Electro-optical Imaging Systems Research Articles

Q Selection for an electro-optical earth imaging system: theoretical and experimental results

This paper explores practical design considerations for selecting Q for an electro-optical earth imaging system, where Q is defined as (λ FN) / pixel pitch. Analytical methods are used to show that, under imaging conditions with high SNR, increasing Q with fixed aperture cannot lead to degradation of image quality regardless of the angular smear rate of the system. The potential for degradation of image quality under low SNR is bounded by an increase of the detector noise scaling as Q. An imaging test bed is used to collect representative imagery for various Q configurations. The test bed includes real world errors such as image smear and haze. The value of Q is varied by changing the focal length of the imaging system. Imagery is presented over a broad range of parameters.

Hidden Markov Models for background clutter

The development of a target acquisition performance model for an electro-optical imaging system is seriously affected by the description of the target and background characteristics at present. Based on the Hidden Markov Model (HMM), a different clutter metric is proposed to quantify the influence of background on target detection in this article. It first simulates the process of recording a target in the human brain by optimizing the HMM parameters to represent the target as far as possible. And then the background clutter is defined to be the similarity, estimated by the computed model parameters, between the target and background. Finally, the newly proposed clutter metric is applied to the Search2 database, and the experiment results prove its superiority to other metrics.

Validation of atmospheric propagation models in littoral waters

Various atmospheric propagation effects are limiting the long-range performance of electro-optical imaging systems. These effects include absorption and scattering by molecules and aerosols, refraction due to vertical temperature gradients and scintillation and blurring due to turbulence. In maritime and coastal areas, ranges up to 25 km are relevant for detection and classification tasks on small targets (missiles, pirates). From November 2009 to October 2010 a measurement campaign was set-up over a range of more than 15 km in the False Bay in South Africa, where all of the propagation effects could be investigated quantitatively. The results have been used to provide statistical information on basic parameters as visibility, air-sea temperature difference, absolute humidity and wind speed. In addition various propagation models on aerosol particle size distribution, temperature profile, blur and scintillation under strong turbulence conditions could be validated. Examples of collected data and associated results are presented in this paper.

Dynamic Electrowetting and Dewetting of Ionic Liquids at a Hydrophobic Solid–Liquid Interface

The dynamic electrowetting and dewetting of ionic liquids are investigated with high-speed video microscopy. Five imidazolium-based ionic liquids ([BMIM]BF(4), [BMIM]PF(6), [BMIM]NTf(2), [HMIM]NTf(2), and [OMIM]BF(4)) are used as probe liquids. Droplets of ionic liquids are first spread on an insulated electrode by applying an external voltage (electrowetting) and then allowed to retract (dewetting) when the voltage is switched off. The base area of the droplet varies exponentially during both the electrowetting and retraction processes. The characteristic time increases with the viscosity of the ionic liquid. The electrowetting and retraction kinetics (dynamic contact angle vs contact line speed) can be described by the hydrodynamic or the molecular-kinetic model. Energy dissipation occurs by viscous and molecular routes with a larger proportion of energy dissipated at the three-phase contact line when the liquid meniscus retracts from the solid surface. The outcomes from this research have implications for the design and control of electro-optical imaging systems, microfluidics, and fuel cells.

Impacts of underwater turbulence on acoustical and optical signals and their linkage

Acoustical and optical signal transmission underwater is of vital interest for both civilian and military applications. The range and signal to noise during the transmission, as a function of system and water optical properties, in terms of absorption and scattering, determines the effectiveness of deployed electro-optical (EO) technology. The impacts from turbulence have been demonstrated to affect system performance comparable to those from particles by recent studies. This paper examines the impacts from underwater turbulence on both acoustic scattering and EO imaging degradation, and establishes a framework that can be used to correlate these. It is hypothesized here that underwater turbulence would influence the acoustic scattering cross section and the optical turbulence intensity coefficient in a similar manner. Data from a recent field campaign, Skaneateles Optical Turbulence Exercise (SOTEX, July, 2010) is used to examine the above relationship. Results presented here show strong correlation between the acoustic scattering cross-sections and the intensity coefficient related to the modulation transfer function of an EO imaging system. This significant finding will pave ways to utilize long range acoustical returns to predict EO system performance.

Sparse-representation-based clutter metric

Background clutter is becoming one of the most important factors affecting the target acquisition performance of electro-optical imaging systems. A novel clutter metric based on sparse representation is proposed in this paper. Based on sparse representation, the similarity vector is defined to describe the similarity between the background and the target in the feature domain, which is a typical feature of the background clutter. This newly proposed metric is applied to the Search_2 data set, and the experiment results show that its prediction correlates well with the detection probability of observers.

