Publication

Sensitivity analysis of polarimetric attenuation correction algorithms

Alexis Berne, Samuel Jolivet
2012
Discussion par affiche
Résumé

Polarimetry improves radar rainfall estimation. It allows a better separation of meteorological and nonmeteorological echoes, a better identification of the type of hydrometeors, and an improved correction of the attenuation due to rain affecting the signal of weather radars working at C- and X-band. The attenuation correction is based on the near-linearity between the specific attenuation at horizontal(vertical) polarization and the specific differential phase shift (on propagation) Kdp. The coefficients of this relationship as well as those of the power law assumed between the specific attenuation and the radar reflectivity depend on the DSD and the dominant microphysical processes. Because raindrop size distribution (DSD) measurements are not available everywhere and all the time, it is difficult to accurately estimate these coefficients. In addition, phase measurements are noisy and can be affected by significant uncertainties, as well as Kdp. Finally, the radar calibration is also important in the process of attenuation correction. In order to investigate and quantify the sensitivity of the classical attenuation correction algorithms to the different parameters involved, a simulation experiment has been conducted. It is based on realistic simulated DSD fields from which all the necessary variables can be derived. The most commonly used algorithms for attenuation correction (namely ZPhi and the self-consistent -SC- version of it) are applied and the obtained corrected reflectivities are compared to the true ones. Uncertainty is added to the main parameters/variables and the respective sensitivities can be quantified. It is shown that ZPhi performs better than SC as long as the parameters are within 30% of their true values. Such accuracy is not easily achievable for all parameters and SC should be preferred if large uncertainties are expected.

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Concepts associés (33)
Radar météorologique
Un radar météorologique est un type de radar utilisé en météorologie pour repérer les précipitations, calculer leur déplacement et déterminer leur type (pluie, neige, grêle, etc.). La structure tridimensionnelle des données obtenues permet également d'inférer les mouvements des précipitations dans les nuages et ainsi de repérer ceux qui pourraient causer des dommages. Enfin, en se servant des précipitations comme traceurs, on peut en déduire la direction radiale et la vitesse des vents dans la basse atmosphère.
Atténuation
En électronique, l’atténuation ou affaiblissement est la diminution relative de la puissance d'un signal au cours de sa transmission. C'est la quantité par laquelle il faut multiplier la valeur du signal à la sortie pour obtenir celle à l'entrée de la section considérée. vignette|upright=0.5|Sonde L'atténuation, que ce soit dans une ligne de transmission ou dans un faisceau hertzien, est une grandeur importante dans les télécommunications, dont elle est un facteur limitatif.
Attenuation coefficient
The linear attenuation coefficient, attenuation coefficient, or narrow-beam attenuation coefficient characterizes how easily a volume of material can be penetrated by a beam of light, sound, particles, or other energy or matter. A coefficient value that is large represents a beam becoming 'attenuated' as it passes through a given medium, while a small value represents that the medium had little effect on loss. The SI unit of attenuation coefficient is the reciprocal metre (m−1).
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