Proceedings Volume 4714

Acquisition, Tracking, and Pointing XVI

Michael K. Masten, Larry A. Stockum
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Proceedings Volume 4714

Acquisition, Tracking, and Pointing XVI

Michael K. Masten, Larry A. Stockum
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 1 July 2002
Contents: 5 Sessions, 24 Papers, 0 Presentations
Conference: AeroSense 2002 2002
Volume Number: 4714

Table of Contents

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Table of Contents

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  • System-Level Applications
  • Stabilization and Control Applications
  • Signal Processing Applications
  • Imaging Trackers I
  • Imaging Trackers II
System-Level Applications
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FLIR/IRST of the European fighter aircraft
Manfred Scheuer
In a four national program European military aircraft companies are developing and producing the Eurofighter (Typhoon). An essential part of the weapon system is its infrared detection system. It consists of equipment, which includes FLIR and IR search and track capabilities (IRST), together in a compact housing. There are various possibilities for air-to-air and air-to-ground operations. The FLIR/IRST, in conjunction with a sensor data fusion process, considerably enhances the combat effectiveness of the Eurofighter. One imaging mode of the FLIR/IRST is optimised for landing approach and for visual navigation. The IR video image can be displayed on a head up display, on a multifunction head down display or on a helmet-mounted display. These modes support the pilot during ground taxiing, take off, flying, air-to-ground engagement, low level operation and landing approach. In the multiple target-tracking (MTT) mode targets within a large field of regard will automatically be extracted from the background and simultaneously be tracked. A further mode provides tracking of a single target at a high update rate. Additionally, there is a mode in which the sensor line of sight is steered by an external control, e.g. helmet pointing angles, with the purpose to gain lock to a target. The basic technical concept of the FLIR/IRST, an overview of the functionality and first test results will be presented.
Effect of carefree handling requirements on an air-launched seeker-guided weapon
Jason F. Ralph, Kenneth L. Edwards
This paper considers the effect of two operational constraints on the size of the release envelope for an air- launched seeker-guided weapon: a requirement for a specified terminal accuracy (as determined by the Circular Error Probable (CEP)) and the requirement for carefree handling (i.e., an insensitivity to release conditions within a specified range of delivery parameters). The system considered in the paper is an air-launched, unpowered weapon with an autonomous guidance capability, provided by an infrared seeker and an inertial navigation system. The weapon is modeled using a six degree-of-freedom ballistic simulation with a simulated infrared seeker and a set of simple target detection algorithms. The paper compares the effect of carefree handling requirements on the size of the weapon's release envelope for two standard delivery profiles (low-level toss delivery and medium-level delivery) and for different requirements on the terminal accuracy.
Aircraft tracking and logging for commercial airports
Lee Wren, David Dwyer, John Thornton, et al.
Airport congestion is becoming a major problem, with many airports stretched to capacity. Monitoring of airport traffic is becoming of increased importance as airport operators try to maximize their efficiency whilst maintaining a high safety standard. This paper describes a fully automatic electro-optic tracking system, designed to track aircraft whilst on, or near, the runway. The system uses a single camera and several surveyed landmarks to predict the 3D location of the aircraft. Two modes of operation are available: take off and landing, with aircraft statistics recorded for each. Aircraft are tracked until they are clear of the runway, either airborne or having turned off onto a taxiway. Statistics and video imagery are recorded for each aircraft movement, detailing the time interval between landings or take offs, the time taken to clear the runway as well as for landing aircraft, details of approach speed, glide slope, point of touch-down and which exit taxiway was used. This information can be analyzed to monitor efficiency and to highlight violations in any safety regulations.
Impact of tracking system knowledge on multisensor 3D triangulation
The three-dimensional (3D) location of objects can be determined using triangulation techniques with two or more passive, angles-only optical sensors. The present work describes how to determine necessary experimental parameters, such as camera resolution, pointing and location knowledge, and target pixel position estimation accuracy, in order to achieve a required 3D position accuracy. Two general types of accuracy requirements are examined, one in which absolute position of the object relative to an external coordinate system is required, and the second in which relative position of one object relative to a second object is required. While the basic approach can be applied to a wide variety of geometries and sensor-to-target ranges, the emphasis of this work is on outdoor applications involving long sensor-to-sensor baselines.
Acquisition, tracking, pointing, and line-of-sight control laboratory experiments for a space-based bifocal relay mirror
Michael G. Spencer, Brij N. Agrawal, Marcello Romano, et al.
