Showing papers by "Norman S. Kopeika published in 2001"

Atmospheric turbulence modulation transfer function for infrared target acquisition modeling

Abstract: A new direction for the US Army Night Vision and Electronic Sensors Directorate is the development of ultra-narrow field of view (UNFOV) infrared target acquisition (TA) systems. Frequently, the per- formance of these systems is limited by atmospheric turbulence in the imaging path. It is desirable to include the effects of atmospheric turbu- lence blur in infrared TA models. The current TA models are currently linear shift invariant (LSI) systems with component modulation transfer functions (MTFs). The use of additional MTFs, to account for atmo- spheric turbulence, requires that the turbulence blur have LSI properties. The primary unresolved issue with the treatment of turbulence blur as an MTF is the LSI characteristics of the blur. Significant variation in spatial blur and temporal blur prohibit the use of a single MTF in an LSI target acquisition model. Researchers at Ben-Gurion University (BGU) use a TA model that includes an LSI blur, which is a temporal average of the turbulence blur. The research described here evaluates the BGU-type treatment of atmospheric MTF and determines it reasonable for inclusion in the US Army's TA model. In addition to the spatial characteristics, the temporal variation of the turbulence blur is also described. © 2001 Society

Laser beam widening as a function of elevation in the atmosphere for horizontal propagation

Abstract: A new lidar system for measuring near simultaneously aerosol extinction, size distribution and turbulence profiles up to 20 km altitude has been developed. On the basis of measurements and a Monte Carlo beam propagation model, the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path at various elevations is estimated and compared with beam widening caused by turbulence.

Acquisition time calculation and influence of vibrations for microsatellite laser communication in space

Abstract: The first step in creating an optical link between two LEO satellites is acquisition. In this process one of the satellites finds the maximal power of a received beam and locks on to it. This starts the tracking. In this paper we examine the time needed to finish the acquisition process and start tracking. The parameters included are the distribution function of satellite position, the size of the uncertainty area, the number of possible satellite positions, and the detection ability of a CCD. A model for the distribution function of position is given for two types of distribution: Gaussian and Uniform. Also considered the vibrations that come from internal systems of satellite, and from external sources. The characteristics of vibrations are considered and their influence on the scanning pattern that can deviate from the original path. A method of filtering the vibrations and compensating for them is suggested. The pointing system must be updated continuously from the star tracker with internal calculations of position, speed, velocity and vibrations characteristics. Examined also are several scanning methods: raster, spiral, Lissajo, Rose. Each method has its own possibilities and advantages, which are compared.

Vibration noise control in laser satellite communication

Abstract: Laser satellite communication has become especially attractive in recent years. Because the laser beam width is narrow than in the RF or microwave range, the transmitted optical power may be significantly reduced. This leads to development of miniature communication systems with extremely low power consumption. On the other hand, the laser communication channel is very sensitive to vibrations of the optical platform. These vibrations cause angular noise in laser beam pointing, comparable to the laser beam width. As result, as significant portion of the optical power between transmitter and receiver is lost and the bit error rate is increased. Consequently, vibration noise control is a critical problem in laser satellite communication. The direction of the laser beam is corrected with a fast steering mirror (FSM). In this paper are presented two approaches for the FSM control. One is the feedback control that uses an LQG algorithm. The second is the direct feed- forward control when vibration noise is measured by three orthogonal accelerometers and drives directly the F SM. The performances of each approach are evaluated using MATLAB simulations.

Enhanced-resolution image restoration from a sequence of low-frequency vibrated images by use of convex projections

Abstract: An algorithm to increase the spatial resolution of digital video sequences captured with a camera that is subject to mechanical vibration is developed. The blur caused by vibration of the camera is often the primary cause for image degradation. We address the degradation caused by low-frequency vibrations (vibrations for which the exposure time is less than the vibration period). The blur caused by low-frequency vibrations differs from other types by having a random shape and displacement. The different displacement of each frame makes the approach used in superresolution (SR) algorithms suitable for resolution enhancement. However, SR algorithms that were developed for general types of blur should be adapted to the specific characteristics of low-frequency vibration blur. We use the method of projection onto convex sets together with a motion estimation method specially adapted to low-frequency vibration blur characteristics. We also show that the random blur characterizing low-frequency vibration requires selection of the frames prior to processing. The restoration performance as well as the frame selection criteria is dependent mainly on the motion estimation precision.

