Low Light Level TV Research Articles

Evaluation of UAS Class and EO Sensor Payload Type for Applications in Hostage Crisis Missions

Donohue V. (2014). Evaluation of UAS class and EO sensor payload type for applications in hostage crisis missions. International Journal of Unmanned Systems Engineering. 2(1): 1-8. Law Enforcement entities are tasked with ensuring the safety of citizens to the best of their ability. They use every advantage at their disposal to capture and restrain criminals while reducing the risk to civilians. This ability is often limited by the constraints of slim and shrinking budgets. Departments with larger budgets and greater flexibility have historically taken advantage of airborne assets, most often helicopters, which provide a tremendous advantage against criminals due to enhanced surveillance, pursuit, and capture capability. The latest technological advancements in remote electronic sensing, along with major strides in aircraft automation and miniaturization, have allowed a surge in the implementation of Unmanned Aircraft Systems (UAS) in Law Enforcement missions. This paper discusses the use of UAS by Law Enforcement in a hostage crisis situation. A scenario is presented and a Concept of Operations (CONOPS) is developed to thoroughly detail the mission goal, strategy and tactics. The class of UAS appropriate for the mission, including Micro Air Vehicles and small UAS, and a refined selection between fixed wing and rotary wing aircraft are identified. The Draganflyer X6 and the RAPTR rotary wing UAVs are discussed in deciding what system best accomplishes the hostage crisis mission. Electro-optical sensors, including high definition video, low light level TV and infrared sensors, provide superior applicability. © Marques Engineering Ltd.

Physical characteristics of very small meteoroids

We have optically recorded faint meteors using a large aperture LLLTV (low light level television) system based on second generation image intensifiers. These data consist of 42 two-station meteors of which 13 were captured during an observing campaign near London, Ontario (Canada) in May 2004, and 29 during a campaign near Kiruna (Sweden) in October 2007. Among 13 meteors recorded in the London campaign, where the baseline between the two sites was 5 km, only four meteors satisfied our requirement for complete lightcurves and deceleration profiles by starting in the field of view, of at least one station and also ending in the field of view of at least one station. From the second set of 29 meteors captured in Sweden, with a baseline of 117.7 km, only two satisfied these criteria. The cameras used in both campaigns had fields of view of 6 degrees, which with an assumed range of 100 km, gives a scale of 13 m/pixel at ∼60 interlaced fields per second. This resolution allows precise measurement of the deceleration of very faint meteors. The limiting magnitude for meteors on these systems is near V =+ 8, while +11th magnitude stars are visible in the individual fields. The meteors detected in these two campaigns have peak brightnesses between absolute magnitude +6.2 and +7.4. Their photometric masses range from 4.2 mg to 0.35 mg. An ablation model was applied to fit each complete two-station event using the high-precision metric and photometric data as a constraint, in an attempt to compute bulk meteoroid densities. Interestingly, a large proportion of our faint meteor events were found to ablate at low altitudes, a result partly of our observing biases. The orbits of these events are consistent with either asteroidal or a Jupiter-family comet origin. The meteoroids’ physical properties, as determined through model fits, suggest high densities, which favors an asteroidal interpretation. The high percentage of apparently dense asteroidal meteoroids at these small sizes may call into question earlier findings that only ∼1% of meteoroids at these masses are asteroidal in origin. Our results are similar to others that find ∼15% of faint TV meteors had spectra consistent with pure iron meteoroids. We find that many of these apparently asteroidal objects also undergo extensive fragmentation, which may reflect melting and spraying of droplets rather than mechanical fragmentation. Some individual cases in our small dataset will be highlighted where high bulk densities (approaching that of iron) are required to adequately match the end height, peak brightness, and observed deceleration. We speculate that these meteoroids may represent metallic condensates from impact-processed asteroid regolith.