Space based bifocal relay mirrors are potentially an enabling/enhancing piece of any architecture making use of long-range laser propagation. Inherent in the bifocal concept is dual line of sight control. This is especially challenging in this space-based application due to spacecraft attitude control issues. This paper presents a summary of the research into acquisition, tracking, pointing (ATP) and control technologies relevant to a bifocal relay mirror system as well as the development of a laboratory experimental test bed to integrate the advanced optics systems onto a Three-axis spacecraft simulator. The relay geometry includes a cooperative source and either a cooperative or non-cooperative target depending on the application. The described test bed is a joint effort with the Air Force Research Laboratory (optics) and the Naval Postgraduate School (spacecraft simulator).
Visual-servoing-based tracking for an UAV in a 3D simulation environment
In order to achieve autonomous behavior of UAVs in surveillance missions, it is of interest to embed a vision sensor as an integral part of the control loop. The major difficulty in this type of applications is the lack of realistic simulation environments. Those, if available, can avoid the obvious dangers and cost of extensive field experimentation with visual servoing controllers for airborne platforms. This paper investigates the performance and possibilities of various visual-servoing techniques applied to acquisition and tracking in the case of UAVs. The work is done in SEAVS, a 3D simulation environment for aerial visual-servoing. SEAVS is a simulation software with a graphical user interface including one 2D window for planning of the aerial mission and two 3D windows -- one for the visualization of the ongoing simulation, and one showing the present camera view. The unique feature of SEAVS is the use of orthographic photos which enhances realistic image processing. The paper describes the design of visual-servoing controllers for the purpose of acquisition and tracking tasks. Two types of controllers are investigated: one based directly on the angle errors and one based on the image Jacobian. The algorithms are validated by simulation in SEAVS.
Environmental scene simulator
Paul G. Robillard, Gerald E. Bender
A technique was sought to generate signals for imaging systems that would permit the simulation of scenes including unusual environments and system defects. The most valuable simulation would be non-intrusive; i.e., no changes need be made to the system under test; this would permit evaluation of hardware and software using fully operational systems. For example, a simulated nominal scene could be degraded through the addition of simulated clutter; system performance could then be measured when the cluttered scenes were generated. A simulator for this use has been built and demonstrated by General Dynamics. Our current application requirements for such a simulator include relatively high update rate, large, linear dynamic range, very high mechanical and radiometric stability and synchronism with the imaging system. Two key areas of discussion will be the approaches used for gray scale generation and crosstalk mitigation.
Imaging and tracking elements of the International Space Station using a 3D autosynchronized scanner
The Neptec Design Group has developed a new 3D auto-synchronized laser scanner for space applications, based on a principle from the National Research Council of Canada. In imaging mode, the Laser Camera System (LCS) raster scans objects and computes high-resolution 3D maps of their surface features. In centroid acquisition mode, the LCS determines the position of discrete target points on an object. The LCS was flight-tested on-board the space shuttle Discovery during mission STS-105 in August 2001. When the shuttle was docked on the International Space Station (ISS), the LCS was used to obtain four high-resolution 3D images of several station elements at ranges from 5 m to 40 m. A comparison of images taken during orbital day and night shows that the LCS is immune to the dynamic lighting conditions encountered on orbit. During the mission, the LCS also tracked a series of retro-reflective and Inconel targets affixed to the Multi-Purpose Lab Module (MPLM), when the module was stationary and moving. Analysis shows that the accuracy of the photosolutions derived from LCS centroid data is comparable to that of the Space Vision System (SVS), Neptec's product presently used by NASA for ISS assembly tasks.
Laser tracking test under satellite microvibrational disturbances by OICETS ATP system
Free-space laser communication systems offer many advantages such as high data rate, small sized equipment, low consumption electric power and others. There are, however, many development factors to construct a realistic laser communication system in space. Precise Acquisition, Tracking, and Pointing (ATP) functions are key issue to establish the laser communication system in space. OICETS (Optical Inter-orbit Communications Engineering Test Satellite) has been developed by National Space Development Agency of Japan (NASDA) to verify an optical data link technology in space. ATP functions of the OICETS satellite for a laser inter-orbit link system must be controlled with an angular accuracy better than a few micro radian under vibrational disturbances of the host satellite. The microvibrational disturbances continually come from the satellite subsystem operations such as reaction wheels, solar paddle motors, scan sensors and so on. NASDA performed an on-ground microvibration test to evaluate vibration characteristics of the OICETS satellite and to verify laser tracking performances of the ATP system. The test was carried out by using a simulated OICETS satellite that consists of a mechanical structure model and an engineering model of the laser communication terminal. The mechanical structure model is equipped with some flight components and mass dummy components. The satellite is suspended from a lifting tackle by four straps and the free-free configuration was simulated using a suspension device. As a result, the incremental residual tracking error of 0.19 micro radians was measured due to the microvibration of the disturbing sources from the satellite platform.
