Theoretical and experimental work has been conducted to assess the feasability of the retrieval of target's emissivity and bi-directional reflectivity from broadband infrared imaging systems. Focus was on the [3-5micrometers ] band II region where very little information is available. For accurate handling of the measured at-sensor radiance, account must be taken of target-to-sensor air layer, even for short distances, particularly in band II where atmospheric CO2 has a strong absorption band around 4.26 micrometers . It is shown that full integral expression over the spectral bandwidth of the instrument must be used and that usual factorization of contributions due to target, atmosphere and radiometer may lead to large errors when inverting the signal for emissivity or bi-directional reflectivity. Although retrieval of band II target's emissivity is, as a rule, extremely difficult outdoor conditions for natural surfaces, this work demonstrates that a multi-temporal regression method gives very good results with attainable accuracy on emissivity within 2%. Estimate of retrieving errors due to necessary approximations made in the formulation of the signal has been made via simulations. Experimental verification based on actual data acquired in outdoor conditions is in progress.

Atmospheric turbulence degrades the performance of laser communication systems in that system bit error rates can be orders of magnitude larger than in the absence of turbulence. Using a partially coherent laser beam may reduce system bit error rates due to irradiance scintillations in the receiver focal plane. In order to better understand the propagation of a partially coherent beam in atmospheric turbulence, we derive an analytic expression for the cross- spectral density of a partially coherent lowest-order Gaussian laser beam (TEM₀₀) in turbulence. From the second moment equation expressions for the average intensity, beam size, radius of curvature and lateral coherence length are derived. These results are valid for any beam type: focused, collimated, divergent, and the limiting cases of the plane and spherical wave. We also present preliminary experimental results that indicate a reduction in bit error rates would occur if a partially coherent beam were used.

In a previous paper the first two authors described two techniques for estimating the optical cross section (OCS) of remotely illuminated objects. This report uses OCS estimates from the Active Imaging Testbed, fielded in 1999 by the Air Force Research Laboratory's Directed Energy Directorate's Surveillance Technologies Branch to analyze the frequency and magnitude of glints. Glints are the transient, non- Lambertian returns from such features as a flat, specular surface or a natural corner cube. The OCS of a satellite is the least well understood element of the range equation used to estimate system performance. Glints caused by natural corner cubes often exceed the radiometric estimate by orders of magnitudes. However, glints also occur that are on the order of five to ten times the expected returns, due perhaps to the transient alignment of a flat surface. These phenomena can provide increased signal for tracking or imaging applications, but can also act as a noise source. Glints may be identified and their statistics analyzed using the OCS estimation technique.

Ozone data are presented which were obtained from seven balloon-borne ECC (Electrochemical Concentration Cell) ozonesonde/radiosonde experiments launched from Gap, France in the Haute Alps between 24 and 27 June 1998. These launches were carried out with the support of the CNES (Centre National d'Etudes Spatiales). Small, 1200 gram balloons were used to provide in situ measurements of ozone, wind speed, wind direction, humidity, temperature and temperature fluctuations. The balloons were launched during the spring/summer transition, a period of minimum upper air winds. The ozone height profiles obtained from the in situ measurements reveal interesting patterns in the ozone concentrations above and below the tropopause level at 12.5 km. There is some evidence that the ozone concentration is affected by wave activity. The balloon data taken over the period from 24 to 27 June 1998 are within 4% to 5% of the TOMS (Nimbus-7 Total Ozone Mapping Spectrometer) data.

Many luminous sources provide continuous or quasi-continuous radiation at near IR and longer wavelengths. The radiation continuum serves as a source of background photons, which can be used for discrete line-of-site absorption measurements by-known atmospheric constituents. The intensity ratio is uniquely determined by the absorption coefficient and range, is independent of broadband attenuations and scattering. The absorption coefficients are known and/or can be accurately calculated for a wide range of practical viewing conditions (i.e., sensor height, viewing angle, etc.). Hence, the intensity ratio and/or integrated intensity ratio can be used to uniquely derive the range of the radiating source. Fabry-Perot interferometers can provide the high throughputs and resolving powers required in compact packages. The measurements and analyses show that ranging accuracies representing down to 1 - 2% of the total range should be achievable at stand-off ranges of upto hundreds of kilometers depending on the size of the collection optics, brightness of the source and available observation times. The paper will provide an overview of the patented Textron concepts, trade-offs associated with instrument resolving powers and hardware implementation issues.

