Papers by Alessandro Battaglia
Forward simulation is an indispensable tool for evaluation of precipitation retrieval algorithms ... more Forward simulation is an indispensable tool for evaluation of precipitation retrieval algorithms as well as for studying snow/ice microphysics and their radiative properties. The main challenge of the implementation arises due to the size of the problem domain. To overcome this hurdle, assumptions need to be made to simplify complex cloud microphysics. It is important that these assumptions are applied consistently throughout the simulation process. ISSARS addresses this issue by providing a computationally efficient and modular framework that can integrate currently existing models and is also capable of expanding for future development.
Page 1. ■Hi Thermal Microwave Radiation: Applications for Remote Sensing Edited by C Matzler Page... more Page 1. ■Hi Thermal Microwave Radiation: Applications for Remote Sensing Edited by C Matzler Page 2. IET ELECTROMAGNETIC WAVES SERIES 52 Series Editors: Professor PJB Clarricoats Professor EV Jull Thermal Microwave Radiation: Applications for Remote Sensing ...
2012 13th International Radar Symposium, 2012
EarthCARE space-borne radar will be the first radar in space with Doppler capability, enabling me... more EarthCARE space-borne radar will be the first radar in space with Doppler capability, enabling measurements of vertical motions of hydrometeors. The vertical velocity is very useful in classifying precipitating systems (convective systems versus stratiform, rain versus snow). Global distribution of hydrometeor vertical velocity is important in estimation of latent heat fluxes and in study of energy transportation in the atmosphere. A renewed interest in space-borne Doppler radars has recently sprouted as a response to the imminent launch (2015) of the W-band cloud profiling radar within the ESA/JAXA EarthCARE mission. Given the many caveats involved with high frequency space-borne Doppler radars (Doppler fading due to the fast satellite movement, small Nyquist velocity folding, non uniform beam filling issues, contamination by multiple scattering, antenna mispointing) a particularly challenging scenario for retrieving mean Doppler velocities is represented by convective clouds. In this work we will couple DOMUS, a Monte Carlo-based DOppler MUltiple Scattering radar simulator capable of accounting for non uniform beam filling (NUBF) conditions and multiple scattering enhancements, with high resolution WRF (Weather Research and Forecasting) mesoscale prediction model runs to study the potential of high frequency Doppler radars in retrieving vertical hydrometeor motions in atmosphere.
Journal of Geophysical Research: Atmospheres, 2013
1] Four years (2007)(2008)(2009)(2010) of colocated 94 GHz CloudSat radar reflectivities and 532 ... more 1] Four years (2007)(2008)(2009)(2010) of colocated 94 GHz CloudSat radar reflectivities and 532 nm CALIPSO Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) backscattering coefficients are used to globally characterize snow-precipitating clouds. CALIOP is particularly useful for the detection of mixed and supercooled liquid water (SLW) layers. Liquid layers are common in snow precipitating clouds: overall/over sea/over land 49%/ 57%/33% of the snowy profiles present SLW or mixed-phase layers. The spatial and seasonal dependencies of our results-with snowing clouds more likely to be associated with mixed phase during summer periods-are related to snow layer top temperatures. SLW occurs within the majority (>80%) of snow-precipitating clouds with cloud tops warmer than 250 K, and is present 50% of the time when the snow-layer top temperature is about 240 K. There is a marked tendency for such layers to occur close to the top of the snow-precipitating layer (75% of the times within 500 m). Both instruments can be synergetically used for profiling ice-phase-only snow, especially for light snow (Z < 0 dBZ, S < 0.16 mm/h) when CALIOP is capable of penetrating, on average, more than half of the snow layer depth. These results have profound impact for deepening our understanding of ice nucleation and snow growth processes, for improving active and passive snow remote sensing techniques, and for planning snow-precipitation missions.
