scholarly journals Assessment of performance of the inter-arrival time algorithm to identify ice shattering artifacts in cloud particle probes measurements

2014 ◽  
Vol 7 (10) ◽  
pp. 10249-10292 ◽  
Author(s):  
A. Korolev ◽  
P. R. Field
Keyword(s):  
Particle Size ◽  
Time Algorithm ◽  
Sample Volume ◽  
Ice Crystals ◽  
Interarrival Time ◽  
Cloud Particle ◽  
Measured Concentration ◽  
Microphysical Properties ◽  
Pass Through ◽  
The Impact

Abstract. Shattering presents a serious obstacle to current airborne in-situ methods of characterizing the microphysical properties of ice clouds. Small shattered fragments result from the impact of natural ice crystals with the forward parts of aircraft-mounted measurement probes. The presence of these shattered fragments may result in a significant overestimation of the measured concentration of small ice crystals, contaminating the measurement of the ice particle size distribution (PSD). One method of identifying shattered particles is to use an interarrival time algorithm. This method is based on the assumption that shattered fragments form spatial clusters that have short interarrival times between particles, relative to natural particles, when they pass through the sample volume of the probe. The interarrival time algorithm is a successful technique for the classification of shattering artifacts and natural particles. This study assesses the limitations and efficiency of the interarrival time algorithm. The analysis has been performed using simultaneous measurements of 2-D optical array probes with the standard and antishattering "K-tips" collected during the Airborne Icing Instrumentation Experiment (AIIE). It is shown that the efficiency of the algorithm depends on ice particle size, concentration and habit. Additional numerical simulations indicate that the effectiveness of the interarrival time algorithm to eliminate shattering artifacts can be significantly restricted in some cases. Improvements to the interarrival time algorithm are discussed.

scholarly journals Assessment of the performance of the inter-arrival time algorithm to identify ice shattering artifacts in cloud particle probe measurements

2015 ◽  
Vol 8 (2) ◽  
pp. 761-777 ◽  
Author(s):  
A. Korolev ◽  
P. R. Field
Keyword(s):  
Particle Size ◽  
Arrival Time ◽  
Time Algorithm ◽  
Sample Volume ◽  
Ice Crystals ◽  
Cloud Particle ◽  
Measured Concentration ◽  
Arrival Times ◽  
Microphysical Properties ◽  
The Impact

Abstract. Shattering presents a serious obstacle to current airborne in situ methods of characterizing the microphysical properties of ice clouds. Small shattered fragments result from the impact of natural ice crystals with the forward parts of aircraft-mounted measurement probes. The presence of these shattered fragments may result in a significant overestimation of the measured concentration of small ice crystals, contaminating the measurement of the ice particle size distribution (PSD). One method of identifying shattered particles is to use an inter-arrival time algorithm. This method is based on the assumption that shattered fragments form spatial clusters that have short inter-arrival times between particles, relative to natural particles, when they pass through the sample volume of the probe. The inter-arrival time algorithm is a successful technique for the classification of shattering artifacts and natural particles. This study assesses the limitations and efficiency of the inter-arrival time algorithm. The analysis has been performed using simultaneous measurements of two-dimensional (2-D) optical array probes with the standard and antishattering "K-tips" collected during the Airborne Icing Instrumentation Experiment (AIIE). It is shown that the efficiency of the algorithm depends on ice particle size, concentration and habit. Additional numerical simulations indicate that the effectiveness of the inter-arrival time algorithm to eliminate shattering artifacts can be significantly restricted in some cases. Improvements to the inter-arrival time algorithm are discussed. It is demonstrated that blind application of the inter-arrival time algorithm cannot filter out all shattered aggregates. To mitigate against the effects of shattering, the inter-arrival time algorithm should be used together with other means, such as antishattering tips and specially designed algorithms for segregation of shattered artifacts and natural particles.

scholarly journals Light Scattering by Single Natural Ice Crystals

2006 ◽  
Vol 63 (5) ◽  
pp. 1513-1525 ◽  
Author(s):  
Valery Shcherbakov ◽  
Jean-François Gayet ◽  
Brad Baker ◽  
Paul Lawson
Keyword(s):  
Surface Roughness ◽  
Specular Reflection ◽  
Ice Crystals ◽  
Particle Orientation ◽  
Ice Crystal ◽  
Cloud Particle ◽  
Microphysical Properties ◽  
Wide Range ◽  
Crystal Properties ◽  
Pass Through

