Particles sinking from the surface to the deep ocean play a key role in the biological carbon pump, whose efficiency depends partly on sinking velocities. Over the last decade, in situ imaging has enabled critical advances in our understanding of particle dynamics in the ocean. Yet, in situ velocity measurements are scarce and often inferred only from the bulk population of particles. Here, we introduce the VisuTrap, a new tool to measure in situ velocities of marine particles. It consists of an Underwater Vision Profiler 6 (UVP6) camera inserted into different types of sediment traps, which isolate a volume of water. Continuous image acquisition during shortterm or long-term deployments enables reconstruction of particle tracks and estimation of their in situ vertical velocities. We detail the configuration and special UVP6 settings for this application, as well as the image processing and track analysis pipeline. Then, we present results from several experiments in the Mediterranean Sea to illustrate the VisuTrap's use as a new approach to understand the dynamical behavior of marine particles in situ. In light of the broad range of morphological data generated by the UVP6, we discuss technical additions to refine in situ velocity measurements and the possibility of integrating such data into carbon flux assessments.

Abstract The effect of mesoscale features on the distribution of planktonic organisms are well documented. Yet, the interaction between these spatial features and the temporal scale, which can result in sudden increases of the planktonic biomass, is less known and not described at high resolution. A permanent mesoscale front in the Ligurian Sea (north‐western Mediterranean) was repeatedly sampled between January and June 2021 using a SeaExplorer glider equipped with an Underwater Vision Profiler 6 (UVP6), a versatile in situ imager. Both plankton and particle distributions were resolved throughout the spring bloom to assess whether the front was a location of increased zooplankton concentration and whether it constrained particle distribution. Over the 5 months, the glider performed more than 5000 dives and the UVP6 collected 1.1 million images. We focused our analysis on shallow (300 m) transects, which gave a horizontal resolution of 900 m. About 13,000 images of planktonic organisms were retained. Ordination methods applied to particles and plankton concentrations revealed strong temporal variations during the bloom, with a succession of various zooplankton communities. Changes in particle abundance and size could be explained by changes in the plankton community. The front had a strong influence on particle distribution, while the signal was not as clear for plankton, probably because of the relatively small number of imaged organisms. This work confirms the need to sample both plankton and particles at fine scale to understand their interactions, a task for which automated in situ imaging is particularly adapted.

The effect of mesoscale features on the distribution of planktonic organisms are well documented. Yet, the interaction between these spatial features and the temporal scale, which can result in sudden increases of the planktonic biomass, is less known and not described at high resolution. A permanent mesoscale front in the Ligurian Sea (north‐western Mediterranean) was repeatedly sampled between January and June 2021 using a SeaExplorer glider equipped with an Underwater Vision Profiler 6 (UVP6), a versatile in situ imager. Both plankton and particle distributions were resolved throughout the spring bloom to assess whether the front was a location of increased zooplankton concentration and whether it constrained particle distribution. Over the 5 months, the glider performed more than 5000 dives and the UVP6 collected 1.1 million images. We focused our analysis on shallow (300 m) transects, which gave a horizontal resolution of 900 m. About 13,000 images of planktonic organisms were retained. Ordination methods applied to particles and plankton concentrations revealed strong temporal variations during the bloom, with a succession of various zooplankton communities. Changes in particle abundance and size could be explained by changes in the plankton community. The front had a strong influence on particle distribution, while the signal was not as clear for plankton, probably because of the relatively small number of imaged organisms. This work confirms the need to sample both plankton and particles at fine scale to understand their interactions, a task for which automated in situ imaging is particularly adapted.

