Array Photometer Research Articles

Experimental Validation of N2 Emission Ratios in Altitude Profiles of Observed Sprites

Recent efforts to compare the sprite ratios with theoretical results have not been successfully resolved due to a lack of theoretical results for sprite streamers in varying altitudes. Advances in the predicted emission ratios of sprite streamers with a simple analytic equation have opened up the possibility for direct comparisons of theoretical results with sprite observations. The study analyzed the blue-to-red ratios measured by the ISUAL array photometer with the analytical expression for the sprite emission ratio derived from the modeling of downward sprite streamers. Our statistical studies compared sprite halos and carrot sprites where the sprite halos showed fair agreement with the predicted ratios from the sprite streamer simulation. But carrot sprites had lower emission ratios. Their estimated electric field has a lower bound of greater than 0.4 times the conventional breakdown electric field (Ek). It was consistent with the results of remote electromagnetic field measurements for short delayed or big/bright sprites. An unexpectedly lower ratio in carrot sprites occurred since sprite beads or glow in carrot sprites may exist and contribute additional red emission.

Practical application of HDRI for discomfort glare assessment at indoor workplaces

Unified Glare Rating (UGR) is a measure of discomfort glare at indoor workplaces. Image luminance measuring device (ILMD), as an array photometer, makes it possible to measure the luminance distribution in the form of luminance map. It is the base for UGR calculation by an appropriate computer program. The range of measured luminance depends mainly on a glare source luminance, which often significantly exceeds the abilities of an array photometer sensor. High dynamic range (HDR) method, which is used in photography, can solve this problem partially. A practical approach to this problem was presented in the paper. A new procedure for preparing the set of photos for building HDR images was introduced. This effective method was developed to be used in UGR calculations. The use of the proposed procedure makes it possible to perform UGR measurements reliably, quickly, and efficiently, even by nonexperts in the field of lighting engineering.

The Imager for Sprites and Upper Atmospheric Lightning (ISUAL)

AbstractThe Imager for Sprites and Upper Atmospheric Lightning (ISUAL) was the first specifically dedicated instrument to observe lightning‐induced transient luminous events (TLE): sprites, elves, halos, and gigantic jets from space. The Imager is an intensified CCD system operating in the visible wavelength region with a filter wheel to select from six positions with filters. The Imager has a 5° × 20° (vertical times horizontal) field of view. The spectrophotometer (SP) is populated with six photometers with individual filters for emissions from the far ultraviolet to the near infrared. An array photometer with two channels operating in the blue and red provides altitude profiles of the emission over 16 altitude bins each. The Associated Electronics Package (AEP) controls instrument functions and interfaces with the spacecraft. ISUAL was launched 21 May 2004 into a Sun‐synchronous 890 km orbit on the Formosat‐2 satellite and has successfully been collecting data ever since. ISUAL is running on the nightside of the orbit and is pointed to the east of the orbit down toward the limb. The instrument runs continuously and writes data to a circular buffer. Whenever the SP detects a sudden signal increase above a preset threshold, a trigger signal is generated that commands the system to keep the data for about 400 ms starting from ~50 ms before the trigger. Over its lifetime of ~11 years the system recorded thousands of TLE and also successfully observed aurora and airglow.

Electric field transition between the diffuse and streamer regions of sprites estimated from ISUAL/array photometer measurements

We analyze optical data of twenty sprites and three halos observed by the array photometer which is a scientific instrument of the ISUAL payload on the FORMOSAT‐2 satellite. The altitude distribution of electric field is derived from the ratio of blue to red emission intensity by assuming all emissions are due to the electron impact excitation of nitrogen molecules. We find a clear transition at ∼75 km altitude from the upper‐diffuse to lower‐streamer region. Estimated electric field intensities in the diffuse region are 0.5–0.7 Ek, which support the theoretical expectation that their optical emissions could be produced without significant ionization. On the other hand, those in the streamer region are 1–2 Ek which is a few times less than predicted fields in the streamer head. We suggest that this discrepancy is due to the long‐lasting components such as the lower portions of the upward branches and bead structures.