Journal of Quantitative Spectroscopy and Radiative Transfer, 1999
We study absorption and scattering by irregularly shaped Gaussian random particles in the Rayleig... more We study absorption and scattering by irregularly shaped Gaussian random particles in the Rayleigh-ellipsoid approximation. For a given sample shape, we determine the best-"tting ellipsoid as the equal-volume ellipsoid with the largest volume overlapping the sample shape. We present an e$cient method for calculating such ellipsoids for Gaussian particles and characterize the goodness of the approximation with the complementary volume. We study the scattering properties of Gaussian particles much smaller than the wavelength with di!erent complex refractive indices, comparing the Rayleigh-ellipsoid approximation to the Rayleigh-volume, discrete-dipole, and second-order perturbation approximations, and to the computations using the variational volume integral equation method. Our new method can prove valuable in microwave remote sensing of terrestrial ice clouds: crystalline structures are often elongated with dimensions in the Rayleigh domain for typical radar frequencies. (A. Battaglia) 0022-4073/99/$ -see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 0 2 2 -4 0 7 3 ( 9 9 ) 0 0 0 2 0 -5 r( , )"r exp s( , )! 1 2 ,
Journal of Quantitative Spectroscopy and Radiative Transfer, 2005
A completely forward Monte Carlo radiative transfer code has been developed with biasing techniqu... more A completely forward Monte Carlo radiative transfer code has been developed with biasing techniques to efficiently solve the polarized radiative transfer equation for the full Stokes vector. The code has been adapted to accommodate plane parallel/3-D vertically/horizontally inhomogeneous scattering atmospheres in Cartesian geometries. Particular attention has been paid in stochastically treating the propagation, the emission and the scattering through anisotropic media particularly suited for clouds containing perfectly or partially oriented particles. Our modelling is very appealing because all its biasing techniques do not introduce unphysical Stokes vector. Numerical results and comparisons with benchmark tests are presented for verification. r
During the European Integrated Project on Aerosol cloud climate 4 air quality interactions (EUCAA... more During the European Integrated Project on Aerosol cloud climate 4 air quality interactions (EUCAARI) campaign, the Advanced Microwave Ra-5 diometer for Rain Identification (ADMIRARI) has been continuously measur-6 ing in parallel with a MicroRainRadar (MRR) at the Cabauw Experimental Site 7 for Atmospheric Research (CESAR) observatory in the Netherlands. Both in-8 struments measured with the same azimuthal orientation at a constant elevation 9 angle of 30 degrees. A data set of linearly polarized brightness temperatures have 10 been collected at the three ADMIRARI observation frequencies (10.7, 21.0 and 11 36.5 GHz) together with slant radar reflectivity profiles at 24.1 GHz from the 12 MRR. The Bayesian inversion algorithm for ADMIRARI for the estimation of 13 slant path integrated values for water vapor, cloud liquid water, and rain liquid 14 water is extended to include physically constraint the rain column structural in-15 formation from the MRR observations. We analyze the quality controlled mea-16 surements from August 23 to November 12, 2008, and present the retrieved pa-17 rameters for the time intervals of pure clouds and the intervals dominated by 18 precipitating clouds. During the intervals when cloud and rain are retrieved si-19 multaneously a mean integrated water vapor of 24.42 kg m −2 , a mean cloud liq-20 uid water of 0.24 kg m −2 , and a mean rain liquid water path of 0.18 kg m −2 21 are observed with an estimated average RMS of 1.54 kg m −2 , 0.16 kg m −2 and 22 0.06 kg m −2 for water vapor, cloud and rain liquid water path, respectively. For 23 the first time estimated distributions of the cloud water/rain water partition are 24 presented for precipitating clouds as observed by a ground-based radiometer. Fi-25 nally, we compare the histograms of the integrated rain water content retrieved 26 X -4
During the GPM Ground Validation LPVEx field campaign in 2010, a large number of instruments have... more During the GPM Ground Validation LPVEx field campaign in 2010, a large number of instruments have been deployed to several sites in the vicinity of Helsinki. Two of these sites hosted the dual-polarized Cband radar at Kumpula Campus (University of Helsinki) and the University of Bonn's radiometer ADMIRARI (10.7, 21.0 and 36.5 GHz, H&V polarized) located at Emäsalo. Additionally ADMIRARI sensed the atmosphere in synergy with a K-band radar (24.1 GHz) and a ceilometer (902 nm). Several ancillary instruments, among them a 2DVD disdrometer, were also co-located Emasälo.
