Showing papers by "Norman S. Kopeika published in 1991"

Image resolution limits resulting from mechanical vibrations. II, Experiment

Abstract: A theoretical model, developed by Wulich and Kopeika that gives the MTF for flow vibration frequency sinusoidal image motion applicable to reconnaissance, robotics, and computer vision, is evaluated experimentally to determine (1) accuracy of the MTF model and the validity of assumptions upon which it is based, (2) accuracy of "lucky shot" theoretical analysis to determine the number of independent images required to obtain at least one good quality image, and (3) accuracy of prediction for average blur radius. In most cases agreement between theory and experiment is quite good. Discrepancies are not too great and are attributed to problems with underlying theoretical assumptions where uniform linear motion cannot be assumed. The theory and experiment here are confined to low-frequency sinusoidal vibration where blur radius and spatial frequency content are random processes.

Numerical calculation of image motion and vibration modulation transfer functions: a new method

Abstract: A new method of numerical calculation of MTF is presented here for image motion in one- dimension. The method is applicable in principle to any type of motion and can be expanded to two-dimensional motion. It is applied here to uniform velocity motion and to sinusoidal vibrations. Comparison to known analytical methods is made where possible, and agreement is excellent. This supports its implementation to any kind of random motion, particularly where no unique analytical MTF is possible.

Numerical calculation of image motion and vibration modulation transfer function

Abstract: In many high-resolution photographic and photoelectronic imaging systems, resolution is limited by image motion and vibration and, as a result, the high-resolution capability of the sensor may be wasted. In normal reconnaissance and robotics the sensor moves during the exposure. Some of the resulting image motion can be removed by mechanical compensation, but not all of it. The residual motion blurs the image, and usually this blur becomes the limiting factor for many high-quality imaging systems. The ever-increasing altitudes and coverage requirements of modern imaging have put a premium on high resolution. An application of this paper is the recovery of the original image by inverse filtering that depends on the modulation transfer function (MTF) of the real-time relative motion between the object and the imaging system. An original method developed here for numerically calculating MTF for any type of image motion is the basis of the paper.

Forecasting optical turbulence strength: effects of macroscale meteorology and aerosols

Abstract: Although optical turbulence is usually modelled with micrometeorology, it is shown here that this can be done successfully too with macrometeorology using meteorological parameters measured with standard weather stations and predicted in standard weather forecasts. This makes it possible to predict 2 according to weather forecast. Two experimentally-derived models are developed - one for practical use and the other for scientific understanding. Correlation of prediction with measurement is on the order of 90% or more, over large dynamic ranges of meteorological parameters. One interesting aspect of these measurements is the statistical evidence that scintillations are affected by aerosols, particularly under conditions of high total aerosol cross sectional area. This is attributed primarily to increased refractive index changes encountered by radiation which penetrates through the aerosols.

Prediction of coarse aerosol statistics according to weather forecast

Abstract: An effort to quantify effects of weather on coarse aerosol concentration and total cross- sectional area per unit volume, so as to permit their prediction according to weather forecast, has begun. Correlations of prediction with measurement are on the order of 92% and 88% respectively. Relative humidity is the dominant parameter. Based on this work, further development is planned so as to predict overall size distribution, scattering coefficients, and aerosol MTF, according to weather forecast.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Prediction of thermal image quality as a function of weather forecasts

Abstract: Thermal image quality depends on properties of hardware, atmosphere, and thermal contrast in the target plane. Weather affects both the modulation transfer function (MTF) of the atmosphere and the thermal contrast in target space. Atmospheric effects are chiefly aerosol light scatter, which causes blurring as well as reduced contrast, and absorption, which reduces contrast. Thermal contrast in the target plane is affected by wind, which tends to equalize temperatures, and by dew, which tends to equalize emissivity. Experiments were carried out over a 2-km line of sight and MTF results and weather parameters processed. Quantitative relationships have been determined relating overall thermal image quality to weather for imaging of passive targets and are suggested as a criterion for forecasting relative quality of thermal imagery according to weather forecast.

Prediction of C n 2 on the basis of macroscale meteorology including aerosols

Abstract: Although optical turbulence is usually modeled with micrometeorology, it is shown here that this can be done successfully with macrometeorology using meteorological parameters measured with standard weather stations and predicted in standard weather forecasts. This makes it possible to predict C2n according to the weather forecast. Two experimentally-derived models are developed--one for practical use and the other for scientific understanding. Correlation of prediction with measurement is 90% or more, over large dynamic ranges of meteorological parameters. One interesting aspect of these measurements is the statistical evidence that scintillations are affected by aerosols, particularly under conditions of high total aerosol cross sectional area. This may be attributed to increased refractive index changes encountered by radiation which penetrates through the aerosols. In addition, validity of the models was examined, and experimental comparisons in two very different climates and surface conditions are presented. High correlation is found in both cases between prediction and measurement.

Prediction of thermal-image quality as a function of weather forecast

Abstract: Thermal image quality depends upon properties of hardware, atmosphere, and thermal contrast in target plane. Weather affects both MTF of the atmosphere and thermal contrast in target space. Quantitative relationships have been determined relating overall thermal image quality to weather for imaging of passive targets and are suggested as a criterion for forecasting relative quality of thermal imagery according to weather forecast.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Overall atmospheric MTF and aerosol MTF cutoff

Abstract: The limits of image quality through the atmosphere depend on the overall atmospheric modulation transfer function (MTF) cutoffs The first spatial frequency cutoff, or 'knee,' of the overall atmospheric MTF curve depends on aerosol MTF The second spatial frequency cutoff, limited by threshold contrast required in the output image, also depends on turbulence Measurements of atmospheric MTF over a 55 km horizontal path near the ground were made for a large range of spatial frequencies at several wavelengths in the visible and near-IR spectrum along with measurements of turbulence by a passive edge wander technique On-line measurements of particulate size distribution were made using a Particle Measurement System, Inc (PMS) probe, and on-line meteorological data (air temperature, relative humidity, wind speed, wind direction, and solar flux) were obtained from a weather station a few meters away from the imager The experimentally-derived MTF curve is compared to well-known models for turbulence MTF and aerosol MTF The determination of aerosol MTF from macroscale parameters is crucial to prediction of image quality through the atmosphere and can be implemented in image restoration