Bending dynamics of circular lightweight mirrors
Analyses are presented of the vibrational frequencies and bending due to slewing of lightweight mirrors suitable for space applications. Two mirror configurations are considered: petals, in which bending resists deformation; and meniscus mirrors in which circumferential stresses resist deformation. For the first case, an exact solution was found for the bending due to slewing while the energy method was used for the vibrational frequencies. The results indicate that the bending frequencies are large enough to validate the constant slewing rate assumption. The bending and rms wavefront error of a small petal mirror was negligible, but the bending of the large mirror led to unacceptable values of the tilt and wavefront error. Additional investigations are warranted to determine if an active structure can overcome the large bending aberrations. For the meniscus mirror, the bending frequencies were found to be a factor of 5 greater, and the deformations two orders of magnitude smaller than the petal mirrors. The bending and vibration frequencies of the secondary mirror tower are also analyzed.
Stabilization and Control Applications
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Fast baseline resolution algorithm for GPS kinematic positioning based on probability computation
Yongliang Xiong, C. K. Shum, Dingfa Huang, et al.
GPS precise positioning depends on the right determination of phase ambiguity vector. Generally there are three methods for integer ambiguity resolution, including direct rounding to integer method, searching method and ambiguity function method. Direct rounding to integer method is the fastest algorithm among the three methods, but it requires highly precise approximation of the ambiguities, which usually can be only obtained through long term of measurement. The efficiency (speed) of searching method has a very close relationship to the precision of real-valued ambiguity solution, and usually this method is very slow, especially for the data which comes from short time measuring. The efficiency of ambiguity function method is determined by the accuracy of approximation position and the volume of the cube centered at the initial position. The original ambiguities are transformed into another space by a modified ambiguity transformation algorithm purposed by this paper, which is the most effective one compared to the others. In the new ambiguity space, new ambiguities are far more precise than their original partners. Then we compute the successful probability of direct rounding to integer method both in original space and new space. If the success probability is larger than a given value, then direct rounding to integer method is used to obtain the true ambiguities, otherwise go to a subroutine for the searching method.
GPS phase measure cycle-slip detecting and GPS base-line resolution based on wavelet transformation
Yongliang Xiong, Dingfa Huang, C. K. Shum, et al.
The errors in GPS measurement generally consist of systematic error (such as clock bias, iron-sphere, trop- sphere effect, etc.), random error (such as measuring error) and outlier. Systematic error can be canceled by differencing technique or adding parameters into the equation system. Outlier may be detected by adding parameters or by statistic method such as expectation shifting or variance inflating. Because wavelet analysis has many good natures both in the time domain and in the frequency domain, as can automatically zoom in or out with different scales (frequencies), the arbitrary details of a signal can be observed and analyzed by the aid of Wavelet analysis. Based on the above features, Wavelet analysis is reputed as a mathematical microscope.
New tracking and measuring control system for optical and electronic theodolite
Wenshu Yang, Jiaguang Ma
This paper describes a new tracking and measuring control system for optical and electronic theodolite. This control system can provide automatic flying object tracking and measuring in visible and infrared band. It also can provide real-time output of the measured results. Use of the multi- mode measuring methods and the on axis tracking control technique can improve the stability of automatic tracking, tracking accuracy and the comprehensive tracking performance of the theodolite. At the same time the smooth switch over among several tracking modes can be carried out. New tracking techniques have been developed to deal with angular tracking rate that exceed one radian in both velocity and acceleration. At the present the tracking and measuring control system has been successfully applied in the optical and electronic theodolite. This paper covers the design concept for the on axis tracking control, the prediction, filtering and smoothing of target measurement, selection of bandwidth, the techniques of automatic video tracking using visible and infrared sensors and the architecture of the servo control algorithms.
Low-speed compensation for the fluctuation of the motor moment in an optoelectronic tracking system
At low speed or zero crossings, the existed nonlinear effects such as friction, the fluctuation of the motor moment will make the system jitter heavily. Our researches focus on the analysis and compensation of the motor moment fluctuation when the optoelectronic tracking system works at low speed. Actually, other nonlinear factors at low speed are also checked. As the fluctuation is always presented in sine orderliness, a repeat controller that bases on the study law is applied to the tracking system. Both simulations and experiments show that with the repeat controller, the tracking precision increase about 3 times comparing to the PID one.
