Cloud thermodynamic phase and particle size estimation using the 0.67 and 1.6 μm channels from meteorological satellites

Abstract. A robust method to estimate the cloud microphysical properties from visible (0.67 μm) and near infrared (1.6 μm) measurements of reflected sunlight is presented. The method does not determine cloud particle phase and size separately. Instead it assigns a cloud particle type to every pixel that is most representative for the radiation measurements. The corresponding radiative transfer model calculations will yield the most accurate values for optical thickness. Furthermore, an estimate of the particle size is obtained, which is used in estimates of liquid water path. Radiative transfer calculations have been performed for eleven cloud particle models assuming a single, plane-parallel and homogeneous layer. Standard gamma distributions with varying effective radii have been chosen for liquid water droplet whereas imperfect hexagonal ice crystal with different aspect ratio and size were selected for ice particles. It is shown that the ratio of the visible reflectivity to the near infrared reflectivity as a function of the visible reflectivity allows a consistent classification of cloud particles with respect to size and phase over a large area. The method is tested with measurements from the Along Track Scanning Radiometer instrument (ATSR-2) on board ERS-2 for a marine stratocumulus cloud and a cirrus cloud over the North Sea. For both cases, the variation of the measured ratio as a function of the measured visible reflectivity is well simulated by liquid water droplet distribution with an effective radius between 4 and 10 micrometers for the stratocumulus and by imperfect hexagonal ice crystal with a size of 60 μm for cirrus. The method was used in the CLIWANET-project and will be the basis to the algorithm for AVHRR and SEVIRI radiances for EUMETSAT's Sattelite Application facility on climate monitoring.

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Lidar multiple scattering factors inferred from CALIPSO lidar and IIR retrievals of semi-transparent cirrus cloud optical depths over oceans

Atmospheric Measurement Techniques ◽

10.5194/amt-8-2759-2015 ◽

2015 ◽

Vol 8 (7) ◽

pp. 2759-2774 ◽

Cited By ~ 40

Author(s):

A. Garnier ◽

J. Pelon ◽

M. A. Vaughan ◽

D. M. Winker ◽

C. R. Trepte ◽

...

Keyword(s):

Particle Size ◽

Multiple Scattering ◽

Infrared Absorption ◽

Satellite Observations ◽

Orthogonal Polarization ◽

Cirrus Cloud ◽

Ice Crystal ◽

Cloud Particle ◽

Scattering Factor ◽

Infrared Radiometer

Abstract. Cirrus cloud absorption optical depths retrieved at 12.05 μm are compared to extinction optical depths retrieved at 0.532 μm from perfectly co-located observations of single-layered semi-transparent cirrus over ocean made by the Imaging Infrared Radiometer (IIR) and the Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) flying on board the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite. IIR infrared absorption optical depths are compared to CALIOP visible extinction optical depths when the latter can be directly derived from the measured apparent two-way transmittance through the cloud. An evaluation of the CALIOP multiple scattering factor is inferred from these comparisons after assessing and correcting biases in IIR and CALIOP optical depths reported in version 3 data products. In particular, the blackbody radiance taken in the IIR version 3 algorithm is evaluated, and IIR retrievals are corrected accordingly. Numerical simulations and IIR retrievals of ice crystal sizes suggest that the ratios of CALIOP extinction and IIR absorption optical depths should remain roughly constant with respect to temperature. Instead, these ratios are found to increase quasi-linearly by about 40 % as the temperature at the layer centroid altitude decreases from 240 to 200 K. It is discussed that this behavior can be explained by variations of the multiple scattering factor ηT applied to correct the measured apparent two-way transmittance for contribution of forward-scattering. While the CALIOP version 3 retrievals hold ηT fixed at 0.6, this study shows that ηT varies with temperature (and hence cloud particle size) from ηT = 0.8 at 200 K to ηT = 0.5 at 240 K for single-layered semi-transparent cirrus clouds with optical depth larger than 0.3. The revised parameterization of ηT introduces a concomitant temperature dependence in the simultaneously derived CALIOP lidar ratios that is consistent with observed changes in CALIOP depolarization ratios and particle habits derived from IIR measurements.

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Calibration of the Cloud Particle Imager Probes Using Calibration Beads and Ice Crystal Analogs: The Depth of Field

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech2096.1 ◽

2007 ◽

Vol 24 (11) ◽

pp. 1860-1879 ◽

Cited By ~ 61

Author(s):

Paul J. Connolly ◽

Michael J. Flynn ◽

Z. Ulanowski ◽

T. W. Choularton ◽

M. W. Gallagher ◽

...

