The paper reports on vertical profiles of aerosol extinction and backscatter in the troposphere which were obtained from multi zenith angle lidar measurements. It is reported that a direct slant path solution was found to be not possible due to horizontal inhomogeneity of the atmosphere. Attention is given to the use of a regression analysis with respect to zenith angle for a layer integration of the angle dependent lidar equation in order to determine the optical thickness and aerosol extinction-to-backscatter ratio for defined atmospheric layers and the subsequent evaluation of cross-section profiles.

Vertical Distribution of Aerosol Extinction Cross Section and Inference of Aerosol Imaginary Index in the Troposphere by Lidar Technique

PM10 emissions from nonpoint sources need to be quantified in order to effectively meet air quality standards. In California's Central Valley, agricultural operations are highly complex but significant sources of PM10 that are difficult to quantify using point sampling arrays. A remote sensing technique, light detection and ranging (lidar), using a small field portable, fast-scanning lidar shows great potential for measuring PM10 emissions from agricultural nonpoint sources. The qualitative capabilities of the lidar instrument are demonstrated for land preparation operations at a wheat field. The range (>5 km), spatial resolution (2.5 m) and fast response times (s) of the lidar allow the following:  (i) plume dynamics to be described in detail and eventually to be modeled as a function of source fluctuations and environmental conditions, (ii) measurements of average wind speed and direction over 50−100 m scales, (iii) quantitative determination of the fraction of dust missed by point sampling arrays, and ...

Application of elastic lidar to PM10 emissions from agricultural nonpoint sources

In urban Seattle, simultaneous measurements were made of backscatter using a ruby laser radar and of the scattering portion of extinction using an integrating nephelometer. Both instruments were calibrated allowing separation of molecular and aerosol contributions to the two scatter coefficients. During the period of the experiment, backscatter and the scattering portion of extinction were well correlated at relative humidities less than 70%. For the aerosol, the ratio of backscatter to the scattering portion of extinction was only one-third that predicted from spherical particle Mie calculations for a power law size distribution aerosol.

Measurement of the Aerosol Total Scatter–Backscatter Ratio

The bistatic, Light Detection And Ranging, LIDAR technique for sensing atmospheric particulates is outlined, and analytical formulations are presented for characterizing both the intensity and polarization of the bistatic signals. Methods are presented on how to handle the remote sensing problem of extracting the particulate angular scattering parameters from the bistatic measurements. Examples are also presented which demonstrate that these methods can be practically applied at least for atmospheric conditions typical of Tucson, AZ.

Bistatic LIDAR: A Tool for Characterizing Atmospheric Particulates: Part I---The Remote Sensing Problem

The bistatic, ghtDetection AndRanging, LIDARtech- niqueforsensing atmospheric particulates isoutlined, andanalytical formulations arepresented forcharacterizing boththeintensity and polarization ofthebistatic signals. Methods arepresented onhowto handle theremote sensing problem ofextracting theparticulate angular scattering parameters fromthebistatic measurements. Examples are alsopresented which demonstrate that these methods canbepractically applied atleast foratmospheric conditions typical ofTucson, AZ.

Bistatic LIDAR: A Tool forCharacterizing Atmospheric Particulates: PartI-TheRemoteSensingProblem

In order to obtain quantitative data on the backscatter function from laser irradiance backscattered from the atmosphere, the ratio of power transmitted to power received must be accurately known. No absolute measurements of power, optical system transmittance, detector quantum efficiency, or electronic gain are necessarily required. The technique of measuring the power ratio by irradiating a smoked or painted target of known diffuse reflectance at a fixed range is used to calibrate a complete lidar system. The relative area of the output power pulse is monitored by a fast response photodiode, and the relative area of the returned pulse is also recorded after passing through a filter of known high optical density. It is essential to control the temperatures of the laser rod and receiver interference prefilter to ensure proper spectral matching. Field experience gained using this technique is described, and examples of calibration measurements and backscatter functions for smog and cirrus clouds are presented.

H. Y. Ageno

Papers

Absolute calibration of a laser system for atmospheric probing.