Matteo Sedehi

Passive bistatic ISAR based on geostationary satellites for coastal surveillance

The paper proposes a new passive bistatic ISAR mode for coastal surveillance based on the exploitation of the signals transmitted by telecommunication geostationary satellites. Specifically it is demonstrated that ISAR images with acceptable quality of ship targets could be obtained by using telecommunication geostationary satellites as opportunity transmitters and stationary passive devices, located near the coast, as receivers. The geostationary satellites assure a continuous and complete coverage of wide areas: moreover satellites available in the near future should also provide a bandwidth suitable for the achievement of medium slant range resolutions. Since in ISAR the target motion is exploited to obtain cross-range resolution, a network of stationary low cost receiving only devices could be therefore properly located on the coast to obtain ISAR images of ship targets of interest for the surveillance and monitoring of the maritime traffic.

Impact of an Electromagnetic Interference on Imaging Capability of a Synthetic Aperture Radar

The imaging capability of a synthetic aperture radar (SAR) could be seriously limited or denied by an electromagnetic interference. The effects of a wideband noise-like interference are to mask the scene visible in the imaged area with a high uniform noise level. In this paper we evaluate the impact of a jammer on the imaging capability of a space-borne SAR. The vulnerability measure is defined as the imaged area over which the jammer denies information acquisition. Simulated results show how a jammer can deny the SAR imaging capability for all range access area and for a long azimuth area. The obscuration extends over a distance that is governed by the one way azimuth pattern of the radar antenna and the jammer equivalent isotropic radiate power (EIRP). The same analysis has been carried out using an antenna nulling technique. Results show a more limited denied area for focusing a SAR image, obtaining improved operability for the sensor.

From the expected scientific applications to the functional specifications, products and performance of the SABRINA missions

Orbital planning and formation flying control of SABRINA mission will allow different observation geometries characterized by inter satellites distances (baseline) variable from hundreds meters to some hundreds of kilometers. In a so vast scenario, a wide range of bistatic techniques are applicable and testable, ranging from cross and along track interferometry to multi-channel techniques and large baseline bistatic observations. This paper contains a brief description of all the bistatic techniques proposed for the SABRINA mission, most of them never experimented previously from two spaceborne platforms. Important scientific and technological applications are associated to each technique: moving target indication, topography, geology, geomorphology, oceanography, biomass evaluation, improvement of monostatic data quality, accurate pointing and attitude determination. Great effort is devoted to individuate the main functional specifications need to obtain the individuated applicative products and the expected performance of the SABRINA mission.

Reduced Order Jammer Cancellation Scheme Based on Double Adaptivity

A doubly adaptive scheme is presented for detection and jammer cancellation by airborne/spaceborne radar equipped with a limited number of receiving channels. In this case where, to guarantee the desired performance in the protection against multiple jammers with a wide range of possible direction of arrivals (DOAs), a number of auxiliary antenna beams greater than the number of channels would be required. For these systems an adaptive auxiliary beam selection technique is proposed to decide which is the most effective subset of auxiliary antennas in each condition, assuming a slowly changing jamming environment. This leads to a doubly adaptive jammer cancellation scheme: we first perform an adaptive selection of the best set of auxiliary beams, and then we apply an adaptive scheme for jammer cancellation and target detection by using only the best set of beams. This especially applies to the case of adaptive radar obtained as a retrofit of existing monopulse radar sensors or of design retrofit for single channel spaceborne radar with a redundant channel. A closed form analytical expression is provided for the detection performance of the proposed reduced degree of freedom (DOF) scheme based on double adaptivity, which provides a complete characterization of the properties of this detection scheme. Based on the derived expression of the detection performance, the proposed scheme is compared with an ideal scheme with a number of channels equal to the number of auxiliary antennas, showing that the proposed approach has near-optimal performance. Finally the implementation issues of the doubly adaptive scheme are discussed, together with its limitations.

