Modeling Backscatter Properties of Snowfall at Millimeter Wavelengths

2007 ◽  
Vol 64 (5) ◽  
pp. 1727-1736 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Rayleigh Scattering ◽  
Spherical Model ◽  
Size Distributions ◽  
Fall Velocity ◽  
Millimeter Wavelength ◽  
Millimeter Wavelengths ◽  
W Band ◽  
Mass Size ◽  
Atmospheric Radiation Measurement ◽  
The Common

Abstract Ground-based vertically pointing and airborne/spaceborne nadir-pointing millimeter-wavelength radars are being increasingly used worldwide. Though such radars are primarily designed for cloud remote sensing, they can also be used for precipitation measurements including snowfall estimates. In this study, modeling of snowfall radar properties is performed for the common frequencies of millimeter-wavelength radars such as those used by the U.S. Department of Energy’s Atmospheric Radiation Measurement Program (Ka and W bands) and the CloudSat mission (W band). Realistic snowflake models including aggregates and single dendrite crystals were used. The model input included appropriate mass–size and terminal fall velocity–size relations and snowflake orientation and shape assumptions. It was shown that unlike in the Rayleigh scattering regime, which is often applicable for longer radar wavelengths, the spherical model does not generally satisfactorily describe scattering of larger snowflakes at millimeter wavelengths. This is especially true when, due to aerodynamic forcing, these snowflakes are oriented primarily with their major dimensions in the horizontal plane and the zenith/nadir radar pointing geometry is used. As a result of modeling using the experimental snowflake size distributions, radar reflectivity–liquid equivalent snowfall rates (Ze–S) relations are suggested for “dry” snowfalls that consist of mostly unrimed snowflakes containing negligible amounts of liquid water. Owing to uncertainties in the model assumptions, these relations, which are derived for the common Ka- and W-band radar frequencies, have significant variability in their coefficients that can exceed a factor of 2 or so. Modeling snowfall attenuation suggests that the attenuation effects in “dry” snowfall can be neglected at the Ka band for most practical cases, while at the W band attenuation may need to be accounted for in heavier snowfalls observed at longer ranges.

Polarimetric radar variables in snowfall at Ka- and W-band frequency bands: A comparative analysis

2020 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Particle Size ◽  
Rayleigh Scattering ◽  
Size Distributions ◽  
Polarimetric Radar ◽  
Dual Frequency ◽  
Particle Size Distributions ◽  
Band Frequency ◽  
Differential Phase ◽  
Data Matching ◽  
W Band

AbstractDual-frequency millimeter-wavelength radar observations in snowfall are analyzed in order to evaluate differences in conventional polarimetric radar variables such as differential reflectivity, ZDR, specific differential phase shift, KDP, and linear depolarization ratio, LDR, at traditional cloud radar frequencies at Ka- and W-bands (~35 and ~94 GHz, correspondingly). Low radar beam elevation (~5°) measurements were performed at Oliktok Point, Alaska with a scanning fully polarimetric radar operating in the horizontal-vertical polarization basis. This radar has the same gate spacing and very close beam widths at both frequencies, which largely alleviates uncertainties associated with spatial and temporal data matching. It is shown that observed Ka- and W-band ZDR differences are, on average, less than about 0.5 dB and do not have a pronounced trend as a function of snowfall reflectivity. The observed ZDR differences agree well with modeling results obtained using integration over non-spherical ice particle size distributions. For higher signal-to-noise ratios, KDP data derived from differential phase measurements are approximately scaled as reciprocals of corresponding radar frequencies indicating that the influence of non-Rayleigh scattering effects on this variable is rather limited. This result is also in satisfactory agreement with data obtained by modeling using realistic particle size distributions. Observed Ka- and W-band LDR differences are strongly affected by the radar hardware system polarization “leak” and are generally less than 4 dB. Smaller differences are observed for higher depolarizations, where the polarization “leak” is less pronounced. Realistic assumptions about particle canting and the system polarization isolation lead to modeling results that satisfactorily agree with observational dual-frequency LDR data.

scholarly journals Snowfall Retrievals Using Millimeter-Wavelength Cloud Radars

2008 ◽  
Vol 47 (3) ◽  
pp. 769-777 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
Matthew D. Shupe ◽  
Irina V. Djalalova
Keyword(s):  
Water Cycle ◽  
Precipitation Radar ◽  
Millimeter Wavelength ◽  
Microphysical Properties ◽  
Global Water Cycle ◽  
Arctic Regions ◽  
W Band ◽  
Gauge Data ◽  
Atmospheric Radiation Measurement ◽  
Typical Difference

