scholarly journals Microwave and submillimeter wave scattering of oriented ice particles

2020 ◽  
Vol 13 (5) ◽  
pp. 2309-2333 ◽  
Author(s):  
Manfred Brath ◽  
Robin Ekelund ◽  
Patrick Eriksson ◽  
Oliver Lemke ◽  
Stefan A. Buehler
Keyword(s):  
Tilt Angle ◽  
Incidence Angle ◽  
Dipole Approximation ◽  
Ice Crystals ◽  
Scattering Data ◽  
Random Orientation ◽  
Ice Particles ◽  
Microwave Imager ◽  
Global Precipitation ◽  
Snow And Ice

Abstract. Microwave (1–300 GHz) dual-polarization measurements above 100 GHz are so far sparse, but they consistently show polarized scattering signals of ice clouds. Existing scattering databases of realistically shaped ice crystals for microwaves and submillimeter waves (>300 GHz) typically assume total random orientation, which cannot explain the polarized signals. Conceptual models show that the polarization signals are caused by oriented ice particles. Only a few works that consider oriented ice crystals exist, but they are limited to microwaves only. Assuming azimuthally randomly oriented ice particles with a fixed but arbitrary tilt angle, we produced scattering data for two particle habits (51 hexagonal plates and 18 plate aggregates), 35 frequencies between 1 and 864 GHz, and 3 temperatures (190, 230 and 270 K). In general, the scattering data of azimuthally randomly oriented particles depend on the incidence angle and two scattering angles, in contrast to total random orientation, which depends on a single angle. The additional tilt angle further increases the complexity. The simulations are based on the discrete dipole approximation in combination with a self-developed orientation averaging approach. The scattering data are publicly available from Zenodo (https://doi.org/10.5281/zenodo.3463003). This effort is also an essential part of preparing for the upcoming Ice Cloud Imager (ICI) that will perform polarized observations at 243 and 664 GHz. Using our scattering data radiative transfer simulations with two liquid hydrometeor species and four frozen hydrometeor species of polarized Global Precipitation Measurement (GPM) Microwave Imager (GMI) observations at 166 GHz were conducted. The simulations recreate the observed polarization patterns. For slightly fluttering snow and ice particles, the simulations show polarization differences up to 11 K using plate aggregates for snow, hexagonal plates for cloud ice and totally randomly oriented particles for the remaining species. Simulations using strongly fluttering hexagonal plates for snow and ice show similar polarization signals. Orientation, shape and the hydrometeor composition affect the polarization. Ignoring orientation can cause a negative bias for vertically polarized observations and a positive bias for horizontally polarized observations.

scholarly journals Microwave and submillimeter wave scattering of oriented ice particles

2019 ◽  
Author(s):  
Manfred Brath ◽  
Robin Ekelund ◽  
Patrick Eriksson ◽  
Oliver Lemke ◽  
Stefan A. Buehler
Keyword(s):  
Tilt Angle ◽  
Wave Scattering ◽  
Conceptual Models ◽  
Incidence Angle ◽  
Scattering Data ◽  
Random Orientation ◽  
Standard Assumption ◽  
Ice Cloud ◽  
Ice Particles ◽  
Angle Scattering

Abstract. Microwave dual-polarization measurements above 100 GHz are so far sparse, but they consistently show that larger ice hydrometeors tend to deviate from the standard assumption of total random orientation. This conclusion has been derived by conceptual models, while the first detailed simulations, recreating the observed polarization patterns, are presented in this study. The ice particles are assumed to be azimuthally randomly oriented with a fixed but arbitrary tilt angle. The scattering data for azimuthal random orientation is much more complex than for total random orientation. The scattering data of azimuthally randomly oriented particles depends in general on the incidence angle and two scattering angles compared to one angle scattering for total random orientation. The additional tilt angle adds an additional dimension. The simulations are based on the discrete dipol approximation in combination with a self developed orientation averaging approach. Data for two particle habits (51 hexagonal plates and 18 plate aggregates) and 35 frequencies between 1 GHz and 864 GHz were produced. The data is publicly available from Zenodo (https://doi.org/10.5281/zenodo.3463003). This effort is also an essential part of preparing for the upcoming Ice Cloud Imager (ICI), that will perform polarized observations at 243 GHz and 664 GHz, which will deliver new insights about clouds.

