Satellite Spectra Research Articles

Effects of hyperspectral data with different spectral resolutions on the estimation of soil heavy metal content: From ground-based and airborne data to satellite-simulated data

Soil heavy metal distribution maps can provide decision-making information for pollution control and agricultural management. However, the estimation of heavy metals is sensitive to the resolution of the soil spectra due to their sparse content in soils. The purposes of this study were to test the sensitivity of Ni, Zn and Pb prediction results to variations in spectral resolution, then to map their spatial distributions over a large area. In addition, the effectiveness of spectral feature extraction was investigated. In total, 92 soil samples and corresponding field soil spectra were obtained from the Tongwei-Zhuanglang area in Gansu Province, China. Airborne HyMap hyperspectral image of this area was acquired simultaneously. Three satellite image spectra (AHSIGF-5, Hyperion, AHSIZY-1 02D) were simulated using the field spectra which were measured under real environmental conditions rather than laboratory conditions. The combination of genetic algorithm and partial least squares regression (GA-PLSR) was used as prediction algorithm. The models calibrated by HyMap image full spectral bands had the highest accuracies (RP2 = 0.8558, 0.8002, and 0.8592 for Ni, Zn, and Pb, respectively) because of high consistency. For field spectra and three simulated satellite spectra, models calibrated by simulated AHSIGF-5 spectra performed best because of appropriate resolution (5 nm in the visible near-infrared [VNIR] and 10 nm in the short-wave infrared [SWIR]). The spectral feature extraction method only improved prediction accuracy of the field spectra, indicating that this method benefited from higher spectral resolution. The mapping of the spatial distribution of soil heavy metals over a large area was realized based on HyMap image. According to the results of the satellite simulation spectra, this study proposes to use GF-5 hyperspectral image to estimate heavy metals content. The outcomes provide a reference for the utilization of aerial and satellite hyperspectral images in prediction of soil heavy metal concentrations.

Soft Frequency Reuse Based Spectrum Sharing Scheme in the Integrated Satellite and Terrestrial Network

The integrated satellite and terrestrial network has become one of the frontier technologies of the next generation mobile communication system. The satellite network is used as an extension and supplement of the ground network to achieve seamless coverage of wireless mobile communications. The spectrum sharing of the integrated satellite and terrestrial network is realized from the perspective of spectrum planning, considering the number of co-frequency terminals and the distance between the terminal and the center of the satellite beam. The existing spectrum sharing schemes use the concept of geographic isolation, which will limit the available bandwidth of the terrestrial network. Therefore, the concept of time domain isolation is proposed, and a soft frequency reuse based spectrum sharing scheme in the integrated satellite and terrestrial network is designed. The allocation of time slots increases the degree of spectrum isolation and improves the signal to interference ratio of the network. In addition, due to the increase in the utilization rate of the satellite spectrum, the capacity of the satellite system is improved.

Multiconfiguration Dirac-Hartree-Fock theory for copper Kα and Kβ diagram lines, satellite spectra, and ab initio determination of single and double shake probabilities

The x-ray spectra of copper $K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ remain a topic of great interest due to the complex open-shell processes involved, with many discrepancies among theories and experiments. We present high-accuracy theory of copper $K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ diagram and satellite spectra in the multiconfiguration Dirac-Hartree-Fock method. Diagram spectra are expanded to $5s$ with simultaneous convergence of 28 000 configuration state functions (CSFs) $(K\ensuremath{\alpha})$ and to $6g$ with simultaneous convergence of 91 000 CSFs $(K\ensuremath{\beta})$, achieving eigenvalue convergence to $\ifmmode\pm\else\textpm\fi{}0.03$ eV or 0.000 25%, approximately a factor of 10 improvement over past work. It is necessary to invoke biorthogonalization, developments of the active space approach, analysis of markers for theoretical convergence of eigenvalues, and the question of self-consistency for both $K\ensuremath{\alpha}$ and $K\ensuremath{\beta}$ spectra. We make use of gauge convergence, eigenvalue convergence, and $A$-coefficient convergence. The satellite spectra are a major outcome---without these, it is not possible to make use of the increased accuracy of the diagram computations. The Cu $K\ensuremath{\alpha}\phantom{\rule{4pt}{0ex}}3{d}^{8}$ double shake satellite spectrum alone contains 1506 unique eigenvalues (transitions) and required simultaneous convergence of 593 000 CSFs. Ab initio shakeoff probabilities for $1s,\phantom{\rule{0.16em}{0ex}}2s,\phantom{\rule{0.16em}{0ex}}2p,\phantom{\rule{0.16em}{0ex}}3s,\phantom{\rule{0.16em}{0ex}}3p,\phantom{\rule{0.16em}{0ex}}3d$, and $4s$ subshells as a result of the $K$-shell photoionization process are presented. Portable spectral representations are provided in the supplemental material, discussed in the text. We investigate the meaning behind shake, shakeoff, and shakeup processes and the computational potential to investigate these at the current time. We separate the notions of total shake, single shake, and double shake, explain how these are observable in high-quality experimental spectra, and how these calculations can be used experimentally.

