Novasar-S and maritime surveillance

Abstract

The paper shows a new algorithm for ship-detection from Synthetic Aperture Radar (SAR) images. The algorithm consists of three main stages: pre-processing, detection and discrimination. In the pre-processing a land mask is obtained considering the different statistics between the sea and the land's backscattered field; the detection stage isolates the bright points over the sea background employing a Constant False Alarm (CFAR) method; while the ships are retrieved, in the discrimination step, by evaluating the scattering contributions of the possible targets detected in the previous stage. The algorithm is tested on an airborne Sband SAR image of Portsmouth harbor, similar to those that will become available with the upcoming UK SAR mission NovaSAR-S.

A new GLRT-based ship detection technique in SAR images

“…Traditional SAR ship-detection algorithms are mainly based on Constant False Alarm Rate (CFAR) methods: the sea background is characterized statistically and then the detector looks for individual pixels (or small group of pixels) whose brightness values are greater than a chosen threshold [1]. The main drawbacks of CFAR algorithms are that targets with intensity values very similar to those of sea clutter might not be detected and that the distribution parameters estimation needed to define the threshold is a computationally expensive procedure if nonGaussian models are adopted [2]. None of the algorithms already present in literature takes in account a model for the backscattering of the ship; as consequence, the detector may present a higher false alarm rate [1].…”

Roughness parameters estimation of sea surface from SAR images

“…As a consequence, the detector may result in a higher false-alarm rate [3]. In [4], the overall ship-detection performances are improved with an algorithm including a simplified model of a canonical ship through a proper scattering evaluation block. The canonical ship can be considered as a complex metallic object, which can be decomposed by using a series of rectangular facets (parallelepiped representation) and, consequently, the total component field can be obtained with a vectorial summation on each facet [5].…”

“…In addition, the computation of the Radar Cross Section (RCS) of large and complex targets involve different scattering mechanisms, such as specular reflection, diffraction by edge and tips, multiple scattering and shadowing effects [6]. In [4] only the electromagnetic field backscattered from a canonical ship is considered: single and multiple scattering contributions are isolated and located on a real SAR image and, finally, non-parallelepiped like targets are rejected to improve the detection performances. Each scattering contribution depends on different parameters: the dielectric constant of the water and the ship, the radar parameters, the orientation angle between the radar and the ship and the average roughness parameters of the sea surface.…”

“…Each scattering contribution depends on different parameters: the dielectric constant of the water and the ship, the radar parameters, the orientation angle between the radar and the ship and the average roughness parameters of the sea surface. The estimation of these roughness parameters is then required for the evaluation of the multiple scattering contributions, whose analysis may lead to an improvement of the performances of the ship-detection algorithm introduced in [4]. In general, the field scattered from the sea surface depends both on its electromagnetic and geometrical aspects; but, while the evaluation of the dielectric constants of the sea is known in literature [7], the estimation of average roughness parameters of the sea surface with SAR is poorly addressed.…”

Ship Detection with Spectral Analysis of Synthetic Aperture Radar: A Comparison of New and Well-Known Algorithms

“…For this reason, ships often appear as bright spots in SAR intensity images. This peculiarity has led to the development of several algorithms aimed at detecting bright points on a darker background [3,[15][16][17][18][19][22][23][24][25][26][27][28][29][30]. The backscattering from the sea is strongly influenced by the sea state, and in some situations, it can be extraordinarily bright, covering the return from small vessels.…”