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Scattering by Ice Crystals in the Earth's Atmosphere

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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Remote Sensing Image Processing".

Deadline for manuscript submissions: closed (30 November 2022) | Viewed by 24660

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Dr. Anthony J. Baran

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Expert Scientist & Visiting Research Fellow, Met Office, FitzRoy Road, Exeter EX1 3PB, Devon, UK & School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB, UK
Interests: ice crystals; scattering; remote sensing; radiative transfer; microphysics; climate modelling; electromagnetism; parametrizations; physical optics; aerosols
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Dear Colleagues,

Scattering by ice crystals in the Earth’s atmosphere is still a challenging problem to solve in a physically consistent manner across the observed electromagnetic spectrum. This is because in ice crystal clouds, or cirrus, there are many differing types of shapes, sizes, areas and masses of ice crystals. There have been a few attempts at modeling the electromagnetic scattering properties of these elaborate ensembles of ice crystals by several colleagues. Recently, some of these models have been shown not to be consistent across the spectrum of measurement.

This is a very pressing problem to solve, owing to the importance of cirrus to the earth–atmosphere radiative balance, this balance being crucial to climate models. Only through the understanding of the role of cirrus in this balance can we improve the predictive quality of climate models. For this to be achieved, a fundamental understanding of the electromagnetic scattering properties of ice crystals is required. This understanding is of equal importance in weather prediction too, through the assimilation of all-sky radiance data within weather models.

To help constrain the cirrus problem outlined above, over the ensuing decade and beyond, global space-based radiance observations of cirrus are planned that will span more of the electromagnetic spectrum than achieved so far. This will be fulfilled through NASA’s support of the A-train, TROPICS and PREFIRE missions, NOAA/NASA’s GOES series, JMA’s Himawari series of satellites, and the CMA’s Feng-Yun satellite series, EUMETSAT's next generation of polar-orbiting and geostationary satellites, ESA’s EarthCARE and far-infrared FORUM missions. To facilitate solutions to the fundamental problems outlined above and to prepare for these exciting remote sensing missions, colleagues are invited to submit papers to this Special Issue that may further illuminate our understanding of the radiative properties of cirrus.

This Special Issue is dedicated to the memory of Dr. Michael Mishchenko, whose profound research greatly enriched the papers in this Special Issue, and who will influence future research in perpetuity.

The Special Issue “Scattering by Ice Crystals in the Earth's Atmosphere” is jointly organized between “Remote Sensing” and “Earth” journals. Contributors are required to check the website below and follow the specific instructions for authors:
https://www.mdpi.com/journal/remotesensing/instructions
https://www.mdpi.com/journal/earth/instructions

The other special issue could be found at: https://www.mdpi.com/journal/earth/special_issues/Earth_Ice_Crystals. You will have the opportunity to choose to publish your papers in Earth, which will offer a lot of discounts or fully waivers for your papers based on peer-review results.

Dr. Anthony J. Baran
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

ice crystals
scattering
remote sensing
polarization
electromagnetism

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Published Papers (9 papers)

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17 pages, 3806 KiB

Open AccessArticle

Time-Dependent Systematic Biases in Inferring Ice Cloud Properties from Geostationary Satellite Observations

by Dongchen Li, Masanori Saito and Ping Yang

Remote Sens. 2023, 15(3), 855; https://doi.org/10.3390/rs15030855 - 3 Feb 2023

Cited by 2 | Viewed by 2165

Abstract

Geostationary satellite-based remote sensing is a powerful tool to observe and understand the spatiotemporal variation of cloud optical-microphysical properties and their climatologies. Solar reflectances measured from the Advanced Baseline Imager (ABI) instruments aboard Geostationary Operational Environmental Satellites 16 and 17 correspond to different spatial pixel resolutions, from 0.5 km in a visible band, up to 2 km in infrared bands. For multi-band retrievals of cloud properties, reflectances with finer spatial resolution need to be resampled (averaged or sub-sampled) to match the coarsest resolution. Averaging all small pixels within a larger pixel footprint is more accurate but computationally demanding when the data volume is large. Thus, NOAA operational cloud products incorporate sub-sampling (selecting one high-resolution pixel) to resample the reflectance data, which could cause potential retrieval biases. In this study, we examine various error sources of retrieval biases of cloud optical thickness (COT) and cloud effective radius (CER) caused by sub-sampling, including the solar zenith angle, viewing zenith angle, pixel resolutions, and cloud types. CER retrievals from ice clouds based on sub-sampling have larger biases and uncertainties than COT retrievals. The relative error compared to pixel averaging is positive for clouds that have small COT or CER, and negative for clouds that have large COT or CER. The relative error of COT decreases as the pixel resolution becomes coarser. The COT retrieval biases are attributed mainly to cirrus and cirrostratus clouds, while the largest biases of CER retrievals are associated with cirrus clouds. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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14 pages, 4538 KiB

