A. Ben-Shalom

Contribution Of Oxygen To Attenuation In The Solar Blind UV Spectral Region

The Solar Blind Ultraviolet (SBUV) spectral region covers the interval between 230 nm and 290 nm. The lower limit of this interval is given by the edge of the Schumann-Runge band and the upper limit is determined by solar radiation penetrating the stratospheric ozone shield. The SBUV region is interesting from the experimental point of view, since the lack of solar background is favorable in such applications as lidar, atmospheric communication and remote sensing. The present models (LOWTRAN-6) include as atmospheric attenuators in this region ozone absorption, aerosol and molecular scattering. New theoretical calculations of the Herzberg I oxygen band predict significant absorption by 02. This prediction is confirmed experimentally in the present study. Field measurements at 252, 255 and 264 nm are reported over optical paths of up to 2750 m. Results show that LOWTRAN-6 is inadequate in the SBUV region, as indicated by the present extinction measurements.

Contribution of oxygen to attenuation in the solar blind UV spectral region

The solar blind ultraviolet (SBUV) spectral region covers the interval between 230 and 290 nm. The lower limit of this interval is given by the edge of the Schumann-Runge band and the upper limit is determined by solar radiation penetrating the stratospheric ozone shield. The SBUV region is interesting from the experimental point of view, since the lack of solar background is favorable in such applications as lidar, atmospheric communications, and remote sensing. The present models (LOWTRAN-6) include as atmospheric attenuators in this region ozone absorption and aerosol and molecular scattering. New theoretical calculations of the Herzberg I oxygen band predict significant absorption by O(2). This prediction is confirmed experimentally in this study. Field measurements at 252, 255, and 264 nm are reported over optical paths of up to 2750 m. Results show that LOWTRAN-6 is inadequate in the SBUV region, as indicated by the present extinction measurements.

Spectral characteristics of infrared transmittance of the atmosphere in the region 2.8–14 μm—preliminary measurements

Abstract We have made preliminary measurements of the atmospheric transmittance spectrum along horizontal paths up to 44 km in length. The equipment, a collimated radiation source and a moderate-resolution measurement system, is described in some detail, and also the method of processing the results. Some examples of measured spectra are shown and compared with the prediction of the lowtran 4 program. In particular, quantitative discrepancies are indicated in the 2.8–5.5 μm region. Smaller differences were detected in the 8–14 μm region at long distances for which the lowtran program appears to predict consistently small values for the transmittance.

Infrared Spectral Radiance Of The Sky

A method of calculating the self-radiance of the sky based on the LOWTRAN-4 computer code is described. The method is a significant improvement on that included as an option in LOWTRAN-4 itself as a result of two modifications: a) Our method, unlike the one included in LOWTRAN-4, takes into account the radiance scattered into the line of sight. b) The model of the atmosphere in the computer code must be divided into a certain number of layers, each one having approximately uniform conditions. Our method uses a correct optimal division. Consequently, our method gives a better agreement with the experimental data, especially for long optical paths in the lower layers of the atmosphere.

Experimental Validation Of Atmospheric Transmittance Codes

This review describes the present computer codes used to predict atmospheric transmittance. Since these codes are based on modeling of the optical properties of the atmosphere, there is a constant need to validate them in long-path atmospheric transmittance measurements. These measurements and their results will be described here.

Different aspects of backgrounds in various spectral bands

Both the theoretical and the experimental problems of backgrounds are examined. The authors show why the current definitions of correlation length should be used with care, with attention paid to the intensity histogram of a scene. Different effects of the sub-pixel features in a measured scene on the clutter for imaging and scanning systems are also explained. The two- dimensional polarization of a scene is measured and found to compare favorably with the theoretical predictions. Finally, the authors show how to simulate backgrounds whose power spectrum is given, together with constraints on the image proper. This is achieved by iteratively transforming between the image plane and its Fourier conjugate, while imposing the appropriate constraints in both planes.

Measurement of the integrated water vapor content in the atmosphere by a radiometric method

An improved version of a two-wavelength radiometric method is described by which the total water vapor amount along an optical path may be determined by the use of a radiometer and a source at the two ends of the optical path. The method requires two transmission measurements: one at 1.14 microm (at the center of an absorption band) and another at 1.06 microm (an atmospheric window). The spectral transmittance is calculated using the FASCODE computer code, convolved with the source, filter, and detector response curves of the transmissometer. Good agreement (1-7%) is obtained with experimental observations of this quantity as a function of total water vapor amount. The method was verified for horizontal paths of up to 10 km.

Long Path Atmospheric Transmittance Measurements: Technique, Instrumentation And Results

The equipment and data analysis used by a field laboratory system to measure atmospheric transmittance spectra are described. Measurements have been made at distances up to 44 Km in the 3-5μm region and up to 24 Km in the 8-12 μm region. The results agree well with the latest version of the LOWTRAN computer code.

Measured spectral extinction coefficient dependence of vehicle dust at visible, infrared and near-millimeter wavelengths

Abstract Measurements were made at visible, infrared (i.r.) and near-millimeter wavelengths (NMMW) to determine the effect of vehicle-generated dust clouds on transmission. Results from these tests indicated little or no attenuation at NMMW frequencies (96, 140 and 220 GHz), while there was appreciable transmittance loss at visible (0.4–1.1 μm) and i.r. (3.0–5.5 μm, 8.0–13.0 μm) wavelengths. Analysis of the visible and i.r. transmittance data indicated that a spectral dependancy occurred after the fallout of the heavier particles and the dust cloud became stabilized. Extinction coefficients were calculated for each of the wavebands. The ratio between the coefficients in the i.r. and NMMW and those for visible wavelengths were: 0.86 for 3.0–5.5 μm, 0.78 for 8–13 μm, and less than 10 −3 for 96, 140 and 220 GHz.

Background properties in arid climates: measurements and analysis

Knowledge of background properties is essential for various applications such as systems engineering and evaluation (e.g. electro-optical sensors or for camouflage design), operational planning and development of ATR algorithms. A series of field tests was conducted in the NEGEV desert in Israel, as a joint effort of the FGAN-FfO (Germany) and EORD (Israel) for characterizing properties of backgrounds in arid climatic regions. Diurnal cycles of background surface temperatures were measured during summer and winter periods in several sites in the NEGEV. The measurement equipment consisted of imaging cameras, most of them calibrated, covering the spectral region from the visible up to the thermal infrared. This paper presents the measurement set- up, the measurement techniques that were used, and some of the first analysis results.