Measured profiles of aerosols and turbulence for elevations of 2 to 20 km and consequences of widening of laser beams

Abstract: A new lidar system for measuring simultaneously aerosol extinction, size distribution and turbulence profiles up to 20 km altitude has been developed. On the basis of measurements and a Monte Carlo beam propagation model, the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path at various elevations is estimated and compared with beam widening caused by turbulence.

Effects of image restoration on target acquisition

Abstract: In our work, we will focus on the atmospheric effects on the acquisition of a target and on image restoration by filtering the atmospheric effects such as: blur caused by absorption and scattering from aerosols and distortion caused by turbulence that changes the wave front angle, moves the image on the image plane, and blurs it. The restoration method using an atmospheric wiener filter is intended to correct the atmospheric effects. This filter is based on the fact that the modulation transmission function (MTF) of the turbulence is composed of a mean value and a random component while the aerosol MTF changes slowly. The project goal is the realization of the atmospheric wiener filter, finding the limitations (in terms of blur to noise ratio) of the filter through psycho-physical experiments and statistical analysis of the results. We found that the atmospheric wiener filter can improve target acquisition probability at low noise levels. As the noise increases the improvement becomes more limited because the restoration increases the noise level in the image.

Stabilization, restoration, and resolution enhancement of a video sequence captured by a moving and vibrating platform

Abstract: Image sequences recorded from moving platforms are often distorted by undesired motion. The image motion within a video sequence captured from a moving platform is compounded in general from a smooth component such as camera panning and a high frequency component such as mechanical vibration or shocks. The undesired high frequency component of the motion may affect severely the perception of the image sequence content. This motion component causes two types of distortion. The first is the unexpected scene change caused by motion and vibration of the line-of-sight from frame to frame. The second effect is blur of each frame of the sequence due to frame motion during its exposure. In this work we propose an algorithm that eliminates the undesired component of the motion and increases the spatial resolution of each frame in the image sequence. The resolution is increased by deblurring the images and by utilizing information within adjacent frames with superresoluion restoration techniques.

Medical Image Restoration of Dynamic Lungs using Optical Transfer Function of Lung Motion

Abstract: When carrying out medical imaging based on detection of isotopic radiation levels of internal organs such a lungs or heart, distortions, and blur arise as a result of the organ motion during breathing and blood supply. Consequently, image quality declines, despite the use of expensive high resolution devices and, such devices are not exploited fully. A method with which to overcome the problem is image restoration. Previously, we suggested and developed a method for calculating numerically the optical transfer function (OTF) for any type of image motion. The purpose of this research is restoration of original isotope images (of the lungs) by restoration methods that depend on the OTF of the real time relative motion between the object and the imaging system. This research uses different algorithms for the restoration of an image, according to the OTF of the lung motion, which is in several directions simultaneously. One way of handling the three-dimensional movement is to decompose the image into several portions, to restore each portion according to its motion characteristics, and then to combine all the image portions back into a single image. An additional complication is that the image was recorded at different angles. The application of this research is in medical systems requiring high resolution imaging. The main advantage of this approach is its low cost versus conventional approaches.

Influence of severe vibrations on the visual perception of video sequences

Abstract: There are two kinds of video image sequence distortions caused by vibration of the camera. The first is the vibration of the line- of-sight, causing location changes of the scene in successive frames. The second distortion is the blur of each frame of the sequence due to frame motion during its exposure. The relative effects of these two types of degradations on the ability of observers to recognize targets are in- vestigated. This study is useful for evaluating the amount of effort re- quired to compensate each effect. We found that the threshold contrast needed to recognize a target in a vibrating video sequence under certain conditions is more affected by the motion blur of each frame than the oscillation of the line-of-sight. For digital sequence restoration methods, this study determines the required precision of the deblurring and regis- tration processes. It shows that the deblurring process should not be neglected, as it often is. © 2001 Society of Photo-Optical Instrumentation Engineers.