The 94 GHz EarthCARE radar (expected to be launched within three years) will be the first radar i... more The 94 GHz EarthCARE radar (expected to be launched within three years) will be the first radar in space with Doppler capabilities. The retrieval of hydrometeor fall speeds and air motions from the radar signal will be extremely challenging due to a variety of complications. In EarthCARE configuration (height=395 km, beam-width=0.08°, PRF around 6000 Hz) the following caveats have to be accounted for: a) the high satellite speed matched to the finite antenna beam-width produces consistent Doppler fading (σDoppler ≈ 3.25 m/s); b) Nyquist Doppler interval ( 4.5 m/s) can introduce relevant folding; c) non uniform beam filling conditions may cause biases in the mean Doppler velocity estimates; d) multiple scattering widens the Doppler spectrum and de-correlate the signal from the real mean velocity. A forward Doppler radar simulator capable of accounting both for non uniform beam filling conditions and multiple scattering enhancements has been coupled to an instrument simulator in order to reproduce the signal at the antenna port. In this paper the EarthCARE radar simulator has been applied to a variety of scenarios (convective rain, drizzle, cirrus sedimentation). The performance of different standard Doppler moment estimators is discussed for the three different situations. In convective scenarios it will be utterly tough to extract useful velocity information from EarthCARE observations.
Journal of Applied Meteorology and Climatology, Dec 1, 2006
A numerical model based on the Monte Carlo solution of the vector radiative transfer equation has... more A numerical model based on the Monte Carlo solution of the vector radiative transfer equation has been adopted to simulate radar signals. The model accounts for general radar configurations such as airborne/ spaceborne/ground based and monostatic/bistatic and includes the polarization and the antenna pattern as particularly relevant features. Except for contributions from the backscattering enhancement, the model is particularly suitable for evaluating multiple-scattering effects. It has been validated against some analytical methods that provide solutions for the first and second order of scattering of the copolar intensity for pencil-beam/Gaussian antennas in the transmitting/receiving segment. The model has been applied to evaluate the multiple scattering when penetrating inside a uniform hydrometeor layer. In particular, the impact of the phase function, the range-dependent scattering optical thickness, and the effects of the antenna footprint are considered.
At four GPM/GV field campaigns, polarimetric radars have been scanning in synergy with the radiom... more At four GPM/GV field campaigns, polarimetric radars have been scanning in synergy with the radiometer ADMIRARI . In order to develop a radiometer-radar retrieval scheme, independent estimations of liquid precipitating parameters are first developed to overview the performance of active and passive sensors when observing the same precipitating system. Earlier studies (LPVEx campaign) have shown that radar can be used to estimated for the rain layer attenuation and the radiometer for the cloud and gases, leaving the attenuation due to bright-band as last unknown which can be determined combining both sensors. LPVEx observed light precipitation which polarimetric variables were negligible and a A = aZ b relationship were used but results depend strongly on the DSD taken into account for the coefficients a and b. The present study is an attempt to extend the well known ZPHI method to RHI observations along the radiometer Field-of-View (FOV), to obtain precipitation parameters.