Global survey of upper atmospheric transient luminous events on the ROCSAT-2 satellite

Upper atmospheric transient luminous events (TLEs; sprite, elves, blue jet, etc.) are recently discovered thunderstorm-induced phenomena. Imager of sprites/upper atmospheric lightning (ISUAL) is a scientific payload on the Taiwan's ROCSAT-2 satellite that aims primarily to provide crucial observation data on these TLEs from space. The ISUAL payload includes an intensified CCD imager, a six-channel spectrophotometer, and two array photometers. All the instruments are mounted on a common platform and boresighted in the same direction. The imager is equipped with six selectable filters, which have bandpasses covering the visible spectrum. The spectrophotometer contains six photometers, and each photometer is fitted with a special bandpass filter ranging from ultraviolet to red regions. The two array photometers are identical in every aspect, except one is fitted with a blue band filter and another one is equipped with a red band filter. With this set of well-chosen instrument, this project seeks to determine the location and timing of upper atmospheric transient events above thunderclouds, to investigate their spatial, temporal and spectral properties, to obtain a global survey of them, and to perform a global study of aurora and airglow. ISUAL project is an international collaboration supported by the National Space Program Office in Taiwan, with additional contributions from the National Cheng Kung University, Taiwan, the Space Science Laboratory of the University of California at Berkeley, and Tohoku University, Japan. ROCSAT-2, the platform of ISUAL, is scheduled to launch around October 2003.

Energy estimation of electrons producing sprite halos using array photometer data

Sprite halos are brief diffuse glows with an average duration of ∼1 ms occurring at altitudes from 70 to 85 km preceding the development of sprite streamers. Their horizontal scale is ∼50– 100 km and they move downward as if focusing into the center. To investigate the energies of electrons producing sprite halos and their spatial and temporal variations, we analyzed photometric and CCD imaging data recorded at Yucca Ridge Field Station, Colorado, USA, during the Sprites’99 campaign. We estimated the electron energies from the intensity ratios of blue (350– 500 nm ) to red (560– 800 nm ) emissions captured separately by two array photometers on the assumption that the electron energy distribution is given by the Maxwell–Boltzmann or Druyvesteyn distribution. It is found that the electron energies reach their peaks preceding the luminosity peaks of the red emission (mostly due to the N 2 first positive and the N 2 + Meinel band systems), exhibiting energy increases in the lower part of the sprite halo. The estimated peak electron energies are in the range 6–23 and 7– 16 eV for the assumed Maxwell–Boltzmann and Druyvesteyn distribution, respectively. These results suggest that more energetic processes occur at the initiation of the sprite halo, particularly in its lower part. Nevertheless, the estimated values of electron energies should be interpreted as a measure of the energetic processes producing sprite halos, represented by the equilibrium temperatures, since the real electron energy distributions would be undoubtedly deviated from the equilibrium states due to additional high-energy tails produced by the thermal runaway electron mechanism.

Activities of sprites and elves in the winter season, Japan

Sprites and elves observation has been carried out in three winter seasons in Japan since December 1998. Thirtyfive sprites’ features have been imaged with CCD cameras and 95 optical emission from elves have been captured with hi-speed array photometers. The number of events observed on a night is dependent on the occurrence of intense cloud to ground lightning activity and cloud condition above the observation site. Most of the sprites/elves are directly associated with storms produced by a cold front passing over Japan. It is found that sprites/elves appear not only in the west coast of Japan but also above the Pacific Ocean. The average vertical length of winter sprites in the west cost is shorter than that of summer sprites in the US by about a factor of 2. The altitude of the causative thunderstorm for winter sprites and elves is comparatively lower than that of the summer events in the US and the horizontal width of the cloud is sometimes smaller than 30 km . The sprites’ detection in winter in Japan suggests the possibility of winter sprite occurrence in Scandinavia and/or Israel where the climate condition is similar to Japan.

