An Unsupervised Port Detection Method in Polarimetric SAR Images Based on Three-Component Decomposition and Multi-Scale Thresholding Segmentation

It is difficult to detect ports in polarimetric SAR images due to the complicated components, morphology, and coastal environment. This paper proposes an unsupervised port detection method by extracting the water of the port based on three-component decomposition and multi-scale thresholding segmentation. Firstly, the polarimetric characteristics of the port water are analyzed using modified three-component decomposition. Secondly, the volume scattering power and the power ratio of the double-bounce scattering power to the volume scattering power (PRDV) are used to extract the port water. Water and land are first separated by a global thresholding segmentation of the volume scattering power, in which the sampling region used for the threshold calculation is automatically selected by a proposed homogeneity measure. The interference water regions in the ports are then separated from the water by segmenting the PRDV using the multi-scale thresholding segmentation method. The regions of interest (ROIs) of the ports are then extracted by determining the connected interference water regions with a large area. Finally, ports are recognized by examining the area ratio of strong scattering pixels to the land in the extracted ROIs. Seven single quad-polarization SAR images acquired by RADARSAT-2 covering the coasts of Dalian, Zhanjiang, Fujian, Tianjin, Lingshui, and Boao in China and Berkeley in America are used to test the proposed method. The experimental results show that all ports are correctly and quickly detected. The false alarm rates are zero, the intersection of union section (IoU) indexes between the detected port and the ground truth can reach 75%, and the average processing time can be less than 100 s.

Correlations between the Parameters of the Light Volume Scattering Functions in the Mediterranean Sea Surface Waters

Purpose. The aim of the work is to study relationships between the parameters of the light volume scattering functions based on the data of their measurements in the Mediterranean Sea surface waters. Methods and Results. The data of measurements of the light volume scattering functions in the water samples taken in a few regions of the southern Mediterranean Sea, namely from the Strait of Gibraltar to the Levant Sea, as well as in the central part of the Aegean Sea and near the Dardanelles Strait (May, 1998) were used. The following parameters of the volume scattering functions were calculated: total scattering coefficient, and asymmetry and variation coefficients. The maximum and minimum values of the scattering coefficient were 0.21 and 0.09 m–1, respectively; and those for the asymmetry coefficient – 77.8 and 33.9. The variation coefficient of the angle scattering coefficients changed within 35–79%, its maximum and minimum values fell on the angles 7.5° and 162.5°, respectively. Obtained were the relations between the variation coefficient and the scattering angle, the asymmetry coefficient and the scattering coefficient, and the angle scattering coefficients and the total scattering coefficient. All of them possess high (more than 0.9) correlation coefficients. The coefficient value (51.7%) at the angle 2° does not correspond to general relation of the variation coefficient to the scattering angle. This fact is explained by different contributions of coarse and fine suspended matter to the light volume scattering function. At the angle 2°, the main contribution is made by a coarse (organic) suspended matter, whereas at the angles exceeding 7.5° – by a fine (mineral) suspension. Conclusions. The values of the variation coefficient of the angle scattering coefficient at the angles equal to 2° and exceeding 7.5° demonstrate variability of the coarse and fine suspended matter in the Mediterranean Sea, respectively. The equation for the relation between the asymmetry coefficient of the light volume scattering functions and the total scattering coefficient obtained for the Mediterranean Sea waters is close to the analogous one obtained for the Atlantic Ocean tropical waters. The angle 3.5° is optimal for determining the total scattering coefficient using the angle scattering coefficient for the Mediterranean Sea functions.

Numerical model for evaluating the speckle activity and characteristics of bone tissue under the biospeckle laser system

This paper discusses and studies the composition and characteristics of biospeckle on the surface of bone tissues. We used a laser speckle device to capture biospeckle patterns from fresh pig bone tissue. Traditional speckle activity metrics were used to measure the speckle activity of ex vivo bone tissue over time. Both Gaussian and Lorentzian correlation functions were used to characterize the ordered and disordered motion of the bone surface, together with volume scattering, to construct the model. Using the established mathematical model of the spatio-temporal evolution of the biospeckle pattern, it is possible to account for the presence of volume scattering from the biospeckle of bones, quantify the ordered or disordered motions in the biological speckle activity at the current time, and assess the ability of laser speckle correlation technique to determine biological activity.

An Adaptive Decomposition Approach with Dipole Aggregation Model for Polarimetric SAR Data

Polarimetric synthetic aperture radar (PolSAR) has attracted lots of attention from remote sensing scientists because of its various advantages, e.g., all-weather, all-time, penetrating capability, and multi-polarimetry. The three-component scattering model proposed by Freeman and Durden (FDD) has bridged the data and observed target with physical scattering model, whose simplicity and practicality have advanced remote sensing applications. However, the three-component scattering model also has some disadvantages, such as negative powers and a scattering model unfitted to observed target, which can be improved by adaptive methods. In this paper, we propose a novel adaptive decomposition approach in which we established a dipole aggregation model to fit every pixel in PolSAR image to an independent volume scattering mechanism, resulting in a reduction of negative powers and an improved adaptive capability of decomposition models. Compared with existing adaptive methods, the proposed approach is fast because it does not utilize any time-consuming algorithm of iterative optimization, is simple because it does not complicate the original three-component scattering model, and is clear for each model being fitted to explicit physical meaning, i.e., the determined adaptive parameter responds to the scattering mechanism of observed target. The simulation results indicated that this novel approach reduced the possibility of the occurrence of negative powers. The experiments on ALOS-2 and RADARSAT-2 PolSAR images showed that the increasing of adaptive parameter reflected more effective scatterers aggregating at the 45° direction corresponding to high cross-polarized property, which always appeared in the 45° oriented buildings. Moreover, the random volume scattering model used in the FDD could be expressed by the novel dipole aggregation model with an adaptive parameter equal to one that always appeared in the forest area.

Brief communication: An empirical relation between center frequency and measured thickness for radar sounding of temperate glaciers

Radar sounding of the thickness of temperate glaciers is challenged by substantial volume scattering, surface scattering and high attenuation rates. Lower-frequency radar sounders are often deployed to mitigate these effects, but the lack of a global synthesis of their success limits progress in system and survey design. Here we extend a recent global compilation of glacier thickness measurements (GlaThiDa) with the center frequency for radar-sounding surveys. From a maximum reported thickness of ∼ 1500 m near 1 MHz, the maximum thickness sounded decreases by ∼ 500 m per frequency decade. Between 25–100 MHz, newer airborne radar sounders generally outperform older, ground-based ones. Based on globally modeled glacier thicknesses, we conclude that a multi-element, ≤30 MHz airborne radar sounder could survey most temperate glaciers more efficiently.