A brief history of principles used in high speed cameras

High-speed imaging records valuable information of events that occur in microscopic timescales and provides an insight into fast changing phenomena that eludes visual understanding. Over the past hundred and fifty years cameras have evolved from very basic devices to present day complex electro optical imaging systems that require computers programmed with innovative software to manage the multitude of operational parameters. This evolutionary process has passed through numerous stages advancing alongside other technologies as they have become available. However, two overriding factors have been influential in camera development; the first being the need to generate sufficiently bright images that can be recorded in microscopic timescales, and the need to synchronize the framing window to allow the critical dissection of the area of interest. Unless these fundamental requirements are satisfied other parameters such as resolution and image numbers become less relevant. The extraction of temporally related data was difficult and time consuming particularly if multiple cameras were used which introduced parallax errors. However, the continued development of solid state imaging sensors has provided flexibility for integration into imaging systems that record image sequences which can be critically interrogated providing a detailed account of events that occur in microscopic timescales.

Numerical simulation of the incoherent electro-optical imaging process in plane-stratified media

A high-fidelity numerical model is developed for the incoherent electro-optical imaging process in media where the inherent optical properties vary with range. Four contributions to the image data are considered: laser light reflected from the scene, volume backscatter of laser light, reflected solar light, and solar backscatter. The model implements rigorous mathematical formulations, incorporates adaptive error control, uses computationally efficient algorithms, and has been rigorously validated. The model is flexible enough to handle many different sensor configurations and sampling techniques, continuous-wave and pulsed laser sources, and range-dependent properties of the optical environment. The derivation of relevant mathematical models is reviewed and unified into a comprehensive and flexible system that can be tailored to fit the various incoherent electro-optical imaging systems currently in use or in development. The numerical implementations are described for each key component of the overall model, and a sampling of new verification and validation results is provided.

High signal-to-noise-ratio electro-optical terahertz imaging system based on an optical demodulating detector array

We present a 64x48 pixel 2D electro-optical terahertz (THz) imaging system using a photonic mixing device time-of-flight camera as an optical demodulating detector array. The combination of electro-optic detection with a time-of-flight camera increases sensitivity drastically, enabling the use of a nonamplified laser source for high-resolution real-time THz electro-optic imaging.

Analysis of point-target detection performance based on ATF and TSF

In many real applications such as remote sensing and space surveillance, traditional method based on ideal imaging has already been well-established. It is widely applied to analyze point-target detection performance of electro-optical imaging system, including signal-to-noise ratio (SNR) and noise equivalent temperature difference (NETD). However, this method cannot accurately predict these performance parameters, as it fails to take into account the influence of optical blurring caused by atmospheric turbulence, optics diffraction, optical aberrations, etc. In this sense, the methods, if proposed to thoroughly incorporate degrading factors into object acquisition model, would succeed to describe point-target detection performance to more degree of accuracy. The main focus of this article is to quantitatively analyze the influence of optical blurs upon point-target detection, and to establish close relationship between optical blurring and metrics of point-target acquisition. This point can be interpreted and achieved mathematically: the mathematical analysis based on image acquisition model is to combine Aperiodic Transfer Function (ATF) and Target Size Function (TSF) with analysis of SNR and NETD. In addition, the concept of NETD, traditionally used to describe extended object detection, is generalized and equivalently applied to analyze point-target detection. This refined method can be directly and conveniently used for faithfully predicting detection performance, and provides a more reliable benchmark for improving measurement setup, if we properly estimate the degree of image distortion.

Near infrared tomographic system based on high angular resolution mechanism – Design, calibration, and performance

This study aims at the design, implementation, and verification of a near infrared (NIR) diffuse optical tomography (DOT) electro-optical imaging system based on a measuring instrument with single rotating source/detector scanning mechanism and an image reconstruction scheme implemented on an off-line PC. The developed measurement instrument possesses a high degree of angular resolution and is operated in a continuous-intensity scheme to acquire output NIR intensity signals. In this paper, some considerations of this measuring instrument are investigated such as phantom preparation, temporal stability, and container influence, etc. Experimental trials were conducted using both homogeneous and heterogeneous phantoms made of high-scattering microspheres or Intralipid. In order to verify the developed imaging system with tomographic image reconstruction, the intensity was acquired from the heterogeneous Intralipid phantom using NIR light at 800 nm, where the homogenous background as the normal tissue is inserted with an inclusion as the tumor. For the comparison of heterogeneous phantoms with homogeneous phantoms, 1-D measured intensity signals indicate the angular position of the inclusion, especially for the case of the inclusion near the phantom boundary. Furthermore, promising results of corresponding optical-property images can be reconstructed with the measured intensities as inputs of the image reconstruction scheme. Obviously, the developed NIR DOT tomographic system has been successfully built upon the experimental, analytical, and computational work.

Theoretical foundations for joint digital-optical analysis of electro-optical imaging systems

We describe the mathematical and conceptual foundations for a novel methodology for jointly optimizing the design and analysis of the optics, detector, and digital image processing for imaging systems. Our methodology is based on the end-to-end merit function of predicted average pixel sum-squared error to find the optical and image processing parameters that minimize this merit function. Our approach offers several advantages over the traditional principles of optical design, such as improved imaging performance, expanded operating capabilities, and improved as-built performance.

Joint digital-optical design of superresolution multiframe imaging systems

Typical electro-optic imaging systems produce image aliasing artifacts. Superresolution algorithms process multiple aliased images to yield a single high-resolution image. We design imaging systems by jointly optimizing the optics and postprocessing to maximize such multiframe imaging performance. We describe efficient software methods that can be used to perform joint design by use of commercially available lens design software.

