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Initial airborne CO{sub 2} DIAL measurements: Discussion of results and data analysis considerations

Description: A detailed discussion of airborne CO{sub 2}, DIAL measurements obtained from the first joint N-ABLE field campaign at INEL is presented. System performance characteristics, including return signal strength, averaging statistics, and temporal correlation as well as multi-line DIAL spectral data are discussed. In particular, we review data acquisition and analysis strategies pertinent to chemical detection from a moving platform, such as range determination and correction, and return signal processing (waveform vs. box-car integration, baseline correction). We also report observed effects and variations due to near-field light scattering, pointing and tracking stability, and stack-release plume dynamics.
Date: July 1, 1997
Creator: Tiee, J.J.; Foy, B.R. & Quick, C.R.
Partner: UNT Libraries Government Documents Department

Laser speckle effects on hard target differential absorption lidar

Description: Reflection of laser light from a diffuse surface exhibits a complex interference pattern known as laser speckle. Measurement of the reflected intensity from remote targets, common to ``hard-target`` differential absorption lidar (DIAL) requires consideration of the statistical properties of the reflected light. The authors have explored the effects of laser speckle on the noise statistics for CO{sub 2} DIAL. For an ensemble of independent speckle patterns it is predicted that the variance for the measured intensity is inversely proportional to the number of speckle measured. They have used a rotating drum target to obtain a large number of independent speckle and have measured the predicted decrease in the variance after correlations due to system drifts were accounted for. Measurements have been made using both circular and linear polarized light. These measurements show a slight improvement in return signal statistics when circular polarization is used. The authors have conducted experiments at close range to isolate speckle phenomena from other phenomena, such as atmospheric turbulence and platform motion thus allowing them to gain a full understanding of speckle. They have also studied how to remove correlation in the data due to albedo inhomogeneities producing a more statistically independent ensemble of speckle patterns. They find that some types of correlation are difficult to remove from the data.
Date: April 1, 1996
Creator: MacKerrow, E.P.; Tiee, J.J. & Fite, C.B.
Partner: UNT Libraries Government Documents Department

Time-resolved flourescence measurements of KrF emission produced by vacuum ultraviolet photolysis of KrF/sub 2/ mixtures

Description: Vacuum ultraviolet (VUV) light radiation was used to produce electronically excited KrF excimers (in D-, B- and C-states) by the photolysis of KrF/sub 2/ and F/sub 2//Kr mixtures at various excitation wavelengths. The excited KrF photoproduct quantum yield was measured over the excitation wavelength range of 120 to 200 nm, and a quantum efficiency of 0.45 was estimated at the peak absorption wavelength of 159 nm for KrF/sub 2/. The collision-free fluorescence lifetime of the B-X transition near 248 nm was determined to be 9.9 /plus minus/ 0.6 ns when the KrF/sub 2/ was excited with the 159 nm light. Near gas kinetic rate constants were measured for the quenching of KrF B-X emission by KrF/sub 2/ and CO/sub 2/. Using the threshold energy needed for observing excited KrF photofragments, an upper bound for the bond dissociation energy of KrF/sub 2/ was determined to be 1.03 /plus minus/ 0.1 eV. 14 refs., 8 figs.
Date: January 1, 1989
Creator: Tiee, J.J.; Quick, C.R.; Hsu, A.H. & Hof, D.E.
Partner: UNT Libraries Government Documents Department

Two-photon optically pumped molecular gas visible laser. [Ammonia]

Description: Recent investigations of the multiphoton ionization (MPI) spectrum of gaseous ammonia have led to the discovery of a novel two-photon pumped molecular gas electronic transition laser. Resonant, two-photon electronic excitation of NH/sub 3/ in the near uv (approx. 305 nm) leads to the first observation of fluorescence from NH/sub 3/ excited states (B and C'), and, at higher pressures, to lasing action (approx. 570 nm) between numerous C' and A state vibronic levels. A frequency-doubled Nd:YAG pumped dye laser (a few mJ) is focused into a cell containing NH/sub 3/ (or ND/sub 3/). Stimulated emission is observed in the forward and backward direction at NH/sub 3/ pressures greater than approx. 200 torr, without external mirrors to provide feedback. Conversion coefficiencies (output NH/sub 3/ pulse energy/input pulse energy) as high as 2% have been observed.
Date: January 1, 1983
Creator: Quick, C.R. Jr.; Glownia, J.H.; Tiee, J.J. & Archuleta, F.L.
Partner: UNT Libraries Government Documents Department

