This paper describes a digital television spectrometer (DITS) for measur-ing the optical radiation from re-entry vehicles. The system has been constructed and is being field tested on an IGOR telescope at White Sands Missile Range.
Historically, television pick-up tubes have been used in the entertainment and/or commercial fields to pick up an event for display to an audience. The use of the vidicon as a radiometric sensor can be much more demanding on the tube and requires a more rigorous definition of terms to describe the performance of the tube.* The method of measuring these characteristics and the manner of stating the derived quantities, also, must be more quantitative and objective than previously needed.
The video data supplied by the DITS (digital television spectrometer) camera is produced in such large quantities and at such a high rate that some form of automated data reduction is necessary. The data are recorded on both photographic film and magnetic tape. The film provides a rapid means for editing the data, while the magnetic tape preserved the accuracy of the data and stores it in a form compatible for computer processing.
The use of signal-generating image tubes (image orthicons) provides a number of features which are important for applications in tracking and surveillance sensor systems. The most significant features are: high quantum efficiency and internal noise-free signal amplification; scanning in the image orthicon of the transfer charge pattern generated by the optical image, which provides a means for time-sequencing of the spatial intensity information contained in the image; electronic image enhancement; digital image transfer and noise elimi-nation; real-time photometric and spectro-radiometric information retrieval; digital pointing-error information for automatic-tracking feed-back loops. The quantity which describes the performance of sensor systems is the modulation transfer function; in image tube systems the transferred spatial modulation of intensity amplitudes can be easily obtained from the video display on an oscilloscope.
The Missile and Space Division of the General Electric Company is actively pursuing advanced image-forming techniques that will lead to a space-qualified camera capable of superior performance in a remote environment. This paper will report on two such techniques that are in advanced state of development.
Equipment is described for making photographs using an image converter tube as an electronic shutter. When operating in the framing mode, the camera will take three frames 10 to 10,000 psec apart with exposure times from 0.5 to 5000 psec. Each frame has a maximum diameter of 25 mm. When operating in the streak mode, the camera has streak times from 10 to 10,000 p.sec. The streak picture is about 60mm long and 25mm wide. The equipment uses the RCA 73435D image converter tube. A standard oscilloscope camera is used to record the images. Design of the equipment is discussed and circuits for controlling and timing the photographs described.
Even with new developments in instrumentation during the past decade, the classical electro-optical Kerr cell shutter continues to be an extremely useful tool in a wide variety of instrumentation applications from high speed photog-raphy and light modulators to Q-spoiling of giant pulse lasers. This paper describes a high voltage pulse modulator system and accessory hardware which enables it to be used as a single exposure nanosecond Kerr cell or image converter camera system and also as a triggerable Q-switch for a generation of giant laser pulses.
The ability to acquire and track low intensity optical targets is an impor-tant factor in the optical monitoring of the re-entry ballistic missile complexes into the atmosphere. The unaided eye is a remarkably sensitive and efficient search instrument but, when an attempt is made to increase its sensitivity through the use of telescopic instruments, fundamental principles limit the product of the sensitivity gain and the solid angle of view. Image intensifiers, through amplification, remove this restriction and allow instruments whose optical gain is independent of the ratio of the real and apparent fields of view. As these devices also are sensitive to a substantially greater spectral range than the eye and are capable of as much amplification as may be practically useful, a study has been made to determine the factors which will set a limit to the ultimate useful sensitivity of optical instruments using such components.
Images of our three dimensional world are two dimensional in form. They are conveniently handled and observed in this form. However, in this form, the third dimension is lost. The angular relationship of objects in a scene relative to the imaging device are recorded but not their distance. We can obtain object distance by analysis of two sets of angular relationships imaged as a stereo pair. Distance information can also be obtained directly by propagation time measurement as in radar or laser ranging. Using a single detector these ranging devices are non-image producing. However, by sequential scanning in angle they can, in time, gather data to produce an image. Thus the stereo pair and the scanning radar provide us with two means to observe and record the three dimensions of our environment.
A slow scan TV system (Vidicon) uses in conjunction with a high performance A/D system permits (a) digital selection of optical density threshold, (b) digital selection of optical density gate for equalgray contour data recovery, (c) storage tube (Iotron) display of the conditioned digital image and (d) data storage on digital magnetic tape for computer entry.
The Video Film Converter is to be described, a precision CRT recording and film scanning device. This is a versatile machine, containing analog and digital positioning circuits having wide ranges of adjustments and is designed with input interfacing circuitry for ultimate connection directly to a digital com-puter. Precision deflection circuits hold the geometrical distortion to about 0.1% without correction over a raster 1" x 1". It contains a precision intensity circuit which utilizes a closed optical loop to linearize intensity. A discussion will be presented considering the tradeoffs concerning bandwidth, resolution, geometric accuracy and intensity linearity.
The development of high speed data acquisition capabilities has made possible the recording of large volumes of data in short time spans. If this data is to be efficiently utilized, means for automatically reading, interpreting and analysing it must be developed. Modern high speed computers provide an effective data analysis tool. This paper presents a system which automatically reads, at high speeds, data recorded on photographic emulsion and which generates dynamic displays, an effective means for observing and demonstrating trends in data. The central component of the system is a UNIVAC 1105 computer which synchronizes and directs the operation of all peripheral components of the system. The film is read by positioning a spot of light on a C.R.T. at a computer specified point via two digital to analog converters, imaging this spot on the film, detecting the amount of light passed through the film with a photomultiplier and placing the binary equivalent of the detected value in the computer via an A-D converter. Dynamic displays are generated with a pulse operated 16mm motion picture camera which is viewing a C.R.T. The motion of the camera film and shutter are controlled by the computer as is the generation of the display points for each film frame.