Keyword(s):

Particle Size ◽

Calibration Method ◽

Depth Of Field ◽

Strong Positive Correlation ◽

Size Distributions ◽

Ice Crystal ◽

Particle Size Distributions ◽

Object Plane ◽

Cloud Particle ◽

Sample Mean

Abstract This paper explains and develops a correction algorithm for measurement of cloud particle size distributions with the Stratton Park Engineering Company, Inc., Cloud Particle Imager (CPI). Cloud particle sizes, when inferred from images taken with the CPI, will be oversized relative to their “true” size. Furthermore, particles will cease to be “accepted” in the image frame if they lie a distance greater than the depth of field from the object plane. By considering elements of the scalar theory for diffraction of light by an opaque circular disc, a calibration method is devised to overcome these two problems. The method reduces the error in inferring particle size from the CPI data and also enables the determination of the particles distance from the object plane and hence their depth of field. These two quantities are vital to enable quantitative measurements of cloud particle size distributions (histograms of particle size that are scaled to the total number concentration of particles) in the atmosphere with the CPI. By using both glass calibration beads and novel ice crystal analogs, these two problems for liquid drops and ice particles can be quantified. Analysis of the calibration method shows that 1) it reduces the oversizing of 15-μm beads (from 24.3 to 14.9 μm for the sample mean), 40-μm beads (from 50.0 to 41.4 μm for the sample mean), and 99.4-μm beads (from 103.7 to 99.8 μm for the sample mean); and 2) it accurately predicts the particles distance from the object plane (the relationship between measured and predicted distance shows strong positive correlation and gives an almost one-to-one relationship). Realistic ice crystal analogs were also used to assess the errors in sampling ice clouds and found that size and distance from the object plane could be accurately predicted for ice crystals by use of the particle roundness parameter (defined as the ratio of the projected area of the particle to the area of a circle with the same maximum length). While the results here are not directly applicable to every CPI, the methods are, as data taken from three separate CPIs fit the calibration model well (not shown).

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Semi-empirical Erosion Model with Particle Size and Liquid Water Content Effects for Ice Crystal Icing Simulations

AIAA AVIATION 2020 FORUM ◽

10.2514/6.2020-2827 ◽

2020 ◽

Author(s):

Virgile Charton ◽

Jean-Mathieu Senoner ◽

Pierre Trontin ◽

Philippe Villedieu

Keyword(s):

Particle Size ◽

Water Content ◽

Liquid Water ◽

Liquid Water Content ◽

Ice Crystal ◽

Erosion Model ◽

Semi Empirical

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Remote Sensing of Cirrus Cloud Particle Size and Optical Depth Using Polarimetric Sensor Measurements

Journal of the Atmospheric Sciences ◽

10.1175/jas3634.1 ◽

2005 ◽

Vol 62 (12) ◽

pp. 4371-4383 ◽

Cited By ~ 9

Author(s):

S. C. Ou ◽

K. N. Liou ◽

Y. Takano ◽

R. L. Slonaker

Keyword(s):

Remote Sensing ◽

Particle Size ◽

Optical Depth ◽

Steepest Descent Method ◽

Stokes Parameters ◽

Retrieval Algorithm ◽

Cirrus Cloud ◽

Transfer Program ◽

Ice Crystal ◽

Cloud Particle

Abstract This paper presents a conceptual approach toward the remote sensing of cirrus cloud particle size and optical depth using the degree of polarization and polarized reflectance associated with the first three Stokes parameters, I, Q, and U, for the 0.865- and 2.25-μm wavelengths. A vector line-by-line equivalent radiative transfer program including the full Stokes parameters based on the adding method was developed. The retrieval algorithm employs the steepest-descent method in the form of a series of numerical iteration procedures to search for the simulated polarization parameters that best match the measured values. Sensitivity studies were performed to investigate the behavior of phase-matrix elements as functions of scattering angles for three ice crystal size–shape combinations. Overall, each phase-matrix element shows some sensitivity toward ice crystal shape, size, and surface roughness due to the various optical effects. Synthetic analysis reveals that the retrieval algorithm is highly accurate, while polarimetric and radiometric error sources cause very small retrieval errors. Finally, an illustrative example of applying the retrieval algorithm to airborne Polarization and Directionality of the Earth’s Reflectances (POLDER) data during the European Cloud and Radiation Experiment (EUCREX) is presented.

