Blasts and detonations release large amount of energy in short time duration. Some of this energy is released through
radiation in the whole optical spectrum. Measurement of this radiation may serve as a base for investigation of the blast
phenomena. A fast multispectral radiometer that operates in proper chosen spectral bands provides extensive information
on the physical processes that govern the blast. This information includes the time dependence of the temperature, area
of the blast as-well-as of the aerosols and gases that are generated. Analysis of this data indicates the order of the
detonation and provides good estimation on the masses and types of the high-explosives (HE) materials and their casing.
This paper presents the methodology and instrumentation of fast multispectral radiometry in application to the blast
measurement and analysis in a Near-ground Explosion Test (NET). In NET, the flash radiation of the blast was measured
for two HE materials: TNT and composition B (CB). The investigation includes charges of different masses (0.25 - 20.0
kg) and of various casing materials (steel, Al, PVC), thickness (2 – 6 mm) and various casing type (open on both face
ends and hermetically closed). Analysis of the data demonstrates the power of fast radiometry methodology and reveals
the governing characteristics of atmospheric blasts.
Knowledge regarding the processes involved in blasts and detonations is required in various applications, e.g. missile
interception, blasts of high-explosive materials, final ballistics and IED identification. Blasts release large amount of
energy in short time duration. Some part of this energy is released as intense radiation in the optical spectral bands. This
paper proposes to measure the blast radiation by a fast multispectral radiometer. The measurement is made,
simultaneously, in appropriately chosen spectral bands. These spectral bands provide extensive information on the
physical and chemical processes that govern the blast through the time-dependence of the molecular and aerosol
contributions to the detonation products. Multi-spectral blast measurements are performed in the visible, SWIR and
MWIR spectral bands. Analysis of the cross-correlation between the measured multi-spectral signals gives the time
dependence of the temperature, aerosol and gas composition of the blast. Farther analysis of the development of these
quantities in time may indicate on the order of the detonation and amount and type of explosive materials. Examples of
analysis of measured explosions are presented to demonstrate the power of the suggested fast multispectral radiometric
analysis approach.
Blasts and detonations release large amount of energy in short time duration. Some of this energy is released in
the form of intense radiation in the whole optical spectrum. In most cases, the study of blasts is mainly based on
cameras that document the event in the visible range at very high frame rates. We propose to complement this
mode of blast analysis with a fast measurement of the radiation emitted by the blast at different spectral bands
simultaneously. A fast multispectral radiometer that operates in the proper spectral bands provides extensive
information on the physical processes that govern the blast. This information includes the time dependence of
the temperature, aerosol and gas composition of the blast, as well as minute changes in the expansion of the
blast - changes that may indicate the order of the detonation.
This paper presents the new methodology and instrumentation of fast multispectral blast radiometry and shows
analysis of measured explosions that demonstrate the power of this methodology.
Transient multi-spectral signatures have become a basis for the development of IRST (IR Search and Track) and automatic target acquisition systems. Multi-spectral signatures must be measured in absolute physical system-independent units in order to be valid for use in system design. The required data comprise a temporal profile of the radiant intensity (or radiance) emitted by the target at the target plane in the required spectral bands. The methodology for converting electronic output signal from a multi spectral radiometer - volts - into the radiant intensity of the object is a complex procedure. In this procedure the following parameters have to be taken into account: the nature of the measured target (gray body or molecular emission spectra), the spectral filter, the detector responsivity, the frequency response and rise time and all ambient parameters such as atmospheric attenuation and solar radiance. Avoiding the correct analysis procedure, leads to erroneous data which may mislead users of multi-spectral signatures. This paper describes the appropriate methodology for multi-spectral signature measurement, analysis and factors that influence the accuracy of the resultant data.
