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Ines Fenni

Publications and source records attributed to Ines Fenni.

4 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

Parameterizing Single Scattering Properties Across the Electromagnetic Spectrum for Water Cloud Retrieval

Water clouds are composed of spherical water droplets, to which the Mie solution applies for their electromagnetic scattering. The essential variable of Mie solutions is ξ ≡ 𝑚𝑘𝐷 (or equivalently 𝑚𝑘𝑟), where 𝑚 is the complex index of refraction of water, 𝑘 = 2π/λ the angular wavenumber, λ the wavelength, and 𝐷 (𝑟) the diameter (radius) of the water droplet. Consequently, all water-droplet single-scattering properties, such as extinction and scattering efficiencies, i.e., 𝑄 and , are functions of , 𝑒 𝑄𝑠 ξ which provides a convenient pathway to parameterize water-droplet single-scattering properties across the electromagnetic spectrum or spectrum segments. In this paper, we first demonstrate that the numerical Mie solution indeed depends only on ξ. We then present our first attempt to parameterize extinction efficiency across the visible-infrared spectrum.

Kwo-Sen Kuo↗
NASA NTRS2021

Evaluation of Higher-order Quadrature Schemes in Improving Computational Efficiency for Orientation-averaged Single-Scattering Properties of Nonspherical Ice Particles

We evaluate several high-order quadrature schemes for accuracy and efficacy in obtaining orientation-averaged single-scattering properties (SSPs). We use the highly efficient MIDAS to perform electromagnetic scattering calculations to evaluate the gain in efficiency from these schemes. MIDAS is shown to be superior to DDSCAT, a popular discrete dipole approximation (DDA) method. This study is motivated by the fact that quality physical precipitation retrievals rely on using accurate orientation-averaged SSPs derived from realistic hydrometeors as input to radiative transfer Models (RTMs). The DDA has been a popular choice for single-scattering calculations, due to its versatility with respect to target geometry. However, being iterative-solver-based (ISB), the most used DDA codes, e.g. DDSCAT and ADDA, must solve the scattering problem for each orientation of the target separately. As the size parameter and geometric anisotropy of the hydrometeor increase, the number of orientations needed to obtain accurate orientation-averages can increase drastically and so does the computation cost incurred by the ISB-DDA methods. MIDAS is a Direct-Solver-Based (DSB) code, its decomposition of the original large matrix with a high rank into multiple more manageable smaller matrices of lower ranks makes it much more computationally efficient while maintaining excellent accuracy. In addition, direct solvers consider all requested orientations at once, giving MIDAS further advantage over popular ISB-DDA methods. MIDAS, when combined with high-order quadrature for orientation averaging, can be greater than three orders of magnitude more efficient in obtaining RTM-ready SSPs of complex-shaped hydrometeors than existing ISB-DDA methods, with the native quadrature schemes they offer.

Ines Fenni↗