帧积分时间对微光电视观察视距的影响

帧积分时间对微光电视观察视距的影响

Current and Future Trends in Military Night Vision Applications

The Army's grand sensor challenges for night vision operations are presented as well as the focused technology quests that offer solutions to the challenges. The technology quests include all solid state low light level TV cameras, mercury cadmium telluride IR detectors on silicon substrates, uncooled thermal imaging, eyesafe laser imaging and aided target recognition. The operational applications, current systems approaches, and technical goals are discussed and the potential breakthroughs are identified. Research opportunities are suggested that could enable new system capabilities, including areas of advanced active thin film research.

Radiants of the Leonids 1999 and 2001 Obtained by Lltv Systems Using Automatic Software Tools

Both amateur and professional meteor groups are more frequently using Low-Light level TV (LLTV) systems to record meteors. Double-station observations can yield orbit data. However, data analysis normally is still done by hand and thus time consuming. This paper addresses the question of whether available automated tools can be used to determine reasonably accurate orbits with minimum human intervention. The European Space Agency performed several observing campaigns to observe the Leonid meteor stream. In November 1999, the ESA meteor group was stationed at two locations in Southern Spain, in November 2001 at two stations close to Broome in North-Western Australia. Double-station observations with LLTV systems were conducted. The data was recorded on S-VHS video tapes. The tapes were processed using automatic detection software from which meteor heights, velocities and radiants were computed. This paper shows the results for the two maximum nights. The radiants determined in 1999 show a very large scatter due to unfortunate observing geometry and inaccurate position determination since one of the cameras was moving because of the wind. The 2001 data is excellent and the radiant was determined to be at RA = 153.96°±0.3° and Dec = 21.09°±0.2°. The error bars for individual meteor radiants are about 0.2° to 0.4°. This demonstrates that is indeed possible to determine good radiant positions using totally automated tools. Orbits, on the other hand, are not well defined due to the fact that the velocity of individual meteors shows large errors. Reasons for this are described.

Observations of transient luminous events (TLEs) associated with negative cloud to ground (−CG) lightning strokes

A balloon campaign was conducted in summer, 1999, to measure the stratospheric electromagnetic fields associated with sprites. Ground observations for detection of sprites included low light level TV (LLTV) observations from three sites. Flight 1 flew from Palestine, Texas at 01:14:31 UTC to 09:45:00 UTC on 07/06/1999. Flight 3 of the campaign flew from Ottumwa, Iowa at 00:39:32 UTC to 11:12:00 UTC on 08/21/99. During flight 3, 26 sprite halos associated with positive cloud‐to‐ground (+CG) strokes and 17 −CG sprite halos were observed. Of these, 22 +CG and 12 −CG sprite halos were observed by the ground observatories. Seven of the +CG and all 17 −CG halos were not followed by sprites. Next the balloon data were examined during and after the times of the recorded NLDN strokes during 4.1 hours of data. An additional 88 −CG TLEs were found in the flight 3 data and 56 TLEs (7 +CG, 49 −CG) were found in the flight 1 data. It appears that −CG TLEs, mostly spriteless halos, occurred 5–7 times more often than the +CG TLEs. The halo appears to be a fundamental mesospheric response to lightning.

Statistics and properties of transient luminous events found in the 1999 Sprites Balloon Campaign

Historically, the process of transient luminous event (TLE) detection has required an alert human observer on a low light level television (LLTV) monitor, either in real time or playback. The 1999 Sprites Balloon Campaign payloads had all-sky upward looking photometers not sensitive to events below the balloons. The photometer data was examined at the time of National Lightning Detection Network (NLDN) lightening strokes to find TLEs that were missed visually. 3602 events were analyzed in 4.1 h of storm time. Threshold current moments of ∼50 kA km for the positive cloud to ground (+CG) TLEs and ∼−5 kA km for negative cloud to ground (−CG) TLEs are found.