Abstract It is demonstrated that millimeter-wavelength radars that are designed primarily for cloud studies can be also used effectively for snowfall retrievals. Radar reflectivity–liquid equivalent snowfall rate (Ze–S) relations specifically tuned for Ka- and W-band radar frequencies are applied to measurements taken by vertically pointing ground-based 8-mm cloud radars (MMCR) that are designed for the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM) Program and by the nadir-pointing spaceborne 94-GHz CloudSat radar. Comparisons of the MMCR-based snowfall accumulations estimated during experimental events with no significant snowflake riming and controlled gauge measurements indicated an 87% standard deviation between radar and gauge data that is consistent with the uncertainties in the coefficients of the Ze–S relations resulting from variability in snowflake microphysical properties. Comparisons of CloudSat-based snowfall-rate retrievals in heavy snowfall were consistent with estimates from surface S-band precipitation surveillance radars made using algorithms that were specifically designed for use with these radars. A typical difference between the CloudSat and the S-band precipitation radar estimates of snowfall rate for approximately collocated resolution pixels was within a factor of 2, which is of the order of the uncertainty of each estimate. The results of this study suggest that the ground-based and satellite-borne radars operating at Ka and W bands can provide valuable retrieval information on vertical profiles of snowfall, which is an important component of the global water cycle. This information is particularly important in Arctic regions where precipitation information from other sources is scarce.

Assessing Snowfall Rates from X-Band Radar Reflectivity Measurements

2009 ◽  
Vol 26 (11) ◽  
pp. 2324-2339 ◽  
Author(s):  
Sergey Y. Matrosov ◽  
Carroll Campbell ◽  
David Kingsmill ◽  
Ellen Sukovich
Keyword(s):  
Size Distribution ◽  
Rayleigh Scattering ◽  
Radar Reflectivity ◽  
Precipitation Rate ◽  
Size Distributions ◽  
Derived Relations ◽  
Scattering Effects ◽  
X Band ◽  
Distribution Parameters ◽  
Mass Size

Abstract Realistic aggregate snowflake models and experimental snowflake size distribution parameters are used to derive X-band power-law relations between the equivalent radar reflectivity factor Ze and the liquid equivalent snowfall precipitation rate S (Ze = ASB). There is significant variability in coefficients of these relations caused by uncertainties in the snowflake bulk densities (as defined by the mass–size relationships), fall velocities, and particle size distribution parameters. The variability in snowflake parameters results in differing Ze–S relations that provide more than a factor of 2 difference in precipitation rate and liquid equivalent accumulation estimates for typical reflectivity values observed in snowfall (∼20–30 dBZ). Characteristic values of the exponent B in the derived for dry snowfall relations were generally in the range 1.3–1.55 (when Ze is in mm6 m−3 and S is in mm h−1). The coefficient A exhibited stronger variability and varied in the range from about 30 (for aircraft-based size distributions and smaller density particles) to about 140 (for surface-based size distributions). The non-Rayleigh scattering effects at X band result in diminishing of both A and B, as compared to the relations for longer wavelength radars. The snowflake shape and orientation also influences its backscatter properties, but to a lesser extent compared to the particle bulk density. The derived relations were primarily obtained for snowfall consisting of dry aggregate snowflakes. They were applied to the X-band radar measurements during observations of wintertime storms. For approximately collocated measurements, the in situ estimates of snowfall accumulations were generally within the range of radar-derived values when the coefficient A was around 100–120.

scholarly journals Snowfall retrieval at X, Ka and W band: consistency of backscattering and microphysical properties using BAECC ground-based measurements

2018 ◽  
Author(s):  
Marta Tecla Falconi ◽  
Annakaisa von Lerber ◽  
Davide Ori ◽  
Frank Silvio Marzano ◽  
Dmitri Moisseev
Keyword(s):  
Cross Sections ◽  
Dipole Approximation ◽  
Microphysical Properties ◽  
Aspect Ratios ◽  
Millimeter Wavelengths ◽  
W Band ◽  
Atmospheric Radiation Measurement ◽  
Using Data ◽  
Biogenic Aerosols

