许多模型将观测到的Z值与降水率联系起来。

A number of models are used to relate theobserved values of Z to rain rates.

这些模型取决于降水类型,例如雪、雷雨、地形雨等。

These models depend on the type ofprecipitation, e.g., snow versus thunderstorm rain versus orographic rain.

一个常见的模型见表2.2,它显示了观测到的Z值(单位为dBZ)与美国NEXRAD国家气象雷达系统中使用的六级降水率之间的等效性。

A common model is that of Table 2.2, whichshows the six-level equivalence between observed Z values (in dBZ) and rainfallrates used in the U.S. NEXRAD national weather radar system.

Table2.2. dBZ反射率与降水率之间的对应关系Correspondencebetween dBZ Reflectivity and Rain Rate

商用“多普勒气象雷达”系统中使用的对应关系与上表非常相似,每个观看电视天气预报的人应该都很熟悉。

Very similar scales are used in thecommercial "Doppler weather radar" systems familiar to every watcherof television weather forecasts.

值得注意的是,表2.2中的dBZ值是以10为底的对Z(单位:mm6/m3)取对数的10倍。

It is importantto note that the dBZ values in Table 2.2 are 10 times the base 10 logarithm ofZ in mm6/m3 .

当Z的单位为m6/m3= m3时,在转换为dB量纲、使用表2.2之前必须乘以1018得到单位为mm6/m3的Z值。

When Z is givenin m6/m3 = m3 , it must be multiplied by 1018to convert it to units of mm6/m3 before converting to adecibel scale and using Table 2.2.

2.2.5雷达散射截面的统计描述

2.2.5. Statistical Description of Radar Cross Section

实际目标的雷达散射截面并不能有效地模拟为一个简单的常数。

The radar crosssection of real targets cannot be effectively modeled as a simple constant.

一般来说,即使对于相对简单的散射体,雷达散射截面也是一个复杂的与视线角、频率和极化相关的函数。

In general, RCSis a complex function of aspect angle, frequency, and polarization, even forrelatively simple scatterers.

例如,图2.4中的导电三面角反射器通常用作现场测量中的校准目标。

For example, theconducting trihedral corner reflector of Fig. 2.4 is often used as acalibration target in field measurements.

Figure 2.4. 方形三面角反射器Square trihedral cornerreflector.

从理论上可以确定沿着对称轴(观察“拐角”)观察时的RCS,即

Its RCS when viewedalong its axis of symmetry (looking "into the corner") can bedetermined theoretically; it is (Knott et al., 1985)

因此,RCS随着频率的增加而增大。

Thus the RCSincreases with increasing frequency.

另一方面,至少存在一个与频率和方向无关的散射体。

On the other hand, atleast one frequency- and aspect-independent scatterer exists.

——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing(Second edition)》