Egu General Assembly Conference Abstracts, Apr 1, 2009
Multiple scattering strongly affects the CloudSat Profiling Radar reflectivity when the satellite... more Multiple scattering strongly affects the CloudSat Profiling Radar reflectivity when the satellite is over-passing moderate and heavy precipitation systems. Following a criterion developed by the authors in the past (Battaglia et al., 2008) and based on the freezing level altitude (FLA) and on the path integrated attenuation (PIA), oceanic CloudSat reflectivities profiles affected by multiple scattering are identified and further analysed. Profiles are clustered according to PIA, FLA, position and value of the profile maximum reflectivity, jump of the reflectivity from pixels close to the surface to the surface pixel. This last variable represents a rough estimate of the multiple-scattering strength, i.e. of the reflectivity enhancement produced by higher-than-one scattering orders in proximity to the surface. The slopes of the reflectivity profiles (which results from the combined effect of vertical variability, attenuation and multiple scattering) are then computed at different altitudes above the surface and their variability is discussed in relationships to the profile characteristic variables. Results from one full year of CloudSat data are discussed and compared with numerical simulation outputs based on Cloud Resolving Model (Battaglia and Simmer 2008). This study has strong relevance for attenuation-based retrievals of rainfall from high frequency space-borne radars (Matrosov et al., 2008). Battaglia, A., J. Haynes, T. L'Ecuyer, and C. Simmer, Identifying multiple-scattering-affected profiles in CloudSat observations over the Oceans, J. Geoph. Res., 113, D00A17, doi:101029/2008JD009960 Battaglia, A., and C. Simmer, How does multiple scattering affect the spaceborne W-band radar measurements at ranges close to and crossing the surface-range?, IEEE Tran. Geo. Rem. Sens., , Vol. 46, No. 6,1644-1651, 2008 Matrosov, S., Battaglia, A., Rodriguez, P. Effects of multiple scattering on attenuation-based retrievals of stratiform rainfall from CloudSat, J. Atm. Oc. Tech., , 25(12), 2199-2208, 2008
Although snow is the predominant type of precipitation in the sub-polar and polar latitudes, not ... more Although snow is the predominant type of precipitation in the sub-polar and polar latitudes, not many reliable remote-sensing methods of determining the vertical distributions of micro-physical snowfall parameters (i.e. snow mass density, snow crystal size and type) today exist. These parameters - together with temperature, humidity and turbulence - govern processes such as riming and aggregation, which in turn determine the ground-based snowfall rate. However, these parameters are highly variable in space and time and thus their measurement - and subsequent modeling - is a difficult task. The "Towards an Optimal estimation based Snow Characterization Algorithm" (DFG-TOSCA) project addresses these points in combining the unique information contained from a suite of ground-based sensors: microwave radiometers (22 - 150 GHz), 24 and 35 GHz radar, lidar, and in-situ measurement methods. During the winter of 2008/2009, such instruments were deployed at the Environmental Research Station Schneefernerhaus (UFS at 2650 m MSL) at the Zugspitze Mountain in Germany for deriving microphysical properties of falling snow. In the high altitude region of the UFS station snow events occur much more frequently than in lower regions and the low water vapor amounts account for clearer scattering signals from ice hydrometeors. We will present results of an extended case study where measured TBs at 90 and 150 GHz were found to be significantly enhanced during snowfall due to scattering of surface radiation at snow crystals and that this enhancement is clearly correlated with the radar derived snow water path. Radiative transfer (RT) simulations highlight the strong influence of the vertical distribution of cloud liquid water (liquid water path LWP<0.1 kgm-2) on the TB which in extreme cases can fully obscure the snow scattering signal. Simulation experiments for this specific case, using typical variations in snow amount, particle shape and snow particle size distribution revealed the equal importance of these contributors to the TB variations. Further, we show a statistical analysis of the whole TOSCA period which highlights the very frequent presence of super-cooled water within snow clouds and their importance to radiative transfer in the microwave spectral region. Finally we present results of RT studies that illustrate the benefit of combining passive and active microwave systems to disentangle the influences of different snow shape, SSD and SWP. The identification of potentially valuable ground-based instrument synergies for the retrieval of snowfall parameters from the surface will also be of importance for the development of new space-borne observational techniques.
