Characterising optical array particle imaging probes: implications for small-ice-crystal observations
<p>The cloud particle concentration, size, and shape data from optical array probes (OAPs) are routinely used to parameterise cloud properties and constrain remote sensing retrievals. This paper characterises the optical response of OAPs using a combination of modelling, laboratory, and field...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/14/1917/2021/amt-14-1917-2021.pdf |
| Summary: | <p>The cloud particle concentration, size, and shape data from optical array
probes (OAPs) are routinely used to parameterise cloud properties and
constrain remote sensing retrievals. This paper characterises the optical
response of OAPs using a combination of modelling, laboratory, and field
experiments. Significant uncertainties are found to exist with such probes
for ice crystal measurements. We describe and test two independent methods
to constrain a probe's sample volume that remove the most severely
mis-sized particles: (1) greyscale image analysis and (2) co-location using
stereoscopic imaging. These methods are tested using field measurements from
three research flights in cirrus. For these cases, the new methodologies
significantly improve agreement with a holographic imaging probe compared to
conventional data-processing protocols, either removing or significantly
reducing the concentration of small ice crystals (<span class="inline-formula"><</span> 200 <span class="inline-formula">µ</span>m)
in certain conditions. This work suggests that the observational evidence
for a ubiquitous mode of small ice particles in ice clouds is likely due to
a systematic instrument bias. Size distribution parameterisations based on
OAP measurements need to be revisited using these improved methodologies.</p> |
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| ISSN: | 1867-1381 1867-8548 |