A brief review of the psychophysical relationships which influence an observer's ability to discern barely perceptible changes in apparent contrast is presented with comments related to meteorological observations and instrument calibrations. Examples of how uncertainties in the specification of the atmospheric optical state might influence slant path contrast transmittances are illustrated.

This paper overviews the application of low resolution transmissometer systems to field measurement of spectral transmission through the atmosphere. A discussion of atmospheric models, such as the Air Force LOWTRAN and the Army E-OSAEL computer Codes is followed by a description of a typical low resolution transmissometer system. The procedure to calibrate the transmissometer in order to produce absolute transmission is presented. Some typical problems associated with field measurement of atmospheric propagation is given. The remainder of the paper deals with spectral transmission results in the 3-5 micrometer region during GRAF I Atmospheric Trials1 in Europe. The data analyzed was provided by the Night Vision and Electra-Optics Laboratory for use in this paper.

An indication is given of the effect which variations in pressure, temperature, relative humidity, water content, aerosols, and gaseous concentrations have on the attenuation and thermal radiance of the atmosphere in the 2-14 µm region for both horizontal and slant paths.

The authors describe a laser Doppler anemometer working in backscatter over distances of 2 to 5 meters based on a pulsed laser source. After a description of the optical set-up and the pulsed laser they describe a number of experiments carried out under conditions normally found in industrial testing facilities.

The characterization of the obscuring medium that one might find on the battlefield of the future is an extremely vital effort because of the communities that could be well served by it. Among these communities are the combat developers or battle planners who look to the way we use our weaponry and personnel to accomplish various military goals; the trainer who develops proficiency in the utilization of our weaponry; the designer of electro-optical devices which serve the weaponry and the designer of obscurants themselves. However, very few of the instruments that we carry to the field to characterize obscurants either directly or indirectly characterize the obscured condition well. This paper will talk to the limitations of some of this instrumentation and to the way the data is being reduced, used and possibly misused.

Dugway Proving Ground (DPG) is one of a network of proving grounds maintained by the US Army Test and Evaluation Command (TECOM). TECOM's mission is for development and acceptance testing within the major command, US Army Materiel Development and Readiness Command (DARCOM) and in that role TECOM has a primary responsibility in testing methodology. In 1976, DPG was designated by TECOM as the testing center for characterizing smoke and for measurement of EO system performance in smoke. The decision was based on the fact that DPG has long been involved with aerosol characterization as the chemical-biological-radiological (CBR) center.

The Point Characterization Instrumentation System (PCIS) is an instrumented 28 ft. fifth wheel trailer designed to obtain in situ measurements of microscale obscurant properties, such as the mass extinction coefficient, of battlefield smokes. PCIS is being developed for the Project Manager of Smoke/Obscurants for a variety of field tests. This paper describes PCIS as it will be configured during the PG-16 field trials to be conducted in France in September 1982 and Norway in February 1983. Examples of data resulting from using PCIS in a partially completed state during Smoke Week IV of November 1981 are discussed.

Data used to characterize the optical properties of military obscurants are obtained in distance scales which may range from less than 10m to greater than 100m. Comparisons of data for the same optical parameters but measured over both large and small distance scales may show significantly different results. Methods for quantitatively comparing these parameters have not been developed. It is proposed that such comparisons can be achieved through statistical methods and by treating time dependent parameters such as transmission in terms of probability density functions. In this way, correlation coefficients can be determined between the two sets of data which can be used to quantitatively assess the degree of agreement.

Questions concerning data types required for electro-optical obscuration modeling of the "dirty battlefield" are addressed. The philosophy is taken that "modeling should lead measurements" in setting requirements and a framework is established to examine questions from this viewpoint. Specific examples for modeling hygroscopic growth effects, fire products and path radiance are given. The major emphasis is on transmission and radiance but other factors required for modeling and which influence the accuracy of measurements are also addressed.

The field measurement capabilities of OMEW for electronic warfare (EW) signatures will be discussed. Tracking, pointing, portability, development time, personnel, sensor interchangeability, power, and weight requirements and solutions to them will be discussed in addition to classical measurement and calibration aspects. Three currently operational field systems and,a fourth under development will be described.

A description will be presented of a large aperture, high precision, simultaneous atmos-pheric propagation and radiant signature field measurement system. Novel features of the system include: simultaneous multispectral measurement of path radiance and transmission through the same air column, absolute laser calibrated transmissometery, visible and 8-12 μm imagery with 8-bit dynamic range digital recording, 2-12 pm Fourier Transform Spectroscopy with 0.03 cm-1 resolution, and digital data acquisition with real time data reduction through the use of on-line minicomputers. The flexible modular approach of the system will be shown as will its ability to address many atmospheric propagation and/or radiant emission problems in an unified manner, thereby permitting separation of combined physical processes in many cases. Preliminary data acquired by the system will be presented from: SMOKE IV (November 1981, Huntsville, Alabama) showing refractive effects of thermal plumes on laser beam propagation, and SNOW lA (January 1982, Burlington, Vermont) showing relative transmission of three broad spectral bands through falling and blowing snow utilizing a stable secondary standard IR source.