Abstract During the South Pole Ice Crystal Experiment, angular scattering intensities (ASIs) of single ice crystals formed in natural conditions were measured for the first time with the polar nephelometer instrument. The microphysical properties of the ice crystals were simultaneously obtained with a cloud particle imager. The observations of the scattering properties of numerous ice crystals reveal high variability of the ASIs in terms of magnitude and distribution over scattering angles. To interpret observed ASI features, lookup tables were computed with a modified ray tracing code, which takes into account the optical geometry of the polar nephelometer. The numerical simulations consider a wide range of input parameters for the description of the ice crystal properties (particle orientation, aspect ratio, surface roughness, and internal inclusions). A new model of surface roughness, which assumes the Weibull statistics, was proposed. The simulations reproduce the overwhelming majority of the observed ASIs features and trace very well the quasi-specular reflection from crystal facets. The discrepancies observed between the model and the experimental data correspond to the rays, which pass through the ice crystal and are scattered toward the backward angles. This feature may be attributed to the internal structure of the ice crystals that should be considered in modeling refinements.

scholarly journals Effects of ice particles shattering on the 2D-S probe

2011 ◽  
Vol 4 (7) ◽  
pp. 1361-1381 ◽  
Author(s):  
R. P. Lawson
Keyword(s):  
Particle Size ◽  
High Speed ◽  
Arrival Time ◽  
Primary Source ◽  
Time Algorithm ◽  
Post Processing ◽  
Cloud Particle ◽  
Ice Particles ◽  
Field Campaigns ◽  
Processing Techniques

Abstract. Recently, considerable attention has been focused on the issue of large ice particles shattering on the inlets and tips of cloud particle probes, which produces copious ice particles that can be mistakenly measured as real ice particles. Currently two approaches are being used to mitigate the problem: (1) Based on recent high-speed video in icing tunnels, probe tips have been designed that reduce the number of shattered particles that reach the probe sample volume, and (2) Post processing techniques such as image processing and using the arrival time of each individual particle. This paper focuses on exposing suspected errors in measurements of ice particle size distributions due to shattering, and evaluation of the two techniques used to reduce the errors. Data from 2D-S probes constitute the primary source of the investigation, however, when available comparisons with 2D-C and CIP measurements are also included. Korolev et al. (2010b) report results from a recent field campaign (AIIE) and conclude that modified probe tips are more effective than an arrival time algorithm when applied to 2D-C and CIP measurements. Analysis of 2D-S data from the AIIE and SPARTICUS field campaigns shows that modified probe tips significantly reduce the number of shattered particles, but that a particle arrival time algorithm is more effective than the probe tips designed to reduce shattering. A large dataset of 2D-S measurements with and without modified probe tips was not available from the AIEE and SPARTICUS field campaigns. Instead, measurements in regions with large ice particles are presented to show that shattering on the 2D-S with modified probe tips produces large quantities of small particles that are likely produced by shattering. Also, when an arrival time algorithm is applied to the 2D-S data, the results show that it is more effective than the modified probe tips in reducing the number of small (shattered) particles. Recent results from SPARTICUS and MACPEX show that 2D-S ice particle concentration measurements are more consistent with physical arguments and numerical simulations than measurements with older cloud probes from previous field campaigns. The analysis techniques in this paper can also be used to estimate an upper bound for the effects of shattering. For example, the additional spurious concentration of small ice particles can be measured as a function of the mass concentration of large ice particles. The analysis provides estimates of upper bounds on the concentration of natural ice, and on the remaining concentration of shattered ice particles after application of the post-processing techniques. However, a comprehensive investigation of shattering is required to quantify effects that arise from the multiple degrees of freedom associated with this process, including different cloud environments, probe geometries, airspeed, angle of attack, particle size and type.

