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首页> 外文期刊>Journal of atmospheric and oceanic technology >A Comparative Study of Rainfall Retrievals Based on Specific Differential Phase Shifts at X- and S-Band Radar Frequencies
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A Comparative Study of Rainfall Retrievals Based on Specific Differential Phase Shifts at X- and S-Band Radar Frequencies

机译：基于X波段和S波段雷达频率特定微分相移的降雨检索的比较研究

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摘要

A comparative study of the use of X- and S-band polarimetric radars for rainfall parameter retrievals is presented. The main advantage of X-band polarimetric measurements is the availability of reliable specific differential phase shift estimates, K_(DP), for lighter rainfalls when phase measurements at the S band are too noisy to produce usable K_(DP). Theoretical modeling with experimental raindrop size distributions indicates that due to some non-Rayleigh resonant effects, K_(DP) values at a 3.2-cm wavelength (X band) are on average a factor of 3.7 greater than at 11 cm (S band), which is a somewhat larger difference than simple frequency scaling predicts. The non-Rayleigh effects also cause X-band horizontal polarization reflectivity, Z_(eh), and differential reflectivity, Z_(DR), to be larger than those at the S band. The differences between X- and S-band reflectivities can exceed measurement uncertainties for Z_(eh) starting approximately at Z_(eh) > 40 dBZ, and for Z_(DR) when the mass-weighted drop diameter, D_m, exceeds about 2 mm. Simultaneous X- and S-band radar measurements of rainfall showed that consistent K_(DP) estimates exceeding about 0.1° km~(-1) began to be possible at reflectivities greater than ～26-30 dBZ while at the S band such estimates can generally be made if Z_(eh) > ～35-39 dBZ. Experimental radar data taken in light-to-moderate stratiform rainfalls with rain rates R in an interval from 2.5 to 15 mm h~(-1) showed availability of the K_(DP)-based estimates of R for most of the data points at the X band while at the S band such estimates were available only for R greater than about 8-10 mm h~(-1). After correcting X-band differential reflectivity measurements for differential attenuation, Z_(DR) measurements at both radar frequency bands were in good agreement with each other for D_m < 2 mm, which approximately corresponds to Z_(DR) ≈ 1.6 dB. The Z_(DR)-based retrievals of characteristic raindrop sizes also agreed well with in situ disdrometer measurements.
机译：提出了使用X波段和S波段极化雷达进行降雨参数检索的比较研究。 X波段极化测量的主要优点是，当S波段的相位测量噪声太大而无法产生可用的K_（DP）时，对于较轻的降雨，可以获得可靠的特定微分相移估计值K_（DP）。具有实验雨滴尺寸分布的理论模型表明，由于某些非瑞利共振效应，在3.2厘米波长（X波段）处的K_（DP）值平均比在11厘米（S波段）时高3.7倍，这比简单的频率缩放预测的差异要大一些。非瑞利效应还导致X波段水平偏振反射率Z_（eh）和差分反射率Z_（DR）大于S波段的水平。对于X_（eh），大约从Z_（eh）> 40 dBZ开始，并且当质量加权液滴直径D_m超过约2 mm时，对于Z_（DR），X和S波段反射率之间的差异可能会超过测量不确定度。 。 X波段和S波段雷达同时进行的降雨测量表明，在反射率大于〜26-30 dBZ时，超过0.1°km〜​​（-1）的一致K_（DP）估计值开始成为可能，而在S波段，这种估计值可以通常在Z_（eh）>〜35-39 dBZ时进行。在轻度至中度的层状降雨（降雨率R在2.5至15 mm h〜（-1）的区间内）中获得的实验雷达数据表明，对于大多数数据点，基于K_（DP）的R估计值均可用在X波段，而在S波段，这样的估计仅适用于大于约8-10 mm h〜（-1）的R。在对X波段差分反射率测量值进行差分衰减校正后，两个雷达频段的Z_（DR）测量值在D_m <2 mm时彼此非常一致，大约对应于Z_（DR）≈1.6 dB。基于Z_（DR）的特征雨滴大小的反演也与原地测速计测量结果非常吻合。

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