As more and more spectral ranges are used by different threat detecting sensors, the effectiveness of a countermeasure is becoming more and more dependent on how similar its emitted spectrum is to the object that it is supposed to simulate. As a result, the need to model and test the countermeasure radiometric output (in radiance units) and contrast (in radiant intensity units) or effective temperature at different wavelengths simultaneously increases in importance during both R&D and production for both the producer of countermeasures (to confuse the seekers) and the producer of missile seekers (to prevent seeker confusion). We have developed a family of multi-spectral radiometers (ColoRad) specifically designed to quantitatively measure countermeasure spectral signatures dynamically for precise characterization. In this paper we describe the design of such instrumentation, including the various modes of operation and highlighting the important instrument features for the present application. In addition an example of measurement is given here to demonstrate its usefulness. The ColoRad performance parameter values are also given in this paper.
Understanding of the temporal and spectral behavior of the radiation emitted from fast transients such as gun shots, explosions, missile launches and kinetic ammunition is very important for the development of IRST, MWS and IRCM systems. The spectral-temporal behavior of the signature of these events is an essential factor for their detection and for the filtering of false alarms. Munitions flashes are fast transient phenomena with time duration that range from the sub-millisecond to a fraction of a second. A full characterization of the infrared signature of these events involves measurement of the evolution of its spectral distribution in time where the temporal resolution required is of the order of microseconds. We describe here a method for utilizing a four-channel radiometer to extract the above-mentioned data from these events. We show that we can derive the temporal evolution of the temperature of an explosion on time scale of 20&mgr;sec and separate energy releasing processes. Several practical examples will be given.
Radiance measurements conducted from a high-altitude platform to retrieve surface properties will potentially involve long, near-horizontal viewing geometries. The computer code MODTRAN is widely used for the prediction of the propagation of infrared radiation through the lower atmosphere. Consequently, we have undertaken to test the predictions of MODTRAN for the 3 - 5 and 8 - 12 micron spectral regions under mid-Eastern desert conditions. This paper compares experimental measurements in geometries of interest with calculations using the latest version of MODTRAN. Results indicate a strong dependence of the remotely sensed radiation on both the aerosol and water vapor content.
The aim of this research is to measure the electromagnetic radiation scattering properties of the atmosphere and to compare the experimental results with a Monte Carlo type model. The radiation scattered by suspended particles, known as aerosols, is the topic of interest. The presence of aerosols between a point source and an observation system causes the formation of a corona around the point source. The intensity of this corona is the Point Spread Function (PSF). A comparison is presented between the measured atmospheric PSF (caused by scattering) and the PSF which is calculated using a Monte Carlo calculation. While in previous studies the maximum path length was 600 meters, in the present research the path length was increased to 2000 meters. The spectral range was extended from the visible to 3.6 micrometers in the infrared. The authors used a collimated black body source for illumination and an IR radiometer as an observation system. The conclusion from the experimental results is that an increase of the beam divergence causes an increase in the scattered light received, as predicted by the model.
Radiance measurements conducted during tropospheric operations to detect objects on the Earth's surface from a manned aircraft or from an unmanned airborne vehicle (UAV) will involve long, near-horizontal viewing geometries. The computer code MODTRAN is widely used for the prediction of the propagation of infrared radiation through the lower atmosphere. Consequently, we have undertaken to test the predictions of MODTRAN for the 3 - 5 and 8 - 12 micron spectral regions under mid-Eastern desert conditions.
KEYWORDS: Atmospheric modeling, Point spread functions, Imaging systems, Data modeling, Aerosols, Scattering, Modulation transfer functions, Radiometry, Monte Carlo methods, Atmospheric physics
This paper presents the results of a field experiment that was carried out in order to verify a physical model which describes the relationship between the optical properties of the atmosphere and the characteristics of an imaging system. The model depicts how different components of the light that are reaching the imaging system, after passing through the atmosphere, are detected by it. The measurements were done using a scanning point radiometer, while a local meteorological station measured the properties of the atmosphere. Theoretical predictions, which were achieved using a Monte-Carlo simulation of atmospheric scattering effects, are compared with the experimental data acquired in the field test. Comparison of theoretical predictions, using the above model, with the experimental data of other researchers is included. Both our data and the results of Luc Bissonnette of Canada supports the suggested model.