Cirrus Microphysical Properties and Air Motion Statistics Using Cloud Radar Doppler Moments. Part I: Algorithm Description

2006 ◽  
Vol 45 (12) ◽  
pp. 1690-1709 ◽  
Author(s):  
Min Deng ◽  
Gerald G. Mace
Keyword(s):  
Particle Size ◽  
Vertical Velocity ◽  
Sample Volume ◽  
Doppler Spectrum ◽  
Convolution Integral ◽  
Mean Particle Size ◽  
Microphysical Properties ◽  
Spectrum Width ◽  
The Mean ◽  
Air Motion

Abstract The first three moments of the millimeter-wavelength radar Doppler spectrum provide valuable information regarding both cloud properties and air motion. An algorithm using these Doppler radar moments is developed to retrieve cirrus microphysical properties and the mean air vertical motion and their errors. The observed Doppler spectrum results from the convolution of a quiet-air radar reflectivity spectrum with the turbulence probability density function. Instead of expressing the convolution integral in terms of the particle fall velocity as in past studies, herein the convolution integral is integrated over the air motion so that the mean vertical velocity within the sample volume can be explicitly solved. To avoid an ill-conditioned problem, the turbulence is considered as a parameter in the algorithm and predetermined from the Doppler spectrum width and radar reflectivity based on the observation that the spread of the particle size distribution in the velocity domain dominates the Doppler spectrum width measurement for most cirrus. It is also shown that the assumed single mode functional shapes cannot reliably represent significant bimodalities. Nevertheless, the IWC can be retrieved more reliably than can the mass mean particle size. Error analysis also shows that the retrieval algorithm results are very sensitive to the power-law relationships describing the ice particle mass and the terminal velocity in terms of the particle maximum length. It is estimated that the algorithm errors will be on the order of 35%, 85%, and ±20 cm s−1 for mass mean particle size, IWC, and sample volume mean air motion, respectively. Algorithm validation with in situ data demonstrates that the algorithm can determine the cloud microphysical properties and air mean vertical velocity within the predicted theoretical error bounds.

scholarly journals Cloud particle size distributions measured with an airborne digital in-line holographic instrument

2009 ◽  
Vol 2 (1) ◽  
pp. 259-271 ◽  
Author(s):  
J. P. Fugal ◽  
R. A. Shaw
Keyword(s):  
Particle Size ◽  
Three Dimensional ◽  
Sample Volume ◽  
Equivalent Diameter ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Holographic Method ◽  
Cloud Particle ◽  
Data Set ◽  
Two Dimensional Image

Abstract. Holographic data from the prototype airborne digital holographic instrument HOLODEC (Holographic Detector for Clouds), taken during test flights are digitally reconstructed to obtain the size (equivalent diameters in the range 23 to 1000 μm), three-dimensional position, and two-dimensional image of ice particles and then ice particle size distributions and number densities are calculated using an automated algorithm with minimal user intervention. The holographic method offers the advantages of a well-defined sample volume size that is not dependent on particle size or airspeed, and offers a unique method of detecting shattered particles. The holographic method also allows the volume sample rate to be increased beyond that of the prototype HOLODEC instrument, limited solely by camera technology. HOLODEC size distributions taken in mixed-phase regions of cloud compare well to size distributions from a PMS FSSP probe also onboard the aircraft during the test flights. A conservative algorithm for detecting shattered particles utilizing their depth-position along the optical axis eliminates the obvious ice particle shattering events from the data set. In this particular case, the size distributions of non-shattered particles are reduced by approximately a factor of two for particles 15 to 70 μm in equivalent diameter, compared to size distributions of all particles.

Correlation and variability between weighing, counting and analytical methods to determine ergot (Claviceps purpurea) contamination of grain

2017 ◽  
Vol 10 (3) ◽  
pp. 209-218 ◽  
Author(s):  
T. Grusie ◽  
V. Cowan ◽  
J. Singh ◽  
J. McKinnon ◽  
B. Blakley
Keyword(s):  
Particle Size ◽  
Ergot Alkaloid ◽  
Total Alkaloid ◽  
High Performance ◽  
Ergot Alkaloids ◽  
Sample Volume ◽  
Small Sample ◽  
Claviceps Purpurea ◽  
Liquid Chromatography Tandem Mass ◽  
The Impact