Vacuum ultraviolet photolysis of acetylene in the 110- to 135-nm region

Description: State-specific photofragmentation of acetylene in the 110- to 135-nm region has been studied using vuv laser and synchrotron sources. Investigations have been focused on learning the spectroscopic identity of the excited photoproducts by examining their time-resolved fluorescence. Results of the quenching of the excited photofragment emission and the emission polarization measurements are presented. An interpretation of these results in relating the observed photoproducts to the vuv photodissociation process is discussed. 13 refs., 3 figs., 1 tab.
Date: January 1, 1986
Creator: Tiee, J.J.; Sander, R.K.; Quick, C.R. & Estler, R.
Partner: UNT Libraries Government Documents Department

Lifetime and quenching measurements of C/sub 2/H emission produced by vacuum ultraviolet photolysis of C/sub 2/H/sub 2/. [C/sub 2/H radicals]

Description: The state-of-the-art tunable vuv sources are used to produce excited C/sub 2/H photofragments (C/sub 2/H*) via the photolysis of acetylene molecules. The quenching rate constants of the C/sub 2/H emission by a number of species are determined. The collision-free fluorescence lifetimes are measured at different excitation wavelengths. The excitation energy threshold for producing the observed emission is determined. In addition, a correlation between the excitation energy and the emission wavelength is observed. 27 refs., 6 figs., 2 tabs.
Date: January 1, 1985
Creator: Tiee, J.J.; Sander, R.K.; Quick, C.R. Jr.; Romero, R.J. & Estler, R.
Partner: UNT Libraries Government Documents Department

Atmospheric effects on CO{sub 2} differential absorption lidar performance

Description: CO{sub 2} differential absorption lidar (DIAL) performance can be adversely affected by the ambient atmosphere between the laser transmitter and the target through a number of different processes. This work addresses two sources of atmospheric interference with multispectral CO{sub 2} DIAL measurements: effects due to beam propagation through atmospheric turbulence and extinction due to absorption by atmospheric gases. The authors compare measurements of the effective beam size after propagation to predictions from a beam propagation model that includes turbulence effects such as beam steering and beam spreading. They also compare the experimental measurements of atmospheric extinction to those predicted by both a standard atmospheric transmission model (FASCODE) and a chemometric analysis.
Date: May 1, 1996
Creator: Petrin, R.R.; Quagliano, J.R.; Nelson, D.H.; Schmitt, M.J.; Quick, C.R.; Sander, R.K. et al.
Partner: UNT Libraries Government Documents Department

Atmospheric measurements using a scanning, solar-blind Raman Lidar

Description: The study of the water cycle by Lidar has many applications. Because micro-scale structures can be identified by their water content, the technique offers new opportunities to visualize and study the phenomena. There are applications to many practical problems in agricultural and water management as well as at waste storage sites. Conventional point sensors are limited and are inappropriate for use in complex terrain or varied vegetation and cannot be extrapolated over even modest ranges. To this end, techniques must be developed to measure the variables associated with evapotranspirative processes over large areas and varied surface conditions. A scanning water-Raman Lidar is an ideal tool for this task in that it can measure the water vapor concentration rapidly with high spatial resolution without influencing the measurements by the presence of the sensor. 3 refs., 5 figs., 1 tab.
Date: January 1, 1991
Creator: Eichinger, W.E.; Cooper, D.I.; Holtkamp, D.B.; Karl, R.R. Jr.; Quick, C.R. & Tiee, J.J.
Partner: UNT Libraries Government Documents Department

Remote detection of atmospherically dispersed vegetative cells using fluorescence LIDAR

Description: A uv fluorescence LIDAR system is employed for the long range detectio of atmospherically dispersed biological particles (e.g. Bacillus thuringiensis) released from an aerosol generator. 1 ref., 2 figs.
Date: January 1, 1991
Creator: Tiee, J.J.; Eichinger, W.E.; Hof, D.E.; Holtkamp, D.B.; Karl, R.R. Jr.; Martinez, R.J. et al.
Partner: UNT Libraries Government Documents Department

