*Article* **A Robust Algorithm Based on Phase Congruency for Optical and SAR Image Registration in Suburban Areas**

#### **Lina Wang 1,2, Mingchao Sun 1, Jinghong Liu 1,2,\*, Lihua Cao 1,2 and Guoqing Ma 3**


Received: 3 September 2020; Accepted: 10 October 2020; Published: 13 October 2020

**Abstract:** Automatic registration of optical and synthetic aperture radar (SAR) images is a challenging task due to the influence of SAR speckle noise and nonlinear radiometric differences. This study proposes a robust algorithm based on phase congruency to register optical and SAR images (ROS-PC). It consists of a uniform Harris feature detection method based on multi-moment of the phase congruency map (UMPC-Harris) and a local feature descriptor based on the histogram of phase congruency orientation on multi-scale max amplitude index maps (HOSMI). The UMPC-Harris detects corners and edge points based on a voting strategy, the multi-moment of phase congruency maps, and an overlapping block strategy, which is used to detect stable and uniformly distributed keypoints. Subsequently, HOSMI is derived for a keypoint by utilizing the histogram of phase congruency orientation on multi-scale max amplitude index maps, which effectively increases the discriminability and robustness of the final descriptor. Finally, experimental results obtained using simulated images show that the UMPC-Harris detector has a superior repeatability rate. The image registration results obtained on test images show that the ROS-PC is robust against SAR speckle noise and nonlinear radiometric differences. The ROS-PC can tolerate some rotational and scale changes.

**Keywords:** optical and synthetic aperture radar (SAR); image registration; phase congruency (PC); radiometric difference