The atmosphere is the optical medium between the imaging system and the observed object. The effect of this optical turbulent, absorbing and scattering element on the quality of an image is difficult to predict. Since the beginning of the sixties there were several attempts to build a model that will describe the degrading effect of the atmosphere on spatial resolution of imaging systems. In the field of atmospheric turbulence there is a common agreement on its relative contribution to the degradation of the spatial resolution of an image. On the other hand in the field of atmospheric scattering there is a disagreement on its degrading effects and an international scientific discussion has been developed in the past five years in this scientific field. A model, that was suggested several years ago by Sadot and Kopeika, claimed that the effect of the atmospheric scattering on the spatial resolution of imaging systems is a function of the properties of the imaging system, apart from the inherent properties of the atmosphere. The results of their model were in contrast with the results of the work of other scientists and therefore, caused a scientific debate. The purpose is to propose an alternative theoretical model which describes the effects of atmospheric scattering by focusing on the point spread function of the imaging system.
The Ozone Meter (OM-2) described in this paper is designed to obtain both ozone profiles and cumulative ozone amount in the earth atmosphere from space measurements of solar backscatter ultraviolet radiation. OM-2 uses a filterwheel- photometer combination to measure UV radiation in the 252.0- 340.0 nm spectral region in 7 fixed wavelengths with 1.0 nm bandwidth. This short form report describes the OM-2 according to its optical scheme, detector, electronic parts, the filter wheel mechanism, the filters and the mechanical design. This technique can detect large variations of ozone a broad range of atmosphere with errors ranging up to 15 percent. The OM-2 instrument has small weight and size, low power consumption and an accuracy similar to that of more complicated instruments used in the past. The OM-2 will be a part of the instrument pack of the Israel microsatellite TechSat-1A that will be launched in 1997.
Remote sensing is based on the ability to measure accurately the spectral radiance of remote objects in the object plane. This ability is limited by the measuring system (resolution and sensitivity) and by the atmospheric transmittance, especially when long distances are involved. As a result, the need to enhance S/N led us to develop new measurements techniques and analysis methods. This presentation deals with two different techniques of modern radiometry -- point spectroradiometry with moderate spectral resolution and spatial radiometry (imaging systems) with low spectral resolution. This presentation will address three issues related to advanced analysis methods of radiometric measurements: (1) The effect of the exact shape of the slit- function of the point radiometer on the results of the spectral analysis, (2) the optimal calculation of a signature from radiometric imager, and (3) the correcting factor that must be introduced into the analysis of a spatial picture of point target which is much smaller than the IFOV of the imaging system (star detection). The experience and knowledge gained by IMOD and EORD in the area of radiometric analysis was implemented in a user friendly software (TIRAS) that is used for the radiometric (and not temperature) analysis of various spatial radiometers. The radiometric data was measured for various applications of IMOD such as data bases of targets and backgrounds, and study of radiometric behavior of IR scene elements.
In this paper a physical model that describes the relationship between the optical properties of the atmosphere and the characteristics of an imaging system is suggested. The model describes how different components of the light reaching the imaging system, after passing through the atmosphere, are detected by it. The model includes the effects of the final size of the detector elements of the imaging system and the dynamic range and the final field of view limits of the imager. It is found that for common imaging systems (with resolution of 8 bit or 12 bit) working in general atmosphere conditions (VIS >= 5 km), the processes of atmospheric scattering and absorption hardly contribute to spatial blurring of the recorded images. A field experiment was carried out in order to verify the predictions of the suggested model. The measurements were performed using a scanning point radiometer, while a local meteorological station and a visibility meter measured the properties of the atmosphere. Theoretical predictions, which were accomplished by using a Monte-Carlo simulation of atmospheric scattering effects, are compared with the experimental data acquired in the field tests. A good agreement was obtained between the measured data and the theoretical predictions.