Oriented particles in microwave and submillimeter radiative transfer simulations of ice clouds

2020 ◽  
Author(s):  
Manfred Brath ◽  
Robin Ekelund ◽  
Patrick Eriksson ◽  
Oliver Lemke ◽  
Stefan A. Buehler
Keyword(s):  
Radiative Transfer ◽  
Incidence Angle ◽  
Ice Crystals ◽  
Particle Orientation ◽  
Scattering Data ◽  
Reasonable Assumption ◽  
Random Orientation ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Ice Particles

<div>Observations of Global Precipitation Measurement Microwave Imager (GMI) at 166 GHz consistently show polarized scattering signals of ice clouds. Conceptual models indicate that these signals emerge from oriented ice particles. Existing databases of scattering data of realistically shaped ice crystals for microwave and submillimeter typically assume total random orientation of ice particles. This is often a very reasonable assumption, but cannot explain the polarized ice cloud signals. Only few works considering oriented ice crystals exist, but they only consider microwave. With the upcoming Ice Cloud Imager (ICI) on board of Metop-SG B satellite, there will be additional dual-polarization measurements at 243 GHz and 664 GHz. These measurements will deliver new insights about clouds and their structure, if we know the scattering properties of oriented and realistically shaped ice crystals.</div><div>We provide publicly available scattering data for 51 different sized hexagonal plates and 18 different sized plate aggregates for 35 frequencies between 1 GHz and 864 GHz. The ice particles are assumed to be azimuthally randomly oriented with a fixed but arbitrary tilt angle. The scattering data for azimuthal random orientation is much more complex than for total random orientation. The scattering data of azimuthally randomly oriented particles depends in general on the incidence angle and two scattering angles compared to only one scattering angle for total random orientation. The scattering data is based on discrete dipole approximation simulations in combination with a self-developed orientation averaging approach.</div><div>We present detailed radiative transfer simulations of polarized GMI observations at 166 GHz and ICI observations at 243 GHz and at 664 GHz using our scattering data. The simulations of GMI recreate the observed polarization patterns. Analysis shows that not only orientation affects the polarization signal but also the hydrometeor composition. Furthermore, particle orientation also affects single polarized observations. Ignoring orientation can cause a negative bias for vertically polarized observations and a positive bias for horizontally polarized observations.</div>

scholarly journals Analysis of the Global Microwave Polarization Data of Clouds

2018 ◽  
Vol 32 (1) ◽  
pp. 3-13 ◽  
Author(s):  
Xiping Zeng ◽  
Gail Skofronick-Jackson ◽  
Lin Tian ◽  
Amber E. Emory ◽  
William S. Olson ◽  
...  
Keyword(s):  
Weather Prediction ◽  
Radar Data ◽  
Ice Crystals ◽  
Ice Particles ◽  
Precipitation Measurement ◽  
Wave Imaging ◽  
Microwave Imager ◽  
Climate Analysis ◽  
Microwave Radiometers ◽  
Global Precipitation

Abstract Information about the characteristics of ice particles in clouds is necessary for improving our understanding of the states, processes, and subsequent modeling of clouds and precipitation for numerical weather prediction and climate analysis. Two NASA passive microwave radiometers, the satellite-borne Global Precipitation Measurement (GPM) Microwave Imager (GMI) and the aircraft-borne Conical Scanning Millimeter-Wave Imaging Radiometer (CoSMIR), measure vertically and horizontally polarized microwaves emitted by clouds (including precipitating particles) and Earth’s surface below. In this paper, GMI (or CoSMIR) data are analyzed with CloudSat (or aircraft-borne radar) data to find polarized difference (PD) signals not affected by the surface, thereby obtaining the information on ice particles. Statistical analysis of 4 years of GMI and CloudSat data, for the first time, reveals that optically thick clouds contribute positively to GMI PD at 166 GHz over all the latitudes and their positive magnitude of 166-GHz GMI PD varies little with latitude. This result suggests that horizontally oriented ice crystals in thick clouds are common from the tropics to high latitudes, which contrasts the result of Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) that horizontally oriented ice crystals are rare in optically thin ice clouds.