Satellite Remote Sensing of Water Quality Variation in a Semi-Enclosed Bay (Yueqing Bay) under Strong Anthropogenic Impact

The semi-enclosed bays impacted by heavy anthropogenic activities have weak water exchange and purification capacities. Most of the sea bays have suffered severe eutrophication, water quality deterioration, ecosystem degradation and other problems. Although many countries and local governments have carried out corresponding environmental protection actions, the evaluation of their effectiveness still requires monitoring technology and data support for long-term water environment change. In this study, we take Yueqing Bay, the fourth largest bay in China, as a case to study the satellite-based water quality monitoring and variation analysis. We established a nutrient retrieval model for Yueqing Bay to produce a long-term series of nutrient concentration products in Yueqing Bay from 2013 to 2020, based on Landsat remote sensing images and long-term observation data, combined with support vector machine learning and water temperature and satellite spectra as input parameters, and then we analyzed its spatiotemporal variations and driving factors. In general, nutrient concentrations in the western part of the bay were higher than those in the eastern part. Levels of dissolved inorganic nitrogen (DIN) were lower in summer than in spring and winter, and reactive phosphate (PO4-P) levels were lower in summer and higher in autumn. In terms of natural factors, physical effects (e.g., seasonal variations in flow field) and biological effects (e.g., seasonal differences in the intensity of plankton photosynthesis) were the main causes of seasonal differences in nutrient concentration in Yueqing Bay. Nutrient concentration generally increased from 2013 to 2015 but decreased slightly after 2015. Over the past decade, the economy and industry of Yueqing Bay basin have developed rapidly. Wastewater resulting from anthropogenic production and consumption was transported via streams into Yueqing Bay, leading to the continuous increase in nutrient concentrations (the variation rates: aDIN>0, aPO4−P>0), which directly or indirectly caused high nutrient concentrations in some areas of the bay (e.g., Southwest Shoal at the mouth of Yueqing Bay). After 2015, the various ecological remediation policies adopted by cities around Yueqing Bay have mitigated, to some extent, the increasing nutrient concentration trends (the variation rates: aDIN<0, aPO4−P<0), but not significantly (P > 0.1). The environmental restoration of Yueqing Bay also requires continuous and long-term ecological protection and restoration work to be effective. This research can provide a reference for ecological environment monitoring and remote sensing data application for similar semi-enclosed bays, and support the sustainable development of the bay.

Improvement of Signal Reception Reliability at Satellite Spectrum Monitoring System

Extensively increasing numbers of radio electronic devices significantly complicate the electromagnetic situation under conditions of radio frequency spectrum deficiency and require improvement in the functions and mechanisms of spectrum monitoring systems. Today, in the framework of the existing ground-borne spectrum monitoring system, it is impossible to qualitatively perform the functions and problems of spectrum monitoring. Spectrum (radio) monitoring is one of the main techniques for spectrum load estimation to solve problems of perspective management of the radio frequency spectrum with the purpose of developing new radio technologies. Therefore, the problem of improving the effectiveness of spectrum monitoring does not lose relevance. When solving such problems, one of the most important factors is the extraction of an effective signal with background noise and interference. Therefore, the effectiveness of the Kalman filter application for satellite-based radio monitoring systems is considered in this study. The proposed method for detecting radio signals using Kalman filters makes it possible to make correct decisions with high accuracy. The simulation results show that Kalman filters work effectively even at a negative signal-to-noise ratio (90% and higher), adapting to the original signal at different noise dispersions in a noisy signal. It can be concluded that this method can be successfully applied to solve problems of detecting sources of radiation of a certain frequency according to the signal registered by the onboard receiver of the satellite spectrum monitoring system. The influence of the Kalman filter decision-making speed on the results of radio signal processing was estimated.

