Analysis of Three Dimensional Aerosol Distributions by Means of Digital Holography
Digital holography presents a modern method for micro particle diagnostics, generating three dimensional snapshots of particle distributions in volumes in a rapid sequence.
Holographic techniques for micro particle analysis were already introduced by Silverman et. al. in 1964 (Silverman et. al. 1964), (Vikram 1992). Scientists pushed that technology forward to analyze atmospheric aerosol distributions in clouds. In 1994 the researchers Borman and Jaenicke made a comparison concerning the performances of a conventional holographic aerosol analysis system with the standard FSSP-100 and PVM-100 devices (Hohmann et al. 1994). The particle range in that investigation was in the range of 3–15μm diameter. With their new holographic method they could store 450 liters (0,45m3) of cloud volume in a hologram using one exposure with a recognizable particle size of 5–500μm (Uhlig 1995). However, the technical requirements for hologram exposure (ruby laser), hologram development (dark room), droplet reconstruction (reconstruction set-up in the lab) were enormous. Furthermore, analyzing the reconstructed cloud volume is extremely time consuming (Vössig et. al. 1997).
To overcome these disadvantages, a mobile system based on the method of digital holography has been developed and tested in a field campaign.
This innovative digital holographic measurement system uses the principle of Fraunhofer inline holography and provides a series of advantages compared to conventional holographic systems regarding time consumption and system design for both holographic storage and hologram reconstruction or hologram analysis.
KeywordsParticle Image Velocimetry Ruby Laser Digital Holography Laser Head Aerosol Distribution
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