Low Light Level TV Research Articles

Long‐lived artificial ion clouds in the Earth's ionosphere

In two barium releases made over the Caribbean during the summer of 1991, the ion cloud was observed to last more than 10 hours. Observations were made with a low light level TV imager and a TV spectrograph operated onboard a Russian research vessel conducting ionospheric research and participating in the NASA‐CRRES mission. The two clouds were observed near the release region for 15 to 25 minutes during the twilight following the initial release. One of the releases was made during evening twilight and the ion cloud reappeared the following morning, while the other was a morning release and the late‐time observations made the next evening. The observations are highly surprising since, generally, it has been assumed that the ion cloud would dissipate within a few hours. However, the long life time appears consistant with current knowledge about dissipative processes. The long lifetime of barium ion clouds may provide for the most sensitive experimental testing of ionospheric convection models, a possibility with clear implications for future barium release experiments.

First observations of super fast auroral waves

Super fast auroral waves, propagating equatorward with speeds of up to 1200 km/s over distances exceeding 1400 km, have been observed at Sanae (L=4) Antarctica by an all sky low light level TV system. Such speeds greatly exceed those previously reported for fast auroral waves, or of any other auroral form, hence the description superfast. The altitude and speed of the waves have been determined using a novel technique that requires only one point of observation. Baseline triangulation from multiple ground based observations can be avoided because the earth is not flat.

Simple, inexpensive optical beacon for use on small satellites

A Vivitar model 283 photography flash unit was modified and tested for use as an aid for acquiring a target in low-Earth orbit. External circuitry was added to control the flash rate and pulse duration; the relative visibility of the flash was then tested with respect to these parameters, using two types of low-light level television camera systems over a range of effective distances. A rate of 40 flashes/min and a pulse duration of 1.8 ms were found to be optimal within the power capabilities of the existing inverter circuit. Removing the color correcting lens in front of the flash tube was also found to improve the efficiency of the unit in this application.

Stereo Imaging System for High-Voltage Electron Microscopy

An analysis of three-dimensional ultrastructure is especially efficient when performed on stereo images. The high voltage electron microscope (HVEM) providing high beam penetration and low radiation damage to specimens has been shown to be the most effective instrument for such studies. The successive HVEM stereo images recorded on films are subsequently photoprinted or stored in an image processor memory can be observed on an RGB monitor. Successful stereo imaging must meet several requirements regarding magnification, specimen thickness, tilt axis and angle. In particular, the optimal tilt for stereo perception depends on the thickness and microscopical magnification. Ultramicrotome settings can provide only approximate information on section thickness; however, their sectioning compression, procedural etching or beam induced shrinkage has to be considered. The situation becomes even more difficult when extractable media are used because an amount of extracted material may seriously affect final thickness. An estimation of an exact thickness of whole cell mounts is practically impossible, and therefore, optimal tilt difficult to predict. Then the most reliable way is the laborious recording of series of images at different tilt angles and selection of the most effective. To overcome this constraint, I designed a very reliable system for AEI HVEM 7MkII allowing exact prediction of the perfect tilt angle. The diagram of the system is presented on Fig. 1 and a photograph of the assembly on Fig. 2. It consists of a low light level TV camera with two independent outputs-SIT/TVC/, image processor-Quantex/QIP/, two high resolution flat square monitors-Hitachi/H1 & H2/ and stereo viewer-Nikon/SN/. A signal from the first TV camera output goes to the QIP, after processing is displayed on monitor H1. A signal from the second output goes directly to the second monitor, H2. Prerequisites for using this system are axis-centered or eucentric goniometer and a rotation-free imaging system of HVEM. The recording procedure happens as follows. The specimen is tilted 1/2 of the value of the roughly predicted optimal angle and the resulting image is stored in the Quantex memory followed by recording on the film sheet. The left monitor displays the stored image from QIP, while the right monitor provides the live image. Then the specimen is tilted while being observed with a stereo viewer. When the strongest stereo effect is noticed, then tilting is stopped and an image recorded. If + and − tilt values differ, then perfectly symmetrical values can be calculated followed by image recording. Figs. 3 and 4 represent the stereo images of a human melanoma cell grown on a film grid. An optimal stereo perception was obtained for different magnifications, at different tilt angles determined using the system I have designed.