Theory of copper Kα and Kβ diagram lines, satellite spectra, and ab initio determination of single and double shake probabilities

High-accuracy MCDHF Cu Kα and Cu Kβ diagram spectra and major satellites are presented. Spectral eigenvalues reach a theoretical expansion convergence of 0.03 eV or 0.00025%, with gauge and amplitude convergence to 0.7% for Cu Kα diagram spectra. Dominant theoretical spectral eigenvalues are shown to be within 0.032 eV of experimental data. Ab initio shake-off contributions are presented in terms of total probability from each subshell and as separated single and double shake probabilities. Discrepancies between theory and experiment in copper X-ray spectra arise from profile asymmetries, relativistic terms and shake spectra not yet accounted for. These results and this improved agreement provide key fundamental parameters for processes towards XFEL evolution and resolving key discrepancies between theory and experiment.

Intelligent spectrum management based on radio map for cloud-based satellite and terrestrial spectrum shared networks

Cloud-based satellite and terrestrial spectrum shared networks (CB-STSSN) combines the triple advantages of efficient and flexible network management of heterogeneous cloud access (H-CRAN), vast coverage of satellite networks, and good communication quality of terrestrial networks. Thanks to the complementary coverage characteristics, anytime and anywhere high-speed communications can be achieved to meet the various needs of users. The scarcity of spectrum resources is a common problem in both satellite and terrestrial networks. In order to improve resource utilization, the spectrum is shared not only within each component but also between satellite beams and terrestrial cells, which introduces inter-component interferences. To this end, this paper first proposes an analytical framework which considers the inter-component interferences induced by spectrum sharing (SS). An intelligent SS scheme based on radio map (RM) consisting of LSTM-based beam prediction (BP), transfer learning-based spectrum prediction (SP) and joint non-preemptive priority and preemptive priority (J-NPAP)-based proportional fair spectrum allocation is than proposed. The simulation result shows that the spectrum utilization rate of CB-STSSN is improved and user blocking rate and waiting probability are decreased by the proposed scheme.

Flexible Resource Optimization for GEO Multibeam Satellite Communication System

Conventional GEO satellite communication systems rely on a multibeam foot-print with a uniform resource allocation to provide connectivity to users. However, applying uniform resource allocation is inefficient in presence of non-uniform demand distribution. To overcome this limitation, the next generation of broadband GEO satellite systems will enable flexibility in terms of power and bandwidth assignment, enabling on-demand resource allocation. In this paper, we propose a novel satellite resource assignment design whose goal is to satisfy the beam traffic demand by making use of the minimum transmit power and utilized bandwidth. The motivation behind the proposed design is to maximize the satellite spectrum utilization by pushing the spectrum reuse to affordable limits in terms of tolerable interference. The proposed problem formulation results in a non-convex optimization structure, for which we propose an efficient tractable solution. We validate the proposed method with extensive numerical results, which demonstrate the efficiency of the proposed approach with respect to benchmark schemes.

Polarization of hard X-ray dielectronic satellite lines from Na-like W ions

One of the important signatures of non-thermal high-atomic-number multiply ionized plasmas is polarization of hard x-ray line emission. Atomic processes in laboratory and astrophysical plasmas with anisotropic electron distribution that can lead to such polarization include dielectronic recombination. All previous research on x-ray line polarization of dielectronic satellite lines was mostly focused on K-shell radiation. Here we present one of the first studies of polarization of L-shell dielectronic satellite lines using the hard x-ray spectra of Na-like W produced by dielectronic recombination. Polarization of dielectronic satellites is calculated using two approaches: density matrix formalism and the FAC code. The most intense dielectronic satellite lines of Na-like W appeared to be positively polarized with the maximum degree of polarization between 0.4545 and 0.6. Polarization-dependent dielectronic satellite spectra of Na-like W are calculated with a gaussian electron distribution function centered at the beam energies from 2400 eV to 4100 eV. Such spectra cover the spectral range from 1.19 Å to 1.38 Å with each spectrum including two traces of line intensities associated with the parallel polarization and perpendicular polarization state. The polarization-dependent spectra were found to be strongly dependent on the energy of the electron beam which can be used for the development of x-ray plasma polarization spectroscopy to study non-thermal multiply ionized W plasmas. Radiative and polarization properties of W radiation studied in this paper are important for fusion research.