Abstract. Radar-based snowfall intensity retrieval is investigated at centimeter and millimeter wavelengths using high-quality collocated ground-based multi-frequency radar and video-disdrometer observations. Using data from four snowfall events, recorded during the Biogenic Aerosols Effects on Clouds and Climate (BAECC) campaign in Finland, measurements of liquid-water-equivalent snowfall rate S are correlated to radar equivalent reflectivity factors Ze, measured by the Atmospheric Radiation Measurement (ARM) cloud radars operating at X, Ka and W frequency bands. From these coupled observations power-law Ze-S relationships are derived for all considered frequencies and distinguishing fluffy from rimed snowfall. Interestingly fluffy-snow events show a spectrally distinct signature of Ze-S with respect to rimed-snow cases. In order to understand the connection between snowflake microphysical and multi-frequency backscattering properties, numerical simulations are also performed by using the particle size distribution provided by the in-situ video-disdrometer. The latter are carried out by using both the T-matrix method (TMM) for soft-spheroids with different aspect ratios and exploiting a pre-computed discrete dipole approximation (DDA) database for complex-shape snowflakes. Based on the presented results, it is concluded that the soft-spheroid approximation can be adopted to explain the observed multi-frequency Ze-S relations if a proper spheroid aspect ratio is selected. The latter may depend on the snowfall type. A further analysis of the backscattering simulations reveals that TMM cross-sections are higher than the DDA ones for small ice particles, but lower for larger particles. These differences may explain why the soft-spheroid approximation is satisfactory for radar reflectivity simulations, the errors of computed cross-sections for larger and smaller particles compensating each other.

Evaluation of Cloud Microphysics in JMA-NHM Simulations Using Bin or Bulk Microphysical Schemes through Comparison with Cloud Radar Observations

2012 ◽  
Vol 69 (8) ◽  
pp. 2566-2586 ◽  
Author(s):  
Takamichi Iguchi ◽  
Teruyuki Nakajima ◽  
Alexander P. Khain ◽  
Kazuo Saito ◽  
Toshihiko Takemura ◽  
...  
Keyword(s):  
Model Simulation ◽  
Weather Prediction ◽  
Cloud Microphysics ◽  
Japan Meteorological Agency ◽  
Doppler Velocity ◽  
Fall Velocity ◽  
W Band ◽  
Single Moment ◽  
Mass Size ◽  
Bulk Model

Abstract Numerical weather prediction (NWP) simulations using the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM) are conducted for three precipitation events observed by shipborne or spaceborne W-band cloud radars. Spectral bin and single-moment bulk cloud microphysics schemes are employed separately for an intercomparative study. A radar product simulator that is compatible with both microphysics schemes is developed to enable a direct comparison between simulation and observation with respect to the equivalent radar reflectivity factor Ze, Doppler velocity (DV), and path-integrated attenuation (PIA). In general, the bin model simulation shows better agreement with the observed data than the bulk model simulation. The correction of the terminal fall velocities of snowflakes using those of hail further improves the result of the bin model simulation. The results indicate that there are substantial uncertainties in the mass–size and size–terminal fall velocity relations of snowflakes or in the calculation of terminal fall velocity of snow aloft. For the bulk microphysics, the overestimation of Ze is observed as a result of a significant predominance of snow over cloud ice due to substantial deposition growth directly to snow. The DV comparison shows that a correction for the fall velocity of hydrometeors considering a change of particle size should be introduced even in single-moment bulk cloud microphysics.

scholarly journals Mass size distributions and size resolved chemical composition of fine particulate matter at the Pittsburgh supersite

2004 ◽  
Vol 38 (20) ◽  
pp. 3127-3141 ◽  
Author(s):  
Juan C. Cabada ◽  
Sarah Rees ◽  
Satoshi Takahama ◽  
Andrey Khlystov ◽  
Spyros N. Pandis ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Chemical Composition ◽  
Fine Particulate Matter ◽  
Size Distributions ◽  
Fine Particulate ◽  
Mass Size

scholarly journals Quasi Optical Multi-Ray Model For Wireless Communication Link in Millimeter Wavelengths