Characterization of background reflectivity for MEDUSA

Description: The DARPA MEDUSA program goal is to detect, locate, and identify electro-optical threats in the vicinity of a moving platform. Laser sensing will be employed to find these threats by looking for anomalous reflections from threat sensors. However, the reflectivity variability (clutter) in both natural and manmade backgrounds will inherently limit target detection levels. In parallel with advanced component development by several aerospace contractors, a study of this clutter limitation was initiated in the long-wave (LW) and midwave (MW) infrared spectral regions to properly drive system design parameters. The analysis of clutter and associated limits on detection has been a major component of LANL efforts in laser remote sensing for non-proliferation. LANL is now analyzing existing data and conducting additional selected measurements in both the LWIR (9 and 10.6 pm) and MWIR (4.6 pm) in support of the DARPA program to increase our understanding of these clutter limitations and, thereby aid in the design and development of the MEDUSA system. The status of the LANL effort will be discussed. A variety of different natural and manmade target types have been investigated. Target scenes range from relatively low clutter sites typical of a southwestern desert to higher clutter downtown urban sites. Images are created by conducting raster scans across a scene interest. These images are then analyzed using data clustering techniques (e g K-means) to identify regions within the scene that contain similar reflectivity profiles. Data will be presented illustrating the reflectivity variability among different samples of the same target type, Le. within the same cluster, and among different data clusters. In general, it is found that the variability of reflectivities among similar targets is well represented by a log-normal distribution. Furthermore, manmade target tend to have higher reflectivities and more variability than natural targets. The implications of this observation for ...
Date: January 1, 2003
Creator: Oldenborg, R. C. (Richard C.); Tiee, J. J. (Joe J.); Foy, B. R. (Bernard R.); Petrin, R. R. (Roger R.) & Wilson, C. W. (Carl W.)
Partner: UNT Libraries Government Documents Department

Huygens-Fresnel Wave-Optics Simulation of Atmosphere Optical Turbulence and Reflective Speckle in CO{sub 2} Differential Absorption Lidar (DIAL)

Description: The measurement sensitivity of CO{sub 2} differential absorption lidar (DIAL) can be affected by a number of different processes. We have previously developed a Huygens-Fresnel wave optics propagation code to simulate the effects of two of these process: effects caused by beam propagation through atmospheric optical turbulence and effects caused by reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. These effects include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, we briefly review a description of our model including the limitations along with previous simulation s of individual effects. The performance of our modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, advanced studies have been performed to demonstrate the utility of our model in assessing the effects for different lidar geometries on RMS noise and correlation ''size'' in the receiver plane.
Date: March 23, 1999
Creator: Nelson, D. H.; Petrin, R. R.; MacKerrow, E. P.; Schmitt, M. J.; Foy, B. R.; Koskelo, A. C. et al.
Partner: UNT Libraries Government Documents Department

Huygens-Fresnel Wave-Optics Simulation of Atmospheric Optical Turbulence and Reflective Speckle in CO

Description: The measurement sensitivity of CO{sub 2} differential absorption LIDAR (DIAL) can be affected by a number of different processes. Two of these processes are atmospheric optical turbulence and reflective speckle. Atmospheric optical turbulence affects the beam distribution of energy and phase on target. The effects of this phenomenon include beam spreading, beam wander and scintillation which can result in increased shot-to-shot signal noise. In addition, reflective speckle alone has been shown to have a major impact on the sensitivity of CO{sub 2} DIAL. The authors have previously developed a Huygens-Fresnel wave optics propagation code to separately simulate the effects of these two processes. However, in real DIAL systems it is a combination of these phenomena, the interaction of atmospheric optical turbulence and reflective speckle, that influences the results. In this work, the authors briefly review a description of the model including the limitations along with a brief summary of previous simulations of individual effects. The performance of the modified code with respect to experimental measurements affected by atmospheric optical turbulence and reflective speckle is examined. The results of computer simulations are directly compared with lidar measurements and show good agreement. In addition, simulation studies have been performed to demonstrate the utility and limitations of the model. Examples presented include assessing the effects for different array sizes on model limitations and effects of varying propagation step sizes on intensity enhancements and intensity probability distributions in the receiver plane.
Date: July 18, 1999
Creator: Nelson, D.H.; Petrin, R.R.; Quick, C.R.; Jolin, L.J.; MacKerrow, E.P.; Schmidtt, M.J. et al.
Partner: UNT Libraries Government Documents Department