 Subjects -> AERONAUTICS AND SPACE FLIGHT (Total: 124 journals)
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- Why Does the Ion Density in a Plasma Sheet Depend on the Density of the
Solar Wind'-
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Abstract: Abstract Measurements of heavy (M/q> 3) ions on the Phobos-2 satellite revealed that the density of these ions in the central plasma sheet of the areomagnetic tail is proportional to the proton density of the solar wind flowing around the planet. ISEE-2 ion measurements in the near-Earth plasma sheet close to the neutral line were also compared to solar wind data obtained on the ISEE-3 satellite. It was found that the density of protons in the near-Earth plasma sheet is proportional to the density of solar wind protons as well. Analysis of the magnetic and plasma pressure balance in the solar wind and inside the magnetotails of the Earth and Mars showed that the previously found correlations are the result of the necessary equality of pressures at the magnetosphere boundary and inside the magnetic tails of the planets.
PubDate: 2024-12-03
- Ballistic Analysis of a Small Spacecraft Mission for Studying the
Earth’s Magnetosphere-
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Abstract: Abstract In this paper, a preliminary ballistic analysis for an Earth magnetosphere monitoring mission is conducted. Spacecraft mass and propulsion system characteristics are specified to satisfy current technological requirements. Low Earth, Sun-synchronous, and geosynchronous transfer orbits are considered as initial orbits. The target orbits are specified in accordance with scientific tasks. The fuel cost and transfer duration are estimated by two methods: an upper bound from the Lyapunov control method and a lower bound from energy-optimal control problem solution. The relationship between optimal longitudes of the ascending nodes for initial and target orbits is examined. The fuel cost estimates validate the feasibility of the mission based on small spacecraft and on the market low-thrust electric engines.
PubDate: 2024-12-03
- Dynamics of Low-Frequency Oscillations of the Magnetic Field and
Solar-Wind Ion Flux Upstream of an Interplanetary Shock-
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Abstract: Abstract Wave trains of magnetic field and ion-flux oscillations generated upstream of the ramp of interplanetary (IP) shock were studied according to BMSW plasma-spectrometer measurements of energy–time spectra of the solar-wind ions supplemented by magnetic-field measurements. It was shown that oscillations of the magnetic field upstream of the ramp of IP shock are accompanied by oscillations of the ion flux. A detailed analysis of two cases is carried out, and the results of statistical study are presented. Right-handed circular or elliptical polarization was observed in all wave trains of magnetic-field oscillations, which is consistent with the characteristics of magnetosonic oscillations corresponding to the low-frequency branch of whistler waves. It was obtained that the mean angles between the propagation direction of whistler waves relative to the magnetic field and shock normal direction were 31° and 40°, respectively. This result suggests that the wave packets upstream of the ramp of IP shock had the properties of propagating whistler waves. It was found that, on average, with an increase in the angle of propagation of whistler waved relative to the shock normal direction θkn, the angle between the wave vector and magnetic-field direction θkB decreases.
PubDate: 2024-12-03
- Neutron Emission of the Lunar Surface at the Poles
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Abstract: Abstract The lunar surface in the vicinity of the poles has special properties compared to the surface at the equator and at moderate latitudes. First, the polar regolith contains quite a large amount of water ice, which significantly affects the neutron radiation generated under the influence of galactic cosmic rays. Second, the temperature of the polar regolith can have extremely low values of about 25 K, as a result of which the thermal component of the neutron flux is partially held in the gravitational field. Based on numerical modeling of neutron radiation from the lunar surface, its main features were shown for the polar regions compared to the equatorial ones: a significant decrease in the ratio of epithermal and thermal neutron fluxes due to an increase in the concentration of hydrogen in the regolith, as well as a significant increase in the density of thermal neutrons near the surface due to gravitational capture.