Kα X-ray satellite spectra of Ge, As, Se and Br by photoionization

First and second order Kα X-ray satellites of the elements Ge, As, Se and Br were investigated by photon excitation. A wavelength dispersive spectrometer with LiF 420 crystal was employed. The energies and relative intensities of these X-ray satellites were measured. Their energy shifts and relative intensities with respect to the Kα diagram line are compared with theoretical estimates. Their dependence on atomic number is also examined.

Gallate semiquinone radical tri-anion. Experimental and theoretical studies of the 13C hyperfine coupling constants

Gallic acid (3,4,5-trihydroxybenzoic acid, GA) is one of the most abundant phenolic acids found in the plant kingdom. In this work, the electron paramagnetic resonance (EPR) spectrum of the gallate semiquinone radical tri-anion (GAS) derived from GA by air oxidation was measured and analyzed by advanced simulation procedures. The observed main spectrum was surrounded by five satellite spectra from which a thorough analysis led to determination of hyperfine splittings (HFS) from five chemically different 13C nuclei in natural abundance. The spectra were further characterized by detailed linewidth analyses. The assignment of the 13C HFS constants was supported by the results of theoretical calculations, using the classical, semi-empirical Karplus-Fraenkel approach, as well as quantum chemical procedures based on density functional theory (DFT), representing the influence of the solvent by polarizable continuum models (PCM). The combined results suggest a consistent assignment of positions and signs for all five 13C constants of GAS, providing a unique insight into the electron spin structure of this radical.

Method for Retrieval of the HDO/H2O Ratio Vertical Profile in the Atmosphere from Satellite Spectra Simultaneously Measured in Thermal and Near-IR Ranges

Method for Retrieval of the HDO/H2O Ratio Vertical Profile in the Atmosphere from Satellite Spectra Simultaneously Measured in Thermal and Near-IR Ranges

Resource Allocation for LEO Beam-Hopping Satellites in a Spectrum Sharing Scenario

In recent years, low earth orbit (LEO) satellite constellation systems have been developed rapidly. However, the scarcity of satellite spectrum resources has become one of the major obstacles to this trend. LEO satellite constellation communication systems sharing the spectrum of incumbent geostationary earth orbit (GEO) satellite system is a feasible way to alleviate spectrum scarcity. Therefore, it has practical significance to study the optimization of satellite resources allocation (RA) in a spectrum sharing scenario. This paper focuses on the RA problem that LEO satellites share a GEO high throughput satellite’s spectrum in a beam-hopping (BH) manner. The GEO satellite system is served as the primary system and the LEO satellite constellation system is served as the secondary system whose frequency bands and transmitting power are strictly limited. Compared with conventional multibeam satellites, BH satellites have the advantage of flexibility in the time dimension. Therefore, we make full use of the flexibility of LEO BH satellites to realize the matching of traffic demand and traffic supply. The RA problem is decomposed into three sub-problems, namely, frequency band selection (FBS) problem, illuminated cell selection (ICS) problem, and transmitting power allocation (TPA) problem. We solve each sub-problem in order and finally form a complete RA scheme. The performance evaluation of the proposed RA scheme is carried out in real-time and simulation results show that the LEO BH satellite paired with the RA scheme we proposed has good adaptability to the uneven distribution of traffic demand in the spectrum sharing scenario.

