scholarly journals 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

2015 ◽  
Vol 8 (2) ◽  
pp. 2143-2189 ◽  
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.

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

2015 ◽  
Vol 8 (7) ◽  
pp. 2759-2774 ◽  
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.

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

2007 ◽  
Vol 24 (11) ◽  
pp. 1860-1879 ◽  
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).

scholarly journals Application of a multiple scattering model to estimate optical depth, lidar ratio and ice crystal effective radius of cirrus clouds observed with lidar.

2018 ◽  
Vol 176 ◽  
pp. 05037
Author(s):  
Diego Gouveia ◽  
Holger Baars ◽  
Patric Seifert ◽  
Ulla Wandinger ◽  
Henrique Barbosa ◽  
...  
Keyword(s):  
Multiple Scattering ◽  
Optical Depth ◽  
Single Scattering ◽  
Effective Radius ◽  
Cirrus Clouds ◽  
Ice Crystal ◽  
Backscatter Signal ◽  
Cloud Optical Depth ◽  
Lidar Measurements ◽  
Lidar Ratio

Lidar measurements of cirrus clouds are highly influenced by multiple scattering (MS). We therefore developed an iterative approach to correct elastic backscatter lidar signals for multiple scattering to obtain best estimates of single-scattering cloud optical depth and lidar ratio as well as of the ice crystal effective radius. The approach is based on the exploration of the effect of MS on the molecular backscatter signal returned from above cloud top.

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

2005 ◽  
Vol 62 (12) ◽  
pp. 4371-4383 ◽  
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.

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

2003 ◽  
Vol 3 (4) ◽  
pp. 4461-4488 ◽  
Author(s):  
D. Jolivet ◽  
A. J. Feijt
Keyword(s):  
Particle Size ◽  
Radiative Transfer ◽  
Liquid Water ◽  
Water Droplet ◽  
Near Infrared ◽  
Homogeneous Layer ◽  
Ice Crystal ◽  
Cloud Particle ◽  
Single Plane ◽  
Hexagonal Ice

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.

Mother-of-pearl cloud particle size and composition from aircraft-based photography of coloration and lidar measurements

2014 ◽  
Vol 54 (4) ◽  
pp. B140 ◽  
Author(s):  
Jens Reichardt ◽  
Susanne Reichardt ◽  
Chris A. Hostetler ◽  
Patricia L. Lucker ◽  
Thomas J. McGee ◽  
...  
Keyword(s):  
Particle Size ◽  
Cloud Particle ◽  
Lidar Measurements

scholarly journals Global Ocean Studies from CALIOP/CALIPSO by Removing Polarization Crosstalk Effects

2021 ◽  
Vol 13 (14) ◽  
pp. 2769
Author(s):  
Xiaomei Lu ◽  
Yongxiang Hu ◽  
Ali Omar ◽  
Rosemary Baize ◽  
Mark Vaughan ◽  
...  
Keyword(s):  
Polarization Plane ◽  
Optical Power ◽  
Satellite Observations ◽  
Global Ocean ◽  
Reference Plane ◽  
Orthogonal Polarization ◽  
True Value ◽  
Before And After ◽  
Oriented Parallel ◽  
532 Nm

Recent studies indicate that the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite provides valuable information about ocean phytoplankton distributions. CALIOP’s attenuated backscatter coefficients, measured at 532 nm in receiver channels oriented parallel and perpendicular to the laser’s linear polarization plane, are significantly improved in the Version 4 data product. However, due to non-ideal instrument effects, a small fraction of the backscattered optical power polarized parallel to the receiver polarization reference plane is misdirected into the perpendicular channel, and vice versa. This effect, known as polarization crosstalk, typically causes the measured perpendicular signal to be higher than its true value and the measured parallel signal to be lower than its true value. Therefore, the ocean optical properties derived directly from CALIOP’s measured signals will be biased if the polarization crosstalk effect is not taken into account. This paper presents methods that can be used to estimate the CALIOP crosstalk effects from on-orbit measurements. The global ocean depolarization ratios calculated both before and after removing the crosstalk effects are compared. Using CALIOP crosstalk-corrected signals is highly recommended for all ocean subsurface studies.

scholarly journals Quantifying the Cloud Particle‐Size Feedback in an Earth System Model

2019 ◽  
Vol 46 (19) ◽  
pp. 10910-10917
Author(s):  
Jiang Zhu ◽  
Christopher J. Poulsen
Keyword(s):  
Particle Size ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Cloud Particle

Characterization of alumina powder using multiple small-angle neutron scattering. I. Theory

1985 ◽  
Vol 18 (6) ◽  
pp. 467-472 ◽  
Author(s):  
N. F. Berk ◽  
K. A. Hardman-Rhyne
Keyword(s):  
Particle Size ◽  
Phase Shift ◽  
Neutron Scattering ◽  
Multiple Scattering ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Volume Fraction ◽  
Scattering Data ◽  
Alumina Powder ◽  
Beam Broadening

Microstructural parameters of high-purity alumina powder are determined quantitatively throughout the bulk of the material using small-angle neutron scattering techniques. A unified theoretical and experimental approach for analyzing multiple scattering data is developed to obtain values for particle size, volume fraction and surface area. It is shown how particle size and volume fraction can be measured in a practical way from SANS data totally dominated by incoherent multiple scattering (`beam broadening'). The general phase-shift dependence of single-particle scattering is incorporated into the multiple scattering formalism, and it is also shown that the diffractive limit (small phase shift) applies even for phase shifts as large as unity (particle radii of order 1 μm). The stability of the Porod law against multiple scattering and the phase-shift scale are described, a useful empirical formula for analysis of beam broadening data is exhibited, and the applicability of the formulations to polydispersed systems is discussed.

Sign in / Sign up

Export Citation Format

Share Document