Associated ground‐based observations of optical aurorae and discrete whistler waves

Discrete VLF wave emissions in association with auroral light intensity fluctuations have been recorded at L=4 during simultaneous operation of a broadband VLF receiver and a low light level TV system. The correlated wave‐particle interaction events are interpreted as being typical examples of the electron cyclotron resonance process responsible for the precipitation of energetic electrons in the vicinity of the plasmapause. A range of delay times between the correlated VLF wave and the optical signals, coupled with the frequency versus time characteristics of the VLF wave emissions, is consistent with the electron cyclotron source region being randomly located within 8000 km of the equatorial plane. The events are shown to be triggered by ducted whistler mode waves that originate from the opposite hemisphere to that of the station at which the observations are made. Events characterized by VLF waves of rising tone are presumed to occur in a region of enhanced plasma density commonly observed within the plasma trough. It is proposed that this region is responsible for ducting the VLF waves from the source to ground.

High-resolution hot-stage experiments

High resolution electron microscopy provides a powerful method for studying controlled dynamic reaction sequences and the development of microstructures on the atomic scale. Temperatures can be controlled with reasonable accuracy using a standard hot-stage, but at elevated temperatures there is some reduction in the contrast, and stability, of images. It is, of course, essential to minimise the effects, including additional heating, of irradiating the sample with a high voltage electron beam in a high vacuum environment, and to take into account the close proximity of two specimen surfaces in designing experiments. TV imaging techniques, in-situ, relocatable ex-situ and environmental methods are being developed for use with two medium voltage side-entry high resolution TEMs, equipped with complementary chemical and structural microanalytical STEM facilities.TV imaging techniques Dynamic reaction sequences are now mostly viewed with a low-light level TV camera (LLTV) using a thin YAG or YAP pickup screen and recorded on U-matic videotape to facilitate subsequent processing. The results can be improved substantially by using a digital framestore based image processor to enhance the signal to noise ratio of the video signal in realtime. A major element in the SNR is the shot noise statistics of the TEM electron beam.

Whistler duct dimensions from TV auroral images

Whistler mode VLF radiation propagates between opposite hemispheres of the earth in field aligned ducts of enhanced plasma density. Despite the fact that whistler theory is firmly based on the existence of such ducts,there is little knowledge of their cross-sectional size or shape. Mid-latitude ( L=4) ground based observations from Sanae, Antarctica, of ionospheric auroral optical emissions (imaged on a low-light level TV system) are observed in association with VLF radio emissions (recorded on a broadband VLF receiver). These optical emissions are Interpreted as arising from electrons which Interact with ducted VLF radiation via the electron cyclotron interaction. These observations provide estimates of 100 km by 400km for whistler duct cross-sections in the equatorial plane.

Observations of electron beam structure in space experiments

Observations of a 100‐mA, 1‐keV electron beam were made with a low light level TV system and other instruments aboard the space shuttle STS 3 in March 1982. When fired at a moderate pitch angle with respect to the magnetic field, the beam electrons initially moved outward along a classical helical trajectory. Within a short distance, however, the beam electrons were deflected away from the helical trajectory into paths parallel to magnetic field lines threading the primary helix. This resulted in the formation of a thin‐walled, cylindrical electron beam structure having a radius equal to the primary beam gyroradius. This structure, which is consistent with earlier laboratory vacuum chamber observations and recent two‐dimensional computer electrostatic plasma simulations, has important implications for determining the extent to which pulsed electron beams can radiate electromagnetic energy in the ionosphere.

Investigation of precipitating electrons during an auroral breakup

We have studied the detailed electron distributions measured in a westward travelling surge. The particle data, obtained by a sounding rocket, have been related to the auroral structures as recorded by a low light level TV. The event took place close to magnetic midnight on January 27, 1979.Two different types of particle spectra were detected. The first type consisted of two populations; a low energy population of secondary electrons with j ∼ E−2 and a plasma sheet population. The second type of spectra contained a Maxwellian population with a characteristic energy of a few hundred eV in addition to the previous two populations. The few hundred eV Maxwellian and the plasma sheet population had been accelerated in a potential drop parallel to the magnetic field lines.The auroral luminosity depends on the integrated energy flux. In regions with medium or low luminosity the spectra could be of either type, while the brightest auroral structures were connected to spectra of the second type, that is accelerated spectra with a low temperature population. It is suggested that the parallel potential drops are created on field lines magnetically connected to regions in the distant magnetosphere where the few hundred eV population is present.