Combined Radar and Radiometer Analysis of Precipitation Profiles for a Parametric Retrieval Algorithm

2005 ◽  
Vol 22 (7) ◽  
pp. 909-929 ◽  
Author(s):  
Hirohiko Masunaga ◽  
Christian D. Kummerow
Keyword(s):  
A Priori ◽  
Three Dimensional ◽  
Tropical Rainfall Measuring Mission ◽  
Dimensional Structure ◽  
Retrieval Algorithm ◽  
Brightness Temperatures ◽  
Precipitation Measurement ◽  
Microwave Imager ◽  
Trmm Microwave Imager ◽  
Global Precipitation

Abstract A methodology to analyze precipitation profiles using the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and precipitation radar (PR) is proposed. Rainfall profiles are retrieved from PR measurements, defined as the best-fit solution selected from precalculated profiles by cloud-resolving models (CRMs), under explicitly defined assumptions of drop size distribution (DSD) and ice hydrometeor models. The PR path-integrated attenuation (PIA), where available, is further used to adjust DSD in a manner that is similar to the PR operational algorithm. Combined with the TMI-retrieved nonraining geophysical parameters, the three-dimensional structure of the geophysical parameters is obtained across the satellite-observed domains. Microwave brightness temperatures are then computed for a comparison with TMI observations to examine if the radar-retrieved rainfall is consistent in the radiometric measurement space. The inconsistency in microwave brightness temperatures is reduced by iterating the retrieval procedure with updated assumptions of the DSD and ice-density models. The proposed methodology is expected to refine the a priori rain profile database and error models for use by parametric passive microwave algorithms, aimed at the Global Precipitation Measurement (GPM) mission, as well as a future TRMM algorithms.

Visualising cryospheric images in a virtual environment: present challenges and future implications

Polar Record ◽  
2007 ◽  
Vol 43 (4) ◽  
pp. 305-310 ◽  
Author(s):  
Lisa M. Ballagh ◽  
Mark A. Parsons ◽  
Ross Swick
Keyword(s):  
The United States ◽  
Google Earth ◽  
Sea Ice Concentration ◽  
Ice Coverage ◽  
The Earth ◽  
Current Perspective ◽  
Ice Concentration ◽  
Microwave Imager ◽  
Image Format ◽  
Snow And Ice

ABSTRACTThe United States National Snow and Ice Data Center (NSIDC) initiated an outreach project to enhance the visibility of and interest in cryospheric images. Methods were utilised to convert cryospheric data into a projection and image format compatible with Google Earth™. The word ‘image’ should be emphasised since raster data in a native polar projection and format cannot be overlaid on the Earth without prior data conversions. The project focused on reaching out to a diverse audience by integrating images from key components of the cryosphere into a single compressed Keyhole Markup Language (KMZ) file. As a result, users can visualise glacier photographs, permafrost type and extent, sea ice concentration and extent, and snow extent superimposed on the Earth. Those interested in browsing the NSIDC collection of over 3,000 glacier photographs have the option of zooming into Alaska for a majority of the images and accessing both the photograph and the associated metadata. For a current perspective of global snow and ice coverage, one could look at satellite imagery derived from passive microwave Special Sensor Microwave/Imager (SSM/I) data. Another option is to select the permafrost layer and observe the various types and extent of permafrost. This paper explores the project by describing the data, methodologies and results and concludes with future implications on how to improve the processing and functionality of polar data in Google Earth.

scholarly journals Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI)

2020 ◽  
Vol 13 (3) ◽  
pp. 1273-1285 ◽  
Author(s):  
Thomas Kuhn ◽  
Sandra Vázquez-Martín
Keyword(s):  
Remote Sensing ◽  
Vertical Direction ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Double Exposure ◽  
Shape Information ◽  
Microphysical Properties ◽  
Ice Particles ◽  
Crystal Properties ◽  
Fall Speed

Abstract. Accurate predictions of snowfall require good knowledge of the microphysical properties of the snow ice crystals and particles. Shape is an important parameter as it strongly influences the scattering properties of the ice particles, and thus their response to remote sensing techniques such as radar measurements. The fall speed of ice particles is another important parameter for both numerical forecast models as well as representation of ice clouds and snow in climate models, as it is responsible for the rate of removal of ice from these models. We describe a new ground-based in situ instrument, the Dual Ice Crystal Imager (D-ICI), to determine snow ice crystal properties and fall speed simultaneously. The instrument takes two high-resolution pictures of the same falling ice particle from two different viewing directions. Both cameras use a microscope-like setup resulting in an image pixel resolution of approximately 4 µm pixel−1. One viewing direction is horizontal and is used to determine fall speed by means of a double exposure. For this purpose, two bright flashes of a light-emitting diode behind the camera illuminate the falling ice particle and create this double exposure, and the vertical displacement of the particle provides its fall speed. The other viewing direction is close-to-vertical and is used to provide size and shape information from single-exposure images. This viewing geometry is chosen instead of a horizontal one because shape and size of ice particles as viewed in the vertical direction are more relevant than these properties viewed horizontally, as the vertical fall speed is more strongly influenced by the vertically viewed properties. In addition, a comparison with remote sensing instruments that mostly have a vertical or close-to-vertical viewing geometry is favoured when the particle properties are measured in the same direction. The instrument has been tested in Kiruna, northern Sweden (67.8∘ N, 20.4∘ E). Measurements are demonstrated with images from different snow events, and the determined snow ice crystal properties are presented.