The effect of mesoscale features on the distribution of planktonic organisms are well documented. Yet, the interaction between these spatial features and the temporal scale, which can result in sudden increases of the planktonic biomass, is less known and not described at high resolution. We targeted a permanent mesoscale front in the Ligurian Sea (NW Mediterranean) that we repeatedly sampled between January and June 2021 using a SeaExplorer glider equipped with a UVP6, a versatile in situ imager. We aimed to resolve mesoscale distribution of plankton and particle distribution during the spring bloom, to assess whether the front was a location of increased concentration of zooplankton, and if it constrained the distribution of particles. During the 5 months, the glider conducted more than 5,000 dives and the UVP6 collected 1.1 million images. We focused our analysis on shallow (300 m) transects, which gave a horizontal resolution of 900 m. About 13,000 images of planktonic organisms were retained. Ordination methods applied to particles and plankton concentrations revealed contrasted periods during the bloom, in which changes in particle abundance and size could be explained by changes in the plankton community. The front had a strong influence on particle distribution, while the signal was not as clear for plankton, probably because of the relatively small number of imaged organisms. This work confirms the need to sample both plankton and particles at fine scale to understand their interaction, a task for which automated in situ imaging is particularly adapted.

The Underwater Vision Profiler (UVP) has been developed to study the number, size and shape of particles (size \textgreater 80µm) and plankton (size \textgreater 700µm) in situ. Over the last decade, thousands of profiles have been collected in the world's oceans by the UVP5 to better understand and quantify processes affecting community compositions of large plankton and the biological carbon pump. These data, used together with modeling approaches helped estimate plankton global carbon biomass and particle vertical flux. The most recent UVP (UVP6) sensors have been developed to be mounted on autonomous platforms, mooring and CTD rosettes down to 6000 m depth. Fully inter-calibrated, they record particles and identify plankton and marine snow after recovery or during deployment using an embedded recognition algorithm. A complete software ecosystem is used to pilot the instrument, record the data, and make them available to fulfill the global need of easy data access expressed by scientists, policy makers and the public. Because of the cost reduction of the UVP6, its capability to be mounted on many platforms including autonomous ones, the Ocean is being quickly populated by this sensor (125 sensors have been in operation in the last 2 years). Recent plankton community composition, particle mass, and flux data from three different basins in the Atlantic will be presented. In the next decade, the massive global monitoring of these key biological Essential Oceanographic Variables will significantly advance our understanding of key aquatic processes including the biological carbon pump.

EUSO-Balloon is a pathfinder for JEM-EUSO, the mission concept of a spaceborne observatory which is designed to observe Ultra-High Energy Cosmic Ray (UHECR)-induced Extensive Air Showers (EAS) by detecting their UltraViolet (UV) light tracks “from above.” On August 25, 2014, EUSO-Balloon was launched from Timmins Stratospheric Balloon Base (Ontario, Canada) by the balloon division of the French Space Agency CNES. After reaching a floating altitude of 38 km, EUSO-Balloon imaged the UV light in the wavelength range ∼290–500 nm for more than 5 hours using the key technologies of JEM-EUSO. The flight allowed a good understanding of the performance of the detector to be developed, giving insights into possible improvements to be applied to future missions. A detailed measurement of the photoelectron counts in different atmospheric and ground conditions was achieved. By means of the simulation of the instrument response and by assuming atmospheric models, the absolute intensity of diffuse light was estimated. The instrument detected hundreds of laser tracks with similar characteristics to EASs shot by a helicopter flying underneath. These are the first recorded laser tracks measured from a fluorescence detector looking down on the atmosphere. The reconstruction of the direction of the laser tracks was performed. In this work, a review of the main results obtained by EUSO-Balloon is presented as well as implications for future space-based observations of UHECRs.

