Abstract: Nonlinear acoustics allows for applications like parametric arrays in underwater acoustics. Broadband para- metric acoustic sonar used in shallow water detection will be discussed, which is able to produce Low frequency signal with wide bandwidth. In tank experiment, difference frequency signal and its pressure level, effective length of broad- band parametric arrays are all tested. Also Berktay's far field solution and KZK (Khokhlov-Zabolotskaya-Kuznetsov) equation are applied to analyze these parameters. Meanwhile, to the broadband difference frequency signal (Linear Frequency Modulation) obtained in the experiment, pulse compression is adopted to improve its detection resolution. The effectiveness and reliability of this system are verified in sea trial. Broadband difference frequency signal and single difference frequency signal are used to profile the shallow water sub-bottom and its buried objects respectively.