Biosynthesis of riboflavin. Single turnover kinetic analysis of GTP cyclohydrolase II.

GTP cyclohydrolase II catalyzes the conversion of GTP into a mixture of 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (Compound 2), formate, and pyrophosphate. Moreover, GMP was recently shown to be formed as a minor product. The major product (Compound 2) serves as the first committed intermediate in the biosynthesis of the vitamin, riboflavin. Numerous pathogenic microorganisms are absolutely dependent on endogenous synthesis of riboflavin. The enzymes of this pathway are therefore potential drug targets, and mechanistic studies appear relevant for development of bactericidal inhibitors. Pre-steady state quenched flow analysis of GTP cyclohydrolase II shows the rate-determining step to be located at the beginning of the reaction sequence catalyzed by the enzyme. Thus, GTP is consumed at a rate constant of 0.064 s(-1), and the reaction product, Compound 2, is formed at an apparent rate constant of 0.062 s(-1). Stopped flow experiments monitored by multiwavelength photometry are well in line with these data. 2-Amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone triphosphate can serve as substrate for GTP cyclohydrolase II but does not fulfill the criteria for a kinetically competent intermediate. A hypothetical reaction mechanism involves the slow formation of a phosphoguanosyl derivative of the enzyme under release of pyrophosphate. The covalently bound phosphoguanosyl moiety is proposed to undergo rapid hydrolytic release of formate from the imidazole ring and/or hydrolytic cleavage of the phosphodiester bond.

Temporal and spatial variations in the intensity ratio of N2 1st and 2nd positive bands in sprites

Abstract In order to investigate the spatial and temporal variations of sprites and elves and their spectral structures, we have carried out photometric observations during the SPRITES' 97 campaign using two multi-anode array photometers (MAPs). Each MAP has 5 fields of view arrayed in vertical and a time resolution of 52 μs, which enables us to detect the rapid vertical motion of sprites/elves. Since the emissions of sprites and elves mainly consist of the 1st and 2nd positive bands of N 2 , the intensity ratio of these bands gives us information on the energy distribution of electrons which excite N 2 molecules via collision processes. Thus, one of the MAP instrument with an optical sharp cut filter was used to measure only the N 2 1st positive band emissions in the wavelength range of 560 – 800 nm, while the otehr MAP without a filter was used to measure both the N 2 1st and 2nd positive band emissions in the range 350 – 800 nm. Comparing the data from these two MAPs, we estimated the relative ratio of the 1st / 2nd positive bands of N 2 . During this campaign, we obtained 66 events data of sprites or elves with the MAPs. It is found that over the entire region of the head of column-shaped sprites the relative ratio of the 1st / 2nd positive bands of N 2 is small at the initial phase of the luminosity enhancements lasting only about 1 ms. In the second luminosity enhancement occurring 1 – 2 ms after the initial phase, the relative ratio of the 1st / 2nd positive bands decreases in the lower part of the head. These facts imply that electrons which excite N 2 molecules have higher energy at the initial phase over the entire head, while the energy of electrons is high only at lower altitude in the second enhancement.

The Nitric Oxide/Superoxide Assay: INSIGHTS INTO THE BIOLOGICAL CHEMISTRY OF THE NO/[formula omitted]2 INTERACTION

