Canbin Hu

Ship Discrimination Using Polarimetric SAR Data and Coherent Time-Frequency Analysis

This paper presents a new approach for the discrimination of ship responses using polarimetric SAR (PolSAR) data. The PolSAR multidimensional information is analyzed using a linear Time-Frequency (TF) decomposition approach, which permits to describe the polarimetric behavior of a ship and its background area for different azimuthal angles of observation and frequencies of illumination. This paper proposes to discriminate ships from their background by using characteristics of their polarimetric TF responses, which may be associated with the intrinsic nature of the observed natural or artificial scattering structures. A statistical descriptor related to polarimetric coherence of the signal in the TF domain is proposed for detecting ships in different complex backgrounds, including SAR azimuth ambiguities, artifacts, and small natural islands, which may induce numerous false alarms. Choices of the TF analysis direction, i.e., along separate azimuth or range axis, or simultaneously in both directions, are investigated and evaluated. TF decomposition modes including range direction perform better in terms of discriminating ships from range focusing artifacts. In comparison with original full-resolution polarimetric indicators, the proposed TF polarimetric coherence descriptor is shown to qualitatively enhance the ship/background contrast and improve discrimination capabilities. Using polarimetric RADARSAT-2 data acquired over complex scenes, experimental results demonstrate the efficiency of this approach in terms of ship location retrieval and response characterization.

SAR image segmentation combining the PM diffusion model and MRF model

This paper addresses the statistical segmentation of SAR (Synthetic Aperture Radar) image combining PM (Perona Malik) nonlinear diffusion model and MRF (Markov Random Field) model. First, the original SAR image is filtered using the modified PM nonlinear diffusion model, in which the diffusion coefficients along the tangent direction and the normal direction are approximated and simplified. Afterwards, the filtered image is segmented using MRF model, in which the clique potential is computed using both the label configuration and the intensity information. The proposed method is marked by PM-MRF for short. Experimental results show that PM-MRF competes favorably with the traditional one to segment SAR image homogeneously.

A method of acquiring tie points based on closed regions in SAR images

This paper presents a method in finding tie points automatically in synthetic aperture radar (SAR) image pairs based on the extracted closed regions. There are mainly three steps during this process. The first step is to extract the closed regions in the SAR image with an image segmentation approach deducted by the geodesic active contour (GAC) model. Then, a polygonal approximation process is adopted to locate the feature points on the boundaries of these regions. With the obtained feature points, geometric hashing theory is employed to match these feature points as the tie points. A pair of simulated SAR images and a pair of high-resolution airborne SAR images are used to test and evaluate the proposed method. The experimental results show that the proposed method is effective and appropriate for the acquisitions of tie points in SAR image pairs.

Harbor detection of remote sensing images based on model

Harbor detection is an important aspect for remote sensing ocean application research. Fast and accurate harbor detection can greatly improve the ability of automatic interpretation for remote sensing image shipside buildings and ships inside ports. By having a detailed research on harbor object disposal, this paper established harbor model and advance knowledge, and proposed a harbor detection method of remote sensing images based on model. Besides, aiming at the shortage that proposed method has a little far in locating harbor range, this paper defined the principal axis of harbor object and calculated harbor circum-rectangle which has a higher location precision. Compared with an existing harbor detection algorithm, our experiments show that novel method has a whole harbor detection, exact location and better universal.

SAR Azimuth ambiguities removal for ship detection using time-frequency techniques

In this paper, a new azimuth ambiguities removal method is introduced for ship detection by Time-Frequency (TF) analysis. A TF coherence indicator is proposed to filter ghost echoes due to the different TF coherence characteristics between real ship target echoes and ambiguous ones. The effectiveness of this proposed TF coherence indicator for ship detection is demonstrated using single polarimetric spaceborne TerraSAR-X coherent data over the test sea/ocean site in Hongkong, China.

Multi-dimensional coherent Time-Frequency analysis for ship detection in polsar imagery

This paper proposes an algorithm for ship detection in complex scenes using multi-dimensional coherent Time-Frequency (TF) techniques and dual-polarization SAR data. The PolSAR multi-dimensional information is analysed by means of a linear TF decomposition approach which permits to describe the ship and background area polarimetric behaviour for different azimuth angles of observation and frequencies of illumination. A statistic descriptor related to the signal polarimetric coherence in the TF domain, is used for ship detection in different backgrounds, including the environments with presence of strong ghost ambiguities or small natural islands. Using polarimetric RADARSAT-2 data, experimental results demonstrate the efficiency of this method.

A Hierarchical Extension of General Four-Component Scattering Power Decomposition

The overestimation of volume scattering (OVS) is an intrinsic drawback in model-based polarimetric synthetic aperture radar (PolSAR) target decomposition. It severely impacts the accuracy measurement of scattering power and leads to scattering mechanism ambiguity. In this paper, a hierarchical extended general four-component scattering power decomposition method (G4U) is presented. The conventional G4U is first proposed by Singh et al. and it has advantages in full use of information and volume scattering characterization. However, the OVS still exists in the G4U and it causes a scattering mechanism ambiguity in some oriented urban areas. In the proposed method, matrix rotations by the orientation angle and the helix angle are applied. Afterwards, the transformed coherency matrix is applied to the four-component decomposition scheme with two refined models. Moreover, the branch condition applied in the G4U is substituted by the ratio of correlation coefficient (RCC), which is used as a criterion for hierarchically implementing the decomposition. The performance of this approach is demonstrated and evaluated with the Airborne Synthetic Aperture Radar (AIRSAR), Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), Radarsat-2, and the Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) fully polarimetric data over different test sites. Comparison studies are carried out and demonstrated that the proposed method exhibits promising improvements in the OVS and scattering mechanism characterization.

Exploiting polarization using multi-frequency SAR data and multi-dimensional time-frequency techniques

During recent years, Time-Frequency (TF) techniques have been introduced to characterize scene polarimetric behaviours using PolSAR data. In this paper, we apply a TF decomposition approach to the analysis of PolSAR data with different frequency bands and show some polarimetric TF behaviours of various scenes. The PolSAR data may be decomposed in azimuth direction, range direction only and in both directions. Two statistical descriptor, i.e., polarimetric TF stationarity and coherence indicators, are used to depict the features of the scene backscattering response. Their individual performance is assessed. The polarimetric TF features, extracted from the scenes of interest, can show some special relevant information compared to the original full resolution case. Moreover, with the availability of new multi-frequency full-polarization high resolution F-SAR data, the results of same site with respect to different frequency bands are exploited and compared with each other.