Abstract
The lack of quantitative characterization of aerosol particles and their loading in the atmosphere is one of the greatest uncertainties in climate-change science. Improved instrumentation capable of determining the size and shape of aerosol particles is needed in efforts to reduce this uncertainty. We describe a new instrument carried by an unmanned aerial vehicle (UAV) that images free-floating aerosol particles in the atmosphere. Using digital holography, the instrument obtains the images in a non-contact manner, resolving particles larger than ten micrometers in size in a sensing volume of approximately three cubic centimeters. The instrument, called the holographic aerosol particle imager (HAPI), has the unique ability to image multiple particles freely entering its sensing volume from any direction via a single measurement. The construction of HAPI consists of 3D printed polymer structures that enable a sufficiently low size and weight that it may be flown on a commercial-grade UAV. Examples from field trials of HAPI show images of freshly emitted tree pollen and mineral dust.
Highlights
particles[41,43,44], conventional methods have largely failed to solve the inverse problem and confidently characterize arbitrary particles in situ[41]
This is achieved with a new field instrument, the holographic aerosol particle imager (HAPI), which attaches to a low-cost unmanned aerial vehicle (UAV) and images coarse mode aerosol (CMA) particles as they are in the atmosphere
The HAPI instrument is deployed at several locations in the vicinity of Kansas State University (KSU) to investigate aerosol particles emitted from two sources
Summary
particles[41,43,44], conventional methods have largely failed to solve the inverse problem and confidently characterize arbitrary particles in situ[41]. We overcome limitations due to the inverse problem using in-line digital holography (DH) and show that images of particles can be obtained while still benefiting from the sample-collection-free nature of conventional light-scattering methods This is achieved with a new field instrument, the holographic aerosol particle imager (HAPI), which attaches to a low-cost unmanned aerial vehicle (UAV) and images CMA particles as they are in the atmosphere. The HAPI instrument is deployed at several locations in the vicinity of Kansas State University (KSU) to investigate aerosol particles emitted from two sources These include live pollen emitted from a spruce tree (picea abies) and mineral dust from agricultural road traffic. The process is not applied directly to Iholo , but rather, to the contrast hologram Icon , which is produced after subtracting a background measurement, Iref This subtraction step improves the hologram fringe contrast and eventual image. A great variety of useful analysis can be derived from this unique property extending beyond aerosol applications including sub-micron imaging of biological cells[49]
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