The morphology and electrodynamics of the boreal polar winter cusp

Thesis (Ph.D.) University of Alaska Fairbanks, 1993The major result of this thesis is the magnetic signatures of the dayside cusp region. These signatures were determined by comparing the magnetic observations to optical observations of different energy particle precipitation regions observed in the cusp. In this thesis, the cusp is defined as the location of most direct entry of magnetosheath particles into the ionosphere. Optical observations show that the observing station rotates daily beneath regions of different incident energy particles. Typically, the station passes from a region in the morning of high energy particles into a region near magnetic noon of very low energy precipitation, and then returns to a region of high energy precipitation after magnetic noon. A tentative identification of the cusp is made on the basis of these observations. The optical observations also are used to determine the upward field aligned current density, which is found to be most intense in the region identified as the cusp. The magnetic field measurements are found to correlate with the optical measurements. When the characteristic energy is high, the spectrogram shows large amplitude broad band signals. The Pc5 component of these oscillations is right hand polarized in the morning, and left hand polarized in the afternoon. During the time the optics detect precipitation with a minimum characteristic energy, the magnetic spectrogram shows a unique narrow band tone at 3-5 mHz. The occurrence statistics of the magnetic oscillations are compared to DMSP satellite observations of the cusp and low latitude boundary layer. The pulses that make the narrow band tone are found to come in wave trains that are phase coherent. These trains of coherent pulses are found to be separated by phase jumps from adjacent wave trains. These jumps in phase occur when a new field aligned current appears on the equatorward edge of the cusp. This combination of phase coherent wave trains associated with poleward propagating auroral forms which are shown to contain intense field aligned currents may be the signature of newly reconnected flux tubes in the ionosphere

Density Invariant Contrast Maximization for Neuromorphic Earth Observations

Contrast maximization (CMax) techniques are widely used in event-based vision systems to estimate the motion parameters of the camera and generate high-contrast images. However, these techniques are noise-intolerance and suffer from the multiple extrema problem which arises when the scene contains more noisy events than structure, causing the contrast to be higher at multiple locations. This makes the task of estimating the camera motion extremely challenging, which is a problem for neuromorphic earth observation, because, without a proper estimation of the motion parameters, it is not possible to generate a map with high contrast, causing important details to be lost. Similar methods that use CMax addressed this problem by changing or augmenting the objective function to enable it to converge to the correct motion parameters. Our proposed solution overcomes the multiple extrema and noise-intolerance problems by correcting the warped event before calculating the contrast and offers the following advantages: it does not depend on the event data, it does not require a prior about the camera motion, and keeps the rest of the CMax pipeline unchanged. This is to ensure that the contrast is only high around the correct motion parameters. Our approach enables the creation of better motion-compensated maps through an analytical compensation technique using a novel dataset from the International Space Station (ISS). Code is available at \url{https://github.com/neuromorphicsystems/event_warping

Analysis of an Energetic Electron Injection at GEO Using FalconSEED: A Low SWaP-C, CubeSat-Compatible Instrument for Space Environments

We present a detailed analysis of an energetic electron injection (10s - 100s keV) observed at geostationary Earth orbit (GEO) on March 5, 2022 in order to highlight the capabilities of the Falcon Solid-state Energetic Electron Detector (SEED). The high time- and energy-resolution of SEED are used to quantify the dispersion of the injection front and to explore the morphology of the energy distribution throughout the injection encounter. Observations of the same event from nearby platforms are included for context. The SEED is a CubeSat compatible, single element particle telescope, designed to measure 14 to 145keV electrons in GEO. The flight payload has a volume of 10 cm x 10 cm x 20 cm, in a 4.3-kg, 3.4-W package. The SEED was manifested on the Department of Defense (DoD) Space Test Program Satellite—6 (STPSat-6) which was launched in December of 2021 to GEO at 112 W longitude. During the first year of mission operations, the SEED has demonstrated the ability, evidenced in this paper, or a low-resource particle detector comprised of predominantly commercial-off-the-shelf components to provide relevant science observations of the space plasma environment

Event-based camera refractory period characterization and initial clock drift evaluation

