The application of lasers in remote sensing conventionally involves a monostatic approach, with the laser and sensor nearly exactly coaligned. This arises from the practical consideration where the remote sensing platform holds both the laser and sensor in close proximity. A major problem in such a system is the calibration for retroreflection, which may amount to up to a factor of 10 above that for a diffuse ground calibration target. The amount of retroreflection peaking depends not only upon the calibration target, but also on the target to be sensed, as well as the polarization properties of the illuminating laser. The optical properties of various natural and man made calibration target materials will be discussed in the wavelength range from the ultraviolet to the near infrared. An attempt will be made to guide the user in the design of polarizing remote sensing systems to enhance contrast.

A mid-infrared laser reflectance sensor operating within the 9-11 micrometer wavelength range was used to study the reflectance characteristics of soil contaminated with various commercially available chemical liquid materials. Measurements were made at ten wavelengths and three incidence angles under both co-polarized and cross-polarized scatter conditions. Data were gathered from bare soil, as well as soil saturated with anti-freeze/coolant, unused motor oil, and used motor oil. Calibration was performed using a Labsphere Diffuse Reflectance Standard of 94% nominal reflectivity. The measurements were used to compute reflectance ratios, i.e., ratios of reflectivities at various two-wavelength combinations. Our study indicates that it is possible to detect the presence of as well as to identify the type of contamination present in the soil by computing reflectance ratios at judiciously selected wavelengths. Use of wavelength ratios obviates the need for absolute calibration if the atmospheric transmission characteristics are the same at the two probing wavelengths. This technique is well-suited for standoff detection of contaminated soil.

Laboratory measurements of microscopic level changes in a water tank were shown to have good correlation with the evaporation rate predicted using Dalton's Law. Submicron level changes in the tank were measured in real-time using an interferometer interfaced to a PC. The methodology developed offers a way to build an instrument that can be used as a standard for an evaporimeter or a hygrometer. The real-time measurement capability provides a tool for determining refined dynamic correlations of evaporation with fast changes in meteorological variables such as wind and solar radiation.

For industrial and weather forecasting purposes it is often necessary to employ electromagnetic waves (optical to microwave wavelengths) to remotely sense manmade or naturally generated rough surfaces. These surfaces are generally anisotropic and contain multiple scales of roughness. For example sheet metal used in industrial applications are usually sandblasted before painting, while rough sea surfaces with swell are generated by fully developed local winds as well as high intensity winds from more remote sources. Several hybrid analytical techniques based on small perturbation and physical/geometrical optics approaches have been used to determine the scatter cross sections for these multiple scale anisotropic models of rough surfaces. However, these hybrid solutions critically depend on the choices of the spatial wave numbers where spectral splitting is assumed between the different scales of rough surfaces. Fully polarimetric unified full wave solutions have been derived for the scattered fields from these multiple scale anisotropic models of rough surfaces. The rough surfaces are regarded as large (compared to correlation length) patches of rough surfaces with arbitrary orientations and the scattering cross sections are shown to be stationary over a wide range of patch (pixel) sizes. Unlike the perturbation solution the full wave solutions are invariant to coordinate transformations (translations and rotations) and are not restricted to surfaces with small mean square heights (compared to wavelength).

In recent years, the use of airborne scanning laser technology has been rapidly increasing. Many governmental as well as private organizations around the world are evaluating this nascent technology as an advanced means of digital elevation data collection. These organizations have been working in conjunction with Optech of Toronto, Canada to conduct demonstrations and experiments as part of a rigorous examination of the capabilities and accuracy of Optech's Airborne Laser Terrain Mapper (ALTM). This paper will present examples of recent projects conducted in the United States, Europe and South Africa along with a brief description of the fundamental concepts inherent to the technology and its operation in different environmental settings. In certain circumstances where traditional survey techniques such as aerial photogrammetry or standard terrestrial methods are impractical or impossible, often an airborne scanning laser survey is more economical and productive. Also, since no ambient light is required, airborne scanning laser systems can operate day or night. Some of the areas in which the use of this technology may be more beneficial include: forest floor mapping, power wire detection, corridor or route surveys, large topographic surveys and mining. An additional application of airborne scanning laser devices is in the measurement of power line proximity to vegetation. Among the varied applications of airborne scanning lasers, forested areas are of particular interest because they are problematic for companies employing traditional remote sensing methods. Unlike photogrammetry, scanning laser systems can actually penetrate the forest canopy and accurately measure the terrain and objects below.

