关于陆地和海洋杂波现象学的两篇优秀参考文献分别是Ulaby and Dotson (1989) and Long (2001)。
Two excellent generalreferences on land and sea clutter phenomenology are Ulaby and Dotson (1989)and Long (2001).
一篇关于杂波的优秀入门文献为Currie (2010)。
A good briefintroduction is Currie (2010).
杂波回波与目标回波的不同之处在于，它们通常会表现出不同的PDF、时间和空间相关性、多普勒特性和功率水平。
Clutter echoes differfrom target echoes in that they will typically exhibit different PDFs, temporaland spatial correlation properties, Doppler characteristics, and power levels.
这些差异可以用来分离目标和杂波信号。
These differences canbe exploited to separate target and clutter signals.
实现分离的方法将在第5章和第9章予以讨论。
Means to do so arethe principal concern of Chaps. 5 and 9.
杂波与噪声的区别主要表现在两个方面：杂波的功率谱不是白的（即，它是相关干扰），而且由于它是发射信号的回波，接收到的杂波功率受天线增益、发射功率和雷达到地形的距离等参数的影响。
Clutter differs fromnoise in two major ways: its power spectrum is not white (i.e., it iscorrelated interference), and, since it is an echo of the transmitted signal,the received clutter power is affected by such radar and scenario parameters asthe antenna gain, transmitted power, and the range from the radar to theterrain.
相比之下，噪声功率不受这些因素的影响，而是受雷达接收机噪声系数和带宽的影响。
In contrast, noisepower is affected by none of those factors, but is affected by the radarreceiver noise figure and bandwidth.
2.3.1. σ0的特性
2.3.1. Behavior of σ0
面杂波（陆地和海面）反射率的特征描述包括：雷达截面的平均值或中值σ0（无量纲）、反射率变化的概率密度函数及其在空间和时间上的相关性。
Area clutter (landand sea surface) reflectivity is characterized by its mean or median value ofradar cross section, σ0 (dimensionless), the probability densityfunction of the reflectivity variations, and their correlation in space and time.
第2.2.5节中的很多PDF也用于σ0的建模。
Many of the same PDFsdescribed in Sec. 2.2.5 are appliedto modeling σ0 as well.
常见的例子包括指数分布、对数正态分布和威布尔分布。
Popular examplesinclude the exponential, log-normal, and Weibull distributions.
雷达观测到的地形面反射率σ0是地形类型和条件（如地表粗糙度和湿度）、天气（风速、风向、降水）、几何结构（尤其是掠射角）和雷达参数（波长、极化）的强相关函数。
The area reflectivityσ0 of terrain observed by the radar is a strong function of terraintype and condition (e.g., surface roughness and moisture), weather (wind speedand direction, precipitation), engagement geometry (especially grazing angle),and radar parameters (wavelength, polarization).
因此，仅仅选择一种PDF是不足以对杂波进行建模的。
Consequently,selection of a PDF is not sufficient to model clutter.
还需要对这些参数依赖σ0的程度进行建模。
It is also necessaryto model the dependence of σ0 on these parameters.
考虑陆地杂波。
Consider landclutter.
σ0通常的范围为-60到-10dB。
Values of σ0commonly range from –60 to –10 dB.
多年来，大量的雷达测量项目采集了各种条件下的地面杂波统计数据，得出了各种地形类型和条件下的许多σ0表格以及σ0变化模型。
Extensive measurementprograms over the years have collected statistics of land clutter under variousconditions and resulted in many tabulations of σ0for variousterrain types and conditions, as well as models for the variation of σ0.
图2.20显示了一组沙漠地形区域反射率与雷达频率和掠射角关系的代表性数据。
Figure 2.20 shows oneset of representative data for the area reflectivity of desert terrain versusradar frequency and grazing angle.
Figure 2.20. 沙漠地形σ0随雷达频率和掠射角的变化Behavior of σ0 of desert terrain versus radar frequencyand grazing angle. (Data from Currie, 2010.)
注意，σ0通常随雷达频率增加而增大，随掠射角减小而减小。
Note that σ0generally increases with radar frequency, and decreases at shallower grazingangles.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
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