Autonomous and cabled platforms are revolutionizing our understanding of ocean systems by providing 4D monitoring of the water column, thus going beyond the reach of ship-based surveys and increasing the depth of remotely sensed observations. However, very few commercially available sensors for such platforms are capable of monitoring large particulate matter (100-2000 μm) and plankton despite their important roles in the biological carbon pump and as trophic links from phytoplankton to fish. Here, we provide details of a new, commercially available scientific camera-based particle counter, specifically designed to be deployed on autonomous and cabled platforms: the Underwater Vision Profiler 6 (UVP6). Indeed, the UVP6 camera-and-lighting and processing system, while small in size and requiring low power, provides data of quality comparable to that of previous much larger UVPs deployed from ships. We detail the UVP6 camera settings, its performance when acquiring data on aquatic particles and plankton, their quality control, analysis of its recordings, and streaming from in situ acquisition to users. In addition, we explain how the UVP6 has already been integrated into platforms such as BGC-Argo floats, gliders and long-term mooring systems (autonomous platforms). Finally, we use results from actual deployments to illustrate how UVP6 data can contribute to addressing longstanding questions in marine science, and also suggest new avenues that can be explored using UVP6-equipped autonomous platforms.

The JEM-EUSO (Joint Experiment Missions for the Extreme Universe Space Observatory) program aims at developing Ultra-Violet (UV) fluorescence telescopes for efficient detections of Extensive Air Showers (EASs) induced by Ultra-High Energy Cosmic Rays (UHECRs) from satellite orbit. In order to demonstrate key technologies for JEM-EUSO, we constructed the EUSO-Balloon instrument that consists of a ∼1 m 2 refractive telescope with two Fresnel lenses and an array of multi-anode photo-multiplier tubes at the focus. Distinguishing it from the former balloon-borne experiments, EUSO-Balloon has the capabilities of single photon counting with a gate time of 2.3 µs and of imaging with a total of 2304 pixels. As a pathfinder mission, the instrument was launched for an 8 h stratospheric flight on a moonless night in August 2014 over Timmins, Canada. In this work, we analyze the count rates over ∼2.5 h intervals. The measurements are of diffuse light, e.g. of airglow emission, back-scattered from the Earth’s atmosphere as well as artificial light sources. Count rates from such diffuse light are a background for EAS detections in future missions and relevant factor for the analysis of EAS events. We also obtain the geographical distribution of the count rates over a ∼780 km 2 area along the balloon trajectory. In developed areas, light sources such as the airport, mines, and factories are clearly identified. This demonstrates the correct location of signals that will be required for the EAS analysis in future missions. Although a precise determination of count rates is relevant for the existing instruments, the absolute intensity of diffuse light is deduced for the limited conditions by assuming spectra models and considering simulations of the instrument response. Based on the study of diffuse light by EUSO-Balloon, we also discuss the implications for coming pathfinders and future space-based UHECR observation missions.

EUSO-Balloon is the first balloon pathfinder of the JEM-EUSO (Joint Experiment Missions - Extreme Universe Space Observatory) framework. It is an ultraviolet (UV) telescope designed to test the key technologies and methods necessary for the indirect detection of Ultra High Energy Cosmic Rays (UHECR) by observing from above the fluorescence emission produced by Extensive Air Showers (EAS) in the 290-430 nm band. The instrument was launched on the 24$^{t}^{h}$ of August, 2014 by the French space agency (CNES) from the stratospheric balloon base in Timmins, Canada and performed an 8 hour night time flight. One of the key technologies of EUSO-Balloon is the refractive optical system which consists of two large aspherical Fresnel lenses (≈ 1 m$^{2}$) and aims at focusing the UV light into a detector plane formed by an array of Multi-Anode Photomultiplying tubes. This work presents a description of the optical system, the test bench and methods used to characterize its performance and the global efficiency. The measured performance can be understood through the addition of a semi-empirical diffusion model to the classic ray-tracing model of the optics.

EUSO-Balloon is a pathfinder mission for the Extreme Universe Space Observatory onboard the Japanese Experiment Module (JEM-EUSO). It was launched on the moonless night of the 25th of August 2014 from Timmins, Canada. The flight ended successfully after maintaining the target altitude of 38 km for five hours. One part of the mission was a 2.5 hour underflight using a helicopter equipped with three UV light sources (LED, xenon flasher and laser) to perform an inflight calibration and examine the detectors capability to measure tracks moving at the speed of light. We describe the helicopter laser system and details of the underflight as well as how the laser tracks were recorded and found in the data. These are the first recorded laser tracks measured from a fluorescence detector looking down on the atmosphere. Finally, we present a first reconstruction of the direction of the laser tracks relative to the detector.