This paper compares the performance of a conventional direct detection CO₂ Differential Absorption Lidar (DIAL) system with the coherent spread spectrum approach developed and patented by Textron. The analysis shows that the coherent approach is far superior in terms of maximum attainable standoff range at a specified transmitter average power and substantially reduced system power and associated size and weight at a predetermined range. The requirements on local oscillator stability are fairly relaxed and the spread spectrum/coherent DIAL concept is fairly easy to implement. Some comparative validation data are provided.

The results of the field experiments on propagation of intensive pulses of CO₂- laser on the near surface atmospheric path have been discussed. The data are given on non-linear aerosol scattering, luminescence of aerosol particles and plasma in a light beam and their influence on the beam characteristics. The field experiments have shown that the optical breakdown and thermal luminescence of aerosol particles are possible under the effect of the CO₂-laser pulses. The heating aerosol particle up to the temperature, when the developed evaporation is occurred, yet does not guarantee the appearance of the plasma initiation core, which is capable to evolve in the regime of light detonation. At the thermal mechanism of development of equilibrium plasma the luminescence intensity maxims in different ranges of the spectrum coincide in time and occur after a maximum of an effecting pulse. The intensity fluctuations in the beam at the beginning of the pulse do not result in the luminescence fluctuations, which arise only to the end of a pulse. It testifies to an essential role of energy of a line-transmitted spectrum of the luminescence core, i.e., not too high temperatures (T approximately 10³ K) and the pressures achievable at absorption by particles of energy of the initiating pulse. The thermal blooming of luminescent particles are new radiation sources with dimensions, exceeding the size of aerosol particles by two orders that results in the 10⁴ increase of the scattering radiation. The essential part of the laser energy scattered on these blooming, as well as on shock waves, will be concentrated in a narrow angle in a forward direction, as their dielectric constant is less, than it is for aerosol particles. The measured aerosol scattering coefficient is higher than the calculated linear coefficient by one order. It is shown, that the overcondensation at explosive destruction of a water aerosol by fragments can also result in the considerable increase of scattering for specific meteorological situations.

During a period of more than 20 years we have performed successively the investigations of the effect of low- frequency spectral range of atmospheric turbulence on the optical characteristics. The influence of the turbulence models as well as an outer scale of turbulence on the characteristics of telescopes and systems of laser beam formations has been determined too.

In a recent paper the authors described a non-imaging technique for estimating the shape of remotely illuminated objects. The approach for non-imaging target shape estimation is model-based. In the absence of up-link energy fluctuations and pointing errors, a raster scan by the transmitter would produce the convolution of the expected far-field pattern with the object, providing a starting point for distinguishing targets. In this setting the referenced paper shows that it is possible to distinguish certain target shapes using a statistical confidence approach based on previous work by the authors. This paper describes a set of target models and a spectrum of far-field pattern full-width-half-maximums (FWHM). Simulations establish the optimal beam size necessary to distinguish among the models using the (chi) ² statistical confidence. This report addresses the impact of up-link energy fluctuations due to transmitter aperture size D_T relative to the Fried coherence length r₀. In the regime D_T/r₀ < 3, the far-field pattern and Strehl fluctuations are well understood. Certain cases, such as small versus large targets, are relatively unaffected by up- link energy fluctuations.

Atmospheric turbulence may have a strong impact on the imaging quality of long range warning sensors and other electro-optical systems. Major effects are beam broadening, intensity fluctuations (or scintillation) and angle-of- arrival fluctuations. The structure constant of refractive index fluctuations, C_n², is the parameter most commonly used to describe the strength of atmospheric turbulence. FGAN-FOM measured C_n² values in two different climates, moderate climate in mid-Europe, Germany and arid climate in Israel. The measurements in arid climate were carried out in cooperation with the EORD (Electro-Optics Research & Development Foundation Ltd.), TECHNION, Haifa, Israel. The measurements were performed with identical laser scintillometers along a horizontal optical path of about 100 m, above grassland in mid-Europe, and above stony ground without vegetation in Israel. The data were collected continuously for a time period of at least one year at a time resolution of 5 minutes. For both climates examples of the diurnal cycle of C_n² are given. Since C_n² usually changes as a function of time-of-day and of season its influence on electro-optical systems can only be expressed in a statistical way. Therefore the cumulative frequencies of occurrence of C_n² were calculated for a time period of one month for both climates. These results were used to calculate the corresponding turbulence modulation transfer function (MTF) and point spread function (PSF) for a typical IR sensor with a Cadmium Mercury Telluride detector (CMT) and a UV sensor.

