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Abstract

Effect of illumination distribution in the circle of confusion on the measurement of the photoelectric coupling coefficient of the second-generation photodetector devices is studied. A theoretical study is carried out using mathematical modeling for illumination patterns of different structure and several ratios of photodetector pitch to the effective size of the photosensitive area. A formula is derived for calculation of the photoelectric coupling coefficient for a known distribution of photodetector sensitivity. The main conditions that affect the reliability of the results on the simulated measurement process are presented.

Abstract

Distributions of dark currents, lifetimes of minority carrier, and microdefects revealed by selective etching are compared. The main reason for increased dark currents and decreased photosensitivity in silicon photodiodes fabricated on n-type silicon using the Czochralski method are the generation–recombination processes on fine oxide precipitates.

Abstract

The results of the development of a recursive algorithm for temporal noise reduction with an adaptive threshold for thermal imaging systems are presented. This algorithm is designed to reduce the level of temporal noise based on the results of analyzing a sequence of images obtained using a thermal imaging channel. A mathematical model of the algorithm is provided, as well as the required amount of computing resources needed for its hardware implementation in field programmable gate arrays (FPGAs). Several characteristics of the thermal imaging system with the developed algorithm were measured and conclusions were made about the positive influence of the algorithm on its noise equivalent temperature difference (NETD).

Abstract

The resonant scattering spectra by the main magnetic mode of a subwavelength linear structure consisting of two dielectric flat thin rings located along the wave vector and excited by the displacement currents of the incident plane electromagnetic wave of the microwave range are investigated experimentally and using computer modeling. As distinct from a single ring, splitting of the resonant frequency is observed in the scattering spectra of the magnetic field in the far wave zone, near wave zone, and near the centers of the rings. The measured spectra coincide with the spectra resulting from computer calculations at all measurement points.

Abstract

For the task of Earth remote sensing (ERS) in the short-wave infrared (IR) range of the spectrum, the most promising are matrix and multi-row photodetector modules of the short-wave infrared (IR) range of the spectrum based on heteroepitaxial structures of materials of the ternary solution of cadmium-mercury-tellurium (HgCdTe) and the ternary solution of indium-gallium-arsenide (InGaAs), sensitive in the spectral range from 1 to 2.5 μm. Possible architectures of photosensitive elements that provide reduced dark currents and noise are analyzed. Ways of improvement are considered and dark currents and parameters of n-on-p-type heterostructures based on HgCdTe in a wide temperature range, as well as the parameters of p+-B–n-N+-type barrier structures based on InGaAs are investigated.

Abstract

An overview of various sensor designs for recording the parameters of microparticles in the accelerator path is provided, which are used to simulate the impact of micrometeoroids and space debris particles on structural elements of a spacecraft. A model of a cylindrical induction sensor (a Faraday cup) and a possible modification of its design for measuring the microparticle distribution in the accelerator path are considered in more detail.

Abstract

The parameters of photodetectors based on photosensitive barrier structures and photodiodes with absorbing layers of InAs1–xSbx and In1–xGaxSb ternary solutions of the mid-wave infrared spectrum range are studied. Temperature dependences of lifetime and dark current in InAs1–xSbx and In1–xGaxSb layers have been calculated. The signal-to-noise ratio in the operating temperature range was determined. Parameter modeling has shown that for photodetectors based on InAs0.8Sb0.2 with a cutoff wavelength λ0.5 ∼ 4.8 µm the detectability at T = 100 K will be D* ≈ 1012 cm W–1 Hz1/2; for photodiodes based on In0.7Ga0.3Sb with cutoff wavelength λ0.5 ∼ 5.2 µm the detectability at T = 100 K will be D* ≈ 1011 cm W–1 Hz1/2, which is suitable for high temperature applications.

Abstract

A new deselection method has been developed for detecting defects in infrared photomodules (IR PMs) with time delay and accumulation mode (TDM). The developed method is used to detect and deselect defective photosensitive elements (PSEs), which most reduce the signal-to-noise ratio (SNR) in IR PM channels. This method increases the SNR of IR PM channels, which improves the ability of IR PMs to detect low-power infrared optical signals. This result is ensured by the fact that the detection of defective PSEs is achieved by processing the signals and noise of all PSEs using the detection criterion of PSEs that most reduce the SNR of the IR PM channels. This method is a general rule for detecting defective PSEs, since the criterion analyzes the influence of all PSEs on the SNR of IR PM channels, including the noisiest elements.

