Space-based optical imaging of blue corona discharges on cumulonimbus cloud tops

The ILAN-ES (Imaging of Lightning And Nocturnal Emissions from Space) experiment was conducted in April 2022 as part of the Axiom company AX-1 private mission to the International Space Station, in the framework of Rakia, an Israeli set of experiments selected for flight by the Ramon Foundation and the Israeli Space Agency. The mission objective was to record transient luminous events from the Cupola window in the ISS, based on preliminary thunderstorm forecasts uploaded to the crew 24-36 hours in advance. A Nikon D6 camera with a 50 mm lens was used, in a video mode of 60 fps. During the 12-day mission, 82 different targets were identified for the ISS, of which 20 were imaged by the astronauts, yielding a total harvest > 80 TLEs: sprites, Elves and BLUEs (blue corona discharges). We report here on opportune nadir observation of a thunderstorm that produced multiple blue events near the Myanmar-Thailand border on April 21st, 2022, at 21:30 UT. The storm produced many visible blue discharges of varying sizes and durations, in sizes ranging from hundreds of meters to a few km2. The emissions were mostly in blue, however the brightest events had also a conspicuous red component. We used meteorological and ENTLN lightning data to establish the relationship between lightning type and the observable properties of the blue corona discharges.Comment: 16 pages, 6 Figures, 1 Tabl

THE MEASUREMENT OF THE INTEGRATED INTENSITY OF THE ν3\nu_{3} BAND OF CH3FCH_{3}F BY THE USE OF A CO2CO_{2} LASER

$^{1}$ T. Y. Chang, T. J. Bridges, and E. G. Burkhardt, Appl. Phys. Lett. 17, 249 (1970). $^{2}$F. Brown, S. Kronheim, and E. Silver, Appl. Phys. Lett. 25, 394 (1974). $^{3}$R. J. Temkin, D. R. Cohn and Z. Drozdowicz, Opt. Communications 14 314 (1975). $^{4}$S. M. Freund, G. Duxbury, M. Romheld, J. T. Tiedje, and T. Oka, J. Mol. Spectrose. 52, 38 (1974). $^{5}$L. A. Gribov, ``Intensity Theory for Infrared Spectra of Polyatomic Molecules'', Consultant Bureau, New York, (1964).Author Institution: Department of Chemistry, Cornell UniversityOne of the most powerful far-infrared lasers found today is the $CH_{3}F$ $laser.^{1,2}$ The operation of this laser is achieved through optical pumping of the $^{Q}Q(12,K) K = 1-7$ transitions of the $\nu_{3}$ band of $CH_{3}F$ by a $CO_{2}$ laser operating at the 9.55 $\mu$ - P(20) $line.^{2,3}$ The absorption coefficients of these transitions, which determine the optical pumping of the $CH_{3}F$ laser, have not been thoroughly measured and can be calculated from the integrated intensity of the $\nu_{3}$ band, $S_{b}$. The value of $S_{b}$ was obtained from the measured value of $\alpha\nu$, the absorption profile of the $^{Q}Q(12,K) K = 1,2$ transitions in this $\nu_{3}$ band, by the use of a semi-tunable $CO_{2}$ laser operating at the 9.55 $\mu$ - p(20) line. The spectral shape of $\alpha_{\nu}$ depends on three parameters: the mid-frequencies of these two transitions and $S_{b}$. Since the measured values of the mid-frequencies of the $^{Q}Q(12,1)$ and $^{Q}Q(12,2)$ transitions matched those found in the $literature,^{4}$ the value of $S_{b}$ was, thus, accurately measured. The value obtained $S_{b} = 619 \pm 28 cm^{-2} atm^{-1}$ is somewhat larger than that found in the $literature,^{5}$ $484 cm^{-2} atm^{-1}$. This result was confirmed by additional measurement of the average value of the absorption profile

In-Field Absolute Calibration of Ground and Airborne VIS-NIR-SWIR Hyperspectral Point Spectrometers

Spectrometer calibration and measurements of spectral radiance are often required when performing ground, aerial, and space measurements. While calibrating a spectrometer in the field using an integrating sphere is practically unachievable, calibration against a quartz halogen (QH) lamp is a quite easy and feasible option. We describe a calibration protocol whereby a professional QH lamp, operating with a stabilized current source, is first calibrated in the laboratory against a US National Institute of Standards and Technology (NIST) traceable integrating sphere and, then, used for the field calibration of a spectrometer before a ground or airborne campaign. Another advantage of the lamp over the integrating sphere is its ability to create a continuous calibration curve at the spectrometer resolution, while the integrating sphere is calibrated only for a few discrete wavelengths. A calibrated lamp could also be used for a secondary continuous calibration of an un-calibrated integrating sphere

Coherence enhancement of light after double passage through a turbulent medium

Experimental observation of coherence enhancement phenomenon are presented and described. We have illuminated an optically rough moving target through turbulence using two coherent point sources and observed the interference of the scattered fields in the region close to the sources (the region of coherence enhancement) with the help of a special interferometric system. Our study shows that the intensity distribution in the region of coherence enhancement depends on the inner scale of turbulence