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CIRBE (Colorado Inner Radiation Belt Experiment), a 3U CubeSat, was launched on 15 April 2023 into a sun synchronous orbit (97.4° inclination and 509 km altitude). The sole science payload onboard is REPTile‐2 (Relativistic Electron and Proton Telescope integrated little experiment—2), an advanced version of REPTile which operated in space between 2012 and 2014. REPTile‐2 has 60 channels for electrons (0.25–6 MeV) and 60 channels for protons (6.5–100 MeV). It has been working well, capturing detailed dynamics of the radiation belt electrons, including several orders of magnitude enhancements of the outer belt electrons after an intense magnetic storm, multiple “wisps”‐ an electron precipitation phenomenon associated with human‐made very low frequency (VLF) waves in the inner belt, and “drift echoes” of 0.25–1.4 MeV electrons across the entire inner belt and part of the outer belt. These new observations provide opportunities to test the understanding of the physical mechanisms responsible for these features. Plain Language Summary Energetic electrons of 100s of keV (1,000 electric volt) to MeV (million electric volt) existing in the near‐Earth environment have detrimental effects on spacecraft subsystems and the bodies of astronauts during their extravehicular activity (e.g., Baker, 2002, https://doi.org/10.1126/science.1074956). Their source, loss, and variations have been a long‐standing research topic. Recent advancements in miniaturization of spacecraft and instrumentation make CubeSats (in the shape of a cube, easier for launch and deployment) a viable means to conduct space‐borne research. Colorado Inner Radiation Belt Experiment (CIRBE) is a 3U (10 cm × 10 cm × 34 cm) CubeSat with only one science instrument onboard: Relativistic Electron and Proton Telescope integrated little experiment −2 (REPTile‐2), which is an advanced version of the previously flown REPTile. REPTile‐2, thanks to its high energy and time resolution, revealed detailed dynamic features of the radiation belt electrons, which will further our understanding of and ability to predict the dynamics of these energetic electrons. Key Points Detailed variations of relativistic electrons over a wide energy range, 0.25–6 MeV, in the Earth's magnetosphere were captured Multiple “wisps,” an electron precipitation phenomenon associated with human‐made VLF waves in the inner belt, were measured “Drift echoes” or “zebra stripes” of 0.25–1.4 MeV electrons across the entire inner belt and part of the outer belt, have been observed

The title of our this plenary presentation, “Overcoming the Limits”, certainly echoes Meadows’ famous “The Limits to Growth,” which has played a prominent role in understanding the path of humanity towards the future. However, during the past fifty years both the concept and understanding of these limits have significantly changed. In this report, the concept of limits is understood more broadly then usual. It includes not only the process of overcoming the limits that hinder development, but also implies situations when such limits become irrelevant. Another important point of our title is that limits are not insurmountable. To put it more precisely, they are serious but solvable challenges which can and should be resolved. This paper reflects the concept, developed by the research team of Moscow State University, on the prospects of future world development.

Through applying a 4‐MHz linear frequency modulation waveform, which has high range resolution and signal intensity, we successfully detected for the first time the ionospheric 150‐km echo enhancement at 430–450 MHz of the Ultra‐High‐Frequency (UHF) band using the newly built Sanya Incoherent Scatter Radar (SYISR). The obtained low signal enhancement (less than 0.5 dB) explains why previous UHF experiments did not detect them. We also found that our measured fine structure shows a much wider forbidden region than previous results and covers a much larger altitudinal and local time region. In comparison with recent upper‐hybrid instability theory and simulation, our results confirmed the predicted higher altitude occurrence, wider gaps between enhancements, the turn corner feature around sunrise, and perhaps the weak enhancement, which provide an independent evaluation of the newly proposed mechanism in UHF band. Future UHF experiments could further improve the physical understanding of 150‐km echo phenomenon. Plain Language Summary In the altitude range of 130–170 km above the Earth's surface, the electrons ionized by the solar radiation effecting on the neutrals can generate enhanced radar echo with specific layered structures if the radar beam points perpendicular to or slightly off perpendicular to the geomagnetic field. Up to date, this phenomenon was only detected by lower frequency radars (30–60 MHz). Its physical mechanism has been a puzzle over several decades. Recently, due primarily to the advancement of numerical simulation technology and the improvement of computing power, this puzzle was resolved well by the newly proposed across scales energy transformation physical mechanism in several recent publications. However, these simulations also concluded that it is hard to be detected by higher frequency radars. In this paper, using our newly built Sanya Incoherent Scatter Radar, we applied a novel experimental setup to gain very high range resolution and signal intensity. We finally successfully detected this phenomenon in 430–450 MHz. By comparing our results with previous measurements and theoretical simulation, we can enhance current physical understanding from the perspective of observations. Key Points Successful first detection of daytime 150‐km echoes in the Ultra‐High‐Frequency band with Sanya Incoherent Scatter Radar We detected wider forbidden region and larger altitudinal and local time coverage than previous results Narrow layering features not following the zenith angle point to field‐aligned irregularitie echoes