Signal Processing Applications
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Assessment metrics for absolute sensor alignment
Gregory A. Watson, Theodore R. Rice
The purpose of absolute sensor alignment is to determine the measurement and attitude biases of a sensor in an absolute reference frame. It has been well-documented that the performance of composite tracking with multiple sensors can severely degrade if the sensor measurements are not corrected for the bias. There are well-established metrics to assess the performance of tracking techniques and quantify the effects of other functions on the tracking process. However, there is a lack of metrics to assess sensor alignment techniques apart from other functions. The purpose of this paper is to present metrics for absolute sensor alignment techniques that assess performance apart from other functions. An absolute sensor alignment technique is presented and simulation results are employed to illustrate the alignment metrics.
Tracking with two asynchronous sensors: solution existence and performance analysis
Sensor data fusion has long been recognized as a means to improve target tracking. Common practice assumes that the sensors used are synchronous, i.e., they have identical data rate, measurements are taken at the same time, and have no communication delays between sensors platform and central processing center. Such assumptions are invalid in practice. Previous work of the authors dealt designing asynchronous track fusion filter that removes such assumptions when considering the multi-sensor target tracking case. This paper deals with the existence of a solution to the asynchronous track fusion problem for the case of two asynchronous sensors. In addition, the performance deterioration of the filter is analyzed as a function of the track fusion update rate.
Radar scheduling with emission constraints
Olivier Baud, Laurent Ratton
In this paper, we investigate the issue of radar emission scheduling for target track maintenance and quantify the benefits of multiple sensor tracking regarding emission constraints. In fact, the target track results from the fusion of passive detection obtained from ESM or IRST sensors and active measurements delivered by the radar when it is pointed towards the target. The tracking algorithm is based on Singer model developed in polar coordinates. We propose to control state covariance estimate provided by the Kalman Filter and compare it to a predefined requirement which is supposed to take into account both operational (tactical situation accuracy) and technical (association ambiguity and radar pointing efficiency) needs. When this threshold is reached, the radar is activated. Theoretical analysis is conducted and sensitivity to several parameters considered, including target dynamics, specified covariance threshold, and radar detection probability. Advantages of multiple (active and passive) sensors tracking is pointed out, especially when emission constraint is required. Finally, simulation results are provided in an air-to-air scenario in which ESM, IRST and Radar sensors are available onboard the own aircraft.
Imaging Trackers I
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Implementation of an embedded image-based tracker in a distributed architecture
Julie R. Schacht, Larisa Stephan
A major purpose of targeting systems is to ease operator workload by keeping the line of sight (LOS) pointed on a designated target. Our airborne electro-optic targeting system uses the latest technology to accomplish this end. If the latitude, longitude and altitude (geo-position) of a stationary ground target are known in advance, this system can use the aircraft's GPS-aided inertial navigation system to keep the LOS pointed at the target. If the operator wants to point at a target whose geo-position is unknown, this system can compute latitude, longitude and altitude using LOS attitude and range. The role of the image-based tracker in this system is to track airborne or moving ground targets and to compensate for drift and other limitations of geo-point for stationary ground targets. The algorithms implemented in our targeting system are not only processing intensive, but also diverse, incorporating a variety of information from numerous sources in order to provide the operator with the best LOS control solution for a given scenario. This, balanced against the low latency requirements of a real-time control system, has resulted in a software design that spans four separate processor boards. We present the implementation of a successful real-time embedded image-based tracker on a distributed architecture.
Centroid tracking using a probability map for target segmentation
John E. Albus, Lloyd J. Lewins, Julie R. Schacht
The central problem of image based centroid tracking is that of target segmentation, that is, determining which pixels belong to the target and which belong to the background. Once the target pixels are identified, the centroid (the center of gravity) of these pixels can be used as the estimated target position. The underlying assumption made in centroid tracking is that the target image contains intensity values that are unlikely to occur in the background. Based on this assumption, the centroid tracker uses three concentric gates to determine which pixels are target pixels. The areas bounded by these gates form three disjoint regions; the inner region, the track region, and the outer region. An inner histogram is collected over inner region that should contain mostly target pixels. An outer histogram is collected over the outer region that should contain only background pixels. These histograms are then used to generate a probability map that indicates the probability that a pixel with a given intensity is part of the target. This probability map is then used to segment the target and find its centroid. This paper describes the methods used to generate the probability map and its use in the centroid tracking algorithm. The performance of this algorithm is compared to that of the previously used dual-threshold segmentation algorithm.