Nitric oxide (NO) is a widespread signaling molecule involved in the regulation of an impressive spectrum of diverse cellular functions. Superoxide anions (O-2) not only contribute to the localization of NO action by rapid inactivation, but also give rise to the formation of the potentially toxic species peroxynitrite (ONOO-) and other reactive nitrogen oxide species. The chemistry and biological effect of ONOO- depend on the relative rates of formation of NO and O-2. However, the simultaneous quantification of NO and O-2 has not been achieved yet due to their high rate of interaction, which is almost diffusion-controlled. A sensitive spectrophotometric assay was developed for the simultaneous quantification of NO and O-2 in aqueous solution that is based on the NO-induced oxidation of oxyhemoglobin (oxyHb) to methemoglobin and the O-2-mediated reduction of ferricytochrome c. Using a photodiode array photometer, spectral changes of either reaction were analyzed, and appropriate wavelengths were identified for the simultaneous monitoring of absorbance changes of the individual reactions. oxyHb oxidation was followed at 541.2 nm (isosbestic wavelength for the conversion of ferri- to ferrocytochrome c), and ferricytochrome c reduction was followed at 465 nm (wavelength at which absorbance changes during oxyHb to methemoglobin conversion were negligible), using 525 nm as the isosbestic point for both reactions. At final concentrations of 20 microM ferricytochrome c and 5 microM oxyHb, the molar extinction coefficients were determined to be epsilon465-525 = 7.3 mM-1 cm-1 and epsilon541.2-525 = 6.6 mM-1 cm-1, respectively. The rates of formation of either NO or O-2 determined with the combined assay were virtually identical to those measured with the classical oxyhemoglobin and cytochrome c assays, respectively. The assay was successfully adapted to either kinetic or end point determination in a cuvette or continuous on-line measurement of both radicals in a flow-through system. Maximal assay sensitivity was approximately 25 nM for NO and O-2. Cross-reactivity with ONOO- was controlled for by the presence of L-methionine. Generation of NO from the NO donor spermine diazeniumdiolate could be reliably quantified in the presence and absence of low, equimolar, and high flux rates of O-2. Likewise, O-2 enzymatically generated from hypoxanthine/xanthine oxidase could be specifically quantified with no difference in absolute rates in the presence or absence of concomitant NO generation at different flux rates. Nonenzymatic decomposition of 3-morpholinosydnonimine hydrochloride (100 microM) in phosphate buffer, pH 7.4 (37 degrees C), was found to be associated with almost stoichiometric production of NO and O-2 (1.24 microM NO/min and 1.12 microM O-2/min). Assay selectivity and applicability to biological systems were demonstrated in cultured endothelial cells and isolated aortic tissue using calcium ionophore and NADH for stimulation of NO and O-2 formation, respectively. Based on these data, a computer model was elaborated that successfully predicts the reaction of NO and O-2 with hemoprotein and may thus help to further elucidate these reactions. In conclusion, the nitric oxide/superoxide assay allows the specific, sensitive, and simultaneous detection of NO and O-2. The simulation model developed also allows the reliable prediction of the reaction between NO and O-2 as well as their kinetic interaction with other biomolecules. These new analytical tools will help to gain further insight into the physiological and pathophysiological significance of the formation of these radicals in cell homeostasis.

Background-Limited Performance in the Submillimeter

We have been awarded NASA funds to construct a Submillimeter (SMM) Array Photometer for use at the Caltech SMM Observatory (CSO) on Mauna Kea. The array will consist of 5×5 composite bolometers illuminated through light cones. On the CSO, each cone will cover 25 arcsecs on the sky, implying a total field-of-view for the array of just over 2×2 arcmins. Our aim is to achieve background-limited performance in the 730 and 870 μm atmospheric windows, thus obtaining a Noise Equivalent Flux Density (NEFD) of approximately 0.1 Jy/√Hz at these wavelengths. This sensitivity level will enable 5-sigma measurements of 10 mJy sources (such as radio-quiet quasars) in about one hour. We also will have the capability to operate at 1.1 mm, but the photometer will not be optimized at this wavelength. This system is expected to be operational on the CSO in January 1994.

An array photometer for air-borne far infrared astronomy

We describe here a far-infrared photometer capable of detecting simultaneously in three bands in the region 20–120 microns, each band having an array of 3 or 4 photoconductive detectors. We present and discuss its laboratory performance and the results obtained on the planet Venus during an air-borne observational programme using a 32.5 cm telescope. We also present the atmospheric spectra obtained by a Michelson interferometer aboard the aircraft.