Radar, as one of the sensors for human activity recognition (HAR), has unique characteristics such as privacy protection and contactless sensing. Radar-based HAR has been applied in many fields such as human–computer interaction, smart surveillance and health assessment. Conventional machine learning approaches rely on heuristic hand-crafted feature extraction, and their generalization capability is limited. Additionally, extracting features manually is time–consuming and inefficient. Deep learning acts as a hierarchical approach to learn high-level features automatically and has achieved superior performance for HAR. This paper surveys deep learning based HAR in radar from three aspects: deep learning techniques, radar systems, and deep learning for radar-based HAR. Especially, we elaborate deep learning approaches designed for activity recognition in radar according to the dimension of radar returns (i.e., 1D, 2D and 3D echoes). Due to the difference of echo forms, corresponding deep learning approaches are different to fully exploit motion information. Experimental results have demonstrated the feasibility of applying deep learning for radar-based HAR in 1D, 2D and 3D echoes. Finally, we address some current research considerations and future opportunities.

Understanding drop size distribution (DSD) variability has important implications for remote sensing and numerical modeling applications. Twelve disdrometer datasets across three latitude bands are analyzed in this study, spanning a broad range of precipitation regimes: light rain, orographic, deep convective, organized midlatitude, and tropical oceanic. Principal component analysis (PCA) is used to reveal comprehensive modes of global DSD spatial and temporal variability. Although the locations contain different distributions of individual DSD parameters, all locations are found to have the same modes of variability. Based on PCA, six groups of points with unique DSD characteristics emerge. The physical processes that underpin these groups are revealed through supporting radar observations. Group 1 (group 2) is characterized by high (low) liquid water content (LWC), broad (narrow) distribution widths, and large (small) median drop diameters D 0 . Radar analysis identifies group 1 (group 2) as convective (stratiform) rainfall. Group 3 is characterized by weak, shallow radar echoes and large concentrations of small drops, indicative of warm rain showers. Group 4 identifies heavy stratiform precipitation. The low latitudes exhibit distinct bimodal distributions of the normalized intercept parameter N w , LWC, and D 0 and are found to have a clustering of points (group 5) with high rain rates, large N w , and moderate D 0 , a signature of robust warm rain processes. A distinct group associated with ice-based convection (group 6) emerges in the midlatitudes. Although all locations exhibit the same covariance of parameters associated with these groups, it is likely that the physical processes responsible for shaping the DSDs vary as a function of location.

Advanced perfusion‐weighted imaging (PWI) methods that combine gradient echo (GE) and spin echo (SE) data are important tools for the study of brain tumours. In PWI, single‐shot, EPI‐based methods have been widely used due to their relatively high imaging speed. However, when used with increasing spatial resolution, single‐shot EPI methods often show limitations in whole‐brain coverage for multi‐contrast applications. To overcome this limitation, this work employs a new version of EPI with keyhole (EPIK) to provide five echoes: two with GEs, two with mixed GESE and one with SE; the sequence is termed “GESE‐EPIK.” The performance of GESE‐EPIK is evaluated against its nearest relative, EPI, in terms of the temporal signal‐to‐noise ratio (tSNR). Here, data from brain tumour patients were acquired using a hybrid 3T MR‐BrainPET scanner. GESE‐EPIK resulted in reduced susceptibility artefacts, shorter TEs for the five echoes and increased brain coverage when compared to EPI. Moreover, compared to EPI, EPIK achieved a comparable tSNR for the first and second echoes and significantly higher tSNR for other echoes. A new method to obtain multi‐echo GE and SE data with shorter TEs and increased brain coverage is demonstrated. As proposed here, the workflow can be shortened and the integration of multimodal clinical MR‐PET studies can be facilitated.

