| 1. |
- Amin, Hadi, et al.
(author)
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Quantifying barystatic sea-level change from satellite altimetry, GRACE and Argo observations over 2005–2016
- 2020
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In: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948. ; 65:8, s. 1922-1940
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Journal article (peer-reviewed)abstract
- Time-varying spherical harmonic coefficients determined from the Gravity Recovery and Climate Experiment (GRACE) data provide a valuable source of information about the water mass exchange that is the main contributor to the Earth’s gravity field changes within a period of less than several hundred years. Moreover, by measuring seawater temperature and salinity at different layers of ocean depth, Argo floats help to measure the steric component of global mean sea level (GMSL). In this study, we quantify the rate of barystatic sea-level change using both GRACE RL05 and RL06 monthly gravity field models and compare the results with estimates achieved from a GMSL budget closure approach. Our satellite altimetry-based results show a trend of 3.90 ± 0.14 mm yr−1 for the GMSL rise. About 35% or 1.29 ± 0.07 mm yr−1 of this rate is caused by the thermosteric contribution, while the remainder is mainly due to the barystatic contribution. Our results confirm that the choice of decorrelation filters does not play a significant role in quantifying the global barystatic sea-level change, and spatial filtering may not be needed. GRACE RL05 and RL06 solutions result in the barystatic sea-level change trends of 2.19 ± 0.13 mm yr−1 and 2.25 ± 0.16 mm yr−1, respectively. Accordingly, the residual trend, defined as the difference between the altimetry-derived GMSL and sum of the steric and barystatic components, amounts to 0.51 ± 0.51 and 0.45 ± 0.44 mm yr−1 for RL05 and RL06-based barystatic sea-level changes, respectively, over January 2005 to December 2016. The exclusion of the halosteric component results in a lower residual trend of about 0.36 ± 0.46 mm yr−1 over the same period, which suggests a sea-level budget closed within the uncertainty. This could be a confirmation on a high level of salinity bias particularly after about 2015. Moreover, considering the assumption that the GRACE-based barystatic component includes all mass change signals, the rather large residual trend could be attributed to an additional contribution from the deep ocean, where salinity and temperature cannot be monitored by the current observing systems. The errors from various sources, including the model-based Glacial Isostatic Adjustment signal, independent estimation of geocenter motion that are not quantified in the GRACE solutions, as well as the uncertainty of the second degree of zonal spherical harmonic coefficients, are other possible contributors to the residual trend.
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| 2. |
- Aol, Sharon, et al.
(author)
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Ground and Space-based response of the ionosphere during the geomagnetic storm of 02-06 November 2021 over the low-latitudes across different longitudes
- 2024
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In: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948. ; 73:6, s. 3014-3032
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Journal article (peer-reviewed)abstract
- The strong geomagnetic storm of class G3 that occurred on 03 November 2021 (Dst min = -118 nT, Kp = 8) was the first of this class recorded during the ascending phase of solar cycle 25. In this study, we examined the response of the ionosphere during the geomagnetic storm period from 02-06 November 2021 using the Total Electron Content (TEC) observations from a chain of Global Navigation Satellite System (GNSS) receiver stations in five longitudinal sectors i.e, Asian, East-African, West-African, South-American, and Pacific-west sectors, in the low-latitudes and space-based Swarm satellite electron density, Ne and TEC measurements. The Rate of Change of TEC Index (ROTI) was derived from the ground and space based TEC measurements to examine the occurrence of ionospheric irregularities. The Rate of change of electron density index (RODI) was also derived from Swarm Ne measurements to identify the occurrence of ionospheric irregularities at Swarm altitudes. A positive ionospheric storm effect was observed in all the longitudinal sectors considered in this study. A clear hemispherical asymmetry, with higher VTEC in the northern hemisphere was observed. The determining factors for ionospheric responses to this storm are; local time of the storm's onset, local time of storm's minimum SYMH, and changes in thermospheric O=N2 ratio. These geomagnetic storm effects were discussed in terms of the Prompt Penetration Electric Field (PPEF) storm induced wind lifting effect and Disturbance Dynamo Electric Field (DDEF). The geomagnetic storm inhibited the occurrence of ionospheric irregularities in all the sectors, during the main phase, except for three IGS receiver stations in South American sector. Overall, a longitudinal dependence of the enhancement/inhibition of ionospheric irregularities was observed. The generation of post-sunset irregularities was attributed to the local time occurrence of maximum ring current, PPEF and DDEF. (c) 2023 Published by Elsevier B.V. on behalf of COSPAR.