Open AccessArticle

An Assessment of the Influences of Clouds on the Solar Photovoltaic Potential over China

by Yuhui Jiang and Bingqi Yi

Remote Sens. 2023, 15(1), 258; https://doi.org/10.3390/rs15010258 - 1 Jan 2023

Cited by 4 | Viewed by 2966

Abstract

Clouds are important modulators of the solar radiation reaching the earth’s surface. However, the impacts of cloud properties other than cloud cover are seldom mentioned. By combining the satellite-retrieved cloud properties, the latest radiative transfer model, and an advanced PVLIB-python software for solar photovoltaic (PV) estimation, the impacts of different types of clouds on the maximum available solar PV potential (measured with the plane-of-array-irradiance, POAI) are quantified. The impacts of ice and liquid water clouds are found to be the highest on Tibetan Plateau over western China in spring, and central and southern China in winter, respectively. The reduction of POAI by liquid water clouds is almost twice of that by ice clouds except for spring. It is found that the POAI can be reduced by 27–34% by all clouds (ice + liquid water clouds) in different seasons. The sensitivities of the solar PV potential to the changes in cloud properties including the cloud fraction, cloud top pressure, cloud effective radius, and cloud water path are also analyzed. Three kinds of settings of PV panel tilting, namely fixed tilt, one-axis tracking, and two-axis tracking, are considered. It is found that the cloud properties are essential to estimate the solar PV potentials, especially for the cloud fraction. The attenuation of solar radiation by clouds are growingly larger as the solar plane tilting settings get more complicated. The outlook of solar PV potential is quite variable as the changes in cloud properties are highly uncertain in the future climate scenarios. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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28 pages, 8305 KiB

Open AccessArticle

The Impacts of Single-Scattering and Microphysical Properties of Ice Particles Smaller Than 100 µm on the Bulk Radiative Properties of Tropical Cirrus

by Seonghyeon Jang, Jeonggyu Kim, Greg M. McFarquhar, Sungmin Park, Suji Han, Seoung Soo Lee, Chang Hoon Jung, Heejung Jung, Ki-Ho Chang, Woonseon Jung and Junshik Um

Remote Sens. 2022, 14(13), 3002; https://doi.org/10.3390/rs14133002 - 23 Jun 2022

Viewed by 1944

Abstract

There are large uncertainties in the single-scattering (i.e., morphologies) and microphysical (i.e., concentrations) properties of ice particles whose size are less than ~100 µm. Insufficient resolutions of the most advanced cloud probes (e.g., cloud particle imager) cannot resolve the micrometer-scale morphologies of small ice particles. Further, the shattering of large ice particles on probes’ inlets or tips causes uncertainties in the measurement of the concentrations of small ice particles. These uncertainties have large impacts on the single-scattering and microphysical properties of small ice particles that are utilized to quantify the bulk radiative properties of cirrus. In this study, the impacts of uncertainties in the morphologies and concentrations of small ice particles on the bulk radiative properties of tropical cirrus were calculated using measurements acquired during the Tropical Warm Pool-International Cloud Experiment. Five different models (i.e., budding Buckyball, Chebyshev particle, droxtal, Gaussian random sphere, and sphere) that represent the shapes of small ice particles were used to calculate the single-scattering properties. The bulk radiative properties, average phase-function (

