式（2.70）和（2.71）的“直流项”表示杂波回波的一个常数非随机分量，有时也称为接收信号的“恒定分量”。

The "DCterm" in Eqs. (2.70) and (2.71) represents a constant, nonrandom componentof the clutter echo that is sometimes called a "persistent component"of the received signal.

对于这样一种分量的存在，所涉及的杂波散射体反射率的幅度和相位都必须是恒定的。

For such a componentto exist, both the amplitude and phase of the reflectivity of the clutterscatterers involved must be constant.

因此，直流分量可归因于裸露地面、岩石和树干等物体的后向散射。

Thus, the DCcomponent is attributable to backscatter from elements such as bare ground,rocks, and tree trunks.

交流分量解释了运动物体（如树叶、树枝和草的叶片等）的后向散射。

The AC term accountsfor backscatter from moving elements such as leaves, branches, and blades ofgrass.

简单的自回归滤波器可用于杂波模型的模拟。

Simple autoregressivefilters can be used to implement the model in simulations (Mountcastle, 2004).

2.3.4. 雷达截面的复合模型

2.3.4. Compound Models ofRadar Cross Section

如第6章所示，雷达探测性能的预测在很大程度上取决于目标和杂波RCS模型的细节。

As is seen in Chap.6, radar detection performance predictions depend strongly on the details oftarget and clutter RCS models.

此外，众所周知，雷达散射截面的统计数据随几何结构、分辨率、波长和极化等因素的变化而变化。

Furthermore, it iswell known that RCS statistics vary significantly with a host of factors suchas geometry, resolution, wavelength, and polarization.

因此，研究良好的统计RCS模型是一个非常活跃的领域。

Consequently, thedevelopment of good statistical RCS models is a very active area of empiricaland analytical research.

以下是对前面描述的基本建模方法扩展的三个简单示例，所有这些都是由杂波建模的复杂性驱动的。

Following are threebrief examples of an extension to the basic modeling approach described earlier,all motivated by the complexities of modeling clutter.

由于有关这些模型的文献主要是根据回波幅度（电压）ζ而不是RCS σ或功率研究的，本节的其余部分也将集中讨论幅度PDFs。

Because theliterature regarding these models is developed primarily in terms of the echoamplitude (voltage) ζ instead of RCS σ or power, the remainder of this sectionalso concentrates on amplitude PDFs.

一些幅度PDF是基于物理动机的，特别是瑞利（指数RCS）模型（源自中心极限定理的论证）和Rice或Rician模型（对应于具有额外主要散射源的瑞利模型）。

Some amplitude PDFsare physically motivated, especially the Rayleigh (exponential RCS) model(which follows from a central limit theorem argument) and the Rice or Ricianmodel (which corresponds to a Rayleigh model with an additional dominantscattering source).

其他如对数正态分布或威布尔分布，都是通过对测量数据进行拟合而得到的。

Others, such as thelog-normal or Weibull, have been developed empirically by fitting distributionsto measured data.

该模型已用于描述海杂波。

This model has beenused to describe sea clutter (Jakeman and Pusey, 1976; Ward, 1981).

随机变量x用一个缓慢去相关的分量来表示，该分量的电压服从自由度为2m的中心chi-square分布，其中m ≥ 2.5。

The random variable xis identified with a slowly decorrelating component having a voltagedistribution following a central chi-square of degree 2m with m ≥ 2.5.

引入该分量是为了解释由于海浪结构和雷达几何引起的“聚束”散射体，并表示幅度平均值随时间的变化。

This component isintroduced to account for "bunching" of scatterers due to ocean swellstructure and radar geometry, and represents variation in the mean of theamplitude over time.

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

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