Lite Cycles has developed a new type of eye-safe, range-gated, lidar sensing element based on Solid-state Raman Image Amplification (SSRIA) in a solid-state optical crystal. SSRIA can amplify low-level infrared images with gains greater than 10⁶ with the addition of only quantum-limited noise. The high gains from SSRIA can compensate for low quantum efficiency detectors and can reduce the need for detector cooling. The range-gate of SSRIA is controlled by the pulsewidth of the pump laser and can be as short as 30 - 100 cm for nanosecond pulses and less than 5 mm if picosecond pulses are used. SSRIA results in higher SNR images throughout a broad range of incident light levels, in contrast to the increasing noise factor with reduced gain in image intensified CCDs. A theoretical framework for the optical resolution of SSRIA is presented and it is shown that SSRIA can produce higher resolution than ICCDs. SSRIA is also superior in rejecting unwanted sunlight background, further increasing image SNR, and can be used for real-time optical signal processing. Applications for military use include eye-safe imaging lidars that can be used for autonomous vehicle identification and targeting.

The Edgewood Research, Development, and Engineering Center (ERDEC) within the Chemical and Biological Defense Command (CBDCOM) is the Army's principal R&D center for chemical and biological defense technology, engineering, and service. ERDEC has been developing tunable 9 - 11 micron CO2 lidar systems for remote sensing of chemical agents for many years. However, due to the extended range requirements for conventional missions such as fixed site defense and reconnaissance, these systems are relatively large. Smaller, even handheld, standoff detection lidar systems would be useful for the individual warfighter or for decontamination efforts, as well as for numerous environmental monitoring applications. Lidar modeling calculations have been performed for such a system at the Night Vision and Electronic Sensors Directorate, (NVESD) the Army's lead laboratory for low energy lasers. The modeling indicates that fewer than 5 mJ of solid-state laser pulse energy would achieve the required detection sensitivity criteria for standoff chemical agent detection at ranges of several kilometers. This result coupled with recent advances in solid-state laser and frequency conversion technologies allow for extremely compact, tunable lasers and lidars to be produced which are suitable for a handheld standoff detection device. ERDEC has therefore begun an effort in development of compact 2 - 12 micron lasers and lidars. Three different approaches are being investigated and will be described. A review of completed efforts in tunable UV laser source development for remote sensing of biological agents via laser induced fluorescence (LIF) will also be presented.

Currently, leaf and canopy level fluorescence measurements are being explored as a means to non-destructively monitor plant productivity. Over the past few decades it has been established that changes in fluorescence characteristics of green vegetation can relate to both anthropogenic and naturally occurring plant stresses. The following studies were conducted to better define changes in fluorescence properties of field grown corn (Zea mays L.) as they relate to varying levels of nitrogen fertilization. Nitrogen was supplied in the form of urea at varying rates to obtain levels corresponding to 150, 125, 100, 75, 50, 25, 0% of the nitrogen required for optimal growth. The recommended rate for nitrogen fertilization on the field site consisting of a Codrous sandy loam soil was determined by the soil testing laboratory at the University of Maryland to be 162 kg N/ha. The field site consisted of seven nitrogen treatments in four randomized complete blocks. Fluorescence spectral measurements were obtained from the uppermost fully expanded leaves at the grain fill stage of growth. Florescence measurements were compared with the following physiological parameters: rate of photosynthesis, elemental composition, pigment and protein concentration, and grain yield. The goals of this study were to characterize leaf level fluorescence emissions as they relate physiological changes within the plant in response to nitrogen supply. Ultimately, this research is directed toward providing a remote non-destructive technique to distinguish inadequate and over fertilization of corn crops with nitrogen fertilizers.

Rapid changes in the intensity of chlorophyll a fluorescence induction (CFI) during dark-light transition reflect the various reactions of photosynthesis, especially of electron transport. The analysis of CFI transients in plant leaves in situ is a sensitive and non-destructive assay of the functional state of the photosynthetic apparatus. We earlier developed an image instrumentation system for analyzing CFI transients. The system gives information on the location of different photosynthetic activities in whole leaves in situ and can allow identification of sites of inhibition caused by environmental stresses. The recent addition of a scanning laser enables us to diagnose photosynthetic injuries to plants at a distance from the instruments.

The work aims to validate the laser-induced fluorescence imaging method for detecting nutrient deficiency of fruit- trees and testing the storage ability of the fruits. Measurements concerned apple-trees (Malus x domestica Borkh.cv.Jonagold 2361) submitted or not to nitrogen fertilization (60 kg/ha) via roots. Besides recordings of fluorescence images of fruits and of leaves at the characteristic emission wavelengths, images which always showed an effect of the nitrogen, chemical and physiological analysis have been performed. The essential results were: (1) For rosette leaves, with a total chlorophyll content significantly lower for nitrogen depleted leaves, and a Chl a/b ratio as well as (phi) _po (PS II efficiency of open reaction centers) independent of the treatment, images recorded in the red and in the far-red (690 and 740 nm chlorophyll a emissions) showed red/far-red intensities ratios higher in the absence of fertilization, in agreement with the lower chlorophyll a content. (2) For leaves of one year shoots, having all similar chlorophyll content and PS II efficiency, nitrogen supply led to a slight decrease of the red/far-red ratio value for 532 nm excitation, and for 355 nm excitation to an important decrease of the blue fluorescence/chlorophyll emission ratio, that was not observed for rosette leaves. (3) For apple fruits, presenting a high K/Ca ratio (approximately equals 42) i.e. a bad storage ability, the chlorophylls content of the green face skin as well as (phi) _po were the same for both samplings, with a dramatic decrease of (phi) _po (0.68 till to 0.45) during conservation (6 months). Under 355 nm excitation, the fluorescence ratios the most sensitive to the nitrogen deficiency were for the green face the blue/red ratios which decreased with nitrogen supply and increased with time, and the blue/green ratio for the apple red face.