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| 3. |
- Aol, Sharon, et al.
(author)
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Spectral properties of sub-kilometer-scale equatorial irregularities as seen by the Swarm satellites
- 2023
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In: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948. ; 72:3, s. 741-752
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Journal article (peer-reviewed)abstract
- The faceplates on-board the Swarm satellites have provided high-resolution measurements of electron density at a frequency of 16 Hz along the satellite paths. The 16-Hz electron density data from Swarm were analyzed to determine the spectral characteristics of the Fregion ionospheric irregularities at Swarm altitudes. The electron density data covered all geographic longitudes with quasi-dipole latitude limited between +/- 30 degrees and the period considered was from October 2014 to October 2018, when the data was available. The Power Spectral Densities (PSDs) observed follows a power law. The values of spectral indices obtained showed a peak centered at around -2.5, located at the Equatorial Ionization Anomaly (EIA) belts. The spectral indices were found to be sensitive to irregularity amplitude. The local time distribution of the spectral indices also showed a peak within the time sector 20:00 LT - 22:00 LT and then decreased gradually after about 22:00 LT till 06:00 LT. The peak of the spectral index was also observed in the South American-Atlantic-African longitudes and it was generally low in the Asian-Pacific region. The angle between the Swarm satellite orbital path and the magnetic field (sic) (B, v)was also examined and it was observed that the highest percentage of occurrence of ionospheric irregularities and the peak in spectral index was obtained only when the(sic) (B, v) was between 20 degrees and 40 degrees. The local turbulence is anisotropic with respect to the background magnetic field as indicated by a more negative spectral index for larger](sic) (B, v).
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| 4. |
- Battisti, M., et al.
(author)
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Onboard performance of the level 1 trigger of the mini-EUSO telescope
- 2022
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In: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 70:9, s. 2750-2766
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Journal article (peer-reviewed)abstract
- The Mini-EUSO telescope was launched for the International Space Station on August 22nd, 2019 to observe from the ISS orbit (-400 km altitude) various phenomena occurring in the Earth's atmosphere through a UV-transparent window located in the Russian Zvezda Module. Mini-EUSO is based on a set of two Fresnel lenses of 25 cm diameter each and a focal plane of 48x48 pixels, for a total field of view of 44 degrees. Until July 2021, Mini-EUSO performed a total of 41 data acquisition sessions, obtaining UV images of the Earth in the 290 nm - 430 nm band with temporal and spatial resolution on ground of 2.5 ls and 6.3x6.3 km2, respectively. The data acquisition was performed with a 2.5 ls sampling rate, using a dedicated trigger looking for signals with a typical duration of tens of ls.In the present paper the analysis of the performance of the 2.5 ls trigger logic is presented, with a focus on the method used for the analysis and the categories of triggered events. The expected functioning of the trigger logic has been confirmed, with the trigger rate on spurious events that remains within the requirements in nominal background conditions. The trigger logic detected several different phe-nomena, including lightning strikes, elves, ground-based flashers and events with EAS-like characteristics.
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| 5. |
- Belova, Evgenia, et al.
