize physiological changes due to induced freezing, chilling, and heat stresses.

This paper presents the measurements of dwarf and semi-dwarf Cox apple trees with a tractor-mounted LIDAR (light detecting and ranging). An analysis is presented which derives structural parameters of the canopy for use in pesticide spraying research by considering the number flux of LIDAR scans intercepted by the crop in a known spatial segment. LIDAR measurements of the crop area normalized by the horizontal projected area of the crop are compared with measurements derived from a destructive sampling method. The distributions of local crop area density and crop interception probability are also presented. Crop area density distribution can be used to estimate the deposition distribution of spray by utilizing a suitable transport and deposition model. Alternatively, crop interception probability distribution can be used as a first order estimate of the spray deposition distribution by making an analogy between light and spray transmission.

In the present paper the theory and experimental study of the changing of polarization of Gauss light beam scattered by a thin slab of identical spherical particles is presented. Theory study of the scattered process is based on the following suppositions: there is a single scattered event; the scattered source is a point like; polarization changings in scattered event were described by conforming amplitude scattering Mie matrix. It is shown that there exists a good agreement between theoretical and experimental results.

A new bistatic carbon-dioxide laser reflection polarimeter has been developed. Measurements were done for a variety of soils and particulate media samples, Mueller matrix extracted and analysis are demonstrated. Dominant scattering mechanism is found to be a Fresnel type local interaction. A fully polarimetric radiative transfer model is developed, with phase matrix appropriate for locally specular reflection. The model is compared with previous absolute measurements of bistatic polarized scattering cross section. Optical constants, sample filling factor and incoherent scattering term are extracted. Excellent agreement is found between measured and modeled quantities.

The reflection polarization properties of a given target evolve according to its surface state and to the illumination angle. The depolarization after reflection produced by an iron target whose surface was progressively debased was studied; its initial surface was polished up to one micron. These results were compared to the depolarization obtained from one teflon sample and one dark dielectric. In the teflon sample depolarization is due to volume diffusion whereas in dielectric surface and volume are involved in this process. Polarization is described in the Stokes-Mueller formalism; the matrix obtained was computed to give the degree of polarization for all incident pure-polarization states. Each sample was measured under different angles of incidence. Noise was reduced by a statistical method to optimize the matrix elements. The results are first presented in a global matrix form then, the depolarization phenomenon is analyzed, and one classification technique is applied.

An experimental profiling airborne laser altimeter system developed at NASA's Goddard Space Flight Center was used to acquire vertical canopy data from several ecosystem types from The Nature Conservancy's Disney Wilderness Preserve, near Kissimmee, Florida. This laser altimeter, besides providing submeter accuracy of tree height, captures a profile of data which relates to the magnitude of reflectivity of the laser pulse as it penetrates different elevations of the forest canopy. This complete time varying amplitude of the return signal of the laser pulse, between the first (i.e., the canopy top) and last (i.e., the ground) returns, yields a waveform which is related to canopy architecture, specifically the nadir-projected vertical distribution of the surface of canopy components (i.e., foliage, twigs, and branches). Selected profile returns from representative covertypes (e.g., pine flatwoods, bayhead, and cypress wetland) were compared with ground truthed forest composition (i.e., species and size class distribution) and structural (i.e., canopy height, canopy closure, crown depth) measures to help understand how these properties contribute to variation in the altimeter waveform.

Two different types of laser-induced fluorescence (LIF) imaging systems, a microfluorescence imaging system and a fluorescence imaging lidar system, have been developed for visualization of the fluorescence of plants to investigate and monitor their physiological status and so on. By using the microfluorescence imaging system, the distribution structures of the fluorescence inside tree leaves was obtained and the relationships among the cell/tissue locations, fluorescences and environmental stresses were investigated. Also, through outdoor experiments with the LIF imaging lidar, parameters related to the chlorophyll content of poplar leaves, which were about 60 m away from the system, were remotely estimated and visualized. It was shown that there was a close relationship between the results with both imaging systems and the LIF spectra emitted through leaf surfaces. The combination of the two systems will surely be a powerful tool for vegetation/plant monitoring.