Verification of tracker position measurement using digital video and instrumentation data recorded in flight
John E. Albus, John R. Marcovici
The function of the tracker image processing in our airborne FLIR tracking system is to continually measure the position of the tracked target relative to the image center. These positions are used by the line of sight control system to maintain the target in the center of the imaging sensor FOV. In order to perform an end-to-end test of the accuracy of the target positions measured by the tracker, we developed a verification method that makes use of instrumentation data and digital video recorded during flight test. The instrumentation data contains the track errors, which we wish to verify. A post-flight image analysis tool was developed to accurately measure the track positions in the flight recorded digital video for comparison to the recorded flight track errors. This tool made use of a correlation technique combined with a non-linear optimization procedure. The off-line track position estimates generated by this tool were then compared to those produced in flight by the tracker. This paper describes the algorithms used in the post-flight analysis to estimate the track positions from the digital video. The results of applying this verification technique to both a correlation tracker and a centroid tracker are then described.
Fitts correlation tracker fidelity in presence of target translation, rotation, and size change
Larisa Stephan, John E. Albus, John R. Marcovici
The Fitts correlation algorithm is known to be optimal in measuring small image translations. As the position measurement portion of an image-based tracker, it yields excellent track fidelity over a sequence of images in which the tracked target exhibits small shifts from the predicted position. Real-world experience, however, informs us that the tracked target rarely confines itself to small-scale translational motion in the image plane, and sometimes changes size during the track period. When does the steady-state Fitts correlation need a boost from auxiliary algorithms to maintain target lock? We describe the envelope within which the Fitts correlation tracker can be expected to report target position accurately. Tolerances for target translation, in-plane rotation, and size change are parameterized by the correlation length of the tracked target. A successful image-based tracker using Fitts correlation for position measurement will require additional logic or modifications to the image-processing algorithm to enable it to operate outside the bounds described.
Target acquisition and tracking based on a priori knowledge and an image sensor
Zhonghua Fang, Tao Chen
When intercepting and tracking low-observable point-source or highly maneuvering big targets, the electro-optical (E-O) system will meet a fatal problem that the target lost easily. No effective method intercepts it again according to the dispersed azimuth and elevation tracking data. First, the paper gives an intelligent ATP control system architecture based on the data mart. Then an automatic real-time control algorithm is proposed, which is found on linguistic cloud model and fuzzy logic techniques. The linguistic cloud model is used to translate a linguistic term of qualitative concept into its numerical representation, such that the ATP control system can take full advantage of a priori knowledge which is always presented in natural language to refine the results of sequence images processing. The fuzzy logic technique is adopted to associate these results to target's trajectories. The paper offers an automatic reacquisition and tracking method to solve the targets lost problem.
Imaging Trackers II
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Image-based tracker performance metric
Teresa L. P. Olson, Robert Stanfill
Currently, there is no standard quantitative measure of the performance of an image-based tracker algorithm. It is usually described as remaining in track for the entire run or losing track at some point during a run. This is purely a qualitative evaluation. Without a quantitative measure it becomes difficult to accurately evaluate the performance of a tracker algorithm. We have developed the Tracker Performance Metric (TPM) specifically for this purpose. It was designed to measure the output performance, on a frame-by-frame basis, using its output position and quality (sometimes referred to as confidence) state. The TPM can also be used as a measure of algorithm performance to compare against the Trackability Metric. The Trackability Metric was developed by AMCOM to determine how trackable a set of data should be. The TPM will be described and results presented.
Screening closing scenarios for tactical targets
The first step in an automatic image target acquisition system is determining the location of candidate objects. Screening for targets must also be done within a tactical scenario timeframe. The screening process must only require a portion of the processing workload since other algorithms must execute in the same time frame. The detection of these candidate objects is allocated to two functions within the same algorithm. The first is a pre-screener and other is a clutter rejection component that will categorize the object nomination into target or non-target classes. This paper describes a screener that meets the necessary requirements for tactical operations. It uses the magnitude and direction of the image gradient. Locations are nominated by looking at local neighborhoods in this gradient space. Regions of interest are then selected and various features are extracted. These features are selected both for their information content and their ease of calculation. Using a Bayes approach, target candidates are selected as plausible targets of interest.