Numerical simulation of laser beam propagation on space-to- ground and ground-to-space paths is carried out. The simulation is performed for different C_n² height profile models in dependence on atmospheric turbulence strength. Atmospheric turbulence severely degrades the performance of ground-to-satellite optical links. Using the wave to be passed from satellite to the optical ground station as the reference wave, it is studied the effectiveness of adaptive correction of laser beam propagating from the ground to satellite. Different schemes of adaptive correction are considered, namely, ideal phase conjugation, correction based on information about reference wave phase restored by mean least square procedure. The effectiveness of the correction by adaptive optics to correct wavefront distortions caused by atmospheric turbulence, and possibly improving the link budgets from ground to space and vice versa is discussed.

The one-dimensional point spread function for long-exposure frames of the whole system atmosphere - instrument is calculated from solar limb observations using data recorded at OCA Observatory (France). It is then compared to the theoretical one deduced from the Von Karman model and various wave-front structure functions. Good agreement is found allowing to deduce the spatial coherence outer scale L₀ and the Fried parameter r₀.

We present the optical setup and wavefront reconstruction algorithms for the multi-conjugate adaptive optics (MCAO) system at the 70 cm German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife. The system is designed to increase the corrected field of view (FOV) from about 10 arcseconds to 30 arcseconds in the visible. It will consist of two Shack-Hartmann wavefront sensors (WFS) and two deformable mirrors (DMs). Both wavefront sensors will be situated in the pupil plane of the telescope. One determines the high order wavefront aberrations for the center of the FOV, the other measures only low order wavefront aberrations, but covers a large FOV in each subaperture. A 35 actuator bimorph mirror and a micro mirror will correct the ground layer and the tropopause, respectively. The system will have first light in early 2002. Scientific operation is expected to start in the second half of 2002.

The method of phase distortion correction used in the Fourier telescopy imaging for laser beams in strongly inhomogeneous atmosphere implies an additional operation preceding the phase closure operation. In this additional operation, power of the radiation scattered by the object illuminated by a selected pair of laser transmitters is divided by the product of powers of radiation scattered by the object illuminated by each of the transmitters. It is proposed to measure these powers by registering radiation scattered by the object illuminated by all transmitters except one belonging to the selected pair. Thus, transmitter with short coherence length can be used. However, high level of additive noise and strongly inhomogeneous atmosphere, which leads to a considerable broadening of the laser radiation, considerably reduce the registered signal and hence, the probability of the object detection in the Fourier telescopy, The probability of detecting the object can be substantially increased by rotating the directional diagrams of the transmitters. This probability is studied as a function of the given threshold value, sizes of the transmitting and receiving apertures, standard deviations and correlation radii of the object surface roughness height distribution, and phase distortions. The suggested version of the Fourier telescopy allows one to make the object detection probability close to unity even for the noise power comparable with the power of the radiation scattered by the object. Under the condition of considerably large arrays of the laser transmitters, the method provides high accuracy of determining the object parameters.

We present results of simultaneous measurements of atmospheric parameters using a SCIDAR instrument and the Calar Alto ALFA adaptive optics (AO) system. First results indicated that SCIDAR measurements can indeed be useful for selecting appropriate closed-loop settings of an AO system. We will further establish this assumption by presenting the fully reduced data sets showing the time series of the Fried parameter and the isoplanatic angle as obtained from the two instruments. The data was recorded under varying seeing conditions on a binary star and an open cluster. Additionally, we will point out possible applications of simultaneous SCIDAR measurements in AO observations and systems.

New method to calculate the statistical characteristics of dislocations in the turbulent atmosphere is proposed based on the relation obtained before which connects the density of phase vortices with the intensity distribution. For the lognormal distribution of intensity fluctuations the integral representation of the average density of dislocations in a cross-section of light beam through the correlation functions of logarithm of intensity is obtained.

