Showing papers by "Norman S. Kopeika published in 2004"

Atmospheric optical turbulence over land in middle east coastal environments: prediction modeling and measurements

Abstract: Beam intensity scintillations, characterized by a refractive-index structure parameter and caused by variations of macrometeorological features of the coastal atmosphere such as air temperature, wind speed and direction, and relative humidity, are examined theoretically and experimentally. In our theoretical analysis we present two well-known models considered separately for over-water and over-land atmospheric optical communication or imaging channels. By means of comparison with our experiments carried out in midland coastal environments in southern and northern Israel, we show the limitations of the models to predict the refractive-index structure Cn2 parameter for both daytime and nighttime turbulent atmospheres in different coastal zone meteorological conditions. We also present an extension of an existing model with two different practical applications that, as is shown experimentally, can be a good predictor of Cn2 for optical atmospheric paths over midland coastal zones.

Behavior of structure function of refraction coefficients in different turbulent fields.

Abstract: Deviations of experimental data on the effect of atmospheric turbulence on electromagnetic wave propagation from a standard Kolmogorov (or Obukhov-Kolmogorov) model are examined from the standpoint of the behavior of atmospheric passive scalar spectrum. It is pointed out that these deviations are not random and can be explained on the basis of today’s ideas of passive scalar behavior in the atmosphere. This approach allows us to view electromagnetic radiation transfer in random media in a new way and to make the necessary steps for developing a generalized model of this phenomenon.

Restoration of images captured by a staggered time delay and integration camera in the presence of mechanical vibrations.

Abstract: Staggered time delay and integration (TDI) scanning image acquisition systems are usually employed in low signal-to-noise situations such as thermal imaging. Analysis and restoration of images acquired by thermal staggered TDI sensors in the presence of mechanical vibrations that may cause space-variant image distortions (severe geometric warps and blur) are studied. The relative motion at each location in the degraded image is identified from the image when a differential technique is used. This information is then used to reconstruct the image by a technique of projection onto convex sets. The main novelty is the implementation of such methods to scanned images (columnwise). Restorations are performed with simulated and real mechanically degraded thermal images.

LIDAR measurements of atmospheric turbulence vertical profiles

Abstract: An imaging LIDAR system for measuring vertical profile of the atmospheric refractive index turbulence has been developed and its performance demonstrated. The turbulence profile retrieval technique is based on image motion analysis. In the present work LIDAR measurements of C n 2 vertical profiles are demonstrated. Unlike the existing turbulence models, the experimental results show the various strata and layers in the vertical turbulence profiles.

Effects of attenuation of 1.064-μm optical waves by humid aerosols and fog over horizontal atmospheric communication links

Abstract: Ben-Gurion University of the NegevDepartment of CommunicationSystems EngineeringP.O. Box 653Beer-Sheva, 84105IsraelAbstract. Effects of humid aerosols and fog on optical wave propaga-tion at 1.064 mm over various horizontal atmospheric communicationlinks are investigated both experimentally and theoretically by use oftheoretical and empirical models as best fits of experimental data. Miescattering is used to describe the attenuation of optical waves by aero-sols for lower elevation horizontal atmospheric links. The geometricaloptics approximation is used to obtain the extinction coefficient for opticalwaves at 1.064 mm passing through clouds, fog, water droplets, andatmospheric particles with dimensions larger than the wavelength. Goodagreement between a new model of propagation effects through suchparticles, and measurements carried out at two different sites in southernand northen Israel, is obtained.

Landsat TM satellite image restoration using Kalman filters

Abstract: The quality of satellite images propagating through the atmosphere is affected by phenomena such as scattering and absorption of light, and turbulence, which degrade the image by blurring it and reducing its contrast. The atmospheric Wiener filter, which corrects for turbulence blur, aerosol blur, and path radiance simultaneously, is implemented in the digital restoration of Landsat Thematic Mapper (TM) imagery. Digital restoration results for Landsat TM imagery using the atmospheric Wiener filter were presented in the past. Here, a new approach for digital restoration of Landsat TM imagery is presented by implementing a Kalman filter as an atmospheric filter, which corrects for turbulence blur, aerosol blur, and path radiance simultaneously. Turbulence MTF is calculated from meteorological data. Aerosol MTF is consistent with optical depth. The product of the two yields atmospheric MTF, which is implemented in both the atmospheric Wiener and Kalman filters. Restoration improves both resolvable detail and contrast. Restorations are quite apparent even under clear weather conditions. Although aerosol MTF is dominant, slightly better results are obtained when the shape of atmospheric MTF includes turbulence, in addition to that of aerosol MTF, as shown by the use of criteria for restoration success. In general, the Kalman restoration is superior.

