Irving R. Abel

Narcissus: reflections on retroreflections in thermal imaging systems.

Narcissus, a composite of self-images of a cryogenically cooled detector array, is an effect peculiar to scanning thermal imaging systems. It occurs when the detectors sense variations in the amount of background radiation reaching them via reflections from lens surfaces. Paraxial surface-contribution formulas derived from Lagrange invariants, coupled with the system spectral response, determine narcissus in terms of its equivalent scene temperature difference (NARCDeltaT). The equations give the intensity and size of the narcissus ghost in terms of paraxial ray data at the contributing surfaces and the system f/No. This Gaussian formulation has sufficient radiometric accuracy to make extensive ray tracing unnecessary.

Wide-Field Correction In Reflective Schmidt Systems By A Nonrotationally Symmetric Element

Wide-field correction is achieved in reflective versions of the Schmidt and Schmidt-Cassegrain systems by the use of a fold mirror serving also as a corrector. The deformation of the corrector surface is divided into two functions one-with and one with-out rotational symmetry. The bulk of the deformation is defined by the rotationally symmetric part while the residual, which is of a much smaller magnitude, is nonrotationally symmetric. This separation of corrective polynomials facilitates fabrication of the elements. The larger rotationally symmetric part can be diamond turned on a two-axis machine under numerical control, whereas the small residual deformation can be hand figured to an overall system null or to a computer-generated holographic reference in an inter-ferometer. Diffraction-limited performance in the infrared region is achievable to an extent determined by tilt angle of the fold mirror and the f-number.

Optics In Adverse Environments

With a steady growth in technology, we are confronted increasingly with adverse environments for both human and human-made systems. Such challenges can be met in two ways: 1) the environment can be changed or controlled so that it becomes or remains conducive to the proper functioning of the system, or 2) the system can be designed and built to withstand the hostile influences. In the case of the human system, design changes within a reasonable time frame are not possible; consequently, its proper functioning is dependent on the creation and maintenance of a suitable environment (e.g. the space suit). But for the human-made system, it is mostly the opposite. To a large extent, it would not be possible to achieve the technological advances (e.g. laser fusion) we now seek without the creation of systems which function properly in the midst of hostile environments. In certain cases, both alternatives are available, but the creation of a fully benign environment would not be cost effective (e.g. spaceborne fiber optic waveguide communication system).

Mirror Systems: Engineering Features, Benefits, Limitations And Applications

The design and building of mirror systems, as contrasted with refractors, is flourishing. This is particularly true in the areas of ground-based and spaceborne astronomical telescopes, spaceborne wide-field mapping and surveillance systems, and X-ray telescopes. In the case of large astronomical telescopes, the Cassegrainian 2-mirror configuration, particularly the Ritchey-Chretien form, still is dominant because of its simplicity and versatility for narrow field imaging. Innovations revolve about the areas of cost reduction through the minimization of overall size in the midst of increasing the collecting aperture. In the case of spaceborne applications, all-reflective systems become even more necessary due to the requirements of broader spectral regions and wavelengths for which no suitable transmitting materials are available. Wide-field configurations are increasingly in demand in order to increase the information rate in mapping and surveillance applications. To this is added the spaceborne explorations in the far-UV and X-ray regions with grazing incidence reflective configurations. In all of these pursuits, the designs are seen to originate in the works of Newton, Schwarzschild, and Schmidt.

Sensors for Atmospheric Measurement

The atmosphere has been a subject of interest and concern throughout history. In the form of clouds, winds, and storms, it affects the lives of people in fundamental, obvious ways. In ways of which we are less conscious, it provides protective and stabilizing functions; for example, the ozone filters out ultra-violet radiation, which, in the present evolutionary state of the human species, would do serious harm to our health. In addition, the earths radiation balance is affected by the composition of the atmosphere. Consequently, with our consumptive practices and increasing abilities to intrude upon its natural condition, the possibilities of long-term, accumulated harmful effects are in evidence.

Influence Of Various Detector Configurations On Serial Scan FLIR Imagery

The Honeywell MiniFLIR, a serial scan TV-compatible system, can be equipped with single or double rows of discrete detectors or with nondelineated bars of detectors. In this paper various configurations and electronic enhancements are described and their related FLIR performance demonstrated through recorded video imagery.

History of Optics at the Honeywell Radiation Center

The Honeywell Radiation Center is a supplier of electro-optical components and systems which detect and track targets, image scenes, and measure radiation in the visible and infrared regions of the spectrum. In particular, it develops and constructs spaceborne spectroradiometers, star trackers, sun sensors, thermal inaging systems, oculometers, and interferometric spectrometers, and detectors.

Skylab Multispectral Scanner (5-192)âÃÂ

In this paper we describe the design and performance of a Multispectral Scanner. The optical system of Skylab Multispectral Scanner (S-192) consists of an image plane scanner (telescope), a spectrometer for separation of the radiation into 13 spectral bands, and a 13-element (Hg,Cd)Te detector array. The image plane scanner is a new system based on three interrelated main features: (1) a reflective adaptation of the Schmidt principle; (2) a conical line scan in which all field elements are brought to and corrected on axis; and (3) a scanning arrangement in which the aperture stop of the system, located in a relay unit, is imaged at the center of curvature of the spherical primary mirror. Replacing the physical stop used in the classical Schmidt configuration with a virtual one makes the system much more compact. As a consequence of the image plane scanning and the Schmidt symmetry, the system scans at a large radial angle (11-degree diameter) and at an extremely high rate (6000 rpm) with relatively small scanning mirrors and a large entrance pupil diameter (43 cm). The spectrometer divides the radiation into 13 spectral bands, 12 of which are located between 0.4 and 2.35 micrometers and the other, 10.2-12.5 micrometers. A dichroic beamsplitter separates the far IR band from the 12 lower wavelength bands, which are dispersed by prisms. Photographic reproductions of the actual flight recordings show 80-meter resolution at an altitude of 440 km.