Distortions, induced by angular and longitudinal errors of telescope segments aligning, are analyzed. Two mechanisms of images averaging are modeled and analytically investigated. Temperature and other slow fluctuations of telescope mirror segments geometric parameters cause one of them. Correlation time of that process is of the order of several hours. That mechanism is investigated in reference 1. Correlation time of the other process is determined by receiving device material time constant. In the second case the certain amount of mirror segments is necessary for the averaging. If the first case, in principle, compensation is possible, the distortions can't be compensated in the second one. It leads to existing in the image some constant component, called 'inner geometric noise' (IGN). We obtained illustrating dependencies and evaluation of the IGN influence on telescope vision range.

In numerical experiment the authors investigate a representation of the phase of random optical wave through the Karhunen-Loeve-Obukhov (KLO) functions obtained with the use of phase correlation function calculated from experimental data. For such KLO basis the averaged relative error of phase expansion is 5% for 10 basis functions in the expansion series, whereas for the KLO basis calculated with the Kolmogorov structure function of phase the error of phase expansion 5% has been obtained for 78 basis functions. When propagation medium is close to Kolmogorov model it is possible to use this KLO basis obtained for a single section of distorted phase distribution for representation of whole phase distribution.

Multispectral sensing is a technique for acquiring measurements of surface radiance in a series of several electromagnetic bands, ranging from the visible spectrum (.4 mm) through the thermal infrared region (3 - 14 mm). Multispectral sensing, by virtue of its many spectral bands can provide the capability of characterizing and identifying natural and man-made targets in terms of both their spatial characteristics and often more importantly, their material properties. The research described in this paper combines spectroscopic tools and techniques, based on physical models of the absorption and scattering spectral phenomenology in the scene, with signal processing techniques, Innovative methods of directly fusing terrain representations and data from separate sensors during spectral feature extraction were also explored. The resulting algorithms were then programmed on a four-processor PCI-bus-based digital signal processing (DSP) board. The DSP board performed end-to-end processing of the multispectral imaging task, including; camera calibration, image acquisition from the four digital imaging cameras, and image processing.

Chemistry and transport models for trace species are detailed numerical formulations intended to represent the atmospheric system as a whole, accounting for all the individual processes and phenomena that influence climate changes. The development of computer resources and the retrieval of emission inventories and observational data of the species of interest have enhanced the model evolution towards three-dimensional global models that account for more complicated chemical mechanisms, wet and dry deposition phenomena, and interactions and feedback mechanisms between meteorology and atmospheric chemistry. The purpose of this study is to ascertain the sensitivity of the solar radiative field in the atmosphere to absorption and scattering by aerosols. This effort is preliminary to the study of feedback mechanisms between photolytic processes that create and destroy aerosols and the radiation field itself. In the study a cloud of water-soluble aerosols, randomly distributed in space within hypothetical 1-cm cubes of atmosphere, is generated. A random radius is assigned to each aerosol according to a lognormal size distribution function. The radiative field characterization is analyzed using a Mie scattering code to determine the scattering phase function and the absorption and scattering coefficients of sulfate aerosols, and a Monte Carlo ray- trace code is used to evaluate the radiative exchange. The ultimate goal of the effort is to create a tool to analyze the vertical distribution of absorption by aerosols in order to determine whether or not feedback between photolytic processes and the radiation field needs to be included in a Third Generation Chemistry and Transport model.

A vicarious calibration was performed for the thermal channels of the airborne DAIS imaging spectrometer during ESA campaigns in Barrax (Spain) in 1998, 1999 and 2000. Ground measurements of temperature were collected in different fields coincidentally with the flights to provide calibration and validation targets for the thermal channels of DAIS. Two calibration targets were selected (water and bare soil) to cover the range of expected surface temperatures in the area. Targets were very homogeneous thus facilitating the acquisition of ground measurements comparable to the remote measurements of DAIS. The derived two-point, linear calibration equations operate on at-sensor radiances and are used to obtain calibrated DAIS data from the original data. Calibrated at-sensor radiances were validated using ground measurements for several fields (other than those used for the calibration). For the present study the validation was made for the two flight lines of June 3, 1999. The comparison of DAIS-derived and ground- measured values was made in terms of both the surface temperature and emissivity. For the processing of the DAIS data, an adjusted normalized emissivity method was used where the input emissivities were selected for each surface according to the field measurements. With this procedure we could derive the six channel emissivities plus the surface temperature for each target. The accuracy of these estimates depends on the selected input emissivity and notably on the atmospheric correction of the DAIS thermal channels. For the Barrax site, the atmospheric correction was calculated with local radiosonde measurements and the MODTRAN 4 code. The results of the validation indicate that surface temperatures and channel emissivities could agree with ground measurements within +/- 1 degree(s)C and +/- 0.01 respectively.

