Michael Y. Engel

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.

Methodology for accurate multi-spectral signature measurement

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.

Multispectral radiometers (ColoRad) for spectro-temporal flares intensity emission measurements

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.

Fast multichannel radiometer for diagnosing munition flashes

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.

Quantitative evaluation of errors in remote measurements using a thermal imager

This work presents quantitative evaluation of errors in measurement that arise in using a thermal imager as a radiometer. The analysis will mainly deal with the 7 13 micron spectral region . The main sources contributing to errors in spatial radiometric measurements can be divided into three categories: 1) inaccuracies in determining atmospheric transmittance and path radiance, 2) calibration errors and dynamic range problems due to nonlinearities of instrument response, 3) errors due to spatial response arising from the finite point spread function and non uniformities of the field of view. The contribution of each of these factors to the final cumulative error in the measured radiometric quantity will be analysed and the sensitivity to the individual factors shown. This analysis is done with respect to an existing measurement system in use, namely the AGEMA 780 Dual Band Thermovision Imager.

Progress in radiometry: measurement techniques and analysis methods

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.

Blast investigation by fast multispectral radiometric analysis

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.

Characterization of passive millimetric-wave scenarios: backgrounds and targets at 140 and 220 GHz

Passive MMW sensing is getting more and more attention as sensors in this spectral region get better. This development requires understanding of the passive MMW target detection scenario. This scenario consists of natural background elements and targets. Understanding of the behavior of backgrounds and targets as function of environmental conditions is vital for the analysis of any future sensor performance for this spectral region. During the past year, EORD has measured the radiometric properties of natural backgrounds and several man made objects using its dual frequency 140/220 GHz radiometer. This work will describe the measurement setup and give some of the results of background and target measurements. The measurement results will be correlated to the thermal IR radiometric data and the actual contact temperatures of the objects.

FPA sensor performance study using computer simulation

The development process of new FPA imaging systems should be accompanied by an operational research study. The tool for such a study should be a model that predicts the performance of the overall system (detector, optics, signal processing, human observer), together with the target signature characteristics and the background properties. This model should yield a figure of merit that will be used for the performance study during the design and development process of the system. The influence of various parameters that will be used in the design process of the system can be studied using this tool. This work presents an approach where an image based sensor model was used to study the ability to detect and recognize different targets at various scenarios. The sensor model was used to simulate images of bar patterns for the evaluation of the modeled sensor MRTD. The results were compared to FLIR 92 predictions and the real sensor MRTD measurements. The model was then used to simulate targets embedded at various types of backgrounds. The images were presented to human observers that determined whether they detect or recognize the targets. This paper will bring a short description of the FPA sensor model and will present the methodology of using the simulation for sensor performance study. An analysis of some of the obtained results will be included as well.