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In this paper we address the problem of tracking low-SNR targets in an environment of heavy, stationary clutter (e.g., ground clutter). The processing approach is Bayesian field tracking, in which a posterior target distribution is developed over the entire position-velocity state space. Development of the Bayesian posterior probabilities is recursive and is driven by likelihood fields evaluated from successive measurement observations. This track-before-detect approach has a demonstrated capability to track at SNR levels below those for which the usual Kalman- based tracker is functional. We have applied two clutter mitigation techniques that correspond individually to the following clutter characteristics: (1) the occurrence of high-amplitude (non- Gaussian) events and (2) the stationary nature of clutter features. The first characteristic is treated by a composite Gaussian environment model and the second by active discrimination against features tracked (by the Bayesian field tracker) at zero velocity. Both mitigation techniques combine to provide a decision theory test of signal versus noise or clutter, and the net impact is rigorously integrated into the Bayesian tracker processing through the likelihood- ratio field that drives the recursive update. Evaluation of ROC curves for simulated and real environments show both mitigation techniques to be highly effective.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Buoys in the open ocean are clearly observed from a range of 90 km with an airborne IR sensor. A simple model which predicts the observed contrast between small floating objects and the sky radiance reflected from the ocean surface at shallow depression angles has been developed. The detectability of the floating object can be predicted as a function of the percentage of the object that is above the water surface and the size of the object. The model treats the surface object as a black-body at the ambient ocean temperature and predicts the Fresnel reflection of the sky radiance from the ocean surface. Model predictions for the radiance contrast between the ocean and the object have been compared to the observations and are in good agreement. Using a time sequence of the IR images, 3D space-time detection processing shows the potential for further improvement of the detectability of these small objects.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Observations of the open ocean have been collected at long range and low grazing angle with an airborne infrared system. These images are geographically registered using the position of a fiducial object in the scene as the reference. The three-dimensional frequency-wavenumber spectra computed from time histories of these images show a strong two-dimensional dispersion surface that is characteristic of wind waves and swell. The wave directions obtained from the spectra compare well with in situ measurements. Moreover, the wave speeds deduced from the spectra are consistent with the mean water depth in the area imaged. Ocean waves have been measured previously with other sensors, but these observations are believed to be the first measurements of ocean waves with an airborne infrared system.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Computational methods are presented for the study of collisions between a linear, symmetric triatomic molecule and an atom by three‐dimensional quasiclassical trajectory calculations. Application is made to the investigation of translational to rotational and translational to vibrational energy transfer in the systems CO2–Kr, CO2–Ar, and CO2–Ne. Potential‐energy surfaces based on spectroscopic and molecular beam scattering data are used. In most of the calculations, the CO2 molecule is initially in the quantum mechanical zero‐point vibrational state and in a rotational state picked from a Boltzmann distribution at 300°K. The energy transfer processes are investigated for translational energies ranging from 0.1 to 10 eV. Translational to rotational energy transfer is found to be the major process for CO2–rare gas collisions at these energies. Below 1 eV there is very little translational to vibrational energy transfer. The effects of changes in the internal energy of the molecule, in the masses of the collidants, and in the potential‐energy parameters are studied in an attempt to gain understanding of the energy transfer processes.

Previously reported photolysis experiments indicate that the frequency factors associated with the hydrogen‐exchange reactions H+DCl μ HCl+D and D+HCl → DCl+H are on the order of 1010 cm3/mol⋅sec. This result indicates that the above processes are associated with very small steric factors, in contrast to what one might be led to expect from recent crossed beam experiments. A series of unadjusted, quasiclassical trajectory calculations have been carried out to compute the thermal rate coefficients and activation parameters for a series of 13 thermal processes of the type A+BC → AB+C, where A=H, D, or Cl and BC=H2, D2, HCl, DCl, or Cl2. In addition, hot‐atom yield ratios have been computed from the IRP equation for the reactions D*+DCl → D2+Cl, D*+Cl2 → DCl + Cl as a function of the initial D* laboratory energy. Previously formulated, valence‐bond representations were employed for the potential‐energy surfaces in all the calculations. The computations yield (1) hot‐atom [DCl]/[D2] yield ratios within a fact...

A nonrandom method for approximating multidimensional integrations is compared to traditional ``random'' Monte Carlo techniques for determining reaction cross sections from quasiclassical trajectories. Reaction cross sections are calculated for the H + H2 collision system to determine the relative rates of convergence for each method as a function of the number of trajectories employed in the calculation. Estimates of the maximum probable error for the nonrandom integrations of a given number of trajectories compare favorably with the errors expected for Monte Carlo integrations and seem to imply that nonrandom integrations are more accurate than Monte Carlo calculations. However, the error of a Monte Carlo integration is easily estimated while that of a nonrandom integration is not. Thus the nonrandom method's advantage in accuracy may be overcome by other characteristics of the Monte Carlo method. For classical trajectory calculations, the nonrandom method should be considered as an alternative, but not...

A numerical integration technique based upon the use of nonrandom number sequences is examined with test integrations of a simple, analytical function. A comparison of the nonrandom technique with the familiar Monte Carlo method shows that the error of the new method decreases faster as more points are used in the calculation. Moreover, the new method needs fewer points to calculate an integral to an accuracy of 10% than does the Monte Carlo method.

An approximate, semiempirical valence-bond formulation is employed to compute potential energy surface reaction barriers for six-center reactions involving the halogens (F/sub 6/, Cl/sub 6/, Br/sub 6/, I/sub 6/) and hydrogen (H/sub 6/). The method is based on approximations comparable to those in the London--Eyring--Polanyi--Sato (LEPS) formulation. The surfaces are not adjusted using data for the systems treated, but are computed using parameter values that have been used in studies of other systems. The predicted energy barriers are in qualitative accord with existing experimental results for related systems.