The tracking algorithm is presented that reduces the influence of the camera motion on the tracking performance. The algorithm uses a change detector. The target motion is described by parameterized optical flow. The flow parameters are estimated using Kalman filtering. The algorithm allows us to estimate the target motion without any bias associated with the camera motion. The effects of thermal blooming on high-energy laser beacon for air-to-ground directed energy system are evaluated. The laser fluence at the target and power in the bucket are evaluated for various tactical engagement scenarios and different atmospheric conditions. The critical laser power that can be efficiently transmitted through the atmosphere is evaluated. Two techniques for mitigating the effects of thermal blooming including a method based on pointing of a high energy beam "downwind" to correct for the thermal blooming tilt and focusing a high energy beam beyond the target range are evaluated. We found that the power in the bucket at the target at the optical axis of a high energy beam for tactical directed energy system increases about one order of magnitude due to correction of the thermal blooming tilt.
Laser weapon systems would be significantly enhanced with the addition of high altitude or space-borne relay mirrors. Such mirrors, operating alone with a directed energy source, or many in a series fashion, can be shown to effectively move the laser source to the last, so-called fighting mirror. This “magically” reduces the range to target and offers to enhance the performance of directed energy systems like the Airborne Laser and even ground-based or ship-based lasers. Recent development of high altitude airships will be shown to provide stationary positions for such relay mirrors thereby enabling many new and important applications for laser weapons. The technical challenges to achieve this capability are discussed.
A technique for profiling of Cn2 over an atmospheric propagation path is proposed, developed and analyzed. The technique employs differential-tilt measurements to arrive at statistics which have unique weighting functions over the propagation path. These weighting functions are computed theoretically and used to derive a reconstructor matrix for Cn2 values throughout the path to be applied to an appropriate set of differential-tilt statistics. A candidate optical system is presented, and the performance of the profile reconstructor is analyzed. This study indicates that the relative error in the Cn2 estimates is approximately 5%. The relative error in estimating key atmospheric parameters such as the Fried parameter, isoplanatic angle, and the Rytov parameter from the reconstructed profiles is approximately 3%.
The problem described in this paper deals with tracking the optical path perturbations introduced by the atmosphere when illuminating a target (missile) with laser light. Due to atmospheric irregularities, the optical path from an observer to an in-flight missile deviates from a straight line, and also changes in time. If the goal of the system is to point a laser beam at a specific point (or area) of the missile body for a given period of time, these optical path variations should be tracked and compensated when pointing the laser beam. The laser beam should be pointed, not to the true but to the apparent location of the desired spot. In the actual system, the missile is illuminated with several lasers (forming a broad beam), and an image of the missile (distorted through the atmosphere) is obtained from the backscattered light. This image contains all the information available about the optical path. The purpose of the work presented here is to estimate the apparent location of five different spots of the missile (distributed evenly along the longitudinal axis, from the nose up to mid-body) from the backscattered images and a- priori information that includes the size and speed of the missile. The dta available is high-fidelity simulated data, and the apparent locations of the desired spots (over time) are known. Two approaches are considered here. The first approach is based on breaking the problem into two parts: a measurement part and an estimation part. For the measurement part, a Neural Network is used to infer a mapping from the image to the apparent location of the points of interest (known for the simulated data). Those measured locations are then used by a Kalman filter to estimate the apparent locations. The Kalman filter exploits the fact that the optical paths (from different spots along the longitudinal axis) are correlated in time. This correlation is caused by the missile's displacement through the atmosphere. The second approach is to compute the centroids of the images and use the resulting points as estimates of the apparent location of a point on the missile. For the first approach, simulation results show a noticeable decrease in the rms error of the apparent location estimates when compared to the average location (mean value). The second approach, while simple, was found to perform quite well.
The profile of atmospheric turbulence strength along a laser propagation or imaging path is thought to significantly influence performance. We use wave optics simulation to evaluate performance under random variations of turbulence profiles along a 50-km propagation path. Performance is given by power in the bucket (PIB) strehl in a (lambda) /D bucket. For a point source and under the conditions we investigated, we conclude that, in addition to the Rytov parameter, knowledge of r0 can significantly improve performance prediction.
Proc. SPIE. 3706, Airborne Laser Advanced Technology II
KEYWORDS: Optical filters, Signal processing, Signal generators, Chemical elements, Electronic filtering, Optimal filtering, Atmospheric propagation, Systems modeling, Filtering (signal processing), Tin
This paper develops an infinite dimensional theory for filtering and control in the presence of non-rational spectra. It begins with a review of the original work of A.V. Balakrishnan for the continues time case. This work formulates an auxiliary state space signal model for the case of non-rational spectra. The result is the recovery of Kalman like signal generation models with the resulting separation principle for control. New results, based on unpublished notes of Balakrishnan, on discretization of the model are developed. Although the results can and will be generalized, this paper only covers the 1D theory.
We study tropospheric aerothermal probe data by using the orthogonal Haar wavelet averages of the dissipation to segment the data. Segmenting the data in this way allows us to isolate regions of distinct mean dissipation. We then use the Haar wavelet transform to derive spectra and structure functions for the segmented regions, thereby recovering Kolmogorov statistics. We also comment on wavelet derived structure functions and point out data anomalies only visible in the wavelet domain.
We present a new approach for analyzing local power law processes and apply it to temperature measurements from the upper atmosphere. We segment the data and use the wavelet scale spectrum to estimate the parameters of the power law, the scale factor and the exponent. These parameters vary from segment to segment. Part of this variation is due to the non-stationary of the data. Another part is due to estimation errors that depend on the segmentation. In this paper show how to remove effectively these segmentation dependent variations.
ABLE ACE was a high-altitude, laser-propagation experiment in which a series of measurements were made of laser propagation between two aircraft flying at 13 to 14 km altitude and at up to 200 km separation. The measurements included a pupil plane scintillation image, an atmospheric tilt sensor, a wavefront sensor, and a differential phase measurement, across a 50 cm aperture. In addition, a small- aperture, high-bandwidth scintillometer and simultaneous aerothermal-probe measurements were made. The purpose of these measurements was to validate wave-optics propagation codes for high-altitude, long horizontal-path propagation, and to better understand what parameters were important to include in the codes. Additionally we sought to directly understand laser propagation characteristics in the regimes of the flights. This paper provides an overview of ABLE ACE. It discusses the sensor suite, the missions, and the code validation methodology as well as the conclusions of the program.