Landsat TM satellite image restoration using Kalman filter

Abstract: Satellites orbit the Earth and obtain continuous imagery of the ground below along their orbital path. The quality of satellite images propagating through the atmosphere is affected by phenomena such as scattering and absorption of light, and turbulence, which degrade the image by blurring it and reducing its contrast. The atmospheric Wiener filter, which corrects for turbulence blur, aerosol blur, and path radiance simultaneously, is implemented in digital restoration of Landsat TM (Thematic Mapper) imagery. Digital restoration results of Landsat TM imagery using the atmospheric Wiener filter were presented in the past. Here, a new approach for digital restoration of Landsat TM is presented by implementing a Kalman filter as an atmospheric filter, which corrects for turbulence blur, aerosol blur, and path radiance simultaneously. Turbulence MTF is calculated from meteorological data or estimated if no meteorological data were measured. Aerosol MTF is consistent with optical depth. The product of the two yields atmospheric MTF, which is implemented in both the atmospheric Wiener and Kalman filters. Restoration improves both smallness of size of resolvable detail and contrast. Restorations are quite apparent even under clear weather conditions. Here, restorations results of the atmospheric Kalman filter are presented along with those for the atmospheric Wiener filter. A way to determine which is the best restoration result and how good is the restored image is presented by a visual comparison and by considering several mathematical criteria. In general the Kalman restoration is superior, and inclusion of turbulence blur also leads to slightly improved restoration.

Influence of motion sensor error on image restoration from vibrations and motion

Abstract: In this paper we investigate the influence of motion sensor errors on the derivation of the MTF and its implementation in image restoration. We present an analytical approach for estimating the vibration MTF from the measured system MTF by the frequency response of the sensor and their noise data. The goal of this research is to describe an automatic system of restoration of pictures blurred by vibration, and to consider its possible disadvantages. Our method is based on point-spread function verification by the data of motion sensor characteristics. We build an analytical model of the sensor and compare the MTF after sensor errors caused by noise of the system and wrong axis direction of the restoration device. Here, we assume that noise and signal are independent and noise of the system is white Gaussian noise. Some image restoration of degraded images is presented based on improvements of the original wiener filter. We compare performance of inverse and wiener filter operations and consider the dependence of restoration quality on the signal to noise ratio and angel between restoration axis and true vibration direction. There is an interesting and useful relationship in the final graphs. This article brings us to improvement of the initial method, as seen from our simulation. Some restorations of degraded images are presented based on improvements of the original wiener filter. The key to the restoration is determination of the improved optical transfer function unique to the image vibration and sensor characteristics.

Mixed-Signal Architecture for Real-Time Two-Dimensional Live TV Image Restoration

Abstract: This paper describes novel electronic architecture for a real-time image restoration of live TV signals at live TV frame rates with a latency of two frames. The spatial filtering is obtained from two electronic analog filters, one for the raster lines and one for the columns. The very fast response of analog filters makes possible truly real-time video frame rate performance. The digital part of the system serves the purpose of pipelined parallel data conversion and flow, rather than that of image processing (filtering). This architecture exhibits some very important advantages. It does not need any computational source, it is very fast, and it is quite inexpensive. In addition, such a “parallel analog computer” can be easily incorporated into any complex system with video signal data as a simple “plug-in” between the camera and monitor. An important aspect is that the system carries low digitalization noise, thus yielding good SNR characteristics. The system can perform any kind of separable spatial frequency filtering and can be electronically tuned to obtain exact performance parameters. Because of these advantages, this architecture is promising for a variety of systems such as supermarket multicamera security, military and aerospace vision systems, and medical diagnostics.

Effect of sampling on target detection

Abstract: Target acquisition is important especially in the military sector, with the evolution of automated systems for target acquisition there is an enormous importance to digital target detection models. Johnson's criterion is based on research with large numbers of observers. The model divides resolution into 4 stages: Detection, Orientation, Recognition and Identification. These stages are separate from one another and involve different levels of resolution. Moving from one stage to a higher stage is by increasing resolution (the number of line pairs is increased). The Johnson model was based on analog images, which are not sampled. An Image converter was the sensor in his experiments. We examined whether Johnson's criteria comply with sampled images as well as with analog ones, or if they should be changed when sampled images are used. Perception experiments with 120 observers were used to check our assumptions and the results were summarized.