Search

A linear self-scanning array of 512 elements was exposed to photoelectron bombardment in a Kron camera tube. This is a demountable tube in which the photocathode and the electron focal plane can be separated by means of a special coin valve. The diode array was mounted in the electron optical focal plane. The video signal amplitude distributions were analyzed when the diode array was exposed to electrons between 30 keV and 35 keV. The distribution of the signals due to single electrons could be resolved from the distribution of signals when no photoelectrons were present. The impairment of the SNR due to the lack of perfect resolution of the distributions amounts to no more than the loss of a few percent of the photoelectrons. The result of these tests encourages the immediate application of the diode array Kron tube spectrography to high resolution spectroscopy of very faint objects.

To investigate the dynamics of auroras and faint upper atmospheric emissions, a new type of imaging instrument was developed. The instrument is a wide field of view, narrow-spectral-band imaging system using an intensified S.E.C. TV camera in a time exposure mode. Pictures were taken at very low light levels of a few photons per exposure per resolution element. These pictures are displayed in the form of a pseudocolor presentation in which the color represents spectral ratios of two of the observed auroral spectral emission features. The spectral ratios play an important part in the interpretation of auroral particle dynamics. A digital picture processing facility is also part of the system which enables the digital manppulation of the pictures at standard TV rates. As an example, hydrogen auroras can be displayed having been corrected for nonspectral background by subtracting a picture obtained by a suitable background filter. The instrumentation was calibrated in the laboratory and was used in several field xperiments. Elaborate exposure sequences were developed to extend the dynamic range and to cover the large range of auroral brightnesses in a fairly linear manner.

A unique multichannel photoelectron counting system can be made by using self-scanning semiconductor arrays in the electron bombardment induced mode provided the SNR in the self-scanning arrays permits the detection of single electrons. To investigate this in an experimental program, self-scanning light sensitive diode arrays were subjected to electron bombardment. In one experiment, a radioactive source Ni(63) was used to show that the 128 element (Reticon RL128L) self-scanned linear diode arrays were responsive to electrons, and good agreement could be derived between the high energy portion of the incident and -measured fluxes. In another experiment using an electron accelerator and 42-keV electrons, clear resolution of the pulse distribution peaks was obtained due to single, double, and triple incidences of electrons. The relative heights of the observed peaks obeyed a Poisson distribution as expected for random electron incidence. The incorporation of this device into a photoelectronic tube will result in a self-scanned photoelectronic detector closely approaching the theoretical performance limit.

It is demonstrated that for maximizing the scientific output of future ionospheric and magnetospheric ion cloud release experiments a new type of instrument is required which will measure the line-of-sight velocity of the ion cloud by the Doppler technique. A simple instrument was constructed using a 5-cm diam solid Fabry-Perot etalon coupled to a low-light-level integrating TV camera. It was demonstrated that the system has both the sensitivity and spectral resolution for detection of ion clouds and measurement of their line-of-sight Doppler velocity. The tests consisted of (1) a field experiment using a rocket barium cloud release to check sensitivity, and (2) laboratory experiments to show the spectral resolving capabilities of the system. The instrument was found to be operational if the source was brighter than approximately 1 kR, and it had a wavelength resolution much better than 0.2 A, which corresponds to approximately 12 km/sec or in the case of barium ion an acceleration potential of 100 V. The instrument is rugged and, therefore, simple to use in field experiments or on flight instruments. The sensitivity limit of the instrument can be increased by increasing the size of the etalon.

A high sensitivity satellite-borne television camera has been developed to measure such faint light sources as auroras. A secondary electron conduction (SEC) television camera tube is used as the image sensor. In the present application for the Rice/NASA satellites code-named Owls, the tube is exposed by the application of a high voltage pulse of 0.1 sec or 0.2 sec duration. The picture is scanned for about 19 sec, and the video is digitized in synchronism with the satellite PCM system. The television data are then telemetered to the ground either real time or stored in one of the tape recorders. The optical system super-imposes star images on the picture for azimuthal aspect reference. The sensitivity of the slow scan camera was measured; it agrees with the sensitivity of a camera scanning at normal scan rate. Comparison was made of the relative sensitivity of the camera at the wavelength of the three most important auroral components. The camera has sensitivity comparable with the dark-adapted human eye. The weight of the system is 3.9 kg, and the power dissipation is 3.9 W.

A combination of a four-stage cascaded image intensifier and a plumbicon television camera system was used to record photoelectrons from faint images. The lens coupled system needs image intensifier gains of the order of 10(6) to overcome TV camera noise by single photoelectron scintillations. The properties of the system were evaluated with special emphasis on recording efficiency. The recorded pulse height distribution was analyzed, and it was shown that inefficiencies in the TV sampling process produce an exponential pulse height distribution.