\bar{P_{11}}

), and average asymmetry parameter (

\bar{g}

) were computed by combining the measured size/habit distributions and the calculated single-scattering properties of ice particles. The impacts of the selection of varying morphologies of small particles on the bulk radiative properties were quantified. For these calculations, the possible range of the concentrations of small ice particles which depend on the degree of shattered large particles were also used. The impacts of varying the single-scattering properties of small ice particles on the bulk radiative properties were the largest in the upper parts of cirrus (T < −60 °C), while they were the smallest in the lower parts of cirrus (−45 < T < −30 °C). The impacts of uncertainties in the concentrations of small ice particles on the bulk radiative properties were largest in the lower parts of cirrus (−45 < T < −30 °C), whereas they were smallest in the upper parts of cirrus (T < −60 °C). The effect of shattering was maximum in the lower parts of cirrus, whilst it was minimum in the upper parts of cirrus. The combined impacts of uncertainties in the single-scattering (i.e., morphologies) and microphysical (i.e., concentrations) properties of small ice particles revealed variations of up to 11.2% (127.1%; 67.3%) of the integrated intensity in the forward (sideward; backward) angles in

\bar{P_{11}}

and a corresponding change in

\bar{g}

by up to 12.61%. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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29 pages, 11941 KiB

Open AccessArticle

Theoretical Calculations of Directional Scattering Intensities of Small Nonspherical Ice Crystals: Implications for Forward Scattering Probes

by Seonghyeon Jang, Jeonggyu Kim, Greg M. McFarquhar, Sungmin Park, Seoung Soo Lee, Chang Hoon Jung, Sang Seo Park, Joo Wan Cha, Kyoungmi Lee and Junshik Um

Remote Sens. 2022, 14(12), 2795; https://doi.org/10.3390/rs14122795 - 10 Jun 2022

Cited by 3 | Viewed by 1852

Abstract

In situ aircraft measurements of the sizes and concentrations of liquid cloud droplets and ice crystals with maximum dimensions (D_max) less than ~50 μm have been measured mainly using forward scattering probes over the past half century. The operating principle of forward scattering probes is that the measured intensity of light scattered by a cloud particle at specific forward scattering angles can be related to the size of that particle assuming the shape and thermodynamic phase of the target are known. Current forward-scattering probes assume spherical liquid cloud droplets and use the Lorenz–Mie theory to convert the scattered light to particle size. Uncertainties in sizing ice crystals using forward scattering probes are unavoidable since the single-scattering properties of ice crystals differ from those of spherical liquid cloud droplets and because their shapes can vary. In this study, directional scattering intensities of four different aspect ratios (ARs = 0.25, 0.50, 1.00, and 2.00) of hexagonal ice crystals with random orientations and of spherical liquid cloud droplets were calculated using the discrete dipole approximation (i.e., ADDA) and Lorenz–Mie code, respectively, to quantify the errors in sizing small ice crystals and cloud droplets using current forward scattering probes and to determine the ranges of optimal scattering angles that would be used in future forward scattering probes. The calculations showed that current forward scattering probes have average 5.0% and 17.4% errors in sizing liquid cloud droplets in the forward (4–12°) and backward (168–176°) direction, respectively. For measurements of hexagonal ice crystals, average sizing errors were 42.1% (23.9%) in the forward (backward) direction and depended on the ARs of hexagonal ice crystals, which are larger than those for liquid cloud droplets. A newly developed size conversion table based on the calculated single-scattering properties of hexagonal ice crystals using the ADDA reduced the sizing errors for the hexagonal ice crystals down to 14.2% (21.9%) in the forward (backward) direction. This study is a purely theoretical examination of the operating principle of forward scattering probes and there are several limitations, such as assumed hexagonal ice crystals with smooth surfaces and random orientations. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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33 pages, 2291 KiB

Open AccessArticle

Fast Radiative Transfer Approximating Ice Hydrometeor Orientation and Its Implication on IWP Retrievals

by Inderpreet Kaur, Patrick Eriksson, Vasileios Barlakas, Simon Pfreundschuh and Stuart Fox