Ergot alkaloid mycotoxins produced by the fungus Claviceps purpurea, are contaminants of cereal crops and grasses. The objectives of this study were to determine the correlation between number of ergot sclerotia and weight compared to the total ergot alkaloid concentration, to evaluate the effect of grinding process (i.e. particle size (PS)) on ergot alkaloid analysis using high performance liquid chromatography – tandem mass spectrometry, and to determine the impact of sample volume on analytical variability. This study demonstrated that correlations exist between both ergot sclerotia count (R2=0.7242, P<0.001) and ergot sclerotia weight (R2=0.9618, P<0.001) compared to the total alkaloid concentration of 6 ergot alkaloids. However, at alkaloid ergot concentrations below 350 µg/kg grain, ergot sclerotia count (R2=0.0002, P=0.956) and ergot sclerotia weight (R2=0.0064, P=0.769) were not correlated to the total alkaloid concentration. A lower variability (P=0.041), defined by coefficient of variation (CV), was observed using a commercial UDY cyclone sample mill (PS=192 µm, CV=9 µg/kg) as compared to a household coffee grinder (PS=516 µm, CV=66 µg/kg). Total amount and concentration of individual ergot alkaloids varied (P<0.05) among sclerotia of similar weight. For the analytical method, CV was numerically reduced as sample volume increased (97% CV for 75 ml to 64% CV for 1000 ml; mean of all concentrations) but increased as sample concentration declined (17% CV for 81,678 µg/kg to 284% for 35 µg/kg; mean of all sample volumes). This implies that analysis of small sample volumes at low ergot alkaloid concentrations may result in highly variable and potentially misleading results. In conclusion, number of ergot sclerotia and weight are unreliable indicators of alkaloid content at ergot concentrations below 350 µg/kg and particle size influences the variability. An analytical approach with fine grinding (mean PS<200 µm, 85% particles <400 µm) of a large sample should be used to assess low-level ergot contamination.

scholarly journals Effects of ice particles shattering on optical cloud particle probes

2011 ◽  
Vol 4 (1) ◽  
pp. 939-968 ◽  
Author(s):  
R. P. Lawson
Keyword(s):  
Particle Size ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Arrival Time ◽  
Primary Source ◽  
Time Algorithm ◽  
Post Processing ◽  
Cloud Particle ◽  
Ice Particles ◽  
Processing Techniques

Abstract. Recently, considerable attention has been focused on the issue of large ice particles shattering on the inlets and tips of cloud particle probes, which produces copious ice particles that can be mistakenly measured as real ice particles. Currently two approaches are being used to mitigate the problem: (1) Based on recent high-speed video in icing tunnels, probe tips have been designed that reduce the number of shattered particles that reach the probe sample volume, and (2) Post processing techniques such as image processing and using the arrival time of each individual particle. This paper focuses on exposing suspected errors in measurements of ice particle size distributions due to shattering, and evaluation of the two techniques used to reduce the errors. Data from 2D-S probes constitute the primary source of our investigation, however, comparisons with 2D-C and CIP measurements are also included. Analysis of 2D-S data shows that a particle arrival time algorithm is more effective than probe tips designed to reduce shattering, although application of both techniques ought to be complementary. This finding contrasts results from a recent investigation that found that modified probe tips were more effective than an arrival time algorithm when applied to 2D-C and CIP measurements. The reason for these differing results may be linked to the improved ability of the 2D-S to image small ice particles. The analysis techniques in this paper can be used to estimate the effects of shattering. For example, the additional spurious concentration of (small) shattered ice particles can be measured as a function of the mass concentration of (large) ice particles. The analysis provides estimates of upper bounds on the concentration of natural ice, and on the remaining concentration of shattered ice particles after application of the post-processing techniques. However, a comprehensive investigation of shattering is required to quantify effects that arise from the multiple degrees of freedom associated with this process, including different cloud environments, probe geometries, airspeed, angle of attack, particle size and type.

scholarly journals Cloud particle size distributions measured with an airborne digital in-line holographic instrument

2009 ◽  
Vol 2 (2) ◽  
pp. 659-688 ◽  
Author(s):  
J. P. Fugal ◽  
R. A. Shaw
Keyword(s):  
Particle Size ◽  
Three Dimensional ◽  
Sample Volume ◽  
Equivalent Diameter ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Holographic Method ◽  
Cloud Particle ◽  
Data Set ◽  
Unique Method

Abstract. Holographic data from the prototype airborne digital holographic instrument HOLODEC (Holographic Detector for Clouds), taken during test flights are digitally reconstructed to obtain the size (equivalent diameters in the range 23 to 1000 μm), three-dimensional position, and two-dimensional profile of ice particles and then ice particle size distributions and number densities are calculated using an automated algorithm with minimal user intervention. The holographic method offers the advantages of a well-defined sample volume size that is not dependent on particle size or airspeed, and offers a unique method of detecting shattered particles. The holographic method also allows the volume sample rate to be increased beyond that of the prototype HOLODEC instrument, limited solely by camera technology. HOLODEC size distributions taken in mixed-phase regions of cloud compare well to size distributions from a PMS FSSP probe also onboard the aircraft during the test flights. A conservative algorithm for detecting shattered particles utilizing the particles depth-position along the optical axis eliminates the obvious ice particle shattering events from the data set. In this particular case, the size distributions of non-shattered particles are reduced by approximately a factor of two for particles 15 to 70 μm in equivalent diameter, compared to size distributions of all particles.

