The IBEX-Lo sensor covers the low-energy heliospheric neutral atom spectrum from 0.01 to 2 keV. It shares significant energy overlap and an overall design philosophy with the IBEX-Hi sensor. Both sensors are large geometric factor, single pixel cameras that maximize the relatively weak heliospheric neutral signal while effectively eliminating ion, electron, and UV background sources. The IBEX-Lo sensor is divided into four major subsystems. The entrance subsystem includes an annular collimator that collimates neutrals to approximately 7°× 7°in three 90°sectors and approximately 3.5°× 3.5°in the fourth 90°sector (called the high angular resolution sector). A fraction of the interstellar neutrals and heliospheric neutrals that pass through the collimator are converted to negative ions in the ENA to ion conversion subsystem. The neutrals are converted on a high yield, inert, diamond-like carbon conversion surface. Negative ions from the conversion surface are accelerated into an electrostatic analyzer (ESA), which sets the energy passband for the sensor. Finally, negative ions exit the ESA, are post-accelerated to 16 kV, and then are analyzed in a time-of-flight (TOF) mass spectrometer. This triple-coincidence, TOF subsystem effectively rejects random background while maintaining high detection efficiency for negative ions. Mass analysis distinguishes heliospheric hydrogen from interstellar helium and oxygen. In normal sensor operations, eight energy steps are sampled on a 2-spin per energyThe IBEX-Lo Sensor 119 step cadence so that the full energy range is covered in 16 spacecraft spins. Each year in the spring and fall, the sensor is operated in a special interstellar oxygen and helium mode during part of the spacecraft spin. In the spring, this mode includes electrostatic shutoff of the low resolution (7°× 7°) quadrants of the collimator so that the interstellar neutrals are detected with 3.5°× 3.5°angular resolution. These high angular resolution data are combined with star positions determined from a dedicated star sensor to measure the relative flow difference between filtered and unfiltered interstellar oxygen. At the end of 6 months of operation, full sky maps of heliospheric neutral hydrogen from 0.01 to 2 keV in 8 energy steps are accumulated. These data, similar sky maps from IBEX-Hi, and the first observations of interstellar neutral oxygen will answer the four key science questions of the IBEX mission.

Bolides are detected by the Geostationary Lightning Mapper onboard the GOES‐16 weather satellite, which takes images of Earth at a rate of 500 Hz in a 1.1 nm wide pass band centered on 777.4 nm wavelength. Ten case studies are discussed. These initial results were obtained using the Level 0 data received during the nonoperational in‐orbit postlaunch test period. GLM positions and timings are sufficiently accurate to assist in trajectory and orbit reconstruction. GLM samples the light curve nearly completely, unaffected by onboard and downlink processes tailored to lightning data. Sufficient data on the instantaneous background scene are provided to reconstruct the baseline drift in the brightest pixels. The agreement to within a factor of 2–3 between measured total radiated energy from GLM and that derived from other space‐borne observations implies that during the bolide's peak brightness the GLM pass band is dominated by continuum emission, rather than O I line emission. The reported flux is corrected for angle‐from‐nadir shifts in the central wavelength of the pass band, which overestimates continuum flux by only up to 20% for most of the GLM field of view, but more so if the bolide is observed far from nadir. Assuming a 6000 K blackbody spectrum, GLM is able to detect bolides with peak visual magnitude (at a normalized 100 km distance) brighter than about −14 in nighttime, and slightly brighter in daytime.

The Geostationary Lightning Mapper (GLM) on the Geostationary Operational Environmental Satellite‐R series of weather satellites provides point geolocations of lightning flashes that are further comprised of a hierarchy of geolocated groups and events. This study describes an open‐source method for reconstruction of imagery from those point detections that retains the quantitative physical measurements made by GLM, restores the spatial footprint of the events, and connects that spatial footprint to the groups and flashes. Meteorological signals are demonstrated to be more apparent in the gridded imagery than in the point detections, leading to their adoption by the United States National Weather Service as the first GLM product available in their real‐time displays. Analysis of a mesoscale convective system over Argentina confirms that there is a class of propagating lightning observed by GLM (distinct from that in storm cores) that can be visualized and quantified using our imagery‐based approach.

The existence of mesoscale lightning discharges on the order of 100 km in length has been known since the radar-based findings of Ligda in the mid-1950s. However, it took the discovery of sprites in 1989 to direct significant attention to horizontally extensive “megaflashes” within mesoscale convective systems (MCSs). More recently, 3D Lightning Mapping Arrays (LMAs) have documented sprite-initiating lightning discharges traversing several hundred kilometers. One such event in a 2007 Oklahoma MCS having an LMA-derived length of 321 km, has been certified by the WMO as the longest officially documented lightning flash. The new Geostationary Lightning Mapper (GLM) sensor on GOES-16/17 now provides an additional tool suited to investigating mesoscale lightning. On 22 October 2017, a quasi-linear convective system moved through the central United States. At 0513 UTC, the GLM indicated a lightning discharge originated in northern Texas, propagated north-northeast across Oklahoma, fortuitously traversed the Oklahoma LMA (OKLMA), and finally terminated in southeastern Kansas. This event is explored using the OKLMA, the National Lightning Detection Network (NLDN), and the GLM. The NLDN reported 17 positive cloud-to-ground flashes (+CGs), 23 negative CGs (−CGs), and 37 intracloud flashes (ICs) associated with this massive discharge, including two +CGs capable of inducing sprites, with others triggering upward lightning from tall towers. Combining all available data confirms the megaflash, which illuminated 67,845 km2, was at least 500 km long, greatly exceeding the current official record flash length. Yet even these values are being superseded as GLM data are further explored, revealing that such vast discharges may not be all that uncommon.

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The GOES-R series is the latest in a long line of American geostationary weather satellites operated by the National Oceanic and Atmospheric Administration (NOAA). The two Geostationary Lightning Mapper (GLM) instruments currently operating on the GOES-16 and GOES-17 satellites give NOAA a unique new capability to map in-cloud and cloud-to-ground lightning flashes across the entire hemisphere within seconds of their occurrence. GLM enables improved warning times for severe weather events, decreased false alarms, persistent coverage over wide geographical areas without sampling bias, and long-term monitoring of trends linked to the changing climate.Viewed from space, emissions from lightning appear as a series of brief (~500 µs) optical pulses diffused through clouds over scales of tens to thousands of km 2 . A significant portion of the emitted optical radiation is in the form of emission lines, including a prominent neutral atomic oxygen triplet whose emission lines are near 777 nm. GLM discriminates lightning flashes from the bright sunlit cloud background by taking advantage of the spatial, temporal, and spectral characteristics of the optical signature of lightning.This paper describes key design drivers in the development of GLM, methods used to calibrate the instrument, and lessons learned from on-orbit testing. We discuss optimization of the entire signal chain, from the telescope optics to the ground processing algorithms.

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