Ice penetrating radar sounding is the primary geophysical technique for imaging the subsurface of planetary ice shells and has the potential to directly detect the ice–ocean interface. However, many sounding measurements may lack laterally extensive features that would aid their physical interpretation. In this scenario, the detection of sparse echoes can also provide rich information on ice shell properties. To explore and demonstrate this possibility, we consider three cases of isolated radar signatures: pore‐curing, eutectic melt, and unattributed echoes. We show that through detection of unattributed sparse echoes, the thickness of the conductive portion of Europa's ice shell can be constrained. These constraints can be improved by attributing sparse echoes to thermally diagnostic signatures such as pore‐curing and eutectic melt. Notably, this approach to radar sounding echo analysis is particularly compatible with joint inversions with other planetary geophysical observations such as tidal deformation, magnetic induction, and rotation state. Plain Language Summary Upcoming missions to explore Europa, the icy moon of Jupiter, include ice penetrating radar sounders as part of their instrument payloads. One of the primary goals of these instruments is to investigate the subsurface structure and thickness of Europa's ice shell. It's possible that the radar profiles returned by these instruments will include imagery of the ice‐ocean interface across much of the moon, providing a direct measurement of ice‐shell thickness. However, we show that, even in the absence of such imagery, a small number of isolated radar echoes can be used to measure the thickness and structure of the ice shell. These echoes include scattering from porous ice near the moon's surface and pockets of melt water within the shell. Key Points Radar‐detectable interfaces from the subsurface of Europa's ice shell can be thermally diagnostic The thickness of the conductive portion of Europa's ice shell can be constrained without direct detection of the ice—ocean interface The detection of sparse echoes places a lower bound on conductive ice shell thickness based on the two‐way integrated radar attenuation

In order to provide proof of consistent quality, survey systems, acquisition methods, and procedures for analyzing the resulting data are subject to regular validation. One method of validation is punctual comparison with data for comparison that entitles as reference data. However, as the conditions at the time of data acquisition critically impact each survey, dedicated parallel surveys employing different methods. This can provide insight into discrepancies and relative consistencies, especially for research purposes. In the literature, multiple techniques and sensors have been presented for the acquisition of underwater reference data, such as multi-beam echo sounders, single-beam echo sounders, and different types of pole measurements. Furthermore, bathymetric LiDAR can be deployed from UAVs, helicopters, and aircraft, each entailing specific data resolution and accuracy. Therefore, this study presents four different bathymetric LiDAR datasets (one UAV, two helicopter and one airplane-based), where for each dataset a different type of reference acquisition approach is used appropriate for the individual water bodies (river, ponds, coastal waters). The results of this comparison display the overall alignment of bathymetric LiDAR and reference data with the highest accuracies for UAV data and pole reference measurements. There, the mean normal distance between the LiDAR data and the reference is 0 cm ± 2 cm standard deviation. The highest difference was seen for the Baltic sea dataset, where airplane-based data and single-beam echo sounder reference were used. In this dataset, the mean normal distance between the LiDAR data and reference is −5 cm ± 10 cm standard deviation. In conclusion, the analyzed bathymetric LiDAR datasets show strong consistency with their respective reference measurements, with observed variations primarily influenced by environmental conditions and system configurations.

The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component for the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The geometric boundary conditions and in particular the nature of the subglacial bed of the NEGIS are essential to understand its ice flow dynamics. We present a record of more than 8000 km of radar survey lines of multi-channel, ultra-wideband radio echo sounding data covering an area of 24 000 km2, centered on the drill site for the East Greenland Ice-core Project (EGRIP), in the upper part of the NEGIS catchment. Our data yield a new detailed model of ice-thickness distribution and basal topography in the region. The enhanced resolution of our bed topography model shows features which we interpret to be caused by erosional activity, potentially over several glacial–interglacial cycles. Off-nadir reflections from the ice–bed interface in the center of the ice stream indicate a streamlined bed with elongated subglacial landforms. Our new bed topography model will help to improve the basal boundary conditions of NEGIS prescribed for ice flow models and thus foster an improved understanding of the ice-dynamic setting.

Diffusion weighted magnetic resonance imaging (DWI) data have been mostly acquired with single-shot echo-planar imaging (EPI) to minimize motion induced artifacts. The spatial resolution, however, is inherently limited in single-shot EPI, even when the parallel imaging (usually at an acceleration factor of 2) is incorporated. Multi-shot acquisition strategies could potentially achieve higher spatial resolution and fidelity, but they are generally susceptible to motion-induced phase errors among excitations that are exacerbated by diffusion sensitizing gradients, rendering the reconstructed images unusable. It has been shown that shot-to-shot phase variations may be corrected using navigator echoes, but at the cost of imaging throughput. To address these challenges, a novel and robust multi-shot DWI technique, termed multiplexed sensitivity-encoding (MUSE), is developed here to reliably and inherently correct nonlinear shot-to-shot phase variations without the use of navigator echoes. The performance of the MUSE technique is confirmed experimentally in healthy adult volunteers on 3Tesla MRI systems. This newly developed technique should prove highly valuable for mapping brain structures and connectivities at high spatial resolution for neuroscience studies. ► Our multi-shot EPI reconstruction strategy enables DWI of high spatial-resolution. ► Motion-induced phase errors can be removed inherently with a novel MUSE algorithm. ► The new algorithm produces data with higher SNR than conventional parallel imaging.