The results from the 1999 sprites balloon campaign

A balloon campaign was conducted in summer, 1999, to measure the stratospheric electromagnetic fields associated with sprites. This paper will summarize some of the salient results of this work. The balloon payloads were instrumented with electric field detectors, magnetometers, an upward looking photometer, and other instruments. Ground observations for detection of sprites included low light level TV (LLTV) observations from three sites, Jelm Mt, WY, Bear Mt, SD, and Yucca Ridge, CO. The disagreements between models and these data will be discussed. We have used the photometer data to find TLEs by checking the trace at the times of cloud to ground (CG) strokes reported by the US National Lightning Detection Network (NLDN). In total numbers, the number of −CG transient luminous events (TLEs) (presumably all halos) predominates over the number of +CG TLEs. On the positive side, the TLE events show a current moment threshold. Inclusion of the −CG events that are not seen from the ground raises mesospheric power input estimates by a factor of ∼5–7. Including the mesospheric effect of CGs not associated with TLEs increases this estimate by a factor of 2.

Sprite and elve electrodynamics

Flight 3 of the Sprites99 balloon campaign flew from 00:39:32 to 11:12:00 UTC on 21 August 1999, launched from Ottumwa, Iowa. Three axis electric and magnetic field and ground-based low light level TV observations from three sites were made of more than 68 transient luminous events (TLEs) in the middle atmosphere above thunderstorms in South Dakota and Kansas. At least four TLEs were recorded by two or more stations, including sprites at 0955:36, 0541:58 and 0546:10 UTC and a sprite halo at 0746:35. An event triggered on-board memory, sampling 10 quantities at a rate of 50 kHz per channel for 160 ms per event, recorded bursts for some of the sprites and elves. At the range of the balloon from the lightning and TLE (∼400 km), the vertical electric field perturbation is roughly simulataneous with the light emission. The presence of a radial component of some magnetic pulses suggests that signal propagation was not entirely in the TM mode.

The electrodynamics of sprites

A balloon campaign was conducted in summer, 1999, to measure the stratospheric electromagnetic fields associated with sprites. The balloon payloads were instrumented with electric field detectors, magnetometers, an upward looking photometer, and other instruments. Ground observations for detection of sprites included low light level TV (LLTV) observations from three sites, Jelm Mt., Wyoming, Bear Mt., South Dakota, and Yucca Ridge, Colorado. Flight 3 of the campaign flew from Ottumwa, Iowa at 00:39:32 UTC to 11:12:00 UTC on 08/21/99. A sprite at 0955:36.980 UTC produced a vertical electric field perturbation of ∼0.275 V/m that was similar in time profile to the light emission. There was also a positive azimuthal magnetic pulse of ∼3 nT.

A novel type epithermal neutron radiography detecting and imaging system

The transfer technique is widely used for epithermal neutron radiography (ENR) for making images upon the object to be investigated. We propose to use instead of the photosensitive film a gamma sensitive scintillation screen (NaCe single crystal), that is monitored by a computer controlled low light level TV camera. The exposure time has been reduced to a duration of only a short fraction of that needed for the conventional transfer process. The presented ENR images consist of electronic signals that are handled by an advanced image processing and analyzing program, the Iman 1.4 version, using a task oriented video grabber.

Excitation of Earth‐ionosphere cavity resonances by sprite‐associated lightning flashes

Simultaneously recorded discrete excitations of Earth‐ionosphere cavity resonances at Silberborn, Germany, and Hollister, California, ∼9.1 Mm apart, are used to triangulate source locations of lightning flashes in the continental United States with an accuracy of ∼0.8 Mm, as verified by the National Lightning Detection Network. The identified lightning flashes are mainly associated with positive cloud‐to‐ground discharges with first return stroke peak currents ∼20–70 kA. 80% of these particular lightning flashes are associated with sprites, as verified by simultaneous low‐light level TV camera observations at Yucca Ridge, Colorado. This high probability of sprite detection is attributed to particularly large cloud‐to‐ground lightning currents, simultaneously exciting both Earth‐ionosphere cavity resonances and sprites.

