13 research outputs found
Recommended from our members
Laser speckle effects on hard target differential absorption lidar
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
Recommended from our members
Initial airborne CO{sub 2} DIAL measurements: Discussion of results and data analysis considerations
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
Recommended from our members
Time-resolved flourescence measurements of KrF emission produced by vacuum ultraviolet photolysis of KrF/sub 2/ mixtures
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
Pressure dependence of laser oscillation and superfluorescent emission from an optically pumped CF4 laser
Recommended from our members
Atmospheric measurements using a scanning, solar-blind Raman Lidar
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
Recommended from our members
Remote detection of atmospherically dispersed vegetative cells using fluorescence LIDAR
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