JEM-EUSO is a space mission designed to investigate Ultra-High Energy Cosmic Rays and Neutrinos ( E>5⋅1019eV ) from the International Space Station (ISS). Looking down from above its wide angle telescope is able to observe their air showers and collect such data from a very wide area. Highly specific trigger algorithms are needed to drastically reduce the data load in the presence of both atmospheric and human activity related background light, yet retain the rare cosmic ray events recorded in the telescope. We report the performance in offline testing of the first level trigger algorithm on data from JEM-EUSO prototypes and laboratory measurements observing different light sources: data taken during a high altitude balloon flight over Canada, laser pulses observed from the ground traversing the real atmosphere, and model landscapes reproducing realistic aspect ratios and light conditions as would be seen from the ISS itself. The first level trigger logic successfully kept the trigger rate within the permissible bounds when challenged with artificially produced as well as naturally encountered night sky background fluctuations and while retaining events with general air-shower characteristics.

We summarize the state of the art of a program of UV observations from space of meteor phenomena, a secondary objective of the JEM-EUSO international collaboration. Our preliminary analysis indicates that JEM-EUSO, taking advantage of its large FOV and good sensitivity, should be able to detect meteors down to absolute magnitude close to 7. This means that JEM-EUSO should be able to record a statistically significant flux of meteors, including both sporadic ones, and events produced by different meteor streams. Being unaffected by adverse weather conditions, JEM-EUSO can also be a very important facility for the detection of bright meteors and fireballs, as these events can be detected even in conditions of very high sky background. In the case of bright events, moreover, exhibiting some persistence of the meteor train, preliminary simulations show that it should be possible to exploit the motion of the ISS itself and derive at least a rough 3D reconstruction of the meteor trajectory. Moreover, the observing strategy developed to detect meteors may also be applied to the detection of nuclearites, exotic particles whose existence has been suggested by some theoretical investigations. Nuclearites are expected to move at higher velocities than meteoroids, and to exhibit a wider range of possible trajectories, including particles moving upward after crossing the Earth. Some pilot studies, including the approved Mini-EUSO mission, a precursor of JEM-EUSO, are currently operational or in preparation. We are doing simulations to assess the performance of Mini-EUSO for meteor studies, while a few meteor events have been already detected using the ground-based facility EUSO-TA.

EUSO-Balloon is a prototype detector of the Extreme Universe Space Observatory on the Japanese Experiment Module (JEM-EUSO). EUSO-Balloon was flown successfully as a balloon payload from the Timmins Stratospheric Balloon Launch Facility in Ontario, Canada on 2014 August 24-25 at an altitude of 38 km. To simulate the optical signatures of UV fluorescence photons emitted from cosmic ray air showers generated in the atmosphere, a pulsed UV laser and two UV flashers (LED and Xe) were used. These sources were fired in the instrument field of view for about 2 hours from a helicopter that circled at an altitude of 3 km under the balloon. UV signals were effectively detected, including 270 laser track events. We describe the helicopter laser system and the geometric reconstruction of the laser events that were generated by this system. We report here on the reconstruction of the laser events starting from the information contained in the observed tracks. We note that this work represents the first observation and measurement of aircraft based laser tracks by an optical fluorescence detector flown at near space altitudes.