scholarly journals Inter-calibrating SMMR brightness temperatures over continental surfaces

2020 ◽  
Author(s):  
Samuel Favrichon ◽  
Carlos Jimenez ◽  
Catherine Prigent
Keyword(s):  
Land Surface ◽  
Microwave Remote Sensing ◽  
Calibration Method ◽  
Diurnal Cycles ◽  
Brightness Temperatures ◽  
Linear Correction ◽  
Long Time ◽  
Microwave Imager ◽  
Microwave Radiometers ◽  
Global Precipitation

Abstract. Microwave remote sensing can be used to monitor the time evolution of some key parameters over land, such as land surface temperature or surface water extent. Observations are made with instrument such as the Scanning Microwave Multichannel Radiometer (SMMR) before 1987, the Special Sensor Microwave/Imager (SSM/I) and the following Special Sensor Microwave Imager/Sounder (SSMIS) from 1987 and still operating, to the more recent Global Precipitation Mission Microwave Imager (GMI). As these instruments differ on some of their characteristics and use different calibration schemes, they need to be inter-calibrated before long time series products can be derived from the observations. Here an inter-calibration method is designed to remove major inconsistencies between the SMMR and other microwave radiometers for the 18 GHz and 37 GHz channels over continental surfaces. Because of a small overlap in observations and a ~6 h difference in overpassing times between SMMR and SSM/I, GMI was chosen as a reference despite the lack of a common observing period. The diurnal cycles from three years of GMI brightness temperatures are first calculated, and then used to evaluate SMMR differences. Based on a statistical analysis of the differences, a simple linear correction is implemented to calibrate SMMR on GMI. This correction is shown to also reduce the biases between SMMR and SSM/I, and can then be applied to SMMR observations to make them more coherent with existing data record of microwave brightness temperatures over continental surfaces.

scholarly journals The AMSU-Based Hydrological Bundle Climate Data Record—Description and Comparison with Other Data Sets

2018 ◽  
Vol 10 (10) ◽  
pp. 1640 ◽  
Author(s):  
Ralph Ferraro ◽  
Brian Nelson ◽  
Tom Smith ◽  
Olivier Prat
Keyword(s):  
Land Surface ◽  
Snow Water Equivalent ◽  
Precipitable Water ◽  
Climate Data ◽  
Sea Ice Concentration ◽  
Data Set ◽  
Data Record ◽  
Microwave Imager ◽  
Global Precipitation ◽  
Climate Data Record

Passive microwave measurements have been available on satellites back to the 1970s, first flown on research satellites developed by the National Aeronautics and Space Administration (NASA). Since then, several other sensors have been flown to retrieve hydrological products for both operational weather applications (e.g., the Special Sensor Microwave/Imager—SSM/I; the Advanced Microwave Sounding Unit—AMSU) and climate applications (e.g., the Advanced Microwave Scanning Radiometer—AMSR; the Tropical Rainfall Measurement Mission Microwave Imager—TMI; the Global Precipitation Mission Microwave Imager—GMI). Here, the focus is on measurements from the AMSU-A, AMSU-B, and Microwave Humidity Sounder (MHS). These sensors have been in operation since 1998, with the launch of NOAA-15, and are also on board NOAA-16, -17, -18, -19, and the MetOp-A and -B satellites. A data set called the “Hydrological Bundle” is a climate data record (CDR) that utilizes brightness temperatures from fundamental CDRs (FCDRs) to generate thematic CDRs (TCDRs). The TCDRs include total precipitable water (TPW), cloud liquid water (CLW), sea-ice concentration (SIC), land surface temperature (LST), land surface emissivity (LSE) for 23, 31, 50 GHz, rain rate (RR), snow cover (SC), ice water path (IWP), and snow water equivalent (SWE). The TCDRs are shown to be in general good agreement with similar products from other sources, such as the Global Precipitation Climatology Project (GPCP) and the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2). Due to the careful intercalibration of the FCDRs, little bias is found among the different TCDRs produced from individual NOAA and MetOp satellites, except for normal diurnal cycle differences.

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