PubDate: 2024-12-03
- Evaluation of the Possibility of Using Resonant Orbits for Accompanying
Relay Satellites-
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Abstract: Abstract The paper considers the problem of ensuring stable radio communication during an Earth–Mars flight using relay satellites. We have analyzed the orbits of relay satellites that are in resonance with the Earth–Mars flight trajectory, which makes it possible to provide a channel of communication with Earth for each mission using such trajectory. A single-stage relay scheme is considered using a regenerative transponder that performs complete processing of the received signal, including demodulation, decoding, subsequent coding, modulation, and transfer to the operating frequency. An independent assessment of power budgets of the communication channels “mission-oriented spacecraft–relay satellite” and “relay satellite–ground receiving network” has been performed. The requirements for the possible regions of the relay satellite positioning in the Earth–Mars flight stage are formulated. Families of resonant orbits providing the given quality of communication on the trajectory of the mission-oriented spacecraft using the relay satellite are defined. The most promising variants of relay satellite orbits have been identified based on the following criteria: the maximum transmitted data during the flight and the maximum data rate at the maximum distance from the Earth.
PubDate: 2024-12-03
- The Role of Accelerated Electron Beams in the Generation of Intense
Current Structures and Nonideal Electric Fields in the Outer Region of the
Plasma Sheet-
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Abstract: Abstract We report Magnetospheric Multiscale Mission (MMS) observations of accelerated field-aligned electron beams in the outer ($$\left {{{B}_{x}}} \right \sim \left( {10{\kern 1pt} - {\kern 1pt} 20} \right)\,\,{\text{nT}}$$) regions of the Plasma Sheet (PS). The MMS satellites were located earthward of the magnetic reconnection X-line, inside of the bursty bulk flow. The interval corresponds to the growth phase of the substorm. Field-aligned electron beams was produced by electrons suprathermal population with energy $$ \sim {\kern 1pt} \left( {1{\kern 1pt} - {\kern 1pt} 5} \right)\,\,{\text{keV}}$$. Newly accelerated electron beams are gyrotropic. In the process of evolution, agyrotropy of the beam develops. This leads to the generation of intense (up to ∼80 nA/m2) field-aligned currents. We demonstrate that acceleration of the electrons is pulsed for the time $$ < {\kern 1pt} 5\,\,~{\text{s}}$$. Propagation of the high-velocity electron beam results in the development of plasma instabilities and generation of a strong (∼59 mV/m) nonideal electric field at frequencies lower than electron cyclotron frequency $${{{{\omega }}}_{{c,e}}}$$. The presence of a nonideal electric field leads to the violation of the frozen-in condition of electron plasma and energy dissipation. The energy transformation power density reaches ∼–1000 pW/m3. Fluctuations in the spectrum of a nonideal electric field experience spectral flattering between ion plasma $${{{{\omega }}}_{{p,i}}}$$ and electron cyclotron $${{{{\omega }}}_{{c,e}}}$$ frequencies. This evidences energy transfer from particles to waves at this spectral range. The studied phenomena may provide significant contributions to the development of turbulence on electronic kinetic scales in the outer region of the PS.
PubDate: 2024-12-03
- Magnetospheric Electron Precipitation Recorded in the Atmosphere at Middle
and Polar Latitudes in 2022–2023-
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Abstract: Abstract The study of precipitation of high-energy electrons from the magnetosphere into the Earth’s atmosphere is important for studying the physical mechanisms of electron acceleration during interplanetary disturbances in near-Earth space, the processes of formation of trapped electron fluxes in the magnetosphere and their subsequent precipitation into the atmosphere. In addition, the precipitating electrons affect the spacecraft operation and often lead to significant destruction of mesospheric ozone, etc. Since 1957, the Dolgoprudny Scientific Station of the Lebedev Physical Institute has been conducting continuous measurements of cosmic ray fluxes at altitudes of 0–30 km in the atmosphere of polar latitudes (Murmansk oblast, Antarctica) and at middle latitude (Moscow oblast). During this time, almost 600 cases of electron precipitation were recorded, mainly from the Earth’s outer radiation belt near its polar boundary due to measurement in Murmansk oblast. At the same time, several cases of electron precipitation were recorded at mid-latitude (Moscow oblast) and at the Mirny station in Antarctica, in particular, in 2022–2023. The paper discusses interplanetary and geomagnetic conditions during these events. Analysis of measurement data in the stratosphere made it possible to establish the absorption spectra of secondary bremsstrahlung photons and, on their basis, using the method we developed, to determine the primary energy spectra of precipitating magnetospheric electrons.