(author)
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High-speed echoes in the polar winter mesosphere: Infrasound as a probable cause
- 2023
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In: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948. ; 72:8, s. 3181-3201
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Journal article (peer-reviewed)abstract
- We considered three events on 4 November 2015, 22 December 2016, and 12 November 2018, when the signals travelling in the polar winter mesosphere with high horizontal velocities above 300 m/s were measured by the atmospheric radar ESRAD (Chilson et al., 1999) located at Esrange, near Kiruna in northern Sweden. We proposed four mechanisms of generation of such special cases of polar mesosphere echoes, e.g. high-speed PMWE, that involve microbaroms, i.e. infrasound waves at 0.1 - 0.35 Hz frequencies created by ocean swell. These mechanisms are (i) generation of viscous waves, (ii) generation of thermal waves, (iii) direct contributions of infrasound, and (iv) generation of secondary waves at sound dissipation. These processes necessarily accompany sound propagation in inhomogeneous, thermally conducting and viscous fluid (air). The four models were theoretically analysed and their efficiency was estimated. The infrasound measurements at the IS37 station (Gibbons et al., 2019) located about 170 km north-west from the ESRAD radar, modelled maps of the microbarom sources, infrasound propagation conditions and ionospheric conditions for these three PMWE events support the proposed models. Infrasound-generated thermal waves are suggested to be the most probable specific cause of the observed high-speed, high-aspect-ratio PMWE events. However, absence of in-situ infrasound and plasma measurements did not allow us to quantify contributions of individual physical mechanisms to the fast-travelling echoes generation.
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| 6. |
- Bhat, Bratati, et al.
(author)
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Radiative transfer modeling of the observed line profiles in G31.41+0.31
- 2022
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In: Advances in Space Research. - : Elsevier BV. - 1879-1948 .- 0273-1177. ; 69:1, s. 415-437
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Journal article (peer-reviewed)abstract
- An inverse P-Cygni profile of H13CO+ (1 → 0) in G31.41+0.31 was recently observed, which indicates the presence of an infalling gas envelope. Also, an outflow tracer, SiO, was observed. Here, exclusive radiative transfer modelings have been implemented to generate synthetic spectra of some key species (H13CO+, HCN, SiO, NH3, CH3CN, CH3OH, CH3SH, and CH3NCO) and extract the physical features to infer the excitation conditions of the surroundings where they observed. The gas envelope is assumed to be accreting in a spherically symmetric system towards the central hot core region. Our principal intention was to reproduce the observed line profiles toward G31.41+0.31 and extract various physical parameters. The LTE calculation with CASSIS and non-LTE analysis with the RATRAN radiative transfer codes are considered for the modeling purpose. The best-fitted line parameters are derived, which represents the prevailing physical condition of the gas envelope. Our results suggest that an infalling gas could explain the observed line profiles of all the species mentioned above except SiO. An additional outflow component is required to confer the SiO line profile. Additionally, an astrochemical model is implemented to explain the observed abundances of various species in this source.
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| 7. |
- Chintalapati, Bharadwaj, et al.
(author)
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Opportunities and challenges of on-board AI-based image recognition for small satellite Earth observation missions
- 2024
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In: Advances in Space Research. - : Elsevier. - 0273-1177 .- 1879-1948.
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Journal article (peer-reviewed)abstract
- The satellite industry is rapidly growing. There has been a significant increase in the number of new small satellites that are launched, which is complemented by the rapid pace of the development of image recognition algorithms. Convolutional neural networks (CNNs) in particular, have achieved state-of-the-art performance in computer vision related applications. Combining both and running an AI algorithm on-board the satellite to observe and recognize any natural disaster directly from the orbit is an important opportunity. This paper presents notable challenges that are generally involved in an Earth Observation small satellite mission and further challenges that are posed by combining it with AI-based image recognition on-board the satellite. This study discusses an approach that is feasible mainly for a fleet of small satellites.