Remote Sens. 2022, 14(7), 1594; https://doi.org/10.3390/rs14071594 - 26 Mar 2022

Cited by 4 | Viewed by 2102

Abstract

The accurate simulation of microwave observations of clouds and precipitation are computationally challenging. A common simplification is the assumption of totally random orientation (TRO); however, studies have revealed that TRO occurs relatively infrequently in reality. A more appropriate assumption is that of azimuthally random orientation (ARO), but so far it has been a computationally expensive task. Recently a fast approximate approach was introduced that incorporates hydrometeor orientation into the assimilation of data from microwave conically scanning instruments. The approach scales the extinction in vertical (V) and horizontal (H) polarised channels to approximate ARO. In this study, the application of the approach was extended to a more basic radiative transfer perspective using the Atmospheric Radiative Transfer Simulator and the high-frequency channels of the Global Precipitation Measurement Microwave Imager (GMI). The comparison of forward simulations and GMI observations showed that with a random selection of scaling factors from a uniform distribution between 1 and 1.4–1.5, it is possible to mimic the full distribution of observed polarisation differences at 166 GHz over land and water. The applicability of this model at 660 GHz was also successfully demonstrated by means of existing airborne data. As a complement, a statistical model for polarised snow emissivity between 160 and 190 GHz was also developed. Combining the two models made it possible to reproduce the polarisation signals that were observed over all surface types, including snow and sea ice. Further, we also investigated the impact of orientation on the ice water path (IWP) retrievals. It has been shown that ignoring hydrometeor orientation has a significant negative impact (∼20% in the tropics) on retrieval accuracy. The retrieval with GMI observations produced highly realistic IWP distributions. A significant highlight was the retrieval over snow covered regions, which have been neglected in previous retrieval studies. These results provide increased confidence in the performance of passive microwave observation simulations and mark an essential step towards developing the retrievals of ice hydrometeor properties based on data from GMI, the Ice Cloud Imager (ICI) and other conically scanning instruments. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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18 pages, 16806 KiB

Open AccessFeature PaperArticle

Optical Property Model for Cirrus Clouds Based on Airborne Multi-Angle Polarization Observations

by Yi Wang, Ping Yang, Michael D. King and Bryan A. Baum

Remote Sens. 2021, 13(14), 2754; https://doi.org/10.3390/rs13142754 - 13 Jul 2021

Cited by 3 | Viewed by 2324

Abstract

We present an improved remote sensing technique to infer an optimal habit/shape model for ice particles in cirrus clouds using multi-angle polarimetric measurements at 865 nm made by the Airborne Multi-angle SpectroPolarimeter Imager (AirMSPI) instrument. The common method of ice model inference is based on intensity (total reflectivity) measurements, which is generally not applicable to optically thin ice clouds (i.e., cirrus clouds) where single scattering dominates. The new approach is able to infer an ice model in clouds with optical thicknesses smaller than 5. The improvement is made by first assuming the optical thickness retrieved using total reflectivity. Subsequently, the polarized reflectivity is calculated based on look-up tables generated from simulated polarized reflectances computed for cirrus clouds in conjunction with eight ice particle models. The ice particle model that leads to the closest fit to the measurements is regarded as the optimal ice particle model. Additionally, an alternative method is applied that does not consider polarized reflectivity. These two methods are applied to a data sample as a proof-of-concept study where AirMSPI observed a single cirrus layer. In this case study, the hexagonal column aggregate model works for most pixels both with and without considering polarized reflectivities. The retrieval cost function is high when the camera pairs with large zenith angles are included in the retrievals. This result suggests that further studies will be necessary to have a better understanding of all eight selected ice particle models at scattering angles smaller than 100°. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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31 pages, 9272 KiB

Open AccessArticle

The Use of Superspheroids as Surrogates for Modeling Electromagnetic Wave Scattering by Ice Crystals

by Lan-Hui Sun, Lei Bi and Bingqi Yi

Remote Sens. 2021, 13(9), 1733; https://doi.org/10.3390/rs13091733 - 29 Apr 2021

Cited by 12 | Viewed by 2665

Abstract

Electromagnetic wave scattering by ice particles is commonly modeled by defining representative habits, including droxtals, columns, plates, and aggregates, although actual particles in the atmosphere can be even much more complex. In this study, we examined a superspheroidal approximation method for modeling electromagnetic wave scattering by ice crystals. Superspheroid can be associated with a shape index (SI) defined by the particle volume and average projected area. Corresponding to realistic ice crystals, suitable superspheroid models with the same SI (that means, identical volume and average projected area) and aspect ratio can be identified as surrogates for optical property calculations. We systematically compared the optical properties of ice crystals and superspheroids at 33 microwave bands in the range of 3–640 GHz and at three representative visible or infrared wavelengths (0.66, 2.13, and 11 μm). It was found that the single-scattering properties of compact ice crystal habits and their superspheroidal model particles were quite close. For an aggregate with sparse distribution of elements, a superspheroid model produces relatively large errors because the aspect ratio may not be sufficient to describe a particle shape. However, the optical similarity of a superspheroid and an aggregate is still encouraging. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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20 pages, 3940 KiB