Chapter 15 Characteristics of Low Light Level Television Cameras

Publisher Summary This chapter discusses the characteristics of low light level television cameras. There are two approaches to the production of a video camera with sufficient sensitivity for low light level work. The approaches include employment of a device with high quantum efficiency such as a charged coupled device (CCD) and use of a photoemissive device such as an image intensifier. Both approaches have been used with success for video imaging of living preparations. The noise of the ideal low light level video camera is solely due to that associated with emission from the photocathode. As with photomultiplier tubes, signal to noise may be increased by image averaging with the resultant reduction in temporal resolution. The tradeoff between spatial and temporal resolution is of prime consideration in the selection and use of low light level video systems. The best photocathodes for image tube applications in video microscopy are the S-20 or multialkali. Quantum efficiency of these photosensors is in the 20–30% range and the S-25 photocathode is about 10 to 15% quantum efficient. It is found that the speed of response of low light level cameras depends on photoconductive and capacitative effects at the photocathode.

Software pattern recognition applied to nanodiffraction patterns from a STEM instrument

In recent developments, the ASU HB5 has been modified so that the timing, positioning, and scanning of the finely focused electron probe can be entirely controlled by a host computer. This made the asynchronized handshake possible between the HB5 STEM and the image processing system which consists of host computer (PDP 11/34), DeAnza image processor (IP 5000) which is interfaced with a low-light level TV camera, array processor (AP 400) and various peripheral devices. This greatly facilitates the pattern recognition technique initiated by Monosmith and Cowley. Software called NANHB5 is under development which, instead of employing a set of photo-diodes to detect strong spots on a TV screen, uses various software techniques including on-line fast Fourier transform (FFT) to recognize patterns of greater complexity, taking advantage of the sophistication of our image processing system and the flexibility of computer software.

The Danish state-of-the-art airborne oil pollution monitoring system

This paper recounts Danish developments in the field of airborne remote sensing covering side-looking airborne radar (SLAR), microwave radiometry (MWR) and low light level television (LLLTV) and reports results obtained in ice surveys and oil slick monitoring.

Study on the flute-type hollow cathode discharge by using a low-light-level TV camera

The ignition process of the hollow cathode discharge (HCD) of flute-type is studied by using a low light level TV camera of the SEM (Silicon Electron Multiplication) type. On the basis of the observation, a theoretical explanation of the mechanism of the ligh development is given. It is clarified that there are two stages in the development of discharges: The stage of sustained dark discharge is between the anode and the outer-cylinder and the stage of discharge goes through the hole into the cylinder. Corresponding to these two stages, there exist two γ-processes, i.e., one is occurring at the metal surface surrounding the hole and the other is occurring at the inner surface of the cathode cylinder.

Correlated pulsations in auroral light intensity and narrow band VLF emissions

Observations at Sanae, Antarctica of pulsating aurora with a low light level TV system have been combined with simultaneous records of narrow band VLF emissions. Both auroral light and VLF intensities display a significant peak at 1.3 ± 0.3 Hz in the power spectrum. The peaks in the auroral light intensity variations lead those in the VLF by times between zero and 200 ms, as revealed by cross-spectral analysis. Furthermore the 4 kHz VLF component leads the 3.5 kHz component by zero to 100 ms. These results are explained in terms of cyclotron resonance between the auroral electrons and VLF in a region displaced 8000 km from the equatorial plane.

On the crystal structure of small gold crystals and large gold clusters

A large gold cluster with the formula Au 55[(C 6H 5) 3P] 12Cl 6, was imaged with a high-resolution transmission electron microscope (HRTEM) and a proposed model was confirmed. Growth of gold crystals of approximately 4.0 nm size could be followed, row by row of atoms, with the use of a low light level TV camera and on-line image processing.