Event-based camera (EBC) technology provides high-dynamic range operation and shows promise for efficient capture of spatio-temporal information, producing a sparse data stream and enabling consideration of nontraditional data processing solutions (e.g., new algorithms, neuromorphic processors, etc.). Given the fundamental difference in camera architecture, the EBC response and noise behavior differ considerably compared to standard CCD/CMOS framing sensors. These differences necessitate the development of new characterization techniques and sensor models to evaluate hardware performance and elucidate the trade-space between the two camera architectures. Laboratory characterization techniques reported previously include noise level as a function of static scene light level (background activity) and contrast responses referred to as S-curves. Here we present further progress on development of basic characterization methods and test capabilities for commercial-off-the-shelf (COTS) visible EBCs, with a focus on measurement of pixel deadtime (refractory period) including results for the 4th-generation sensor from Prophesee and Sony. Refractory period is empirically determined from analysis of the interspike intervals (ISIs), and results visualized using log-histograms of the minimum per-pixel ISI values for a subset of pixels activated by a controlled dynamic scene. Our tests of the Prophesee gen4 EVKv2 yield refractory period estimates ranging from 6.1 msec to 6.8 μsec going from the slowest (20) to fastest (100) settings of the relevant bias parameter, bias_refr. We also introduce and demonstrate the concept of pixel bandwidth measurement from data captured while viewing a static scene – based on recording data at a range of refractory period setting and then analyzing noise-event statistics. Finally, we present initial results for estimating and correcting EBC clock drift using a GPS PPS signal to generate special timing events in the event-list data streams generated by the DAVIS346 and DVXplorer EBCs from iniVation

Falcon Neuro: an event-based sensor on the International Space Station

We report on the Falcon neuro event-based sensor (EBS) instrument that is designed to acquire data from lightning and sprite phenomena and is currently operating on the International Space Station. The instrument consists of two independent, identical EBS cameras pointing in two fixed directions, toward the nominal forward direction of flight and toward the nominal Nadir direction. The payload employs stock DAVIS 240C focal plane arrays along with custom-built control and readout electronics to remotely interface with the cameras. To predict the sensor’s ability to effectively record sprites and lightning, we explore temporal response characteristics of the DAVIS 240C and use lab measurements along with reported limitations to model the expected response to a characteristic sprite illumination time-series. These simulations indicate that with appropriate camera settings the instrument will be capable of capturing these transient luminous events when they occur. Finally, we include initial results from the instrument, representing the first reported EBS recordings successfully collected aboard a space-based platform and demonstrating proof of concept that a neuromorphic camera is capable of operating in the space environment

ARTICLE Plasma irregularities in the D-region ionosphere in association with sprite streamer initiation

Sprites are spectacular optical emissions in the mesosphere induced by transient lightning electric fields above thunderstorms. Although the streamer nature of sprites has been generally accepted, how these filamentary plasmas are initiated remains a subject of active research. Here we present observational and modelling results showing solid evidence of pre-existing plasma irregularities in association with streamer initiation in the D-region ionosphere. The video observations show that before streamer initiation, kilometre-scale spatial structures descend rapidly with the overall diffuse emissions of the sprite halo, but slow down and stop to form the stationary glow in the vicinity of the streamer onset, from where streamers suddenly emerge. The modelling results reproduce the sub-millisecond halo dynamics and demonstrate that the descending halo structures are optical manifestations of the pre-existing plasma irregularities, which might have been produced by thunderstorm or meteor effects on the D-region ionosphere

Effects of Phosphor Persistence on High-Speed Imaging of Transient Luminous Events

International audienceHigh-speed intensified cameras are commonly used to observe and study the transient luminous events known as sprite halos and sprite streamers occurring in the Earth's upper atmosphere in association with thunderstorm activity. In such observations, the phosphor persistence in the image intensifier, depending on its characteristic decay time, might lead to a significant distortion of the optical signals recorded by those cameras. In this paper, we analyze the observational data obtained using different camera systems to discuss the effects of phosphor persistence on high-speed video observations of sprites, and introduce a deconvolution technique to effectively reduce such effects. The discussed technique could also be used to enhance the high-speed images of other transient optical phenomena in the case when the phosphor persistence has a characteristic decay time that is comparable with the temporal resolution of the cameras required to resolve the phenomena

Falcon Neuro: an event-based sensor on the International Space Station

We report on the Falcon neuro event-based sensor (EBS) instrument that is designed to acquire data from lightning and sprite phenomena and is currently operating on the International Space Station. The instrument consists of two independent, identical EBS cameras pointing in two fixed directions, toward the nominal forward direction of flight and toward the nominal Nadir direction. The payload employs stock DAVIS 240C focal plane arrays along with custom-built control and readout electronics to remotely interface with the cameras. To predict the sensor’s ability to effectively record sprites and lightning, we explore temporal response characteristics of the DAVIS 240C and use lab measurements along with reported limitations to model the expected response to a characteristic sprite illumination time-series. These simulations indicate that with appropriate camera settings the instrument will be capable of capturing these transient luminous events when they occur. Finally, we include initial results from the instrument, representing the first reported EBS recordings successfully collected aboard a space-based platform and demonstrating proof of concept that a neuromorphic camera is capable of operating in the space environment.ISSN:0091-3286ISSN:1560-230