Showing papers by "Saab Automobile AB published in 2017"

False Alarm Reduction in Wavelength-Resolution SAR Change Detection Using Adaptive Noise Canceler

Abstract: This paper introduces a method to reduce false alarms in wavelength-resolution synthetic aperture radar (SAR) change detection and aims at very high frequency-band systems like the Coherent All Radio Band System (CARABAS). The false alarms are usually caused by the elongated structures, such as power lines and fences, which stand out from the background. The responses of elongated structures are sensitive to flight path. The introduced method aims at minimizing the false alarms caused by the elongated structures and is based on the well-known adaptive processing mechanism, i.e., the so-called adaptive noise canceler (ANC) where a separate reference signal is required. The changes between measurements are considered by the input signal of ANC while the separate reference signal comes from the measurements without change. Hence, the method requires three SAR images associated with three measurements, with no changes between two of them. The reference data for the study are provided by CARABAS. The experimental results indicate that the method can reduce false alarms significantly and provide high probability of detection (≥98%). The experimental results also show that the method still works well even in the case where the flight tracks of the SAR system in the change detection measurements are slightly different.

Shielding Effectiveness of Modern Energy-Saving Glasses and Windows

Abstract: Thin metal coatings on glass are widely used in modern windows to improve their thermal properties. However, while there are some available papers on the properties of microwave propagation through commercial metallized windows glass below 6 GHz there seems to be a lack of papers regarding metallized multiglazed windows at higher frequencies. Such data are of the great importance when designing modern microwave communication systems working in urban environments. In this paper, the shielding effectiveness (SE) of modern energy-saving glasses and windows were investigated at microwave frequencies from 1 to 20 GHz. Wide measurement range together with proposed fast calculation procedure based on the matrix multiplication method, allowed us to elucidate the reasons responsible for the extremes in dependencies of SE on frequency. It was also shown that by comparing measured and calculated results, the conductivity of the thin metallic layer used in modern energy-saving windows can be determined. During the study, we found that attenuation of microwave radiation passing through modern windows can be as high as 60 dB.

Early Insights on FMI-based Co-Simulation of Aircraft Vehicle Systems

Abstract: Modelling and Simulation is extensively used for aircraft vehicle system development at Saab Aeronautics in Linkoping, Sweden. There is an increased desire to simulate interacting sub-systems toget ...

Fully polarimetrie wideband RCS measurements for small drones

Abstract: Localization and identification of small unmanned aircraft systems become more and more of interest In this context radar cross sections for such objects have been investigated by extensive measurements utilizing a fully polarimetric, bi-static wideband mm-wave radar system The influence of the shapes and orientations of the drones, and of the bi-static angles of the measurement system setup are compared and discussed

Command Governor Approach to Maneuver Limiting in Fighter Aircraft

Abstract: Modern fighter aircraft require maximum control performance in order to have the upper hand in a dogfight or when they have to outmaneuver an enemy missile. Therefore pilots must be able to maneuver the aircraft very close to the limit of what it is capable of while at the same time focus on the tactical tasks of the mission. To enable this, modern flight control systems have automatic systems for angle of attack and load factor limiting. These types of systems can utilize predictions of the aircraft response to pilot inputs and alter the properties of the closed loop system to minimize the predicted overshoot. Two such design techniques are model predictive control and reference and command governors. Model predictive controllers are most often used as inner loop feedback controllers which alter the control signal as function of the predicted output while reference and command governors are applied in an outer feedback loop around a nominal controller. There can be several benefits from using reference and command governors compared to model predictive controllers. First, the governors can be used as add-ons to existing legacy controllers so there is no need to redo the complete design. Furthermore the nominal inner loop controller can be tuned to achieve good performance in the nominal case, e.g., use nonlinear feedbacks to linearize the closed loop system, and the governor focus on the maneuver limiting task. It also gives a good modularity such that one can replace parts of the control system without the need to redo all of the design. Last but not least from a flight safety perspective it might be easier to certify optimization algorithms running in an outer loop which can be turned off in case of failures without affecting stability. While model predictive controllers have been extensively investigated for flight control applications [1–28] most of them consider reconfigurable flight control systems and only few focus on envelope protection and maneuver limiting [7, 13, 17, 21]. Even though reference governors have been subject to research for quite some time very little research has been performed on applying reference and command governors to flight control design and maneuver limiting [23, 29–33]. Most of these papers consider simplified conditions with only a single linear or nonlinear system and no complex simulation environments. In the papers by Petersen et al. [23] and Zinnecker et al. [29] the authors apply reference governors to the control of hypersonic vehicle. In the paper by Zinnecker the focus is mainly on input constraints. Kolmanovsky and Kahveci [30] uses a reference governor to handle control actuator limitations of a UAV glider and compare this to an adaptive anti-windup scheme and in the paper by Martino [31] the author investigates command governors for handling amplitude and rate constraints on a small commercial aircraft. The authors, Ye et al. [32], investigate reference governors for maneuver limiting in high angle of attack maneuvers. They investigate and compare static and dynamic reference governors with a reference governor structure based on a step response