PubDate: 2024-12-03
- Fine Structure of the Solar Corona in High-Frequency Resolution Radio
Observations-
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Abstract: Abstract The existence of continuous cooling and heating processes is an important condition governing the behavior of the solar corona, which is characterized by temperatures of several million Kelvin. These processes can be significantly influenced by small-scale coronal formations, which largely determine the thermal balance of the corona and solar-wind disturbances. High-sensitivity observations of polarized radiation allow us to evaluate the complex structure of magnetic fields that accumulate the energy necessary to excite coronal eruptions, bursts and flares. However, at high altitudes the corona becomes optically thin, and observations of it pose a major challenge, requiring the use of instruments with a large effective area. Many researchers note that the emerging field of coronal magnetometry is hard to develop due to the fact that experimental observations in optical range are limited by the low plasma density in the corona, high temperature, and insufficient sensitivity of the instruments. In contrast, higher sensitivity is achievable in the radio frequency range. In particular, the 1–3 GHz range is optimal for detecting very weak coronal structures of emerging activity, despite limitations in spatial resolution. To carry out radio requency observations of the corona on the RATAN-600 large reflector-type radio telescope, a wide-range spectrometer in the range of 1–3 GHz was created. It has continuous coverage of the entire frequency range with maximum frequency and time resolutions, as well as high sensitivity to radiation flux. The results of the first series of observations of weak coronal structures are presented, and their interpretation in terms of their effect on thermal processes in the corona is discussed.
PubDate: 2024-12-03
- Characteristics of the Optical System of the Solntse–Terahertz
Scientific Equipment-
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Abstract: Abstract The article presents a brief description of the main scientific objectives of the Solntse–Terahertz project. As part of this project, the Lebedev Physical Institute is manufacturing scientific equipment for installation on the Russian segment of the International Space Station. The optical system of each of the eight scientific equipment’s radiation receivers consists of a system of mirrors, an optical chopper, low-pass and bandpass filters. Spectral characteristics were obtained for each element of this system. When calibrating the device, a source—a black-body simulator (BBS)—is used, and, therefore, using numerical integration methods, the intensity of radiation from the BBS that passes through the filter system was calculated. To estimate the characteristic signal from the quiet Sun, the radiation intensity passing through the filter system was calculated using numerical integration methods using the standard ASTM E-490 solar spectrum.
PubDate: 2024-12-03
- Electron-Scale Current Sheets Observed by MMS in the Plasma Sheet of the
Magnetotail during Bursty Bulk Flows-
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Abstract: Abstract MMS four-spacecraft observations with high temporal and spatial resolution made it possible to study the characteristics of intense superthin current sheets (SCSs) with a current density J> 30 nA/m2, formed in bursty bulk flows (BBFs), propagating in the Plasma Sheet (PS) of the magnetotail from the remote X line. Statistical analysis of>1000 SCSs observations showed that, in the majority of cases, the current in the SCSs is parallel to the ambient magnetic field and is carried by field-aligned accelerated electron beams. The half-thickness of the SCSs is several electron gyroradii, and in such thin layers the electric current is carried by demagnetized electrons. Bursts of strong nonideal electric fields E'> 10 mV/m are often observed at the edges and/or inside the SCSs. The generation of such fields brings about energy conversion in the SCSs of hundreds of pW/m3, and in some cases up to several nW/m3, which is comparable to the energy conversion in the electron diffusion region of magnetic reconnection. The strongest energy release is observed in the SCSs formed in the fastest BBFs and under strong variations of the magnetic field in the tail lobes.
PubDate: 2024-12-03
- Variation Spectra and Anisotropy of Cosmic Rays during Forbush Effects in
March 2023-
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Abstract: Abstract Based on ground-based observations of cosmic rays (CRs) on the global network of neutron monitors, the Yakutsk complex of muon telescopes, and the URAGAN muon hodoscope (Moscow), the spectra of CR variations and anisotropy during the Forbush effects of March 15 and 23, 2023 were calculated using the spectrographic global survey method. It is shown that the spectrum of CR variations during these periods is not described by a power function in a wide range of rigidities. It was found that the Earth was in a loop-shaped structure of the interplanetary magnetic field on March 15 and that it entered a magnetic cloud with closed field lines on March 23.