A joint IROE-CNR, NASA/GSFC, and USDA/ARS measurement campaign was conducted in Italy for a three week period in July, 1997. The campaign was split into two parts: the first part for aquatic vegetation studies and the second part for terrestrial vegetation studies. The main objective of the campaign was to study optical properties of intact plant material as it relates to photosynthetic activity of living vegetation. The aquatic studies were carried out at an aquarium-laboratory in the seashore city of Livorno on the West coast of Italy. The investigations involved an important sea grass species that is native to the Mediterranean Sea. The terrestrial studies were carried out Northeast of the Town of St. Stefano di Cadore (Belluno), Italy. Measurements were taken in a wooded site at an Italian Department of Forestry Station on species of natural alpine vegetation. Instrumentation available for the studies were the Italian Fluorescence Light Detection And Ranging (FLIDAR) System, the NASA/USDA Fluorescence Imaging System (FIS), the Perkin Elmer Spectrofluorometer and LI-COR 6400 infrared gas exchange analyzer for photosynthesis measurements. Preliminary evaluations, analysis, and summaries were made by personnel from both Italian and United Sates groups on data collected during the measurement campaign. The joint Italian/American data collection effort with Aquatic and Terrestrial Optical Measurements produced a range of data for characterizing the relationships between fluorescence and the photosynthetic potentials of vegetative scenes.

Terrestrial vegetation studies were carried out in the Italian Northeastern Alps in Val Visdende. The measurement site was 15 Kilometers Northeast of the town of St. Stefano di Calore (Belluno), Italy. Measurements were acquired on a wooded site at the Italian Department of Forestry Station on species native to the Italian Alps. The species included spruce (Picea abies) and alder (Alnus incana) trees. Characterization was also made of the fluorescence responses of several under-story species such as Dactylorhiza fuchsii of the Orchidaceae family, Caltha palustris and Ranunculus ficaria of the Ranuncolcee family, and Trifolium pratense and Trifolium repens of the Leguminosae family. Terrestrial vegetation monitoring was conducted with the Italian FLIDAR remote sensing instrument mounted in a mobile van, the NASA/USDA Fluorescence Imaging System (FIS), and the Spectron SE-590 for optical properties. Photosynthetic CO₂ gas exchange rates we made with LI-COR 6400 infrared gas analyzer. Pigments from the samples were extracted and analyzed with a Perkin Elmer Lamda 7 Spectrometer to determine pigment concentrations. Fluorescence responses were collected from vegetation samples grown under different ambient light regimes of sun-lit versus shaded. The vegetation showed different fluorescence characteristics. A fluorescence algorithm, (F740/F680)/F550, and rate of photosynthesis showed a strong linear relationship.

Aquatic vegetation studies were carried out from Tuesday July 15th, 1997 to Tuesday July 22, 1997 in a sea-side aquarium- laboratory in the city of Livorno on the Tyrrhenian Sea. The investigations involved an important sea grass species Posidonia oceanica that is the main higher aquatic vegetation found in the Mediterranean Sea. Fluorescence measurements were acquired on the aquatic plants treated with different levels of Mercury and Cadmium heavy metal contamination. The measurements included steady state fluorescence and fluorescence induction kinetics, pigment extraction, and photosynthetic gas exchange rates. Fluorescence instrumentation used for the studies included the high spectral resolution fluorescence lidar System (FLIDAR$CPY), the NASA/USDA Fluorescence Imaging System (FIS), and Perkin Elmer Spectrofluorometer. Fluorescence responses showed a significant variations within the leaf as a function location from the base. Heavy metal treatments resulted in distinguishable differences in fluorescence responses.

This paper calculates signal levels that would be obtained from oceanographic lidar by solving the one-dimensional transient radiative transfer equation for remote sensing. As an example, detection of fish schools is considered. In this technique a pulsed laser is directed into the ocean, and the time-dependent back-scattered flux is measured at different locations. A large number of parameters such as the spatial and temporal variability of optical properties within the ocean, ocean depth, type of ocean water, and presence of biological matters can significantly affect the radiative transport through oceans. But since the emphasis of the work is on the scattering phenomenon, important parameters associated with it, namely the scattering albedo and scattering phase function distribution, are considered in detail.