Open AccessFeature PaperArticle

Potential of Hyperspectral Thermal Infrared Spaceborne Measurements to Retrieve Ice Cloud Physical Properties: Case Study of IASI and IASI-NG

by Lucie Leonarski, Laurent C.-Labonnote, Mathieu Compiègne, Jérôme Vidot, Anthony J. Baran and Philippe Dubuisson

Remote Sens. 2021, 13(1), 116; https://doi.org/10.3390/rs13010116 - 31 Dec 2020

Cited by 3 | Viewed by 3128

Abstract

The present study aims to quantify the potential of hyperspectral thermal infrared sounders such as the Infrared Atmospheric Sounding Interferometer (IASI) and the future IASI next generation (IASI-NG) for retrieving the ice cloud layer altitude and thickness together with the ice water path. We employed the radiative transfer model Radiative Transfer for TOVS (RTTOV) to simulate cloudy radiances using parameterized ice cloud optical properties. The radiances have been computed from an ice cloud profile database coming from global operational short-range forecasts at the European Center for Medium-range Weather Forecasts (ECMWF) which encloses the normal conditions, typical variability, and extremes of the atmospheric properties over one year (Eresmaa and McNally (2014)). We performed an information content analysis based on Shannon’s formalism to determine the amount and spectral distribution of the information about ice cloud properties. Based on this analysis, a retrieval algorithm has been developed and tested on the profile database. We considered the signal-to-noise ratio of each specific instrument and the non-retrieved atmospheric and surface parameter errors. This study brings evidence that the observing system provides information on the ice water path (

I W P

) as well as on the layer altitude and thickness with a convergence rate up to 95% and expected errors that decrease with cloud opacity until the signal saturation is reached (satisfying retrievals are achieved for clouds whose

I W P

is between about 1 and 300

g / m^{2}

). Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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12 pages, 2966 KiB

Open AccessTechnical Note

Passive Remote Sensing of Ice Cloud Properties at Terahertz Wavelengths Based on Genetic Algorithm

by Lei Liu, Chensi Weng, Shulei Li, Letu Husi, Shuai Hu and Pingyi Dong

Remote Sens. 2021, 13(4), 735; https://doi.org/10.3390/rs13040735 - 17 Feb 2021

Cited by 21 | Viewed by 2661

Abstract

Ice clouds play a critical role in the balance of the earth–atmosphere radiation system, but there are some limitations in the existing remote sensing methods for ice clouds. Terahertz wave is expected to be the best waveband for retrieving ice clouds, with terahertz wavelengths in the order of the size of typical ice cloud particles. An inversion method for the remote sensing of ice clouds at terahertz wavelengths based on genetic algorithm is proposed in this paper. First, suitable channel sets in the terahertz band, which are mainly a combination of absorption lines and window regions, are determined. Then, to improve the efficiency of the generation of the retrieval database, based on the brightness temperature simulated by the atmospheric radiative transfer simulator (ARTS) for different cloud parameters, a fast forward operator is constructed using three-dimensional interpolation to simulate the brightness temperature difference between clear sky and a cloudy scene. Finally, an inversion model to retrieve the ice cloud base height, the effective particle diameter and the ice water path is established based on the genetic algorithm, and an analysis of the inversion errors is performed. The results show that the forward operator, constructed by the nearest interpolation, can accurately calculate the brightness temperature difference at a high speed. The proposed inversion method at terahertz wavelengths based on the genetic algorithm can achieve the expected scientific requirement. The absolute error of the cloud height is around 0.2 km, and the absolute error of the low ice water path (below 20 g/m²) is small, while the relative error of the high ice water path is generally maintained at around 10%, and the absolute error of the effective particle diameter is mostly around 4 μm. Full article

(This article belongs to the Special Issue Scattering by Ice Crystals in the Earth's Atmosphere)

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