PubDate: 2024-12-03
- Scientific Goals and Perspectives of the Plasma-Instrument Complex in the
Venera-D Space Mission-
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Abstract: Abstract The article present a list of realistic scientific goals that can be achieved by the complex of modern plasma instruments onboard the Venera-D spacecraft. Structures and operating principles of three plasma instruments—an ion energy–mass analyzer, electron spectrometer, and energetic neutral-atom detector—are also presented.
PubDate: 2024-12-03
- Spatiotemporal Plume Variability of Terek and Sulak Rivers from Satellite
Data and Concurrent In Situ Measurements-
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Abstract: Abstract The article is devoted to the study of spatiotemporal variability of the plumes of the Terek and Sulak rivers flowing into the Caspian Sea and to the determination of the three-dimensional structure of the plumes based on a joint analysis of satellite data and concurrent in situ measurements. In the study, high spatial resolution visible data from Sentinel‑2 MSI and Landsat-8, -9 OLI/OLI-2 satellite sensors were used. In situ measurements of the main plume parameters were made in June 2023, from a small vessel, concurrently with the satellite survey. As a result of satellite monitoring of the Terek and Sulak estuarine zones for the period 2014–2022, it was determined that the 73-km-long coastline of Dagestan north of the city of Makhachkala is potentially exposed to pollution entering the sea with waters of these rivers. An analysis of the satellite images showed that there is a pronounced spatial asymmetry in the direction of plume spreading. For both rivers, the dominant spreading direction over a large time interval is southeast. A seasonal variability of Terek and Sulak plumes signatures in satellite images was revealed. Based on satellite data and concurrent in situ measurements in June 2023, the three-dimensional structure of the Terek and Sulak plumes was obtained and the spatial distributions of the main parameters, such as temperature, salinity, turbidity and chlorophyll-a concentration, were determined. It was found that the depth of river water penetration does not exceed 1.5–2 m and, regardless of the amount of suspended matter carried with river runoff and river discharge, the bulk of the suspended matter is deposited in the same localized area, within a distance of about 500 m from the shore. On the basis of XRD analysis of water samples taken at the stations nearest to the river mouths and at plume boundaries, the mineral composition of suspended matter and its variation in different plume areas were determined. Repeated coincidence of the boundaries of the area affected by river water, established from satellite data and measured in situ, makes it possible to confidently use remote sensing methods for monitoring estuarine zones without involving in situ data.
PubDate: 2024-12-01
- Seasonal Anomalies of the Thermal Upwelling Index in the Eastern Pacific
Ocean-
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Abstract: Abstract Seasonal anomalies of the thermal upwelling index are considered using the example of the Pacific upwellings (Chilean, Peruvian, and California), which are part of the eastern boundary upwelling system. It is shown that, for the northern and southern parts of the Pacific upwellings, the peak of the maximum area of the positive ocean surface temperature anomaly in the upwelling zone coincides (with an accuracy of up to one month) with the maximum absolute value of the thermal index. The statement is also true for the negative temperature anomaly, with the exception of the northern part of the Chilean upwelling. In most cases, positive temperature anomalies over the occupied area are significantly larger than negative ones. Temperature anomalies in the upwelling zone are mainly caused by changes in the intensity of upwellings, which, in turn, are associated with variations in the surface wind field. A comparison of the seasonal variability of the thermal index for two twenty-year periods (1982–2001, 2002–2021), as well as a comparison of areas with anomalously increased surface ocean temperatures, showed a slight increase in the northern and southern parts of all Pacific upwellings, with the exception of the southern part of California, which weakened slightly.
PubDate: 2024-12-01
- Reconstruction of Sea Surface Relief and Sea Wave Spectra Using a Sea
Surface Image-
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Abstract: Abstract We consider a method for diagnosing sea waves based on processing of spatiotemporal images of the sea surface in scattered light of the sky with a grazing angle of observation. An original method of reconstructing wave slopes and sea surface relief which does not require information on parameters of optical receiver and absolute values of sky brightness has been developed. The method is based on formation of relative fluctuations of sea surface brightness in the approximation of linear dependence of the sea surface brightness on wave slopes. A polarization method for increasing the contrast and accuracy of determining wave slopes in an image of sea surface is proposed. This method was tested in full–scale conditions using the example of processing spatiotemporal images of the sea surface in scattered light of the sky, and the relief of sea surface slopes, i.e., the spatiotemporal distribution of wave slopes, was obtained. We propose a method for determining the time spectrum of long waves by integrating the spatial frequency spectrum of the spatiotemporal relief of the sea surface in the vicinity of a parabolic dispersion curve. This method of calculating the time spectrum of wave slopes makes it possible to distinguish long waves that obey the dispersion relation and get rid of unnecessary noise that can be contained in the optical image (stripes, breakdowns, wave group structure, slicks, nonlinear distortions of the transfer function of sea surface brightness to wave slope, etc.). The wave elevation spectrum obtained by the optical method and the synchronously recorded wave elevation spectrum obtained using a string waveform are compared. The variability of statistical characteristics of the visible slopes of long waves with the distance from the optical receiver is studied.
