说明：  ex9_15 比较相参积累和非相参积累。仿真先产生信号回波。得到回拨求模的结果，计算回波的信噪比。进行非相参积累和相参积累处理，计算相参处理和非相参处理后的信噪比。
(Comparison ex9_15 coherent and noncoherent. Simulation of the first echo signal. Be the result of the call-back mode for calculating the echo signal to noise ratio. For noncoherent and coherent processing, the calculation of non-coherent processing and coherent treatment of the signal to noise ratio.)