05 Jan 2022
05 Jan 2022
Status: this preprint is currently under review for the journal AMT.

A Comparative Evaluation of Snowflake Particle Size and Shape Estimation Techniques used by the Precipitation Imaging Package (PIP), Multi-Angle Snowflake Camera (MASC), and Two-Dimensional Video Disdrometer (2DVD)

Charles Nelson Helms1,2, Stephen Joseph Munchak1, Ali Tokay1,3, and Claire Pettersen4 Charles Nelson Helms et al.
  • 1Mesoscale Atmospheric Processes Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 2NASA Postdoctoral Program—Universities Space Research Association, Columbia, MD, USA
  • 3Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, MD, USA
  • 4Climate and Space Sciences and Engineering Department, University of Michigan, Ann Arbor, MI, USA

Abstract. Measurements of snowflake particle size and shape are important for studying the snow microphysics. While a number of instruments exist that are designed to measure these important parameters, this study focuses on the measurement techniques of three digital video disdrometers: the Precipitation Imaging Package (PIP), the Multi-Angle Snowflake Camera (MASC) and the Two-Dimensional Video Disdrometer (2DVD). To gain a better understanding of the relative strengths and weaknesses of these instruments and to provide a foundation upon which comparisons can be made between studies using data from different instruments, we perform a comparative analysis of the measurement algorithms employed by each of the three instruments by applying the algorithms to snowflake images captured by PIP during the ICEP-POP 2018 field campaign.

Our analysis primarily focuses on the measurements of area, equivalent diameter, and aspect ratio. Our findings indicate that area and equi-area diameter measurements using the 2DVD camera setup should be the most accurate, followed by MASC, which is slightly more accurate than PIP. In terms of the precision of the area and equi-area diameter measurements, however, MASC is considerably more precise than PIP or 2DVD, which provide similar precision once the effects of the PIP image compression algorithm are taken into account. Both PIP and MASC use shape-fitting algorithms to measure aspect ratio. While our analysis of the MASC aspect ratio suggests the measurements are reliable, our findings indicate that both the ellipse and rectangle aspect ratios produced by PIP under-performed considerably due to the shortcomings of the PIP shape-fitting techniques. That said, we also demonstrate that reliable measurements of aspect ratio can be retrieved from PIP by reprocessing the PIP images using either the MASC shape-fitting technique or a tensor-based ellipse-fitting technique. Because of differences in instrument design, 2DVD produces measurements of particle horizontal and vertical extent rather than length and width. Furthermore, the 2DVD measurements of particle horizontal extent can be contaminated by horizontal particle motion. Our findings indicate that, although the correction technique used to remove the horizontal motion contamination performs remarkably well with snowflakes despite being designed for use with rain drops, the 2DVD measurements of particle horizontal extent are potentially unreliable.

Charles Nelson Helms et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-427', Anonymous Referee #1, 30 Jan 2022
    • AC1: 'Reply on RC1', Charles N. Helms, 25 Apr 2022
  • RC2: 'Comment on amt-2021-427', Anonymous Referee #2, 03 Feb 2022
    • AC2: 'Reply on RC2', Charles N. Helms, 25 Apr 2022
  • RC3: 'Comment on amt-2021-427', Anonymous Referee #3, 03 Feb 2022
    • AC3: 'Reply on RC3', Charles N. Helms, 25 Apr 2022

Charles Nelson Helms et al.

Charles Nelson Helms et al.


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Short summary
This study compares three instruments used to measure snowflake size and shape: PIP, MASC, and 2DVD. Our findings indicate that 2DVD produces the most accurate measures of area, based on resilience to motion blurring, followed by MASC, which is slightly more accurate than PIP. In terms of precision, however, MASC is by far the most accurate due to the high pixel resolution while PIP and 2DVD have similar precision to one another.