图1.24描述了目标检测的概念。
Figure 1.24 illustrates the concept.
Figure 1.24. 阈值检测的描述Illustration of thresholddetection.
“杂波+目标”信号可能代表接收信号强度相对于单个发射脉冲在距离（快速时间）上的变化。
The “clutter + target” signalmight represent the variation in received signal strength versus range (fasttime) for a single transmitted pulse.
图中的回波信号幅度在三个不同的时间位置跨越阈值，表明在不同的距离单元上存在三个目标。
It crosses the threshold at three differenttimes, suggesting the presence of three targets at different ranges.
因为回波检测是统计过程的结果，所以阈值检测的决策具有有限的错误概率。
Because they are the result of astatistical process, threshold detection decisions have a finite probability ofbeing wrong.
例如，噪声尖峰可能超过阈值，导致错误的目标检测，通常称为虚警。
For example, a noise spike could cross thethreshold, leading to a false target declaration, commonly called a falsealarm.
如果目标尖峰强烈地突出于背景干扰中，即，如果SIR尽可能大时，这些虚警误差将被最小化。
These errors are minimized if the targetspikes stand out strongly from the background interference, i.e., if the SIR isas large as possible.
如果是这种情况，阈值可以设置得相对较高，只会产生很少的虚警，同时仍然能够检测出大多数目标。
If this is the case the threshold can beset relatively high, resulting in few false alarms while still detecting mosttargets.
这一事实也说明了匹配滤波在雷达系统中的重要性。
This fact also accounts for the importanceof matched filtering in radar systems.
匹配滤波器使SIR最大化，从而提供最佳的阈值检测性能。
The matched filter maximizes the SIR, thusproviding the best threshold detection performance.
此外，可实现的SIR随着发射脉冲能量E单调地增加，从而鼓励使用更长的脉冲在目标上获得更多的能量。
Furthermore, the achievable SIR increasesmonotonically with the transmitted pulse energy E, thus encouraging the use oflonger pulses to get more energy on the target.
由于较长的简单脉冲降低了距离分辨率，因此脉冲压缩技术也很重要，以便在保持良好检测性能的同时获得良好的分辨率。
Since longer simple pulses reduce rangeresolution, the technique of pulse compression is also important so that fineresolution can be obtained while maintaining good detection performance.
阈值检测的概念可以应用于许多不同的雷达信号处理系统。
The concept of threshold detection can beapplied to many different radar signal processing systems.
图1.24说明了阈值检测在快时间(距离)上信号追踪的应用，但它同样可以较好地应用于由固定距离上不同多普勒频率组成的信号，或者以二维形式应用于组合的距离-多普勒数据或SAR图像。
Figure 1.24 illustrates its application toa fast-time (range) signal trace, but it can be equally well applied to asignal composed of measurements at different Doppler frequencies for a fixedrange, or in a two dimensional form to combined range-Doppler data or to SARimagery.
在实现阈值检测时，有许多重要的细节。
There are numerous significant details inimplementing threshold detection.
各种检测器的设计工作在复信号样本的幅度、平方幅度甚至对数幅度上。
Various detector designs work on themagnitude, squared-magnitude, or even log-magnitude of the complex signalsamples.
根据干扰的统计信息计算阈值，以便将虚警限制在可接受的范围内。
The threshold is computed from knowledge ofthe interference statistics so as to limit false alarms to an acceptable rate.
然而，在实际系统中，干扰统计信息很少能够精确到足以预先计算出固定阈值。
However, in real systems the interferencestatistics are rarely known accurately enough to allow for precomputing a fixedthreshold.
——本文译自Mark A. Richards所著的《Fundamentals of Radar Signal Processing（Second edition）》
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