A reduced order jammer cancellation scheme based on double adaptivity

In this paper a doubly adaptive scheme is presented for detection and jammer cancellation by airborne monopulse radar, equipped with three receiving channels. An adaptive auxiliary selection technique is proposed to decide which is the most effective couple of auxiliary antennas in each condition, assuming a slowly changing jamming environment. This leads to a doubly adaptive jammer cancellation scheme: we first perform an adaptive selection of the best set of auxiliary beams, and then apply an adaptive scheme for jammer cancellation and target detection using only the best set of three receiving channels. This can be used also to obtain an adaptive ECCM as a retrofit on an existing 2D monopulse radar. This paper characterizes the performance of this approach, together with its limitations.

A modified M/N logic for track initiation of low observable targets using amplitude information

This paper deals with the optimization of the track initiation procedure for fast moving low observable targets. The standard approach consisting in applying a first detection threshold to each scan followed by an M/N logic, requires very low threshold values to guarantee an acceptable detection probability, which results in turn in a high probability to initiate false tracks. We derive a new technique to initiate tracks of low observable targets by exploiting the full amplitude information as well as the monopulse ratio information and evaluate its performance. The new technique outperforms the M/N decision logic, while keeping comparable a simplicity and low computational cost.

SAR imaging via iterative adaptive approach and sparse Bayesian learning

We consider sidelobe reduction and resolution enhancement in synthetic aperture radar (SAR) imaging via an iterative adaptive approach (IAA) and a sparse Bayesian learning (SBL) method. The nonparametric weighted least squares based IAA algorithm is a robust and user parameter-free adaptive approach originally proposed for array processing. We show that it can be used to form enhanced SAR images as well. SBL has been used as a sparse signal recovery algorithm for compressed sensing. It has been shown in the literature that SBL is easy to use and can recover sparse signals more accurately than the l 1 based optimization approaches, which require delicate choice of the user parameter. We consider using a modified expectation maximization (EM) based SBL algorithm, referred to as SBL-1, which is based on a three-stage hierarchical Bayesian model. SBL-1 is not only more accurate than benchmark SBL algorithms, but also converges faster. SBL-1 is used to further enhance the resolution of the SAR images formed by IAA. Both IAA and SBL-1 are shown to be effective, requiring only a limited number of iterations, and have no need for polar-to-Cartesian interpolation of the SAR collected data. This paper characterizes the achievable performance of these two approaches by processing the complex backscatter data from both a sparse case study and a backhoe vehicle in free space with different aperture sizes.

Wideband adaptive antenna nulling schemes for synthetic Aperture Radar

In this paper we introduce a batch frequency domain scheme for wideband jammer nulling with multichannel synthetic aperture radar (SAR). This is compared to the wideband extension of the SLC approach. We analyze the nulling performance for several image acquisition modes and interference scenarios and show that both algorithms are adequate in terms of cancellation level. The frequency domain approach is shown to be attractive for the possibility to integrate it with the SAR focusing algorithm, thus compensating a higher computational cost.

Dual Channel Adaptive Antenna Nulling with Auxiliary Selection for Spaceborne Radar

A doubly adaptive scheme is proposed for detection and jammer cancellation by spaceborne radar, characterized by a dual receiving channel scheme. Generally many auxiliary antenna elements are required to protect a radar with a high gain antenna without tapering, from a single jammer with generic direction of arrival. However, assuming a slowly changing jamming scenario, we show that it is possible to apply first an adaptive selection of the best auxiliary element, and then to apply an adaptive scheme for jammer cancellation and target detection using only two receiving channels, connected respectively to the main antenna beam, and to the best selected auxiliary antenna beam. This paper characterizes the performance of this approach, together with its limitations.

A weighted least squares approach for multi-target Doppler-only localization

In this paper a multi target Doppler-only tracking scheme as well as its related algorithms are proposed and analyzed. Specifically the Doppler-only single target localization is firstly addressed in an heteroscedastic environment exploiting a weighted least square approach. Then this approach is extended to a multi target case introducing an algorithm to solve the inherent measurements to targets association problem. Finally the integration of these algorithms with a Kalman filter based tracking stage is analyzed and evaluated through simulations.