Publisher Summary This chapter describes the low noise proximity focused image intensifiers. The performance of image intensifiers is often rated in terms of the capability to increase detection and recognition ranges at low light levels. Several models exist in which detection or recognition ranges for a given target, background and light level are related to objectively measurable tube parameters. To gain more insight into the parameters that affect the noise figure, a formula can be derived. For the derivation, the electron multiplication process is divided into two parts, the first collision of the electrons with the channel walls, and the rest of the multiplication process. It is assumed that the secondary emission process can be described by Polya statistics. It has been shown experimentally that by pulse saturation of the microchannel plate (MCP) a gain noise figure of 1.06 can be obtained, but these values could not be reproduced in a tube. It is found that by evaporating materials of a high secondary emission coefficient into channels of the MCP, gain noise figures as low as 1.15 were measured.

Low Noise Proximity Focused Image Intensifiers

A short review is given concerning some general aspects of thermal imaging quality criteria. Some of the most important figures of merits (e.g.MTF, Minimum Resolvable Temperature - MRT, Signal Noise Power Densi-ty-SNPD) are discussed with the aid of a test system and illustrated by measurements with a mechanical scanner (AGA 680) and a pyroelectric vidicon (Heimann).© (1974) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

MTF Measurements And Assessment Of Thermal Imaging Devices

Three hand-held image intensifiers were studied. Two of these were passive visual aids (Starlight Scope and Uniscope) and one was an active IR viewer (Find-R-Scope). These devices were evaluated in terms of number of targets (trucks, boats, village) recognized on a 1000:1 scale terrain model. Simulated air-to-ground views of 20 observers were provided as they circled the model at a simulated 520 MPH and 8500 ft slant range under a moon-light illumination level. Although all targets were visible through the devices when observers were shown when and where to look, almost no target recognition occurred when any of the aids were used in a search viewing-mode under the conditions of the study.

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Air-to-Ground Target Acquisition with Night Vision Devices

The oldest teleoision. camera tube, the iconoscop e; is now used only for transmtttmg still pictures (e.g. the signal 'Picture of a certain station) and film pictures. Further development of camera tubes in Europe has followed a course different from that in America. In the U.S.A. the image orthicon has becomepredominant, whilst in Europe the image iconoscope is widely used. Ofthe latter there are British and French versions and also one that has been developed in the Philips Laboratory at Eindhoven (Netherlands). This Philips image iconoscope is described here and compared with other camera tubes.

The Image Iconoscope--A Camera Tube for Television

The observation of objects under low illumination conditions is made possible using photo-electronic image intensification of the available light. The intensifier is normally used in conjunction with a large aperture objective lens so as to gather the maximum number of photons. These photons are then imaged onto the photocathode and after electronic amplification the reconstituted optical image can be viewed at the phosphor by means of an eyepiece. At present the limitation of passive night vision devices is the inadequate spatial frequency response of the image intensifier.© (1974) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Considerations For The Design And Evaluation Of Objective Lenses For Low Light Level Applications

: The purpose of this report is to present in orderly fashion the key factors in the design, analysis, and characterization of low-light-level devices. The parameters of interest are those that have the greatest effect on the transfer of information from the scene before the lens of the television camera to the human looking at the picture tube. Part I examines specifications for low-light-level devices. Part 2 discusses criteria for image quality. Part 3 examines the human visual process and optical aids to that process under conditions of low illumination. Part 4 discusses the image intensifier as a device to aid vision at low light levels and lists the parameters of a variety of available image intensifiers. Part 5 introduces television camera tubes and develops the concepts leading to display signal-to-noise ratio, Rosell's signal- to-noise ratio at the display. It is this, the authors believe, that is the most powerful means of evaluating 'resolution,' a term usually used loosely and incorrectly. Part 6 compares camera tubes on the basis of lag and display signal-to-noise ratio and discusses adverse factors such as 'burning' and 'blooming.' Part 7 sums up with some brief comments on important tube parameters and their specification.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD0735006&Location=U2&doc=GetTRDoc.pdf

Low-Light-Level Devices: A Designers' Manual

: The paper deals with aliasing, an important effect of one-and two- dimensional sampling on image quality. Aliasing changes the normal criteria of utility of the modulation transfer function (MTF) as a measure of system quality. Aliasing can be eliminated by letting the MTF fall to zero at one-half the sampling frequency. This, of course, markedly reduces the signal-to-noise ratio at the display (SNR(D)) near cutoff and thus reduces operator performance. Several factors control the amount of information an observer extracts from an image and the rate at which he extracts it. The paper presents the results of a series of experimental programs relating observer performance to the modulation transfer function area (MTFA) and to the SNR(D) and derives the relationship between MTFA and SNR(D). The paper discusses the tradeoffs as they are presently understood.

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD0733663&Location=U2&doc=GetTRDoc.pdf

Lucien M. Biberman

Papers

Low-Light-Level Devices: A Designers' Manual

Image Quality in Sampled Data Systems