Laser-induced incandescence (LII) has proved to be a useful diagnostic tool for spatially and temporally resolved measurement of particulate (soot) volume fraction and primary particle size in a wide range of applications, such as steady flames, flickering flames, and Diesel engine exhausts. We present a novel LII technique for the determination of soot volume fraction by measuring the absolute incandescence intensity, avoiding the need for ex situ calibration that typically uses a source of particles with known soot volume fraction. The technique developed in this study further extends the capabilities of existing LII for making practical quantitative measurements of soot. The spectral sensitivity of the detection system is determined by calibrating with an extended source of known radiance, and this sensitivity is then used to interpret the measured LII signals. Although it requires knowledge of the soot temperature, either from a numerical model of soot particle heating or experimentally determined by detecting LII signals at two different wavelengths, this technique offers a calibration-independent procedure for measuring soot volume fraction. Application of this technique to soot concentration measurements is demonstrated in a laminar diffusion flame.

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An overview is presented of airborne systems for in situ measurements of aerosol particles, clouds and radiation that are currently in use on research aircraft around the world. Description of the technology is at a level sufficient for introducing the basic principles of operation and an extensive list of references for further reading is given. A number of newer instruments that implement emerging technology are described and the review concludes with a description of some of the most important measurement challenges that remain. This overview is a synthesis of material from a reference book that is currently in preparation and that will be published in 2012 by Wiley.

Conducting accurate cloud microphysical measurements from airborne platforms poses a number of challenges. The technique of phase Doppler interferometry (PDI) confers numerous advantages relative to traditional light-scattering techniques for measurement of the cloud drop size distribution, and, in addition, yields drop velocity information. Here, we describe PDI for the purposes of aiding atmospheric scientists in understanding the technique fundamentals, advantages, and limitations in measuring cloud microphysical properties. The performance of the Artium Flight PDI, an instrument specifically designed for airborne cloud measurements, is studied. Drop size distributions, liquid water content, and velocity distributions are compared with those measured by other airborne instruments.

A method is described for obtaining real-time in situ size and velocity measurements of spherical particles or droplets using crossed-beam interferometry. The optical arrangement, which is similar to a dual-scatter laser Doppler velocimeter (LDV), consists of two laser beams focused to a crossover region. Droplets passing through the focal volume scatter light to the collecting lens situated at some off-axis angle. The dual-beam light scatter is analyzed by the geometric optics theory to relate the scattered fringe pattern to the droplet diameter. Because the droplet size measurement is based on the relative phase shift between the two light waves passing through it, the method is independent of the incident intensity, droplet absorption, or absolute scattering intensity. Experimental measurements of monodisperse droplet streams show good agreement with the theory. The technique can be applied to spray-droplet measurements over the size range of 3 microm to 5 mm. By using large off-axis scatter detection angles, the measurement of the droplet size and velocity distributions in relatively dense spray environments is made possible.