We describe an adaptive optics system for the 1.5m diameter solar telescope GREGOR which is currently developed for the Teide Observatory on Tenerife. In a first development step, the AO will provide compensation of 77 modes of wavefront deformation, corresponding to the first 10 radial degrees of a Karhunen-Loeve decomposition of wavefront error. We estimate that such a performance will render GREGOR nearly diffraction limited at visible wavelengths in conditions which correspond to the best 25% of the seeing In Tenerife. The AO uses a Shack-Hartmann wavefront sensor which operates on fine structure anywhere on the solar disk. The required control bandwidth will be about 200 Hz. We show how such a system can be realized using existing technology. Substantial increases in performance in terms of corrected wavefront error and field requires significant technological advances, in particular in the field of large field high speed detectors.

In several Lidar techniques molecular backscattering from atmospheric gases is considered, e.g. Raman lidar technique, and elastic molecular scattering by HSR1 technique are employed. When larger particles are also present in the sounded zone, Mie scattering contributions are superposed to the Lidar molecular signal. Because the efficiency of the Mie scattering is very high with respect to the molecular one, the effect of Mie scattering can be very strong for typical tropospheric clouds or aerosol structures, when multiple scattering contribution becomes important. In this case the incident, or the molecular scattered radiation, can be multiply scattered from the aerosols. There is no significant multiple molecular scattering, but larger particle scattering processes occur in addition to one molecular scattering. A Monte Carlo code developed for studying this effect is described by means of a flow diagram showing the details of the procedure. The code allows the consideration of depolarization for the molecular return due to the intervening effect of Mie scattering. Some results in some cases of realistic models of atmospheric structures are presented, showing increase of the molecular returns by factors even of the order of a few units. Comparisons with published data by other authors will be shown.

MATISSE is a new atmospheric radiative transfer code currently under development at Onera. Its purpose is to compute background radiance images by taking into account atmospheric, cloud and ground radiation and the variability of atmospheric properties. Propagation is calculated using a Correlated K model (CK) developed at Onera. The spectral range is between 3 to 13 micrometers with a resolution of 5 cm^-1. Weather forecast outputs and aerosol climatology are used as inputs to account for spatial variability of atmospheric properties in radiance computations. Partial stratocumulus cloud cover can be generated and the radiation computations use Independent Pixel Approximation (IPA) and Bidirectional Reflectivity Distribution Functions (BRDF). Ground emission and reflectance are computed from spectral emissivities, BRDF and a simple thermal model for the local ground temperature. Databases include a Digital Terrain Elevation (DTED) and a land use database with 30' spatial resolution. Texture models are used to add realistic ground and cloud clutter down to 10 meter resolution. A line-by-line model is included to compute the spectral intensity propagated from high temperature exhaust plumes. Refraction effects are computed, but only along one single line of sight.

We study the noise propagation for MultiConjugate Adaptive Optics (MCA)) systems working with Shack-Hartmann wavefront sensors (WFS). Two approaches are considered to control the deformable mirrors using WFS data: a classical Least Square approach and a Maximum A Posteriori (MAP) estimator. Analytical results, based on a Fourier transform analysis, allow us to study and quantify the reconstruction phase error for the two estimators. Consequences of the noise propagation on system design and performance is analyzed.

We developed a code aimed at determining the laser parameters leading to the maximum return flux of photons at 0.33 micrometers for a polychromatic sodium Laser Guide Star. This software relies upon a full 48-level collisionless and magnetic-field-free density-matrix description of the hyperfine structure of Na and includes Doppler broadening and Zeeman degeneracy. Experimental validation of BEACON was conducted on the SILVA facilities and will also be discussed in this paper.