2018 ◽  
Vol 210 ◽  
pp. 03006 ◽  
Author(s):  
Liat Rapaport ◽  
Ariel Etinger ◽  
Boris Litvak ◽  
Gad Pinhasi ◽  
Yosef Pinhasi
Keyword(s):  
Millimeter Waves ◽  
Wide Spectrum ◽  
Communication Link ◽  
Multiple Reflections ◽  
High Frequencies ◽  
Fifth Generation ◽  
Millimeter Wavelengths ◽  
W Band ◽  
Theoretical Results ◽  
Indoor And Outdoor

The spectrum of millimeter waves lay above 30GHz. The band between 30GHz up to 300GHz is called Extremely High Frequencies (EHF). This wide spectrum is relatively free of users and have recently became relevant for realizations of wireless communications an radars, including the fifth generation (5G) of cellular communications. Due to the short wavelengths, the propagation of millimeter waves can be analyzed using quasi-optical ray techniques. We present a multi-ray analysis of millimeter wave wireless link in the presence of multipath. The analysis is applicable for indoor and outdoor links and considers reflections from walls and buildings. It is shown that line-of-sight is not necessarily required in scenarios where multiple reflections exist as in long corridors, canyons and tunnels. The theoretical results are verified experimentally with a link in the W-band (94GHz).

scholarly journals Single Particle Soot Photometer intercomparison at the AIDA chamber

2012 ◽  
Vol 5 (12) ◽  
pp. 3077-3097 ◽  
Author(s):  
M. Laborde ◽  
M. Schnaiter ◽  
C. Linke ◽  
H. Saathoff ◽  
K.-H. Naumann ◽  
...  
Keyword(s):  
Single Particle ◽  
Detection Efficiency ◽  
Particle Morphology ◽  
Ambient Air ◽  
Mass Range ◽  
Size Distributions ◽  
Position Measurement ◽  
Fullerene Soot ◽  
Mass Size ◽  
Calibration Material

Abstract. Soot particles, consisting of black carbon (BC), organic carbon (OC), inorganic salts, and trace elements, are emitted into the atmosphere during incomplete combustion. Accurate measurements of atmospheric BC are important as BC particles cause adverse health effects and impact the climate. Unfortunately, the accurate measurement of the properties and mass concentrations of BC particles remains difficult. The Single Particle Soot Photometer (SP2) can contribute to improving this situation by measuring the mass of refractory BC in individual particles as well as its mixing state. Here, the results of the first detailed SP2 intercomparison, involving 6 SP2s from 6 different research groups, are presented, including the most evolved data products that can presently be calculated from SP2 measurements. It was shown that a detection efficiency of almost 100% down to 1 fg BC per particle can readily be achieved, and that this limit can be pushed down to ∼0.2 fg BC with optimal SP2 setup. Number and mass size distributions of BC cores agreed within ±5% and ±10%, respectively, in between the SP2s, with larger deviations in the range below 1 fg BC. The accuracy of the SP2's mass concentration measurement depends on the calibration material chosen. The SP2 has previously been shown to be equally sensitive to fullerene soot and ambient BC from sources where fossil fuel was dominant and less sensitive to fullerene soot than to Aquadag. Fullerene soot was therefore chosen as the standard calibration material by the SP2 user community; however, many data sets rely solely on Aquadag calibration measurements. The difference in SP2 sensitivity was found to be almost equal (fullerene soot to Aquadag response ratio of ∼0.75 at 8.9 fg BC) for all SP2s. This allows the calculation of a fullerene soot equivalent calibration curve from a measured Aquadag calibration, when no fullerene soot calibration is available. It could be shown that this approach works well for all SP2s over the mass range of 1–10 fg. This range is suitable for typical BC mass size distributions in the ambient air far from sources. The number size distribution of purely scattering particles optically measured by the 6 SP2s also agreed within 15%. Measurements of the thickness of non-refractory coatings (i.e. product from α-pinene ozonolysis) on the BC particles, relying on BC mass optical size and on an additional particle position measurement, also compared well (within ±17%). The estimated coating thickness values were consistent with thermo-optical analysis of OC and elemental carbon (EC) content, though absolutely accurate values cannot be expected given all the assumptions that have to be made regarding refractive index, particle morphology, etc. This study showed that the SP2 provides accurate and reproducible data, but also that high data quality is only achieved if the SP2 is carefully tuned and calibrated. It has to be noted that the agreement observed here does not account for additional variability in output data that could result from the differences in the potentially subjective assumptions made by different SP2 users in the data processing.

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