Errors Associated With Measurements from Imaging Probes

Abstract:

Imaging probes, collecting data on particles from about 20 or 50 microns to several centimeters, are the probes that have been collecting data on the droplet and ice microphysics for more than 40 years. During that period, a number of problems associated with the measurements have been identified, including questions about the depth of field of particles within the probes’ sample volume, and ice shattering, among others, have been identified. Many different software packages have been developed to process and interpret the data, leading to differences in the particle size distributions and estimates of the extinction, ice water content and radar reflectivity obtained from the same data.

Given the numerous complications associated with imaging probe data, we have developed an optical array probe simulation package to explore the errors that can be expected with actual data. We simulate full particle size distributions with known properties, and then process the data with the same software that is used to process real-life data. We show that there are significant errors in the retrieved particle size distributions as well as derived parameters such as liquid/ice water content and total number concentration. Furthermore, the nature of these errors change as a function of the shape of the simulated size distribution and the physical and electronic characteristics of the instrument. We will introduce some methods to improve the retrieval of particle size distributions from real-life data.