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Sensitivity of Multispectral Imager Liquid Water Cloud Microphysical Retrievals to the Index of Refraction

Remote Sensing ◽

10.3390/rs12244165 ◽

2020 ◽

Vol 12 (24) ◽

pp. 4165 ◽

Cited By ~ 1

Author(s):

Steven Platnick ◽

Kerry Meyer ◽

Nandana Amarasinghe ◽

Galina Wind ◽

Paul A. Hubanks ◽

...

Keyword(s):

Remote Sensing ◽

Particle Size ◽

Liquid Water ◽

Infrared Imaging ◽

Sensitivity Study ◽

Bulk Water ◽

Index Of Refraction ◽

Bulk Liquid ◽

Cloud Particle ◽

Laboratory Index

A cloud property retrieved from multispectral imagers having spectral channels in the shortwave infrared (SWIR) and/or midwave infrared (MWIR) is the cloud effective particle radius (CER), a radiatively relevant weighting of the cloud particle size distribution. The physical basis of the CER retrieval is the dependence of SWIR/MWIR cloud reflectance on the cloud particle single scattering albedo, which in turn depends on the complex index of refraction of bulk liquid water (or ice) in addition to the cloud particle size. There is a general consistency in the choice of the liquid water index of refraction by the cloud remote sensing community, largely due to the few available independent datasets and compilations. Here we examine the sensitivity of CER retrievals to the available laboratory index of refraction datasets in the SWIR and MWIR using the retrieval software package that produces NASA’s standard Moderate Resolution Imaging Spectroradiometer (MODIS)/Visible Infrared Imaging Radiometer suite (VIIRS) continuity cloud products. The sensitivity study incorporates two laboratory index of refraction datasets that include measurements at supercooled water temperatures, one in the SWIR and one in the MWIR. Neither has been broadly utilized in the cloud remote sensing community. It is shown that these two new datasets can significantly change CER retrievals (e.g., 1–2 µm) relative to common datasets used by the community. Further, index of refraction data for a 265 K water temperature gives more consistent retrievals between the two spectrally distinct 2.2 µm atmospheric window channels on MODIS and VIIRS. As a result, 265 K values from the SWIR and MWIR index of refraction datasets were adopted for use in the production version of the continuity cloud product. The results indicate the need to better understand temperature-dependent bulk water absorption and uncertainties in these spectral regions.

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Remote sensing of cloud sides of deep convection: towards a three-dimensional retrieval of cloud particle size profiles

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-4267-2008 ◽

2008 ◽

Vol 8 (2) ◽

pp. 4267-4308 ◽

Cited By ~ 1

Author(s):

T. Zinner ◽

A. Marshak ◽

S. Lang ◽

J. V. Martins ◽

B. Mayer

Keyword(s):

Remote Sensing ◽

Particle Size ◽

Radiative Transfer ◽

Early Stage ◽

Deep Convection ◽

Three Dimensional ◽

Preceding Paper ◽

Test Bed ◽

Cloud Particle ◽

Cloud Data

Abstract. The cloud scanner sensor is a central part of a recently proposed satellite remote sensing concept – the three-dimensional (3-D) cloud and aerosol interaction mission (CLAIM-3D) combining measurements of aerosol characteristics in the vicinity of clouds and profiles of cloud microphysical characteristics. Such a set of collocated measurements will allow new insights in the complex field of cloud-aerosol interactions affecting directly the development of clouds and precipitation, especially in convection. The cloud scanner measures radiance reflected or emitted by cloud sides at several wavelengths to derive a profile of cloud particle size and thermodynamic phase. For the retrieval of effective size a Bayesian approach was adopted and introduced in a preceding paper. In this paper the potential of the approach, which has to account for the complex three-dimensional nature of cloud geometry and radiative transfer, is tested in realistic cloud observing situations. In a fully simulated environment realistic cloud resolving modelling provides complex 3-D structures of ice, water, and mixed phase clouds, from the early stage of convective development to mature deep convection. A three-dimensional Monte Carlo radiative transfer is used to realistically simulate the aspired observations. A large number of cloud data sets and related simulated observations provide the database for an experimental Bayesian retrieval. An independent simulation of an additional cloud field serves as a synthetic test bed for the demonstration of the capabilities of the developed retrieval techniques.

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Optical depths of semi-transparent cirrus clouds over oceans from CALIPSO infrared radiometer and lidar measurements, and an evaluation of the lidar multiple scattering factor

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-8-2143-2015 ◽

2015 ◽

Vol 8 (2) ◽

pp. 2143-2189 ◽

Cited By ~ 2

Author(s):

A. Garnier ◽

J. Pelon ◽

M. A. Vaughan ◽

D. M. Winker ◽

C. R. Trepte ◽

...