Modeling and measurements of near-ground atmospheric optical turbulence according to weather for Middle East environments

Abstract: Refractive index structure parameter, C 2 n , which characterizes turbulence caused by local gradients of microscale meteorological parameters and by variations of macrometeorological features of the atmosphere such as air temperature, wind speed and direction, relative humidity, etc., is examined theoretically and experimentally for near ground Middle East environments. In our theoretical analysis, we present several known models for over-land atmospheric optical communication or imaging channels to predict the turbulence intensity (represented by C 2 n ). Via comparison with our two-year continuous experiments carried out in Israel we show their limitations for both day- and nighttime turbulent atmospheres under different meteorological conditions. An extension of an existing "practical" model, applicable for two summer and winter seasons, is presented in this work which, as is shown experimentally, can be a good predictor of C 2 n for optical atmospheric paths in Middle East climates.

Motion-blurred image restoration using modified inverse all-pole filters

Abstract: The restoration of vibration-blurred images using mea- sured motion function is considered. Since the blurring filter is of the finite impulse response type, the inverse one is of the all-pole infinite impulse response type. Direct application of the inverse filter to re- store images blurred by vibration is attractive because of reduced computation requirements. Space domain filtering allows high par- allelization of the process and reduction of required processor speed. However, a pure inverse filter provides excessive noise am- plification and is possibly unstable. The proposed technique is to construct a modified inverse filter with preserved all-pole structure and optimized noise and stability properties. A mathematical con- cept was developed using z-transform properties. An experiment testing the proposed technique was setup and the results indicate restoration is 60%-80% of that possible with ideal Wiener filtering. However, the reduced computation and high parallelization can fa- cilitate real-time restoration. © 2004 SPIE and IS&T.

Atmospheric turbulence at different elevations: consequences on laser beam wander and widening at target

Abstract: The estimation of the performance of atmospheric electro-optical systems depends on the accuracy of the atmospheric models being used in the propagation prediction codes. On the basis of a large set of imaging LIDAR measurements a Middle East model of refractive turbulence strength (Cn2) vertical profile has been developed. The model is presented in this work, and laser beam wander and widening at different elevation heights in target plane is estimated. Implications can be important for optical communication, laser weaponry, imaging through the atmosphere, and adaptive optics.

Aerosol models for Middle East coastal zones: a modified NAM model

Abstract: Recently several investigators proposed an extension of the Navy Aerosol Model (NAM) based on analysis of an extensive series of measurements at the Irish Atlantic Coast and at the French Mediterranean Coast. This work extends NAM by use of a similar analysis using data collected at three different Middle East Coastal areas: the Negev Desert (Eilat) Red Sea Coast, the Sea of Galilee (Tiberias) Coast, and the Mediterranean (Haifa) Coast. Results of the aerosol size distribution are compared with those obtained through measurements carried out over the Atlantic Ocean and Mediterranean Coasts. An analysis of these different results allows a better understanding of the similarities and differences between different coastal and open ocean zones. Parameterization is introduced. The aerosol particle concentrations and their dependences on wind speed for these coastal zones are analyzed and discussed.

Validity of Kolmogorov turbulence at higher elevations

Abstract: Atmospheric turbulence and aerosol particles are significant sources of laser-based and imaging system performance degradation. Quantitative estimation and characterization of turbulence and aerosol properties in the atmosphere therefore are very important for system development and applications (optical communications, laser weaponry, image restoration, etc.) To investigate the influence of aerosols and turbulence on laser-based sensing systems and to profile aerosol extinction, size distribution, and turbulence strength, a LIDAR system was developed. The new setup combines LIDAR and imaging techniques and permits measurement of aerosol and turbulence vertical profiles near simultaneously. It is usually assumed that the turbulent field is of the Kolmogorov type and calculations of intensity and angle of arrival fluctuations variance and other parameters for prediction of optical systems performance are based on this type of turbulence. However, we find that in the atmospheric boundary layer and at higher altitudes the turbulence can be different from Kolmogorov’s case. In this work, on the basis of LIDAR measurements, we investigate spectra of aerosol concentration fluctuations at different altitude elevations and at different wavelengths and use the results for turbulence strength profile retrieval. The turbulence profile retrieval technique is based on LIDAR measurements of angle of arrival fluctuation variance. Implications can be important for optical communication and imaging through the atmosphere.

Prediction and modeling of line-of-sight bending near ground level for long atmospheric paths

Abstract: Line-of-sight bending, called "beam bending", is an effect caused by strong atmospheric turbulence, where during daytime targets are seen lower and during nighttime higher than their real locations This effect takes place in conditions of very low or absence of wind speed and relatively high turbulence, which characterize non-uniform atmospheres During past three years high-resolution experiments in different desert and low vegetation areas of the Middle East (Israel) were performed A model for predicting line-of-sight bending based on effects of turbulence and atmospheric conditions, described by pressure, temperature, relative humidity, etc, was developed and investigated This paper describes investigations made to parameterize this model based on high-percentage prediction of results for different areas, day/night time, and heights above the ground surface© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only