Two imaging systems for positioning and navigation

Abstract: We present two approaches for using imaging sensors on-board small unmanned aerial systems (UAS) for positioning and navigation. Two types of sensors are used; laser scanners and a camera operating in the visual wavelengths. The laser scanners produce sparse 3D data that are registered to produce a local map. For the images from the video camera the optical flow and height estimates are fused and then matched with a geo-referenced aerial image. Both approaches include data from the inertial navigation system. The approaches can be used for accurate ego-positioning, and thus for navigation. The approaches are GPS independent and can work in GPS denied conditions, for example urban canyons, indoor environments, forest areas or while jammed. Applications are primarily within societal security and military defense.

Development of a Multidisciplinary Design Optimization Framework Applied on UAV Design by Considering Models for Mission, Surveillance, and Stealth Performance

Abstract: This paper presents a Multidisciplinary Design Optimization (MDO) framework that is intended to be employed in the early design stages of Unmanned Aerial Vehicles (UAVs) when the primary focus is o ...

Angle of Attack and Load Factor Limiting in Fighter Aircraft using Command Governors

Abstract: Modern fighter aircraft require maximum control performance in order to have the upper hand in a dogfight or when they have to outmaneuver an enemy missile. Therefore pilots must be able to maneuve ...

Wavelength-resolution SAR change detection with constant false alarm rate

Abstract: The paper introduces an incoherent change detection algorithm with constant false alarm rate (CFAR). The algorithm is based on a CFAR detector that preceded with an adaptive noise smoothing filter while the input of the filter is preliminary changes retrieved from a subtraction of surveillance SAR image to reference SAR image. The algorithm is tested with 24 data sets provided by CARABAS. The average probability of detection calculated for 1200 deployed vehicles is up to 96% while the false alarm rate calculated for an area of 288 square kilometers is only 0.15 per square kilometer. In our test, the algorithm did not require a longer processing time than other wavelength-resolution SAR change detection algorithms. Based on these evaluations, the introduced algorithm is seen to be effective.

Residual Stresses in Dengeling-Treated Aluminum Alloy AA 7050

Abstract: Dengeling is a new method for mechanical surface treatment of metallic parts to enhance fatigue properties. The treatment produces consecutive lines of indents by a spherical indenter, resulting in ...

Modeling of LTE DRX in RRC Idle state

Abstract: In LTE/LTE-A the Discontinuous Reception (DRX) mechanism is the main approach for power saving in User Equipments (UEs) when in Connected and Idle mode. In this paper, an Idle mode DRX mechanism model is proposed also enabling evaluation of closely related mechanisms such as paging and Tracking Area Update (TAU). Two performance metrics are derived, namely the reachability delay and the power saving factor.

Incoherent detection of man-made objects obscured by foliage in forest area

Abstract: The paper introduces a new likelihood ratio test (LRT) for incoherent detection of man-made objects obscured by foliage in forest area. The test is performed to detect changes between a reference image and a surveillance image. The method is developed for change detection in high resolution Synthetic Aperture Radar (SAR). For simplicity and lack of more appropriate models, the new LRT is still based on simple and efficient models. If there is no man-made object, the statistical model for clutter and noise of two images will be a bivariate Rayleigh distribution. In contrary, a joint distribution of Rayleigh and uniform is used to model for target, clutter, and noise. The proposed LRT is evaluated using radar data acquired by CARABAS in northern Sweden. The probability of detection is up to 96% with much less than one false alarm per square kilometer.

SAR processing without a motion measurement system

Abstract: This paper leads a discussion on how to form a SAR image without knowing the track. That is within the scope of Factorized Geometrical Autofocus (FGA). The FGA algorithm is a base-2 fast factorized back-projection formulation with six free geometry parameters (per sub-aperture pair). These are tuned step-by-step until a sharp image is obtained. This innovative autofocus technique can compensate completely for an erroneous geometry. The FGA algorithm has been applied successfully on two UWB data sets, acquired by the CARABAS II system at VHF-band. The tracks are known (measured accurately). We however adopt and modify a basic geometry model. A linear equidistant track at fixed altitude is initially assumed. Apart from deviations due to linearization, a ∼2.5 m/s along-track velocity error is also introduced. Resulting FGA images are compared to reference images and verified to be focused. This indicates that it is feasible to form a SAR image without support from a motion measurement system.