Keyword(s):

Particle Size ◽

Multiple Scattering ◽

Satellite Observations ◽

Orthogonal Polarization ◽

Ice Crystal ◽

Cloud Particle ◽

Lidar Measurements ◽

Detailed Evaluation ◽

Scattering Factor ◽

Infrared Radiometer

Abstract. This paper provides a detailed evaluation of cloud absorption optical depths retrieved at 12.05 μm and comparisons to extinction optical depths retrieved at 0.532 μm from perfectly co-located observations of single-layered semi-transparent cirrus over ocean made by the Imaging Infrared Radiometer (IIR) and the Cloud and Aerosol Lidar with Orthogonal Polarization (CALIOP) flying on-board the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite. The blackbody radiance taken in the IIR Version 3 algorithm is evaluated, and IIR retrievals are corrected accordingly. IIR infrared absorption optical depths are then compared to CALIOP visible extinction optical depths when the latter can be directly derived from the measured apparent 2-way transmittance through the cloud. Numerical simulations and IIR retrievals of ice crystal sizes suggest that the ratios of CALIOP extinction and IIR absorption optical depths should remain roughly constant with respect to temperature. Instead, these ratios are found to increase quasi-linearly by about 40% as the temperature at the layer centroid altitude decreases from 240 to 200 K. This behavior is explained by variations of the multiple scattering factor ηT to be applied to correct the measured transmittance, which is taken equal to 0.6 in the CALIOP Version 3 algorithm, and which is found here to vary with temperature (and hence cloud particle size) from ηT = 0.8 at 200 K to ηT = 0.5 at 240 K for clouds with optical depth larger than 0.3. The revised parameterization of ηT introduces a concomitant temperature dependence in the simultaneously derived CALIOP lidar ratios that is consistent with observed changes in CALIOP depolarization ratios and particle habits derived from IIR measurements.

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Rigorous inversion of absorption coefficient from spectral properties of particulate material

10.5194/epsc2021-689 ◽

2021 ◽

Author(s):

Antti Penttilä ◽

Timo Väisänen ◽

Julia Martikainen ◽

Cristian Carli ◽

Fabrizio Capaccioni ◽

...

Keyword(s):

Particle Size ◽

Refractive Index ◽

Radiative Transfer ◽

Imaginary Part ◽

Random Media ◽

Near Infrared ◽

Complex Refractive Index ◽

Geometric Optics ◽

Size Fractions ◽

Spectral Behavior

The optical constant of the material, meaning the complex refractive index m=n+ik, is an essential parameter when considering the reflection and absorption properties of that material. The refractive index is a function of wavelength of the light, and usually the imaginary part k is what governs the reflection or transmission spectral behavior of the material. The knowledge of the complex refractive index as a function of wavelength, m(&#955;), is needed for light scattering simulations. On the other hand, rigorous scattering simulations can be used to invert the refractive index from measured or observed reflection spectra. We will show how the combination of geometric optics and radiative transfer codes can be used in this task. In this work, the possible application is with the future visual-near infrared observations of Mercury by the ESA BepiColombo mission. That application in mind, we have used four particulate igneous glassy materials with varying overall albedo and in several size fractions in reflectance spectra measurements (hawaiitic basalt, two gabbronorites, anorthosite, see details from Carli et al, Icarus 266, 2016). The grounded material consist of particle with clear edges and quite flat facets, and we choose to model the particle shapes by geometries resulting from Voronoi division of random seed points in 3D space. The refractive index inversion is done here using first a geometric optics code SIRIS (Muinonen et al, JQSRT 110, 2009) to simulate the average Mueller matrix, albedo, and scattering efficiency for a single Voronoi particle. Then, these properties are fed into radiative transfer code RT-CB (Muinonen, Waves in Random Media 14, 2004) to produce the reflective properties of a semi-infinite slab of these particles. This procedure is repeated for a 2D grid of particle size parameters x=2&#960;r/&#955;, where r is the radius of particle, and imaginary part k of refractive index. In Vis-NIR wavelengths, the real part n is quite constant and is estimated to be about 1.58 for all the four glasses. From the simulated slab reflectance data with the 2D x, k parameter grid, we can first interpolate, and then invert the k parameter for any reflectance value with given wavelength and particle size. The resulting spectral behavior of k for the four glasses and for all the size fractions was seems very realistic. Carli et al. (Icarus 266, 2016) inverted the k spectral behavior for these same samples using Hapke modeling, and the results are quite similar. Furthermore, we have measured the transmission of the material using polished slabs of varying thinkness, and will compare the results that can be dervied from these transmission results to those from relfectance measurements.

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