A precise characterization of the Earth’s UV background during night is essential for the observation of ultra-high-energy cosmic ray induced extensive air showers (EAS) from space. We have analyzed data from the flight of the EUSO-Balloon pathfinder mission that took place near Timmins (Canada) in the moonless night from 24 to 25 August 2014. The EUSO-Balloon telescope imaged the UV background in the wavelength range of 290 – 430 nm from an altitude of ∼ 38 km with an 1 m2 refractor telescope with ∼ 11◦ field-of-view pointed in nadir direction. The UV data were complemented by the data of the Infrared camera onboard EUSO-Balloon, which was operating in the wavelength ranges of 10.37 – 11.22 µm and 11.57 – 12.42 µm. We have combined the UV and IR images to study the upward UV radiance from the Earth’s surface and Earth’s atmosphere. This allowed us to estimate the level of UV background in clear atmosphere conditions without man-made light and also to investigate the influence of clouds on the UV background. Comparison of the UV and IR images reveals an evident dependence of the upward UV radiance on the atmospheric conditions. This opens a possibility to use the UV albedo measurement for characterization of the cloud coverage. The efficiency of detection of EAS from space by EUSO like detectors varies depending on the level of the UV background. Using the available EUSOBalloon data, we discuss the role of UV background variations due to clouds and man-made light on the exposure and effective area of EAS observations.

Les rayons cosmiques ont été découverts il y a un siècle par Victor Hess à bord d'un vol scientifique en ballon. La physique des rayons cosmiques et les ballons stratosphériques ont partagé depuis lors une histoire commune, que ce soit pour d'authentiques découvertes ou en utilisant les ballons comme plateformes de test technologique pour de nouvelles missions satellites. Cette thèse, développée au sein de la collaboration JEM-EUSO, traite d'un démonstrateur en ballon stratosphérique. Notre but scientifique final est l'étude des Rayons Cosmiques de Ultra-Haute Energie (RCUHE), les particules les plus énergétiques connues dans l'Univers. Les RCUHES ont des énergies macroscopiques de plus de 10^20eV mais étant extrêmement rares, leurs origines sont encore inconnues. Ces derniers pénètrent notre atmosphère à une fréquence de un par km2 par siècle, produisant une gerbe atmosphérique géante, détectable notamment par la lumière de fluorescence ultraviolette qu'elle émet. Le principe de détection proposé par notre collaboration consiste dans l'utilisation d'un observatoire spatial, JEM-EUSO. Son objectif est d'observer un très grand volume d'atmosphère afin d'enregistrer un nombre significatif des événements ultra-violet de fluorescence initiés par les RCUHEs. Le démonstrateur EUSO-Ballon a été développé par la collaboration JEM-EUSO dans le but de démontrer les technologies et méthodes utilisées par le futur instrument spatial. Le 25 août 2014, EUSO-Ballon a été lâché depuis la base de ballons stratosphériques de Timmins (Ontario, Canada) par la division ballon du CNES. L'instrument a fonctionné pendant toute une nuit astronomique, observant depuis 38km d'altitude la lumière UV provenant de divers types de sols et de centaines de gerbes atmosphériques simulées. Ces dernières ont été produites par des flashers et un laser embarqués dans un hélicoptère volant sous EUSO-Ballon pendant deux heures. Ces résultats ont été rendus possibles par la restitution de l'attitude de l'instrument effectuée à l'IRAP, c'est-à-dire une analyse exhaustive des données du vol des différents appareils de mesure d'attitude de la nacelle du ballon. Une caractérisation précise de chaque sous-système était aussi indispensable à l'exploitation des données du vol. Le système optique innovant, composé de deux grandes lentilles de Fresnel, a été intégré et entièrement testé à l'IRAP. Face au large système réfractif de l'instrument, une nouvelle méthodologie de test a été développée. Les performances de l'optique, efficacité et spot focal, ont ainsi été mesurées et se sont révélées étonnamment différentes des prédictions des modèles numériques. Ces mesures sont utilisées pour l’analyse des données du premier vol et pour mieux comprendre le comportement de ces toutes nouvelles optiques, éléments clés dans la conception de l'instrument JEM-EUSO.