Prototyping Sentinel-2 green LAI and brown LAI products for cropland monitoring

For agricultural applications, identification of non-photosynthetic above-ground vegetation is of great interest as it contributes to assess harvest practices, detecting crop residues or drought events, as well as to better predict the carbon, water and nutrients uptake. While the mapping of green Leaf Area Index (LAI) is well established, current operational retrieval models are not calibrated for LAI estimation over senescent, brown vegetation. This not only leads to an underestimation of LAI when crops are ripening, but is also a missed monitoring opportunity. The high spatial and temporal resolution of Sentinel-2 (S2) satellites constellation offers the possibility to estimate brown LAI (LAIB) next to green LAI (LAIG). By using LAI ground measurements from multiple campaigns associated with airborne or satellite spectra, Gaussian processes regression (GPR) models were developed for both LAIG and LAIB, providing alongside associated uncertainty estimates, which allows to mask out unreliable LAI retrievals with higher uncertainties. A processing chain was implemented to apply both models to S2 images, generating a multiband LAI product at 20 m spatial resolution. The models were adequately validated with in-situ data from various European study sites (LAIG: R2 = 0.7, RMSE = 0.67 m2/m2; LAIB: R2 = 0.62, RMSE = 0.43 m2/m2). Thanks to the S2 bands in the red edge (B5: 705 nm and B6: 740 nm) and in the shortwave infrared (B12: 2190 nm) a distinction between LAIG and LAIB can be achieved. To demonstrate the capability of LAIB to identify when crops start senescing, S2 time series were processed over multiple European study sites and seasonal maps were produced, which show the onset of crop senescence after the green vegetation peak. Particularly, the LAIB product permits the detection of harvest (i.e., sudden drop in LAIB) and the determination of crop residues (i.e., remaining LAIB), although a better spectral sampling in the shortwave infrared would have been desirable to disentangle brown LAI from soil variability and its perturbing effects. Finally, a single total LAI product was created by merging LAIG and LAIB estimates, and then compared to the LAI derived from S2 L2B biophysical processor integrated in SNAP. The spatiotemporal analysis results confirmed the improvement of the proposed descriptors with respect to the standard SNAP LAI product accounting only for photosynthetically active green vegetation.

Unraveling intrinsic correlation effects with angle-resolved photoemission spectroscopy

Interaction effects can change materials properties in intriguing ways, and they have, in general, a huge impact on electronic spectra. In particular, satellites in photoemission spectra are pure many-body effects, and their study is of increasing interest in both experiment and theory. However, the intrinsic spectral function is only a part of a measured spectrum, and it is notoriously difficult to extract this information, even for simple metals. Our joint experimental and theoretical study of the prototypical simple metal aluminum demonstrates how intrinsic satellite spectra can be extracted from measured data using angular resolution in photoemission. A nondispersing satellite is detected and explained by electron-electron interactions and the thermal motion of the atoms. Additional nondispersing intensity comes from the inelastic scattering of the outgoing photoelectron. The ideal intrinsic spectral function, instead, has satellites that disperse both in energy and in shape. Theory and the information extracted from experiment describe these features with very good agreement.

Effect of Saline Soil Cracks on Satellite Spectral Inversion Electrical Conductivity

The dehydration cracking of saline soil is a kind of common natural phenomenon, and the cracks of saline soil will affect the satellite spectrum, and then affect the accuracy of satellite spectral inversion of electrical conductivity (EC). This study introduces the concept of crack rate (CR) to describe the crack information of saline soil, and quantifies the influence of saline soil crack on the EC of satellite spectral inversion. In 2014 and 2020, the satellite-ground synchronous observation experiments of soda-type inland saline soil and coastal chlorinated-type saline soil were carried out, and the CR of surface cracked saline soil was extracted by an image processing algorithm. For the saline soil spectrum data, the correlation analysis method is used to establish the best band combination that characterizes the relationship between the different saline soil spectrum data and salinity, and the EC inversion model is established using the BP neural network method. The results show that: after the CR is introduced, the determination coefficient (R2) for the EC of soda-type saline soil satellite spectral inversion increased from 0.59 to 0.67, with an increase of 14.42%, and the mean square error (MSE) reduced from 0.20 to 0.16, with a decrease of 19.49%. The R2 for the EC of coastal chlorinated-type saline soil satellite spectral inversion increased from 0.64 to 0.75, an increase of 17.73%, and the MSE decreased from 0.16 to 0.12, a decrease of 25.15%. The study proved the influence of the cracks in the saline soil on the satellite spectrum and provided a new way to improve the accuracy of the satellite spectrum inversion of the EC of the cracked saline soil.