A numerical code is used to examine the features of the effect of atmospheric turbidity on the modulation transfer function of an optical system operating on ground, on an airplane or a satellite. Models of size distributions and optical properties of particulate suspended in the atmosphere are considered. The relevant scattering phase functions are calculated by Mie theory and are later used by a code using both Monte Carlo and geometrical optics procedures to evaluate the contribution of atmospheric turbidity to the augmentation of the point spread function. Comparison of ours with other researchers procedures is shown. The effect of atmospheric turbidity is evaluated as due to the presence of scatterers (the secondary sources) whose defocused images are distributed on the plane of the image of the primary source. The positions of the scatterers are determined by a Monte Carlo procedure, while the contribution of each secondary source to the irradiance on the image plane is evaluated by means of geometrical optics. Cases of different aerosols types, geometry aspects of viewing through the atmosphere and atmospheric absorption effects on the MTF are shown.
Recent investigations of the atmospheric transmittance in the 15- to 25-μm spectral region have produced experimental results of the absorption of the water vapor continuum. From these results it is evident that the excessive absorption of the water vapor (the water continuum) cannot be explained simply by the theoretical continuum model based on the modified impact theory and the Van Vleck-Huber model of line broadening. The measured continuum absorption has spectral features similar to those roughly predicted by the water dimer theory. A quantitative agreement between the experimental results and the prediction according to the dimer theory was found.
Restoration of thermal images distorted by the atmosphere is presented. The method is based on atmospheric MTF analysis, both theoretical and experimental. Thermal IR atmospheric MTF measurements performed simultaneously in both atmospheric IR windows (3- to 5- and 8- to 12-μm wavelengths) are also presented. The MTFs were evaluated via point spread function measurements, under various meteorological conditions and different SNRs. Results are analyzed and shown to be in very good agreement with theoretical predictions.
Restoration of thermal images distorted by the atmosphere is presented. The method is based upon atmospheric modulation transfer function (MTF) analysis, both theoretical and experimental. Thermal infrared (IR) atmospheric MTF measurements carried out simultaneously in both atmospheric IR windows (3 - 5 and 8 - 12 micrometers wavelengths) are presented too. The MTFs were evaluated via point spread function (PSF) measurements, under various meteorological conditions and different signal to noise ratios (SNRs). Results are analyzed and shown to be in very good agreement with theoretical predictions.
The computer code LOWTRAN is widely and extensively used for the prediction of propagation of IR radiation through the atmosphere. The latest version of this code, LOWTRAN 7, is assumed to be the most elaborate and accurate one. Hence it was decided to test its validity by comparing its prediction for ground-to-space slant paths with actual transmittance measurements with the sun as a blackbody source. A good agreement between the theoretical predictions and the experimental results were obtained in the 8 - 12 micrometers spectral region for all zenith angles between 90 degree(s) and 60 degree(s) (0 degree(s) to 30 degree(s) above the horizon). In the 3 - 5 micrometers spectral region some spectral discrepancy was observed though the value of the integrated measured transmittance agreed well with the predicted one. The reasons for this can be assumed to be in the new band model absorption parameters (in the 3 - 4 micrometers region) and in the water continuum model (in the 4.4 - 5.2 micrometers region).
The factors affecting the spectral composition of radiation reaching a distant observer from a natural object, and thus determining its apparent color, are experimentally studied. A method to calculate the apparent color is examined in which the spectral radiance of a distant object is first measured at zero distance and variations in the apparent radiance are then studied as a function of the distance. Sample results are given.
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.
Recent investigations of the atmospheric transmittance in the 15-25jm spectral
region have produced experimental results regarding the absorption of the water
continuum. From these results it is quite evident that the excessive absorption of
the water vapor (the water continuum) cannot be explained only by the theoretical
continuum model based on the modified impact theory and the Van Vleck-Huber model of
line broadening. The measured continuum absorption has spectral features similar to
those roughly predicted by the water dimer theory. A quantitative agreement between
the experimental results and the prediction according to the dimer theory was found.
This work describes a new technique that can be used to determine the IR transmittance and path radiance of an obscuring atmosphere. The method is based on alternate measurements of contrast through a clear and obscuring atmosphere respectively. An advantage of this technique is that it utilizes existing thermal imagers and does not require an additional transmissometer in the field. The technique was tested using an AGEI4A 780 Thermovision camera operating in the 7.7-13.2 micron spectral region. A good agreement between theory and the experimental results was obtained.
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