scholarly journals On the importance of small ice crystals in tropical anvil cirrus

2009 ◽  
Vol 9 (15) ◽  
pp. 5519-5537 ◽  
Author(s):  
E. J. Jensen ◽  
P. Lawson ◽  
B. Baker ◽  
B. Pilson ◽  
Q. Mo ◽  
...  
Keyword(s):  
Sample Volume ◽  
Cirrus Clouds ◽  
Radiative Heating ◽  
Ice Crystals ◽  
Interarrival Time ◽  
Large Crystal ◽  
Small Crystal ◽  
Small Crystals ◽  
Ice Concentration ◽  
Anvil Cirrus

Abstract. In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (< 50 μm diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small-crystals could be artifacts of large-crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2-Dimensional Stereo (2D-S) probe, which detects particles as small as 10 μm. The 2D-S has detector "arms" instead of an inlet tube. Since the 2D-S probe surfaces are much further from the sample volume than is the case for the instruments with inlets, it is expected that 2D-S will be less susceptible to shattering artifacts. In addition, particle inter-arrival times are used to identify and remove shattering artifacts that occur even with the 2D-S probe. The number of shattering artifacts identified by the 2D-S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small-crystal concentration. The 2D-S measurements in tropical anvil cirrus suggest that natural small-crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D-S ratio of small-crystal concentrations and large-crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D-S large-crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large-crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D-S contribute relatively little cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D-S ice concentrations in fresh anvil cirrus may often exceed 1 cm−3, and are observed to exceed 10 cm−3 in turrets, they are typically ~0.1 cm−3 and rarely exceed 1 cm−3 (<1.4% of the time) in aged anvil cirrus. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus may be caused by ice nucleation driven by either small-scale convection or gravity waves. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC-4.

In Situ Observations of the Microphysical Properties of Wave, Cirrus, and Anvil Clouds. Part II: Cirrus Clouds

2006 ◽  
Vol 63 (12) ◽  
pp. 3186-3203 ◽  
Author(s):  
R. Paul Lawson ◽  
Brad Baker ◽  
Bryan Pilson ◽  
Qixu Mo
Keyword(s):  
Particle Size ◽  
Number Concentration ◽  
Cirrus Clouds ◽  
Average Particle ◽  
Cloud Particle ◽  
Microphysical Properties ◽  
Irregular Shapes ◽  
Ice Particles ◽  
Research Aircraft ◽  
Particle Size And Shape

A Learjet research aircraft was used to collect microphysical data, including cloud particle imager (CPI) measurements of ice particle size and shape, in 22 midlatitude cirrus clouds. The dataset was collected while the aircraft flew 104 horizontal legs, totaling over 15 000 km in clouds. Cloud temperatures ranged from −28° to −61°C. The measurements show that cirrus particle size distributions are mostly bimodal, displaying a maximum in number concentration, area, and mass near 30 μm and another smaller maximum near 200–300 μm. CPI images show that particles with rosette shapes, which include mixed-habit rosettes and platelike polycrystals, constitute over 50% of the surface area and mass of ice particles >50 μm in cirrus clouds. Approximately 40% of the remaining mass of ice particles >50 μm are found in irregular shapes, with a few percent each in columns and spheroidal shapes. Plates account for <1% of the total mass. Particles <50 μm account for 99% of the total number concentration, 69% of the shortwave extinction, and 40% of the mass in midlatitude cirrus. Plots and average equations for area versus particle size are shown for various particle habits, and can be used in studies involving radiative transfer. The average particle concentration in midlatitude cirrus is on the order of 1 cm−3 with occasional 10-km averages exceeding 5 cm−3. There is a strong similarity of microphysical properties of ice particles between wave clouds and cirrus clouds, suggesting that, like wave clouds, cirrus ice particles first experience conversion to liquid water and/or solution drops before freezing.

Sign in / Sign up

Export Citation Format

Share Document