Spectroscopic uncertainty impacts on OCO-2/3 retrievals of XCO2

Estimates of atmospheric carbon dioxide concentration from satellites now span multiple years and are providing information on key processes in the carbon cycle. Methodology for retrieving CO2 from satellite spectra continues to change as understanding of instrument calibration, other atmospheric constituents, and trace gas spectroscopy improve. In this work, we provide an update to linear error estimates for retrieval of carbon dioxide for the Orbiting Carbon Observatory-2/3 (OCO-2/3) due spectroscopic uncertainties. Linear error analysis is used to propagate uncertainties in laboratory conditions and spectroscopic model assumptions to sensitivity in retrieved XCO2 and surface pressure from OCO-2/3. Error estimates due to modeling assumptions for line mixing, collision-induced absorption, and water vapor exhibit noticeable variability across locations and seasons. On the other hand, error estimates due to perturbations in laboratory conditions are nearly constant in space and time.

Shakeup and shakeoff satellite structure in the electron spectrum of Krm83

The isotope $^{83}$Kr$^m$, a 1.8-hr isomer of stable $^{83}$Kr, has become a standard for the calibration of tritium beta decay experiments to determine neutrino mass. It is also widely used as a low-energy electron source for the calibration of dark-matter experiments. The nominally monoenergetic internal conversion lines are accompanied by shakeup and shakeoff satellites that modify the line shape. We draw on theoretical and experimental information to derive a quantitative description of the satellite spectrum of the K-conversion line.

Examining the effects of on-orbit aging of SL-12 rocket bodies using visible band spectra with the MMT telescope

The characterization of deep space debris has posed a significant challenge in the study of space objects. To be most effective, characterization must be performed quickly and under non-ideal operational conditions, generally using non-resolved techniques. Multi-color photometry and the resultant color indices offer the potential to rapidly discriminate between debris and intact space objects such as rocket bodies and satellites. However, these studies are not well informed by high resolution spectra of these same objects, due to the lack of prior measurements with large astronomical telescopes. We present a spectroscopic study of orbital debris aimed at characterizing changes over time in object properties, using ground-based spectroscopy of several similar rocket bodies in geosynchronous orbit, launched at different times. High and moderate resolution spectroscopy is not routinely collected by SSA resources. Nonetheless, several researchers have collected satellite spectra for research purposes. Several researchers have also noted the progressive reddening of spacecraft surfaces.In this study, we have collected high resolution spectra of five Russian SL-12 rocket bodies in geosynchronous orbit. The spectra were collected with the Blue Channel Spectrograph on the 6.5 m MMT telescope at Mt. Hopkins. The measurements were taken using the 300-line grating, which is blazed for the red, and can cover a 520 nm range at dispersion 0.196 nm/pixel. The large collecting aperture of the MMT allowed the rapid collection of multiple high signal-to-noise spectra with only 2 minutes per exposure. This short exposure allowed us to have confidence the solar phase angle was near constant during each collection, but that the spectra were averaged over the rotation of the rocket body. These spectra allow analysis of both the variation in albedo over a large wavelength range, and searches for discrete absorption features. The SL-12 (also called the "Proton K") was a mainstay Russian four-stage to GEO launch vehicle that was used from 1974 to 2012. The SL-12 fourth stage rocket bodies (henceforth referred to as "SL-12 RB") offer a convenient ensemble of objects for which photometric techniques can be developed and tested. For this study, spectra of five SL-12s with a range of years-on-orbit (YOO) ranging from 23-35 years were collected, allowing a comparative study of the evolution of the spectra over a 12-year difference in age. Additionally, all these objects have been previously observed in the near-IR with the UKIRT WFCAM. The spectra are analyzed for evidence of the effects of on-orbit reddening and other changes over time.

Research on Dynamic Allocation Strategy of KU Satellite Spectrum Based on Cognitive Radio Technology

Aiming at the problem of insufficient satellite spectrum resources in the KU band, combined with the most advanced cognitive radio technology in the communication field, this paper proposes a dynamic spectrum allocation strategy for KU satellites based on cognitive radio technology. By dynamically allocating frequency resources, the spectrum resources are greatly improved. Use efficiency, while improving the anti-interference ability of the satellite system.