Journal of Geophysical Research, 2009
1] Multiple scattering strongly affects the CloudSat Profiling Radar reflectivity when the satell... more 1] Multiple scattering strongly affects the CloudSat Profiling Radar reflectivity when the satellite is overpassing moderate and heavy precipitation systems. Therefore it is important to identify profiles that may be contaminated by multiple scattering prior to interpreting the results of any application that involves the use of CloudSat data in raining scenes. On the basis of analysis of multiple-scattering Monte Carlo reflectivity simulations applied to cloud-resolving model-generated microphysical profiles encompassing a large variety of precipitating systems, a relatively straightforward criterion is proposed for flagging profiles potentially affected by multiple scattering. The path-integrated attenuation, that can be estimated from CloudSat's 2B-GEOPROF product, can be used to identify four multiple-scattering regimes: (1) the single scattering approximation is applicable to the entire Z-profile; (2) the single scattering approximation is unreliable but the second order of scattering approximation is valid; (3) the second order of scattering approximation is not valid owing to higher order of multiple-scattering effects which, however, do not affect the surface reference technique-based path-integrated attenuation estimates; and (4) the multiple scattering is affecting the surface return as well, thus spoiling the path-integrated attenuation estimates. Operational path-integrated attenuation thresholds for each of these regimes are then applied to the CloudSat data set over the global oceans, where path-integrated attenuation estimations are more accurate than over land. Case studies and global statistics of the occurrence of multiple scattering are presented: for ocean pixels, around 80% (90%) of the profiles identified as rainy can be treated in the single scattering (second order of scattering) approximation. A threshold value around 20 dB for the one-way path-integrated attenuation is suggested for the applicability of the surface reference technique to the CloudSat Profiling Radar system. This roughly corresponds to 96.5% of the rainy pixels. Owing to the different precipitation regimes, results are strongly regionally and seasonally dependent. For instance in the Inter-Tropical Convergence Zone a not negligible fraction of the raining pixels requires either second-order (10-15%) or higher-order scattering ($10%) to accurately model the observed reflectivity profile.
Http Dx Doi Org 10 1175 Jtech D 13 00085 1, Dec 20, 2013
Spaceborne Doppler radars have the potential to provide key missing observations of con-8 vective... more Spaceborne Doppler radars have the potential to provide key missing observations of con-8 vective vertical air motions especially over the tropical oceans. Such measurements can 9 improve our understanding of the role of tropical convection in vertical energy transport and 10 its interaction with the environment. Several millimeter wavelength Doppler radar concepts 11 have been proposed since the 1990's. The EarthCARE Cloud Profiling Radar (CPR) will 12 be the first dopplerized atmospheric radar in space but has not been optimized for Doppler 13 measurements in deep convective clouds. 14 The key challenge that constraints the CPR performance in convective clouds is the 15 range-Doppler dilemma. Polarization diversity (PD) offers a solution to this constraint, by 16 decoupling the coherency (Doppler) requirement from the unambiguous range requirement.
Atmospheric Research, Oct 1, 2001
Using a modified T-matrix code, some polarimetric single-scattering radar parameters (Z h,v , LDR... more Using a modified T-matrix code, some polarimetric single-scattering radar parameters (Z h,v , LDR h,v , q hv , Z DR and d hv ) from populations of ice crystals in ice phase at 94 GHz, modeled with axisymmetric prolate and oblate spheroidal shapes for a C-size distribution with different a parameter (a = 0, 1, 2) and characteristic dimension L m varying from 0.1 to 1.8 mm, have been computed. Some of the results for different radar elevation angles and different orientation distribution for fixed water content are shown.
