Mapping air contaminants using path-integrated optical remote sensing with a non-overlapping variable path length beam geometry

Abstract

Path Integrated Optical Remote Sensing (PI-ORS) instruments are used to provide Path Integrated Concentration (PIC) data corresponding to a particulate concentration in region scanned by a sequence of optical beams. Prior art methods of developing spatial concentration maps using PIC data have required a relatively large number of intersecting beam paths. The present invention can produce spatial concentration maps using considerably fewer optical beams. Preferably, a non-overlapping radial beam geometry is used to produce PIC data that are processed to produce a spatial concentration map. The PIC data are indicative of the cumulative spatial concentration distribution of the contaminant in the sampling region. Once the PIC data are obtained, a specifically developed reconstruction algorithm is applied to the PIC data to create a map of concentration or contaminants or other constituents in the sampling region. Any of several different reconstruction algorithms can be employed. In general, a method for fitting or interpolating is used to estimate the cumulative distribution function of the contaminants or constituents of interest over the sampling region from the observed PIC data. Continuous or spline functions can be used in the reconstruction algorithm. Preferably, a smooth basis function minimization (SBFM) algorithm is used to fit a superposition of the integrated basis functions to the PIC data. The evaluation of the directional derivatives for the fitted integrated (cumulative) basis functions provides the desired map of concentration values over the sampling region. Using far fewer sources and detectors than the prior art, reasonably accurate concentration mappings can be achieved.