An airborne laser altimeter using a Nd:YAG laser was constructed to test the usefulness of the laser altimetry in snow and ice regions. The experiments were conducted to measure sea ice in the Sea of Okhotsk off the Hokkaido Island, Japan at winter seasons in 1993 - 1995. Distributions of ice freeboards, mean elevations and ice concentrations were investigated from the data. The mean freeboard was found to correlate very well with the ice concentration. This result shows the possibility of estimating ice amount from the ice concentration and approved the effectiveness of the laser altimetry. A new laser altimeter is being developed to incorporate a beam scanning capability to measure sea ice more effectively. Also discussed in this scanning laser altimeter using a coherent detection technique.

A new infrared laser-glint sensor is being developed to measure sea-surface roughness statistics, using a CO₂ laser to maintain the laser signal above background light levels. This new system allows daylight data collection, whereas our previous HeNe-laser-based system operated only at night. Additionally, the new system incorporates real-time correction of ship motion to allow operation on a moving ship. This paper provides an overview of the instrument design and the scientific objectives of its future deployment. A specific scientific objective discussed here is determining the connection between the fractal dimension of the laser-glint process and surface roughness. Evidence is shown here from previously acquired laser-glint data that the laser-glint- count process is fractal, with a dimension that appears to vary with surface roughness. Plans are outlined for deployment of the new laser-glint sensor with fractal signal processing for remotely sensing surface roughness.

Concept based on breaking up the boundary layer into single dynamic components of lower atmosphere, ocean surface and subsurface water mass. Optical model of boundary layer dynamic components is introduced for scattering processes understanding. Returned coherent signal is used to measure the dynamic components. In order to split atmosphere effects, wavy surface contribution and ocean subsurface components speckle technology is developed. The technology based on differentiation of spatial and temporal parameters of speckle patterns.

A spatial coherence analysis of the light scattering in turbid media, illuminated by a laser source, is presented. Classical degree of coherence modulus measurements require the determination of a fringe pattern visibility. This measurement needs complex algorithms for detecting the fringes minima and maxima on the digitized image. We describe here an easy method to extract the average visibility from the digitized fringe pattern histogram. In the first part, we present the mathematical basis of the method which is obtained from the classical intensity distribution of an interference pattern. This method requires slow spatial variations fringes size compared with the spatial carried frequency. Furthermore, the intensity of the two arms of the interferometer must be equal. If these conditions are assumed, we can easily extract the degree of spatial coherence modulus directly from the histogram of the fringe pattern. The efficiency of the method has been proved using computed interference fringes. In the second part, we apply the histogram analysis on real fringe interference measured in turbid media (seawater). The estimated spatial coherence magnitude is compared with results obtained by classical method. This comparison shows the validity of the histogram method. In conclusion a discussion is made about the advantages and the limits of the proposed method.

Experiments were conducted to characterize the fluorescence emission of leaves from four soybean ('Harosoy') plants containing different concentrations of flavonols (kaempferol glycosides). The investigation utilized genetically mutated soybean flavonol isolines grown in a constant environment, thus limiting factors known to affect fluorescence emission characteristics other than different kaempferol glycosides concentrations. Flavonol isolines included OX922, OX941, OX942, OX944. The first two isolines contain kaempferol (K) glycosides; K3, K6, and K9, and the latter two did not have K3, K6, and K9. A fluorescence imaging system (FIS) was used to characterize steady state florescence images of the sample leaves measured at wavelengths centered at 450, 550, 680, and 740 nm with an excitation at 360 nm. Images taken with FIS greatly complement non-imaging fluorescence measurements by characterizing the spatial variation of fluorescence within leaves. We also acquired fluorescence emission spectra to characterize spectral features of the soybean flavonol isolines. The emission spectral shape of the fluorescence emission characteristics were not significantly different between the soybeans that contain kaempferol glycosides and the ones that do not contain kaempferol glycosides. Typical emission maxima of green vegetation in the blue, green, red, and far-red bands were noticed in all four soybean isolines. However, plants containing kaempferol glycosides, OX922 and OX941 had significantly lower intensities throughout the wavelength regions. These results imply that fluorescence emission intensities in the fluorescence emission bands studied are significantly affected by the presence and absence of kaempferol glycosides concentrations (UV radiation screening compounds). Pure kaempferol glycoside dissolved in solution show minimal fluorescence emission when excited with the absorption maximum radiation at 365 nm. However, a broad band emission can be seen in the green region of the spectrum when excited with radiation in the blue region of the spectrum. Thus, green fluorescence emission due to kaempferol glycosides excited by the blue fluorescent compounds with UV excitation (resonance energy excitation) could become a factor in the fluorescence studies of in vivo plants.