Auroral pulsations—Television image and VLF hiss correlation

The association between VLF hiss and auroral-light intensity has been studied for pulsating auroras by coordinated observations with a broad band VLF receiver and a low light level TV system viewing the N 2 + ING emissions. Power spectral analyses of the VLF hiss and auroral-light intensity fluctuations display a common peak at 1.3 ± 0.3 Hz. Cross-spectral analysis shows that the times of the peaks in the auroral-light intensity fluctuations differ from those of the VLF hiss by times ranging between zero and 0.2 s. This result is shown to be compatible with a cyclotron resonance interaction in the vicinity of the equatorial plane. The periodicity of the intensity fluctuations can be accounted for by assuming the process is driven by echoing VLF hiss, which may be single-phase or three-phase.

The effect of atmospheric screening on the visible border of noctilucent clouds

The noctiiucent cloud display of 10/11th July 1979 was observed from two sites in Scotland: Clinterty near Aberdeen, using a low light level TV camera, and Milngavie near Glasgow, using a photographic camera. Coincident observations of the display were made from 23.55 UT until 00.50 UT. By projecting the image of the noctilucent cloud structure as seen by one camera into the field of view of the other camera, the height of the clouds was found to be 82 ± 1 km. Using this result, the effect of atmospheric screening on the visible border of the noctilucent clouds was determined. Taking account of the refraction on the solar grazing rays illuminating the clouds at the visible border and the finite angular diameter of the sun's disc, the altitude of the screening layer was determined to be 7 ± 1 km. Thus, on this occasion, the screening effect of the atmosphere was confined to the troposphere and was probably caused by atmospheric haze and/or tropospheric cloud. This result contrasts markedly with the high values of screening height, ~ 30 km, deduced from measurements made earlier this century, also using the visible boundary of the clouds. The analysis presented herein indicates that these large values were probably in error, due to the poor dynamic range of the photographic films employed.

The use of a digitizing frame store in microscopy

SUMMARYA digitizing frame store giving real time read out of the image for TV or slow scan rates is now available. This equipment has a number of applications in both optical and electron microscopy. Examples of results obtained by linkage to a low light level TV system are given showing that use of the frame store yields image information not otherwise available. Other possibilities of the system are indicated.

Night Roosting Behavior of the Little Brown Bat, Myotis lucifugus

Communal night roosting behavior of Myotis lucifugus was studied in southeastern Ontario using low light level television equipment. Adult females roosted in groups of up to 37 in five mortices in two barns. Night roosting only occurred on cool nights (minimum temperature below 12°C) during May and June, a period corresponding to that of gestation. No roosting occurred on nights above 12°C. On nights between 5 and 12°C each bat used the roosts up to three times per night and marked individuals each had a consistent pattern of behavior. On colder nights (below 5°C), all bats entered the roosts early in the evening and stayed until just before dawn. At night, the night roosts were consistently warmer than ambient and day roost temperatures. Communal night roosting thus serves a thermoregulatory role for pregnant female M. lucifugus which must maintain a high body temperature to promote rapid embryo development, a vital factor in the survival of young over their first winter. Individual patterns of roosting activity and the correlation between temperature and roost use likely result from the trade off between the thermoregulatory benefits and commuting costs of night roosting.

Characteristics of a Microchannel Plate Intensifier

The Atmospheric Emissions Photometeric Imaging Experiment (AEPI) to be flown on the Spacelab 1 mission is designed to study optically faint auroral phenomena occurring as natural and as artificallly stimulated atmospheric emissions. The AEPI detector consist primarily of a dual channel, 3.7?, F2.0, 2×10° wide angle and 12.4?, F/2.5, 2×3° telephoto, low-light level TV system (LLLTV). A complementary 9.4?, F2.5, 2×3° telephoto optical system, boresighted with the LLLTV, images onto the photocathode of a proximity focused multichannel plate photomultiplier which has 100 discrete anodes. In this system, the Photon Counting Array (PCA), photons are counted from individual anodes directly providing the photometric luminosity of an object which is crudely imaged. The object may be viewed simultaneously with high spatial resolution by the LLLTV. The multianode photomultiplier is manufactured by ITT specifically for the AEPI application, however multianode devices are of general use. Performance parameters of the PCA including modal gain, resolution, dynamic range are discussed.