T-matrix computations of light scattering by nonspherical particles: A review

Mishchenko, Michael I.; Travis, Larry D.; Mackowski, Daniel W.

doi:10.1016/0022-4073(96)00002-7

Cited by 1,070 publications

(694 citation statements)

References 135 publications

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“…At 94 GHz the uncertainty of assuming raindrops are spherical Mie scatters is approximately 5 % in integrated backscatter for a gamma DSD with median drop size D 0 = 1.5 mm when compared against estimates for oblate spheroids (e.g. Thurai et al, 2007;Zhang et al, 2001) using the T-matrix method (Mishchenko et al, 1996). Scattering and attenuation effects are included in the radar forward model so that the forward-modelled estimate of the apparent radar reflectivity (Z a ) is directly comparable to ob-servations.…”

Section: Radar Forward Modelmentioning

confidence: 99%

Improved rain rate and drop size retrievals from airborne Doppler radar

2017

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Abstract. Satellite remote sensing of rain is important for quantifying the hydrological cycle, atmospheric energy budget, and cloud and precipitation processes; however, radar retrievals of rain rate are sensitive to assumptions about the raindrop size distribution. The upcoming EarthCARE satellite will feature a 94 GHz Doppler radar alongside lidar and radiometer instruments, presenting opportunities for enhanced retrievals of the raindrop size distribution.We demonstrate the capability to retrieve rain rate as a function of drop size and drop number concentration from airborne 94 GHz Doppler radar measurements using CAP-TIVATE, the variational retrieval algorithm developed for EarthCARE. For a range of rain regimes observed during the Tropical Composition, Cloud and Climate Coupling field campaign, we explore the contributions of mean Doppler velocity and path-integrated attenuation (PIA) measurements to the retrieval of rain rate, and the retrievals are evaluated against independent measurements from an independent 9.6 GHz Doppler radar. The retrieved drop number concentrations vary over 5 orders of magnitude between very light rain from melting ice and warm rain from liquid clouds. In light rain conditions mean Doppler velocity facilitates estimates of rain rate without PIA, suggesting the possibility of EarthCARE rain rate estimates over land; in moderate warm rain, drop number concentration can be retrieved without mean Doppler velocity, with possible applications to CloudSat.

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Section: Radar Forward Modelmentioning

confidence: 99%

Improved rain rate and drop size retrievals from airborne Doppler radar

2017

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“…The values b a,fine and b a,coarse can be calculated from the OPC data, as described in the previous subsection. The values of d a,fine were expected to be near zero because their effective radii were less than 0.2 mm [e.g., Mishchenko et al, 1996aMishchenko et al, , 1996bMishchenko and Sassen, 1998]. The values of d a,coarse were calculated from the OPC data using the T-matrix method, and were almost constant (21.9 $ 22.4%) over the height range of the measurement because the shape of the size distribution in that mode was almost constant (Figure 10).…”

Section: Total Aerosol Linear Depolarization Ratiomentioning

confidence: 99%

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

et al. 2003

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[1] The vertical distributions of tropospheric aerosol properties were measured during the Asian dust event over central Japan (35°-36°N, 136°-137°E), using a ground-based Raman lidar and aircraft-based instruments on 23 April 1996. The lidar measured enhancements of aerosol backscattering below an altitude of 4 km and between 5 and 8 km where the total aerosol linear depolarization ratio showed peaks of 12-15% and the relative humidities were $30%. The aircraft measurements showed that the aerosol particles consisted primarily of irregularly shaped mineral dusts and sea salts with a mode radius (r m ) of $1 mm and sulfates with r m $ 0.1 mm over the measured height range of 0.6-5.5 km. Electron microscopic analyses suggest that $77% of the mineral particles were coated with a solution at 1.8 km and that the fraction of coated particles decreased with height. The aerosol backscattering coefficients (b a ), calculated from the airborne optical particle counter (OPC) data, were smaller than the lidar-derived values by $30% above 3.1 km and by $44% below that altitude. The difference was attributable to the horizontal and temporal inhomogeneities of the aerosol properties between the measurement sites and to the uncertainty in b a , particularly for the coarse particles calculated from the OPC data. The aerosol depolarization ratios (d a ) estimated from the OPC data showed the same increase as those obtained with the lidar above 4.1 km. This suggests that the proportion of backscattering by coarse particles to total particles primarily controlled the d a measured with the lidar in that region.

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“…Recently, the T-matrix method for nonspherical scattering has been significantly improved [Mishchenko et al, 1996]. To study the influence of particle nonsphericity, the T-matrix method is used to generate the base matrix A and synthetic spectral optical depth for given size distributions of finite cylinders.…”

Section: Mie Theory Approximationmentioning

confidence: 99%

Particle size distribution retrieval from multispectral optical depth: Influences of particle nonsphericity and refractive index

Liu¹,

Arnott²,

Hallett³

1999

J. Geophys. Res.

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Abstract. Retrieval of size distributions from multispectral optical depth measurements requires solution of an ill-posed inverse problem. The ill-posedness causes problems such as solution ambiguity. Size distribution retrieval becomes more complicated in the presence of nonspherical particles and/or refractive index errors. A new retrieval algorithm is first developed which allows for both smoothing and nonnegativity constraint along with the L-curve method for choosing the Lagrange multiplier that controls the degree of the imposed smoothing. This new algorithm is compared to an iterative algorithm and the method of truncated singular value decomposition, demonstrating that the new algorithm outperforms the other two. With the new algorithm to perform the size distribution retrieval and with the T-matrix method to calculate optical depth for a given cloud consisting of randomly oriented finite circular cylinders, the influence of particle nonsphericity on the size distribution retrieval is investigated by use of the Mie theory for spheres as well as the anomalous diffraction theory for cylinders. The results show that spurious particles and even spurious particle modes occur for both approximations. The effect of refractive index errors are also investigated, showing that even a small perturbation of refractive indices can cause serious distortions of retrieved size distributions. A further examination reveals that either applying an approximate lightscattering theory (Mie theory or anomalous diffraction theory) to nonspherical particles or using incorrect refractive indices results in systematic errors in the model which in turn conspire with the ill-posedness inherent in the retrieval to cause the distortions of retrieved size distributions. The retrieval process essentially transforms the model error into the error in retrieved size distribution, yet improves the agreement between true and retrieved optical depth. IntroductionVarious properties (e.g., dynamical, optical, electrical, and chemical) of atmospheric particles depend on particle size. Number distribution of particles with respect to size (size distribution) is a fundamental subject in aerosol and cloud physics [Pruppacher and Klett, 1978]. Its importance has been increasingly recognized with the concern over the effects of aerosols

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T-matrix computations of light scattering by nonspherical particles: A review

Cited by 1,070 publications

References 135 publications

Improved rain rate and drop size retrievals from airborne Doppler radar

Improved rain rate and drop size retrievals from airborne Doppler radar

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

Particle size distribution retrieval from multispectral optical depth: Influences of particle nonsphericity and refractive index

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