The techniques adopted include magnetic method, gravity, transient electromagnetic method, frequency domain electromagnetic method, direct current method and seismic method. 其中包括磁法，重力，瞬變電磁法，頻率域電磁法，直流電法和地震法等。
The watermark is embedded in the significant coefficient in the low frequency was found to be robust, but the watermarked image is easily visible distortion. 將浮水印藏在影像頻率域中的低頻帶的重要系數，經(jīng)研究可使浮水印較具強韌性來(lái)抵抗外部影像處理攻擊，但也因此犧牲影像的品質(zhì)。
