Dan Sheffer

Absolute reflectometer for the mid infrared region

An absolute reflectometer for the 0.8-5.5-mum wavelength region is described. It is based on integrating spheres and uses the third Taylor method in the 7 degrees /d configuration. An improved theory for the reduction of the data is presented, and results for several diffuse gold samples are given.

Absolute measurements of diffuse reflectance in the α°/d configuration

An improved theory for data reduction of absolute reflectance measurements using the third Taylor method in the alpha degrees / d configuration is presented. A brief description is given of an absolute reflectometer operating in the 0.8-2.5-microm region. The reflectometer is operated according to the improved theory. Experimental data for some widely used samples are given, as well as data showing agreement between the current measurements and those made by the U.S. National Institute of Standards and Technology.

The informational difference concept in analyzing target recognition issues

A model for analyzing issues involving monospectral target recognition is presented. These issues include modeling target detection, recognition and identification thresholds, and predicting the functional parametric dependencies of the results of observation experiments with human observers. The model makes extensive use of concepts used in information theory. An image of a scene is treated as a sample of an entire set of images of that scene. A difference measure, called the informational difference (InDif) between two image sets is defined. The main assertion is that accomplishing target recognition tasks is equivalent to setting thresholds for the InDif. The applicability of the InDif to the performance of the human visual system (HVS) is shown both analytically, in very simple situations, and in computer calculations involving noisy images. Finally, a single framework for dealing with the HVS and artificial intelligence systems in target recognition applications is shown to result naturally from the InDif formalism.

Absolute reflectometer for the 0.8–2.5-μm region

A reflectometer based on an integrating sphere operating in the 0.8-2.5-microm region is described. The reflectometer is of the absolute type and does not need a standard diffuse reflecting surface to obtain absolute reflectance values. The system is fully automatic, using computer-controlled circular variable filters as monochromators. Results for BaSO(4) in the region between the visible and 2.5 microm show considerable deviations from the accepted values of reflectivity for this substance.

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.

Analyzing target recognition issues using the informational difference concept

A model for analyzing issues involving monospectral target recognition is presented. These issues include modeling target detection, recognition and identification thresholds, and predicting the functional parametric dependencies of the results of observation experiments by human observers. The model makes extensive use of concepts used in Information Theory. An image of a certain scene is treated as a sample of an entire set of images of that particular scene. A difference measure, called the Informational Difference (InDif) between two image sets is defined. The main assertion is that accomplishing target recognition tasks is equivalent to setting thresholds for the InDif. The applicability of the InDif to the performance of the Human Visual System (HVS) is shown both analytically, in very simple situations, and in computer calculations involving noisy images. Finally, a single framework for dealing with the HVS and Artificial Intelligence systems is target recognition applications is shown to result naturally from the InDif formalism.

The use of thermodynamic quantities for improving multispectral class separation

The present paper addresses the issue of extraction, processing, and recognition of information from multi-spectral observations of our surroundings. A new method of dealing with multispectral recognition problems is developed, in which a physical thermodynamic model is used to describe the properties of the object classes in a multispectral image of a certain scene. According to the model, different groups of objects in the image are canonical populations that are in thermodynamic equilibrium with each other and with their surroundings. Between the objects act forces that result from a potential field. Various thermodynamic properties of the populations are calculated. The difference between two populations is evaluated by first bringing them to a common temperature and then using the informational difference as a difference measure. The approach was implemented for a problem of combined formal and spectral classification of trees in a natural environment. The common temperature of two similar populations was varied until the separation between the populations reached a maximal value. A six-fold increase in the separation between the populations was achieved. In the future, we propose to use the Helmholtz free energy function as a quantity which attains a local minimum within each class of objects. An optimal classification scheme is one that minimizes the total free energy of the system.

Remote colorimetry and its applications

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.

Absolute Reflectance Measurements Of Metallic Surfaces In The 0.8-5.5 µm Region

An absolute reflectometer for the 0.8 - 5.5 microns region is described, and reflectance spectra for some diffuse metallic surfaces are given. Some of the spectra show a dip of 5-7% in the reflectance values of the surfaces in the 3.0 - 3.5 microns region. Possible causes for the observed dips are discussed.