Abstract

The electric field on the surface of a metal electrode immersed in plasma with an electron temperature of Te ∼ 10 eV and plasma density ne from 1010 to 1013 cm−3 has been calculated under negative electric potential Ψ0 of the electrode and large values of parameter |eΨ0|/Te  \( \gg \)  1. The obtained asymptotic formula for the field strength at |eΨ0|/Te  \( \gg \)   1 differs significantly from the classical formulas for calculating the electric field and the Debye length of field screening near the electrode surface in plasma, which are valid under condition |eΨ0|/Te  \( \ll \)  1. It has been shown that, at |eΨ0|/Te  \( \gg \)  1, near the electrode in a plasma, a modified Debye layer can exceed the classical Debye length by two orders of magnitude. To calculate the electric field on the electrode surface in plasma, a generalized formula has been proposed in the explicit form, which is valid in a wide range of parameter 0 < |eΨ0|/Te < 104 at negative electrode potentials of up to 10 kV.

Abstract

The electrostatic reflection method is formulated and proven for a point charge located near a plane-layered medium consisting of two films on a dielectric half-space. The method is generalized to the case of an arbitrary system of charges and is used to solve mathematically similar problems of electrostatics and the stationary thermal conductivity of plane-layered media. The problem of finding the electrostatic potential distributions around a conducting sphere located near a plane-layered structure consisting of two dielectric films on a dielectric half-space is solved. Solutions to similar problems of finding the temperature distribution of uniformly heated bodies located near a heat-conducting plane-layered structure of two heat-conducting films on a heat-conducting half-space are discussed.

Abstract

Global ionospheric total electron content (TEC) map prediction is important for improving the accuracy of global navigation satellite systems. There are two main issues with the current TEC prediction: (1) The deep learning models used for TEC prediction are mainly designed using a stacked structure. When stacking multiple layers, the input data will undergo continuous multi-layer convolution operations, leading to the loss of fine-grained features and the degradation of model performance; (2) The model optimization methods for TEC prediction are relatively outdated, mainly using manual optimization or grid search methods. To address these two issues, an automatic framework for global TEC map prediction and optimization is proposed, named as CGAOA-STRA-BiConvLSTM. It includes a global TEC map prediction model, STRA-BiConvLSTM, which can simultaneously extract both coarse-grained and fine-grained spatiotemporal features. It also contains an optimization algorithm, CGAOA, to optimize the model. We first experimentally verified the effectiveness of CGAOA. Then, the effectiveness of STRA-BiConvLSTM was verified through ablation experiments. Finally, we conducted comparative experiments from multiple perspectives between our framework and 5 mainstream methods: C1PG, C2PG, ConvLSTM, ConvGRU, and ED-ConvLSTM. The results show that in all cases, the proposed CGAOA-STRA-BiConvLSTM outperforms the comparative models.

Nature Geoscience, Published online: 20 January 2025; doi:10.1038/s41561-024-01634-8

The Martian dichotomy boundary receded hundreds of kilometres in the Mawrth Vallis region and left behind mounds that record changing aqueous conditions during the Noachian (4.1–3.7 Ga), according to a geomorphological and spectroscopic study.

Abstract

The Rashid-1 lunar rover represented the first attempt by the United Arab Emirates to explore the surface of the Moon. The mission of Rashid-1 was supposed to begin only a few hours following the planned landing by the iSpace Hakuto-R M1 lunar lander inside the Atlas crater of the Moon. Unfortunately, the lander was unable to successfully complete the landing maneuver and it crashed on the surface of the Moon destroying both itself and its payloads in the process. In this paper, we present the characterization of the optical image acquisition systems onboard the Rashid-1 rover which consisted of two wide-field ( \(82^{\circ } \times 82^{\circ }\) ) identical cameras aptly named CAM-1 and CAM-2 and mounted on the front and back of the rover respectively. Additionally, a third high resolution optical imager (CAM-M) with a spatial resolution of approximately 27 μm/pixel was placed on the front of the rover and was tasked with obtaining what would have been, at that time, the highest resolution in-situ images ever taken of the lunar regolith. We discuss the basic calibration processes such as the thermal, radiometric, color, distortion and perspective corrections of the three optical systems. We also provide an overview of both the onboard as well as the ground processing steps that were set up to receive and examine the images the rover would have sent from the lunar surface.