Les rayons cosmiques ont été découverts il y a un siècle par Victor Hess à bord d'un vol scientifique en ballon. La physique des rayons cosmiques et les ballons stratosphériques ont partagé depuis lors une histoire commune, que ce soit pour d'authentiques découvertes ou en utilisant les ballons comme plateformes de test technologique pour de nouvelles missions satellites. Cette thèse, développée au sein de la collaboration JEM-EUSO, traite d'un démonstrateur en ballon stratosphérique. Notre but scientifique final est l'étude des Rayons Cosmiques de Ultra-Haute Energie (RCUHE), les particules les plus énergétiques connues dans l'Univers. Les RCUHES ont des énergies macroscopiques de plus de 10^20eV mais étant extrêmement rares, leurs origines sont encore inconnues. Ces derniers pénètrent notre atmosphère à une fréquence de un par km2 par siècle, produisant une gerbe atmosphérique géante, détectable notamment par la lumière de fluorescence ultraviolette qu'elle émet. Le principe de détection proposé par notre collaboration consiste dans l'utilisation d'un observatoire spatial, JEM-EUSO. Son objectif est d'observer un très grand volume d'atmosphère afin d'enregistrer un nombre significatif des événements ultra-violet de fluorescence initiés par les RCUHEs. Le démonstrateur EUSO-Ballon a été développé par la collaboration JEM-EUSO dans le but de démontrer les technologies et méthodes utilisées par le futur instrument spatial. Le 25 août 2014, EUSO-Ballon a été lâché depuis la base de ballons stratosphériques de Timmins (Ontario, Canada) par la division ballon du CNES. L'instrument a fonctionné pendant toute une nuit astronomique, observant depuis 38km d'altitude la lumière UV provenant de divers types de sols et de centaines de gerbes atmosphériques simulées. Ces dernières ont été produites par des flashers et un laser embarqués dans un hélicoptère volant sous EUSO-Ballon pendant deux heures. Ces résultats ont été rendus possibles par la restitution de l'attitude de l'instrument effectuée à l'IRAP, c'est-à-dire une analyse exhaustive des données du vol des différents appareils de mesure d'attitude de la nacelle du ballon. Une caractérisation précise de chaque sous-système était aussi indispensable à l'exploitation des données du vol. Le système optique innovant, composé de deux grandes lentilles de Fresnel, a été intégré et entièrement testé à l'IRAP. Face au large système réfractif de l'instrument, une nouvelle méthodologie de test a été développée. Les performances de l'optique, efficacité et spot focal, ont ainsi été mesurées et se sont révélées étonnamment différentes des prédictions des modèles numériques. Ces mesures sont utilisées pour l'analyse des données du premier vol et pour mieux comprendre le comportement de ces toutes nouvelles optiques, éléments clés dans la conception de l'instrument JEM-EUSO.

EUSO-Balloon is a pathfinder for JEM-EUSO, the Extreme Universe Space Observatory which is to be hosted on-board the International Space Station. As JEM-EUSO is designed to observe Ultra-High Energy Cosmic Rays (UHECR)-induced Extensive Air Showers (EAS) by detecting their ultraviolet light tracks "from above", EUSO-Balloon is a nadir-pointing UV telescope too. With its Fresnel Optics and Photo-Detector Module, the instrument monitors a 50 km2 ground surface area in a wavelength band of 290-430 nm, collecting series of images at a rate of 400,000 frames/sec. The objectives of the balloon demonstrator are threefold: a) perform a full end-to-end test of a JEM-EUSO prototype consisting of all the main subsystems of the space experiment, b) measure the effective terrestrial UV background, with a spatial and temporal resolution relevant for JEM-EUSO. c) detect tracks of ultraviolet light from near space for the first time. The latter is a milestone in the development of UHECR science, paving the way for any future space-based UHECR observatory. On August 25, 2014, EUSO-Balloon was launched from Timmins Stratospheric Balloon Base (Ontario, Canada) by the balloon division of the French Space Agency CNES. From a float altitude of 38 km, the instrument operated during the entire astronomical night, observing UV-light from a variety of ground-covers and from hundreds of simulated EASs, produced by flashers and a laser during a two-hour helicopter under-flight.