Journal of Applied Meteorology and Climatology, Mar 6, 2014
With the launch of the Global Precipitation Mission core satellite expected for 2013, NASA is pla... more With the launch of the Global Precipitation Mission core satellite expected for 2013, NASA is planning and pursuing an intense ground validation program with campaigns all over the world (Brazil 2010, Finland 2010, Oklahoma 2011, Canada winter campaign 2011-2012) focused on physical validation of microwave-based rainfall algorithms. The ADvanced MIcrowave RAdiometer for Rain Identification (ADMIRARI) exploits its multi-frequency (10.7-21.0-36.5 GHz) polarimetric (H and V channel) capabilities to partition simultaneously rain and cloud water, thereby addressing an open key issue for improving precipitation estimates. This potentiality has already been extensively demonstrated during the field campaigns COPS over Southern Germany and EUCAARI in the Netherlands. During CHUVA (Cloud processes of tHe main precipitation systems in Brazil: A contribUtion to cloud resolVing modeling and to the GlobAl Precipitation Measurement ) ADMIRARI measures together with numerous ancillary instruments co-located at Alcântara observatory in Northern Brazil (e.g. microwave radiometer profiler, polarimetric X-band radar, disdrometers, micro rain radar, lidar, etc.). These measurements are intended to study warm rain convective systems and to create and validate a 3-D cloud processes database for such precipitation regimes. The operational ADMIRARI retrievals will contribute to the GPM effort in the following areas: 1) Identification of the microphysical cloud properties at the onset of precipitation in warm rain processes; 2) Improved understanding of bright band effects in radiative transfer models for microwave radiometry; 3) Characterization of the microphysical and electromagnetic/radiative properties of ice and mixed-phase precipitating clouds; 4) Partitioning of total liquid water content into cloud and precipitation (rain or snow) water equivalents for different climatological regimes including the validation of cloud resolving and weather forecast models to this respect. Until now, climatological rain/cloud partitioning statistics represent the major outcome of ADMIRARI measurements and will be presented for different climatological regimes. Moreover, ADMIRARI measurements from the CHUVA campaign and preliminary results regarding the observed cloud/rain partition will be shown, and a first assessment on the retrieval performance for an atmospheric regime not yet observed by ADMIRARI. We hope that these first results will lead to feedback from the GPM international community in order to improve and re-arrange the observational strategies in future GPM/GV field campaign where ADMIRARI is scheduled to take part.
CloudSat observations of deep convective clouds reveal significant contributions from multiply sc... more CloudSat observations of deep convective clouds reveal significant contributions from multiply scattered photons, resulting in "pulse stretching", where echoes appear to originate from beyond the end of the cloud and even below the ground. Spaceborne lidar returns from liquid water clouds suffer from the same effect. It is essential to account for this phenomenon if we are to retrieve accurate microphysical profiles from space, but no satisfactory method for doing so has yet been devised. In this paper an efficient multiple scattering model is described that may be incorporated into retrieval schemes as the "forward model" for both radar and lidar, thereby allowing multiple scattering to be accounted for. It splits the photons into those that have taken a near-direct path out to and back from a single backscattering event (in the case of lidar, accounting for small-angle forward scatterings on the way), and those that have experienced wide-angle multiple-scattering events leading to pulse stretching. The latter are modeled using the time-dependent two-stream approximation, which reduces the problem to solving a pair of coupled partial differential equation. The method performs well in comparison to Monte Carlo calculations, but is far more efficient. This offers the prospect not only of accounting for a troublesome effect in CloudSat and Calipso data, but also of making use of multiple scattering to extract extra information about clouds and convective systems.
Journal of the Atmospheric Sciences, Dec 1, 2008
A fast, approximate method is described for the calculation of the intensity of multiply scattere... more A fast, approximate method is described for the calculation of the intensity of multiply scattered lidar returns from clouds. At each range gate it characterizes the outgoing photon distribution by its spatial variance, the variance of photon direction and the covariance of photon direction and position. The result is that for an N-point profile the calculation is O(N) efficient yet implicitly includes all orders of scattering, contrasting with the O(N m /m!) efficiency of models that explicitly consider each scattering order separately for truncation at m-order scattering. It is also shown how the shape of the scattering phase function near 180 • may be taken into account for both liquid water droplets and ice particles. The model considers only multiplescattering due to small-angle forward scattering events, which is suitable for most ground-based and airborne lidars due to their small footprint on the cloud. For spaceborne lidar, it must used in combination with the wide-angle multiple scattering model described in Part 2 of this two-part paper.
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Papers by Alessandro Battaglia