PubDate: 2024-12-01
- New 1.38-µm Water Vapor Band Spectroscopy for a CO2 Atmosphere: H2O
Measurements in the Martian Atmosphere in the SPICAM/MEX and ACS NIR/TGO
Experiments-
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Abstract: Abstract The H2O 1.38-µm band has been used to measure water vapor in the Martian atmosphere since the MAWD (Mars Atmospheric Water Detector) experiment on Viking-1 and -2. Currently, two experiments in orbit around Mars—SPICAM IR (SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars InfraRed) on Mars Express and ACS NIR (Atmospheric Chemistry Suite Near InfraRed) on the Trace Gas Orbiter—are measuring water vapor in this spectral range. The spectrometers provide monitoring of the seasonal cycle of the column water vapor abundance and its vertical distribution over several Martian years. The HITRAN (High Resolution Transmission) database was used as a spectroscopic information for water vapor retrievals in these experiments. To take into account the broadening of water vapor lines in the carbon dioxide atmosphere of Mars, a scaling factor of 1.7 was adopted relative to the broadening by air, presented in HITRAN. This could lead to systematic uncertainty in the results, even despite the low pressure in the Martian atmosphere. Recent laboratory measurements of the broadening of water vapor lines in CO2 for the lines of three vibrational bands ν1 + ν3, 2ν2 + ν3, and 2ν1 in the spectral region of 6760–7430 cm–1 have improved the spectroscopic parameters for the carbon dioxide atmosphere. We performed water vapor retrievals with new spectroscopy at 1.38 µm for SPICAM IR nadir measurements and ACS NIR occultation measurements. In the case of SPICAM IR, changes due to spectroscopy were below the sensitivity of the instrument due to the low resolution and signal-to-noise ratio. For the ACS NIR, which is a high resolution spectrometer, the new spectroscopy resulted in systematic deviations of 2–5% depending on the height in the atmosphere, exceeding the random errors of the instrument.
PubDate: 2024-12-01
- Statistical and Machine Learning Methods for River Water Level Time Series
Construction Using Satellite Altimetry-
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Abstract: Abstract The use of satellite altimetry data for monitoring the water level regime of rivers in Arctic regions is limited due to the negative effect of complex fluvial morphology and ice cover on altimetric radar measurements. The generation of time series of river water level consists of two main stages: (1) accurate geographic selection of satellite measurements over the river channel and (2) calculation of the average level for a given date after filtering outliers. This work is based on measurements from the European altimetry satellites Sentinel-3A and Sentinel-3B. The paper proposes a method for detection of aberrant values in altimetric measurements (outliers) acquired over a wide floodplain section of the Kolyma River. The method improved the accuracy of resulting satellite time series of water level by 0.04–1.59 m (or 4–85%) compared to the widely used standard statistical method of altimetric measurement filtering. The suggested method is based on the combination of three algorithms of different complexity: statistical (Mahalanobis distance), clustering (Density-Based Spatial Clustering of Applications with Noise (DBSCAN)), and machine learning (Isolating Forest) methods. In the combined approach, values classified as outliers by at least two algorithms were considered as outliers. This approach allowed us to reduce the impact of potential individual shortcomings of each of the three methods.