Abstract

Metasomatism refers to the process during which a pre-existing rock undergoes compositional and mineralogical transformations associated with chemical reactions triggered by the reaction of fluids which invade the protolith. It changes chemical compositions of minerals, promotes their dissolution and precipitation of new minerals. In this paper, we review metasomatic alteration of type 3 ordinary (H, L, LL) and carbonaceous (CV, CO, CK) chondrites, including (i) secondary mineralization, (ii) physicochemical conditions, (iii) chronology (53Mn-53Cr, 26Al-26Mg, 129I-129Xe) of metasomatic alteration, (iv) records of metasomatic alteration in H, O, N, C, S, and Cl isotopic systematics, (v) effects of metasomatic alteration on O- and Al-Mg-isotope systematics of primary minerals in chondrules and refractory inclusions, and (vi) sources of water ices in metasomatically altered CV, CO, and ordinary chondrites, and outline future studies.

In this paper, we augment airborne gravity anomaly data from Antarctica, expanding the coverage area by 10.4% based on the existing data set. These data are combined with a gravity field model to establish a m...

Abstract

Latest harmonic developments of the Earth tide-generating potential (TGP), e.g., HW95 (Hartmann and Wenzel in Geoph Res Lett 22:3553, 1995), RATGP95 (Roosbeek in Geophys J Int 126:197, 1996), KSM03 (Kudryavtsev in J Geodesy 77:829, 2004), include a number of terms caused by the joint effect of the Earth’s polar flattening (that can be numerically described by the \({J}_{2}\) geopotential coefficient) and the Moon/the Sun gravitational attraction. In the present study, we additionally consider the effect of the Earth’s equatorial flattening due to the Earth’s triaxiality. Explicit analytical expressions for the relevant part of the TGP are derived. New terms of the TGP development due to the Earth’s triaxial figure are found. Amplitudes of nineteen of them exceed the threshold level of 10–8 m2s−2 used by the modern tidal potential catalogs. Three of the new terms have the frequency sign opposite to that of the Earth rotation. It is not the case for any previously known term of the Earth TGP development. Every term has a new feature that an integer multiplier of the mean local lunar time used in its argument is not equal to the order of the spherical harmonic associated with the term. It necessitates a relevant modification of the standard HW95 format for representing the Earth TGP. The new terms are suggested for including in the current and future tidal potential catalogs.

Abstract

On February 6, 2023 the Kahramanmaraş Earthquake Sequence caused significant ground shaking and catastrophic losses across south-central Türkiye and northwest Syria. These seismic events produced ionospheric perturbations detectable in Global Navigation Satellite System (GNSS) total electron content (TEC) measurements. This work aims to develop and incorporate a near-real-time (NRT) ionospheric disturbance detection method into JPL’s GUARDIAN system. Our method uses a Long Short-Term Memory (LSTM) neural network to detect anomalous ionospheric behavior, such as co-seismic ionospheric disturbances among others. Our method detected an anomalous signature after the second \(M_w\)  7.5 earthquake at 10:24:48 UTC (13:24 local time) but did not alert after the first \(M_w\)  7.8 earthquake at 01:17:34 UTC (04:17 local time), which had a visible disturbance of smaller amplitude likely due to lower ionization levels at night and potentially the multi-source mechanism of the slip.

Plain Language Summary Seismic activity, including the destructive Kahramanmaraş Earthquake Sequence on February 6, 2023 in the Republic of Türkiye, result in vertical ground displacement that cause atmospheric waves. These waves propagate upwards to the outer atmosphere, disturbing the ionospheric electron content. This disturbance impacts the signals broadcast by positioning satellites (such as GPS) and received by ground-based receivers. If the receiver position is known, the impact to these signals can be used to measure the electron density disturbance caused by these seismically-induced atmospheric waves. Such studies usually rely on being aware of the event a priori. Using deep learning neural networks, we instead aim to detect anomalous signals automatically. We propose to utilise this method to detect seismically-induced disturbances over a large geographical area. The detection method proposed in this paper successfully detected an anomalous event in the ionosphere approximately ten minutes after the second earthquake in the Kahramanmaraş Earthquake Sequence.

Publication date: Available online 2 December 2024

Source: Earth and Planetary Science Letters

Author(s): Shuo Chen, Pu Sun, Yaoling Niu, Pengyuan Guo, Tim Elliott, Remco C. Hin

Publication date: 1 January 2025

Source: Advances in Space Research, Volume 75, Issue 1

Author(s): D. Sierra-Porta

Publication date: 1 January 2025

Source: Advances in Space Research, Volume 75, Issue 1

Author(s): Yuqing Liu, Hu Wang, Lina He, Hongyang Ma, Yingying Ren, Yafeng Wang, Jing Jiao, Yamin Dang