Observations of the 1996 Leonid meteor shower by radar, visual and video techniques

The activity of the 1996 Leonid shower from two radars, global visual and single-station low-light-level TV (LLTV) observations is presented and summarized. Radar observations from Ondřejov in the Czech Republic indicate a peak rate of (>+1) Leonids near λ⊙ = 235°2±0.1 (Equinox 2000). As observed by this radar, this peak interval was characterized by a significant increase in the number of bright Leonids as demonstrated by a noticeable lowering of the mass index near the peak. From radar observations in Ontario, Canada (using the CLOVAR system), a raw peak flux of 1.3±0.3×10−2 meteoroid km−2 h−1 brighter than radio magnitude +7.7 was reached at λ⊙ = 235°3±0.1, uncorrected for initial train radius effects. Single-station LLTV observations suggest a peak shower flux of 1.8±0.4×10−2 meteoroid km−2 h−1 brighter than absolute magnitude +5±0.5 between 235°3 and 235°39. The position of the radiant on the night of maximum of the shower is found to be α=152°9±1°0 and δ=22°1±1°0 from CLOVAR observations and α=153°3±1°7 and δ=22°1±1°7 from LLTV observations. Visual observations of the shower yield a peak zenithal hourly rate (ZHR) of 86±22 at 235°17±0°07 or an equivalent flux of 1.2±0.4×10−2 meteoroid km−2 h−1 brighter than absolute visual magnitude +6.5. The visual peak was short-lived (1.5 ± 0.5 h HWHM) and richer in fainter meteors than neighbouring intervals. Discrepancies in the estimated absolute Leonid flux found using differing methods are noted and possible reasons for the differences discussed. The stream in 1996 showed two distinct meteoroid populations: a population of recently ejected meteoroids rich in smaller particles near 235°17 which is very narrow in nodal extent (HWHM 0°07±0°02), and an older component (of order 10 revolutions in age) peaking near 235°4 which is rich in larger stream meteoroids, of long duration (FWHM 1°2 ±0°4), which contributed most to the total mass flux at Earth from the stream in 1996.

Positioning of auroral arcs in all-sky TV images as an inverse problem

Positioning of auroras in all-sky images taken by instruments such as low-light level TV cameras has long been important in understanding how an ambiguity of luminous positions is removed with appropriate models which take into account specific altitude profiles of auroras in the ionosphere. We have developed a method to estimate locations of auroral columns along the earth's magnetic lines of force by an inversion procedure. Two-dimensional luminosity distribution in raw data is considerably large in the data size to be processed at a given time and we show that the problem can be reduced into a simple one-dimensional problem. Models of auroral arcs with simple altitude profile are used. Locations of reconstructed image profiles show decomposing arcs well concentrated only around the lower border of the arcs in the original image data. The method is shown to be effective when it is applied to observed data including a simple auroral arc.

The optical spectrum of aircraft St. Elmo's fire

On February 26, 1995, during a NASA sponsored mission to Peru to study red sprites and blue jets, the instrumented Westwind 2 jet aircraft encountered spectacular St. Elmo's fire from the wing pods, tail and nose while flying through a cloud at an altitude of 13.83 km (45,376 ft). The phenomenon was captured on low light level monochromatic and color television systems aboard the aircraft, and its spectrum was recorded on a low light level TV spectrograph with response from 395.0 to 750.0 nm. The cameras and spectrograph also recorded scattered intra‐cloud lightning and a possible lightning discharge near, or to, the aircraft. The spectrum of St. Elmo's fire was primarily the second (2nd) positive bands of N2. The data were consistent with a population of electrons having relatively low energy (<18 eV).

Dynamic neutron radiography instrumentation and applications in Central Europe

Characteristic features of simultaneous dynamic neutron and gamma radiography installations built in the last ten years at the Budapest/Hungary and at the Seibersdorf/Austria research reactors are surveyed. For image detection scintillation detectors and a low-light level television camera with video output are used, thereby providing the possibility for visualizing medium speed movements inside the investigated object. The radiography stations have been used for inspecting industrial products, with the aim of research and development.