Simplifying BRDF input data for optical signature modeling

Abstract: Scene simulations of optical signature properties using signature codes normally requires input of various parameterized measurement data of surfaces and coatings in order to achieve realistic scene object features. Some of the most important parameters are used in the model of the Bidirectional Reflectance Distribution Function (BRDF) and are normally determined by surface reflectance and scattering measurements. Reflectance measurements of the spectral Directional Hemispherical Reflectance (DHR) at various incident angles can normally be performed in most spectroscopy labs, while measuring the BRDF is more complicated or may not be available at all in many optical labs. We will present a method in order to achieve the necessary BRDF data directly from DHR measurements for modeling software using the Sandford-Robertson BRDF model. The accuracy of the method is tested by modeling a test surface by comparing results from using estimated and measured BRDF data as input to the model. These results show that using this method gives no significant loss in modeling accuracy.

Isotropic transmission cross section of loaded and unloaded apertures

Abstract: The isotropic transmission cross sections of loaded and unloaded apertures have been studied. Results from numerical calculations as well as measurements are presented for three different load configurations, consisting of an absorber frame surrounding the aperture on either both or only one side. Presented results shows that, with a carefully designed absorber frame, the total transmitted power can be reduced substantially using only a small amount of lossy material. Furthermore, it is shown that identical results are obtained whether the absorber frame is placed on the side illuminated by the isotropic source or on the opposing side. Simulation and measurements results are generally in good agreement.

A novel method to increase the accuracy of material characterization using free space transmission measurements

Abstract: This paper describes a method to accurately determine the electromagnetic material properties of thin dielectric sheets. For non-magnetic materials, free space transmission measurements relative to an empty setup are sufficient to determine the complex permittivity of the sheet material. Measurements have been performed on a thin resistive sheet and a transformation procedure has been applied where the edge distortion at the lower frequency band is reduced. This is accomplished by shifting the band limited frequency spectrum down to DC before applying an inverse Fourier for gating purpose. The procedure yields accurate material characterization over the entire measured frequency band.

Data-Driven Pilot Behavior Modeling Applied to an Aircraft Offset Landing Task

Abstract: This paper shows studies for the development of a mathematical model that adequately represents a pilot behavior in the specific task of offset landing, using data-driven modeling techniques. Flight test data was used for the identification procedure. Considerations on the pilot’s cognitive process and mathematical modeling possibilities were discussed to select the most appropriate inputs and outputs for the model. This data was used to identify the model using artificial neural network techniques. The models obtained were validated against the identification data and different data not used in the training process to evaluate the quality of the models. Conclusions include the difficulties of showing the generalization capabilities of those non-linear models and further studies.

Adaptive Interaction Criteria for Future Remotely Piloted Aircraft

Abstract: There are technical trends and operational needs within the aviation domain towards adaptive behavior. This study focus on adaptive interaction criteria for future remotely piloted aircraft. Criteria that could be used to guide and evaluate design as well as to create a model for adaptive interaction used by autonomous functions and decision support. A scenario and guidelines from the literature, used as example criteria, was presented in a questionnaire to participants from academia/researchers, end users, and aircraft development engineers. Several guidelines had a wide acceptance among the participants, but there was also aspects missing for the application of supporting adaptive interaction for remotely piloted aircraft. The various groups of participants contributed by different aspects supports the idea of having various stakeholders contributing with complementary views. Aspects that the participants found missing includes, predictability, aviation domain specifics, risk analysis, complexity and how people perceive autonomy and attribute intentions.

Advances in SAR-ISAR blending

Abstract: Radar signature measurements of targets with or without camouflage in different backgrounds using airborne SAR are complex and expensive. Measurements at many orientations as well as illumination angles have to be performed for each target for completeness. A more efficient solution is to use ground based ISAR measurements of the desired targets and then blend these images into measured SAR scenes. A SAR-ISAR blending method where the target and background are modelled by point scatterer representations is described in this paper. The point scatterer representations for the target and the SAR background are determined by solving two separate inverse problems using l 1 and l 2 -minimization methods. The model for the target measured by ISAR is naturally sparse in the image domain and is therefore solved using an l 1 -minimization method while the model for the SAR background image that is not sparse is solved using an l 2 -minimization method. The proposed method is demonstrated and it is determined that it provides an efficient way of evaluating measured ISAR target signatures in measured SAR backgrounds.

Engine Failure Induced Task Load Transient for Simulation Based Certification Aiding for Aircraft

Abstract: This study is one of a series of studies, researching various aspects that all aim at enhanced simulation based certification aiding for aircraft. An experimental within-group design study was performed with 10 participants (5 male, and 5 female). The results showed a significant difference, F(2,16) = 5.11, p = 0.019, in mental workload between an engine failure condition and an normal condition for eye blink frequency. No effect of speed at the engine failure event on mental workload was found.