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| 8. |
- Danilovic, Sanja
(author)
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Modeling of chromospheric features and dynamics in solar plage
- 2023
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In: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 71:4, s. 1939-1947
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Journal article (peer-reviewed)abstract
- The chromosphere is a dynamic and complex layer where all the relevant physical processes happen on very small spatio-temporal scales. A few spectral lines that can be used as chromospheric diagnostics give us convoluted information that is hard to interpret without realistic theoretical models. What are the key ingredients that these models need to contain? The magnetic field has a paramount effect on chromospheric structuring. This is obvious from the ubiquitous presence of chromospheric dynamic fibrilar structures visible on the solar disk and at the limb. The numerical experiments presented in this manuscript illustrate the present state of modeling. They showcase to what extent our models reproduce various chromospheric features and their dynamics. The publication describes the effect different ingredients have on chromospheric models and provides a recipe for building one-to-one models. Combining these models with observations will provide insight into the physical processes that take place in the solar atmosphere.
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| 9. |
- Darugna, Francesco, et al.
(author)
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Mitigation of severe weather events and TID impact on the interpolation of SSR atmospheric parameters
- 2021
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In: Advances in Space Research. - : Elsevier BV. - 0273-1177 .- 1879-1948. ; 68:6, s. 2401-2420
-
Journal article (peer-reviewed)abstract
- In Global Navigation Satellite (GNSS)-based positioning, a user within a region covered by a network of reference stations can take advantage of the network-estimated parameters. The use of State Space Representation (SSR) parameters as GNSS-augmentation is valuable for Network-Real Time Kinematic (N-RTK) positioning and enables the ambiguity resolution for Precise Point Positioning (PPP) in the so-called PPP-RTK. SSR atmospheric corrections, i.e. tropospheric and ionospheric delays, are commonly estimated for the approximate user position by interpolation from values estimated for the reference stations. Widely used techniques are Inverse Distance Weighted, Ordinary Kriging and Weighted Least Squares (WLS). In this work, we analyze the interpolation quality of such techniques during severe weather events and Traveling Ionospheric Disturbances (TID). Furthermore, we propose modified WLS methods taking advantage of the physical atmospheric behavior during such events. Here, we exploit the use of Numerical Weather Models for tropospheric horizontal gradients information, and estimated TID parameters like wavelength and direction of propagation. Firstly, the interpolation is assessed using simulations considering artificial and real network geometries. Secondly, the proposed techniques are evaluated in post-processing using real SSR parameters generated by network computation of GNSS measurements. As examples, two severe weather events in North Europe in 2017, and one TID event over Japan in 2019 have been analyzed. The interpolation of SSR tropospheric and ionospheric parameters is evaluated. Considering the reference station positions as rover locations, the application of the modified WLS approach reduces the root mean square error in up to 80% of the cases during sharp weather fluctuations. Also, the average error can be decreased in 64% of the cases during the TID event investigated. Improvements up to factors larger than two are observed. Furthermore, specific cases are isolated showing particular tropospheric variations where significant errors (e.g. larger than 1 cm) can be reduced up to 20% of the total amount. Finally, tropospheric and ionospheric messages are proposed to transmit to the user the information needed to implement the suggested interpolation properly.
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| 10. |
- Elgered, Gunnar, 1955, et al.
(author)
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Assessment of GNSS stations using atmospheric horizontal gradients and microwave radiometry
- 2024
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In: Advances in Space Research. - 1879-1948 .- 0273-1177. ; 74:6, s. 2583-2592
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Journal article (peer-reviewed)abstract
- We have assessed the quality of four co-located GNSS stations by studying time series of estimated linear horizontal gradients in the signal delay. The stations have different electromagnetic environments. We also examine the consistency of the results by using two different GNSS softwares, GipsyX and c5++, and applying three different elevation cutoff angles: 5°, 10°, and 20°. The estimated gradients are compared with the corresponding ones estimated from microwave radiometer observations acquired during six months (April–September 2021). For all four stations and using both softwares we find that is is possible to track gradient variations over time scales from less than one hour using GPS observations only. We have indications that it is an advantage to equip the area below the GNSS antenna with microwave absorbing material. However, the differences are small, a reduction in rms differences in the gradients compared to those from the microwave radiometer of less than 2 %. More studies are needed to decide if such an investment is reasonable in terms of cost and maintenance.
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