A digital thermal imagery system which operates at TV frame rates has been developed for the US Army Atmospheric Sciences Laboratory. The system has been developed from principally commercially available components with appropriate interfaces, control electronics and software custom designed by OptiMetrics personnel. The system can acquire and store 15 minutes of 8-bit dynamic range thermal imagery at the rate of 30 frames per second. The data can be replayed, reduced and processed under the control of an HP 1000 minicomputer immediately after recording at the field measurement site.

The Mobile Tracking Imaging Radiometer (MTIR) has been developed at White Sands Missile Range to support future tests of experimental laser systems. The MTIR features a high angular resolution Forward Looking Infrared imaging system (FLIR) capable of simultaneous operation at 3.7 - 5.5 and 8 - 12 micrometers. The FLIR, which is mounted behind a long focal-length tracking telescope, utilizes internal calibration sources as well as external targets to obtain,radiometric data. Radiometric calibration considerations are discussed and measurement results presented.

Instrumentation and procedures for performing absolute spectral transmittance and radiance measurements over very long atmospheric horizontal paths, up to 50 km, are described. A collimated chopped radiation source was developed using a 64 cm diameter optical collimator and an electrically heated graphite element which operated at 2400 K. For detection a 20 cm diameter spectro-radiometer was developed and used successfully in many field measurements of absolute transmittance. The contribution of the measured data towards improving the LOWTRAN propagation model is presented. The successful development of the instrumentation and its operation make it a very powerful tool for obtaining significant absolute atmospheric transmittance data over very long horizontal paths.

Radiometric imaging techniques have direct application for measurement of reflected laser energy distribution. Common camera techniques have certain shortcomings stemming from limited dynamic range and imaging characteristics associated with specific detector and camera systems. This paper discusses various techniques which can be used to overcome camera deficiencies and a technique for cascading multiple camera systems over a range of sensitivities, thereby increasing the overall dynamic range. When coupled with suitable software routines, multiple camera systems can be used as an imaging radiometer suitable for measuring laser energy distribution and developing distribution maps.

Field research in remote sensing is reviewed. Current measurements, instruments, and procedures are detailed. The status of current techniques and needed instrumentation are discussed.

A low-cost, hand-held multiband radiometer was used to measure reflected sunlight from barley canopies with varying levels of spot blotch, a foliar disease of barley. Spectrora-diometric measurements indicated that reflection of light in the .75 - .9 μm range was significantly less (P = < .01) from diseased canopies than from healthy ones. Yield of grain from the susceptible cultivar 'Larker' was correlated positively with amount of reflectance in the .75 - .9 μm range (P < .01). The results suggest the instrument may be useful for the objective assessment of foliar disease and the possible development of models to estimate losses from foliar disease.

Electro-optical field measurements of scene reflectance, together with appropriate target characterization, will play an increasingly important role in the testing, intercomparison, and extension of scene radiation models. Such models, in turn, will serve to extrapolate the range of applicability of field measurements to a wider set of environmental conditions and sensor/source viewing geometries than could practically be obtained by direct measure-ment. This paper presents several issues which must be addressed before such a symbiotic relationship between modeling and measurement approaches can be achieved. The direct comparison of model predictions with field measurements is seen to be a somewhat more subtle task than might be suspected.

Hand-held radiometers that measure reflected solar and emitted thermal radiation are useful for evaluating agronomic parameters. An example application is presented which shows that thermal measurements can detect water stress before visual signs appear. Reflected solar measurements can be used to document the history of stress, and are useful for calibrating the thermal parameter at various degrees of stress. Some special requirements of instruments that are to be used in field experiments are discussed.

A crops and soils data base has been developed at Purdue University's Laboratory for Applications of Remote Sensing using spectral and agronomic measurements made by several government and university researchers. The data are being used to (1) quantitatively determine the relationships of spectral and agronomic characteristics of crops and soils, (2) define future sensor systems, and (3) develop advanced data analysis techniques. Researchers follow defined data acquisition and preprocessing techniques to provide fully annotated and calibrated sets of spectral, agronomic, and meteorological data. These procedures enable the researcher to combine his data with that acquired by other researchers for remote sensing research. The key elements or requirements for developing a field research data base of spectral data that can be transported across sites and years are appropriate experiment design, accurate spectral data calibration, defined field procedures, and thorough experiment documentation.

There is a need to calibrate satellite data obtained at large polar (i.e. off-nadir) view angles for effects caused by scanner geometry and by the atmosphere. If such effects are not corrected for, then recorded radiance data will contain systematic and random errors which will make accurate target identification and quantification difficult. Adequate calibration of digital radiance data requires both an inductive analysis of digital satellite images and a deductive analysis based upon a priori simulation studies. The inputs to a simulation model (ground reflectance, atmospheric transmission and bandscatter) and their variability are dependent upon (for example) sun-target-sensor geometry. There is a major need to make accurate ground reflectance measurements to provide calibration information on the anisotropy of ground reflectance. There is also a need to assess atmospheric transmission and backscatter from the image itself. A potential simple, inexpensive method for making ground reflectance measurements in the above context is discussed.

Several methods for the in-flight calibration of advanced remote sensing systems are reviewed. Pre-f light and in-flight detector-based calibration are discussed. Calibration by reference to instrumented ground targets is suggested for current systems. Preliminary data are presented on the accuracy and sensitivity required of measurements of ground targets and the atmosphere between the targets and the sensor to achieve an uncertainty in absolute terms of less than ±3% in the calibration of Landsat-4 systems.