Concept, absolute calibration, and validation of a new benchtop laser imaging polar nephelometer
<p>Polar nephelometers provide in situ measurements of aerosol angular light scattering and play an essential role in validating numerically calculated phase functions or inversion algorithms used in space-borne and land-based aerosol remote sensing. In this study, we present a prototype of a...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-08-01
|
| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/16/3653/2023/amt-16-3653-2023.pdf |
| Summary: | <p>Polar nephelometers provide in situ measurements of aerosol angular light scattering and play an essential role in validating numerically calculated phase functions or inversion algorithms used in space-borne and land-based aerosol remote sensing. In this study, we present a prototype of a new polar nephelometer called uNeph. The instrument is designed to measure the phase function, <span class="inline-formula"><i>F</i><sub>11</sub></span>, and polarized phase function, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><msub><mi>F</mi><mn mathvariant="normal">12</mn></msub><mo>/</mo><msub><mi>F</mi><mn mathvariant="normal">11</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="a6e3f1eb3299ee1cf773cb5249d5f2b9"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-16-3653-2023-ie00001.svg" width="46pt" height="14pt" src="amt-16-3653-2023-ie00001.png"/></svg:svg></span></span>, over the scattering range of around 5 to 175<span class="inline-formula"><sup>∘</sup></span>, with an angular resolution of 1<span class="inline-formula"><sup>∘</sup></span> at a wavelength of 532 nm. In this work, we present details of the data processing procedures and instrument calibration approaches. uNeph was validated in a laboratory setting using monodisperse polystyrene latex (PSL) and di-ethyl-hexyl-sebacate (DEHS) aerosol particles over a variety of sizes ranging from 200 to 800 nm. An error model was developed, and the level of agreement between the uNeph measurements and Mie theory was found to be consistent within the uncertainties in the measurements and the uncertainties in the input parameters for the theoretical calculations. The estimated measurement errors were between 5 % and 10 % (relative) for <span class="inline-formula"><i>F</i><sub>11</sub></span> and smaller than <span class="inline-formula">∼</span> 0.1 (absolute) for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><msub><mi>F</mi><mn mathvariant="normal">12</mn></msub><mo>/</mo><msub><mi>F</mi><mn mathvariant="normal">11</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="46pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="be17217608c9cbadb57f86dd6a9e9edd"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-16-3653-2023-ie00002.svg" width="46pt" height="14pt" src="amt-16-3653-2023-ie00002.png"/></svg:svg></span></span>. Additionally, by applying the Generalized Retrieval of Aerosol and Surface Properties (GRASP) inversion algorithm to the measurements conducted with broad unimodal DEHS aerosol particles, the volume concentration, size distribution, and refractive index of the ensemble of aerosol particles were accurately retrieved. This paper demonstrates that the uNeph prototype can be used to conduct accurate measurements of aerosol phase function and polarized phase function and to retrieve aerosol properties through inversion algorithms.</p> |
|---|---|
| ISSN: | 1867-1381 1867-8548 |