Coordinated measurements of auroral light intensities and Riometric radio‐wave absorption

Digitized allsky images of auroral optical emissions, recorded by a low light level TV system at Sanae (70.3°S, 2.4°W, L=4.0), have been mapped onto the angular sensitivity functions of both a broad, single‐beam riometer and narrow beams of an imaging riometer. During the rising phase of a substorm before local magnetic midnight, on 11 May, 1992, the integrated optical intensities in the inner four beam directions of the 16‐beam imaging riometer followed each other fairly closely, while the absorptions showed marked spatially inhomogeneous distributions. Regions of ionospheric absorption appeared not to coincide spatially with regions of discrete optical structures, but were adjacent to these structures. A small step of ∼0.09 dB in absorption was observed shortly after onset of the substorm on 27 July, 1979, and again on 11 May, 1992, but before the sharp increase in absorption. This step in absorption may be due to highly enhanced E‐region electron temperatures arising from strong dc electric fields connected to auroral arcs. During the event of 9 June, 1991, which started with an SSC at 00:40 UT, enhancements in absorptions followed enhancements in optical emissions repeatedly after 52 s.

Optical and radar observations of auroral arcs with emphasis on small-scale structures

During a campaign in January 1988 we observed auroral arcs with the EISCAT UHF radar system and a low light level TV camera. The aim was to compare apparent motions of the arc and its small scale structures with plasma motions in the adjacent F-region. It was found (1) that there was a relative motion between arc and plasma of the order of 100–200 m/s southward and (2), in confirmation of earlier findings, that folds and curls, i.e. auroral rays seen edge-on, with wavelengths ranging from 2 to 20 km, moved along the are with average velocities of 10 to 20 km/s. At the same time, the tangential plasma velocity at 300 km height varied between −0.3 and 0.8 km/s westward. Most importantly, for all luminous bands exhibiting fast motions of small-scale structures, the direction of this motion was westward on the equatorward edge, and on most occasions, an eastward directed counterflow could be observed on the poleward edge. The existence of such a counterflow appears to be a fundamental property and may even be used for a physical definition of an auroral arc. We support the interpretation of Davis (1978) that auroral ray, fold, or curl motion is a visible expression of a physical motion of small-scale structures in the local plasma. environment of the auroral acceleration region at about 1 R E altitude. The attendant electric fields are shorted out by parallel potential drops. The counterflow pattern is consistent with the existence of a U-shaped potential at that altitude. The observed asymmetry in brightness, definition, and speed of the countertiowing folds or curls is attributed to their location at the leading or trailing edges of the arc propagating relative to the plasma frame.

Preliminary results from the Sprites94 Aircraft Campaign: 1. Red sprites

The dual jet aircraft Sprites94 campaign yielded the first color imagery and unambiguously triangulated physical dimensions and heights of upper atmospheric optical emissions associated with thunderstorm systems. Low light level television images, in both color and in black and white (B/W), obtained during the campaign show that there are at least two distinctively different types of optical emissions spanning part or all of the distance between the anvil tops and the ionosphere. The first of these emissions, dubbed “sprites” after their elusive nature, are luminous structures of brief (< 16 ms) duration with a red main body that typically spans the altitude range 50–90 km, and possessing lateral dimensions of 5–30 km. Faint bluish tendrils often extend downward from the main body of sprites, occasionally appearing to reach cloud tops near 20 km. In this paper the principal characteristics of red sprites as observed during the Sprites94 campaign are described. The second distinctive type of emissions, “blue jets,” are described in a companion paper [Wescott et al., this issue].

Advances in strain measurement using electron-backscatter diffraction in the Scanning Electron Microscope

The technique of electron back scatter diffraction, EBSD, is well established for measurement of crystal orientation in bulk polycrystalline samples. Analytical procedures for determining crystal phase from them have also been established. In addition several papers have been published describing the application of the method for strain measurement. In these latter studies the EBSPs were recorded on photographic film and all measurements made after digitising the patterns and transferring the data to a SEMPER image processing package. Strain measurement was based on determination of the diffuseness of the diffraction pattern. In the present studies analysis was carried out on digitised television images of the diffraction patterns imaged live on a phosphor screen.EBSPs were obtained in a JEOL 6400 SEM fitted with a tungsten filament. The patterns were imaged on a P20/P40 phosphor directly coupled through a coherent fibre optic bundle to a SIT low light level television camera with 700 line resolution.