Maximum <italic>a priori</italic> estimation of focus aberration in imaging systems

A maximum a priori (MAP) estimation technique for the detection of focus aberrations in electro-optical imaging systems is developed. The technique simplifies the equipment required in focus aberration detection over previous methodologies. The magnitude of the focus aberration is estimated from a single image. The MAP estimation technique uses a Poisson distribution of the photons arriving at the detector from the object. A Gaussian distribution is added to the statistical model to account for the focus aberration. Using the imaging system statistical model and real laboratory images from a charge-coupled device (CCD) camera, the focus aberration detection (FAD) algorithm produces estimates of the focus aberrations. The results demonstrate a viable approach for estimation and potential removal of focus aberrations in electro-optical systems, without the need to divert any light from the primary channel, or for additional complicated equipment and associated calibration requirements.

Use of Continuous Zoom on Electro-Optical Imaging Systems: Comparisons between Automatic and Manual Target Tracking

The use of continuous zoom in an electro-optical sensor system was investigated with respect to target tracking. Using a simulation of an operator-machine interface in an airborne multi-sensor surveillance system, targets were tracked by manually directing the sensor or by an automated tracker. It was hypothesized that frequency of using the continuous zoom would be higher in the manual tracking mode than in auto-tracking, and negatively correlated with tracking error. Sensor, and targets to be tracked, were either moving or stationary in three types of tracking scenarios. Results showed that the zoom function was used more often when tracking manually, although the way continuous zoom was used differed between the two tracking modes. Also, tracking error was lower when the zoom function was used in manual mode. Tracking error was additionally affected by whether or not the target and/or the sensor were moving or stationary. Results improve our understanding of the way complex sensor systems are used, and will assist in ascertaining whether providing a continuous zoom into optical imaging systems is of benefit to operators.

Probability of identification cycle criterion <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mo>(</mo><msub><mi>N</mi><mn>50</mn></msub><mo>∕</mo><msub><mi>N</mi><mn>90</mn></msub><mo>)</mo></mrow></math></inline-formula> for underwater mine target acquisition

This research describes the derivation of a 50% probability of identification cycle criterion (N50) for a set of underwater mines. Various levels of blur were applied to eight underwater mines and four nonmine objects with nine aspects in the visible spectra. Results were analyzed as a function of blur level and target size to give identification probability as a function of resolvable cycles on target. The results are applicable to underwater mine target acquisition estimates for visible electro-optical imaging systems and for laser-illuminated, range-gated imaging systems. This research provides for the design and analysis of electro-optical systems in the identification of underwater mines.

Super-resolution technique of microzooming in electro-optical imaging systems

Super-resolution technique of microzooming in electro-optical imaging systems

Super-resolution technique of microzooming in electro-optical imaging systems

The main resolution limit for an electro-optical imaging system comprising a focal plane array (FPA) sensor obeys Nyquist theorem which states that an object must be sampled at more than twice the cut-off frequency to avoid aliasing. A novel super-resolution technique, microzooming (MZ), is presented. MZ provides electro-optical imagery with an extended unaliased bandwidth using multiple aliased images at different optical magnifications. A number of simulation and experiment results demonstrate that MZ is a practical advance for reducing aliasing and enhancing resolution as well as helping to suppress white noise.

Tracking Uncertainty in Derived Height Data

This chapter discusses the tracking of uncertainty in height data derived from stereo imagery that has been obtained from an airborne electro-optical digital multi-spectral imaging system. The overall objective of the software described has been to prepare the data for input into Geographic Information Systems, and to provide the ground coordinates of the data with the greatest accuracy possible. This article has two objectives: to provide a brief overview of the digital imagery procedures used to process the raw imagery and ancillary inertial navigation system data to achieve photogrammetric adjustment, geometric correction, and terrain height extraction, and, second, to illustrate the results of processing a representative data set. One of the final products produced by the software processing systems is a mosaic of ortho-imagery, using the nadir views and the terrain height data generated from the stereo imagery.

Tracking Uncertainty in Derived Height Data

This chapter discusses the tracking of uncertainty in height data derived from stereo imagery that has been obtained from an airborne electro-optical digital multi-spectral imaging system. The overall objective of the software described has been to prepare the data for input into Geographic Information Systems, and to provide the ground coordinates of the data with the greatest accuracy possible. This article has two objectives: to provide a brief overview of the digital imagery procedures used to process the raw imagery and ancillary inertial navigation system data to achieve photogrammetric adjustment, geometric correction, and terrain height extraction, and, second, to illustrate the results of processing a representative data set. One of the final products produced by the software processing systems is a mosaic of ortho-imagery, using the nadir views and the terrain height data generated from the stereo imagery. The chapter discusses the methods and the procedures that are being developed at the Canada Centre for Remote Sensing for tracking or carrying the absolute and relative accuracies of the derived data products from the raw data through to the final products. The paper concludes with an example of some processed imagery and derived height data along with the confidence measure or uncertainty of the derived height.