PubDate: 2024-12-01
- Assessment of Dependence between the Degree of Fire Impact
on Vegetation and the Fire Radiative Power-
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Abstract: Abstract The article provides the results of analysis of the characteristics of wildfires in various predominant stands of Siberia (50°–75° N, 60°–150° E) based on satellite monitoring data from 2015 to 2021. Thirty-six fires were selected for seven types of different tree stands (vegetation types) with a total area of 19 382 km2. Seventy-two images of the Landsat-8 OLI/TIRS (Operational Land Imager/Thermal Infrared Sensor) satellite were used in the analysis, as well as data from standard products of MODIS (Moderate Resolution Imaging Spectroradiometer). Based on the processing of remote data (threshold classification of dNBR (differenced normalized burn ratio)) values, statistical patterns of the ratio of disturbance classes for various types of tree stands were revealed. It is shown that, in the case of fires in light coniferous stands, the ratio of disturbance classes is on average 44, 29, and 27% for low, medium and high levels of fire impact, respectively. While this proportion is 63, 14 and 23% in the case of dark coniferous forests, and 59, 26, and 15% in the case of tundra vegetation, respectively. The conjugate analysis of the radiation power of active fire zones using the fire radiative power (FRP) technique demonstrated an increase in the intensity of fires in terms of integral FRP values, proportional to the increase in the degree of fire impact on vegetation. For a representative sample of fires (in various postfire polygons in seven variants of vegetation cover), a significant (R2 = 0.77–0.94, p
PubDate: 2024-12-01
- Variability of Fire Radiative Power under the Conditions of Burning in
Larch Forests of Siberia-
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Abstract: Abstract The variability of heat emission from fires in Siberian larch stands (within the boundaries of 60°–65° N, 100°–130° E) was studied. We used the sample of the seven largest wildfires with a total area of 10 000 km2 recorded in 2018, 2020, and 2021. For comparison, we analyzed a selection of wildfires recorded in 2015–2021 (29 fires, on a total area of up to 18 000 km2) with reference to other predominant variants of vegetation in Siberia: spars larch, stands of pine, spruce, Siberian pine (cedar), as well as tundra vegetation and Siberian dwarf pine (Pinus pumila). We operated with the data on radiation power from active combustion zones, calculated using the fire radiative power (FRP) method and standard MODIS products. It is pointed out that the relative burn area of larch stands (γ = 0.69%) exceeds by at least 2 times the same characteristic of other variants of vegetation in Siberia. It is shown that quasi-normal distribution of FRP values is typical for all large-scale fires (with area $$ \gg $$20 km2) of Siberia, including fires in larch forests. FRP from fires in larch forests can range from 12 000 to>260 000 MW. At the same time, the sporadic extremes of integral FRP (FRPint) are an order of magnitude higher than the values corresponding to other variants of vegetation. The average FRP per a pixel of MODIS for fires in larch forests are 15% higher than the ones for pine stands and 25–35% higher than the typical values for fires in dark coniferous forests. The relation of FRPint with the area of active combustion is approximated by a linear function with a confidence of at least 0.6 (p
PubDate: 2024-12-01
- Application of Remote Sensing Data in Large-Scale Monitoring of Wetlands
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Abstract: Abstract The present review examines existing technologies for mapping wetland ecosystems (WEs) based on remote sensing data. WEs are the most valuable ecosystems with a high conservation role. There are many classifications of WEs, including dozens of types. However, existing global or national-level WE maps typically do not consider their landscape specificity and are limited to only a few classes. Peatlands, swamp forests, high-productivity meadows, and riparian vegetation formations store substantial carbon reserves, which are released due to fires. The intensity of these fires has been increasing in recent years as a result of climate change. These issues necessitate the development of new large-scale monitoring methods for assessing the state of WEs, including mapping their types, determining biomass and carbon stocks, assessing the consequences of landscape fires, and evaluating greenhouse gas emissions and other combustion byproducts. First and foremost, it is necessary to develop a classification system for Russia’s WEs that considers their landscape diversity while being sufficiently generalized for satellite monitoring and annual updating of WE maps. Various remote sensing data types, including aerial imagery, lidar, and radar data, are used for WE mapping. The most promising direction for the development of WE monitoring technologies at the national level involves the use of long-term homogeneous time series data from MODIS (Moderate Resolution Imaging Spectroradiometer) and VIIRS (Visible Infrared Imaging Radiometer Suite), in combination with ground-based calibration measurements and high-resolution satellite optical and radar data.
PubDate: 2024-12-01
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