Ground-based Counterpart Research Articles

Bilby in space: Bayesian inference for transient gravitational-wave signals observed with LISA

ABSTRACT The Laser Interferometer Space Antenna (LISA) is scheduled to launch in the mid-2030s, and is expected to observe gravitational-wave candidates from massive black hole binary mergers, extreme mass ratio inspirals, and more. Accurately inferring the source properties from the observed gravitational-wave signals is crucial to maximize the scientific return of the LISA mission. bilby, the user-friendly Bayesian inference library, is regularly used for performing gravitational-wave inference on data from existing ground-based gravitational-wave detectors. Given that Bayesian inference with LISA includes additional subtitles and complexities beyond its ground-based counterpart, in this work we introduce bilby_lisa , a python package that extends bilby to perform parameter estimation with LISA. We show that full nested sampling can be performed to accurately infer the properties of LISA sources from transient gravitational-wave signals in (a) zero noise and (b) idealized instrumental noise. By focusing on massive black hole binary mergers, we demonstrate that higher order multipole waveform models can be used to analyse a year’s worth of simulated LISA data, and discuss the computational cost and performance of full nested sampling compared with techniques for optimizing likelihood calculations, such as the heterodyned likelihood.

Empirical 2MASS–WFC3/IR Filter Transformations Across the H-R Diagram from Synthetic Photometry

Near-infrared bandpasses on spaceborne observatories diverge from their ground-based counterparts as they are free of atmospheric telluric absorption. Available transformations between respective filter systems in the literature rely on theoretical stellar atmospheres, which are known to have difficulties reproducing the observed spectral energy distributions of cool giants. We present new transformations between the Two Micron All Sky Survey JHK S and Hubble Space Telescope WFC3/IR F110W, F125W, and F160W photometric systems based on synthetic photometry of empirical stellar spectra from four spectral libraries. This sample comprises over 1000 individual stars, which together span nearly the full H-R diagram and sample stellar populations from the solar neighborhood out to the Magellanic Clouds, covering a broad range of ages, metallicities, and other relevant stellar properties. In addition to global color-dependent transformations, we examine band-to-band differences for cool, luminous giant stars in particular, including multiple types of primary distance indicators.

Analyzing and evaluating floating PV systems in relation to traditional PV systems

The various benefits of floating photovoltaic technology, a relatively new kind of energy generation, have piqued the interest of many people (FPVT). FPVT technology not only helps to lessen water loss due to evaporation, but it also helps to increase energy production. Science can't progress without the analysis of mechanical and electrical systems. Many researchers have looked at FPVT systems from different angles. This article undertakes a logical investigation and provides a thorough summary of the state of the art, elaborating on the numerous features and components of FPVT systems as a means of producing electricity. The advantages and disadvantages of each type have been compared in detail. A common way of capturing solar energy for use in electrical generation is the installation of solar arrays on the roof of a structure. However, although most homes only need 5–20 kW, most enterprises require 100 kW or more. On average, floating solar panels produce 11 percent more energy than their ground-based counterparts. Approximately 40% of the water in open reservoirs is lost to evaporation, according to studies. Covering only 30% of the water's surface can reduce evaporation by 49%. At 104 GW, the solar panel market will see a compound annual growth rate of 6%. Global photovoltaic capacity climbed by 27% in 2018, reaching 512 GW. This represents about 55% of the total capacity. This study also predicts that the FPVT system will help spur a 7.38 percent increase in solar technology, which is equal to 485.4 GW of additional installed electricity around the world.

Floating photovoltaic module temperature estimation: Modeling and comparison

As the power demand increases, photovoltaic (PV) energy evolves with time, and besides the traditional ground-mounted and roof-based PV systems, floating photovoltaic (FPV) systems have gained popularity due to higher efficiency from lower module temperatures and water evaporation reductions. This paper estimates and compares the temperature of the floating PV module using thermal, empirical, and computational fluid dynamics (CFD) models. The dynamic thermal model considers a three-level energy-balance equation for the FPV module. From that, a simplified thermal model has been developed, which requires fewer parameters and is easier to estimate the module temperature. Secondly, the least squares regression was used to generate the empirical model, resulting in the smallest possible root mean square error when comparing the observed and predicted values. Finally, the FPV system has been developed in the COMSOL environment for CFD analysis using the same heat transfer method. The estimated results from the models were compared with the actual data collected from a Brazilian site and the existing FPV and ground-mounted temperature models. The RMSE performance of the FPV models was comparable to that of the data obtained from an installed FPV system and performed much better than other similar FPV models and their ground-based counterparts.

Can global rainfall estimates (satellite and reanalysis) aid landslide hindcasting?

Predicting rainfall-induced landslides hinges on the quality of the rainfall product. Satellite rainfall estimates or rainfall reanalyses aid in studying landslide occurrences especially in ungauged areas, or in the absence of ground-based rainfall radars. Quality of these rainfall estimates is critical; hence, they are commonly crosschecked with their ground-based counterparts. Beyond their temporal precision compared to ground-based observations, we investigate whether these rainfall estimates are adequate for hindcasting landslides, which particularly requires accurate representation of spatial variability of rainfall. We developed a logistic regression model to hindcast rainfall-induced landslides in two sites in Japan. The model contains only a few topographic and geologic predictors to leave room for different rainfall products to improve the model as additional predictors. By changing the input rainfall product, we compared GPM IMERG and ERA5 rainfall estimates with ground radar–based rainfall data. Our findings emphasize that there is a lot of room for improvement of spatiotemporal prediction of landslides, as shown by a strong performance increase of the models with the benchmark radar data attaining 95% diagnostic performance accuracy. Yet, this improvement is not met by global rainfall products which still face challenges in reliably capturing spatiotemporal patterns of precipitation events.

Tractable Optical Channel Modeling Between UAVs

More recently, the research on potential use of free-space optical (FSO) link as a powerful communication link between unmanned aerial vehicles (UAVs) has created much interest in academia and industry. Due to the need of higher number of UAV-based FSO links relative to the conventional ground-based FSO links, the optimum design of UAV-based FSO system parameters (such as optimum values for beam divergence angle, photodetector size, receiver lens radius, and transmit power, among many others) is much more needful and challenging relative to the ground-based counterpart. Moreover, to avoid the time consumed in Monte-Carlo simulations, existence of a simple and tractable channel model is very important and necessary. To address this need, in this paper, for the weak turbulence conditions, we construct a novel channel model for the considered system model under the effect of log-normal atmospheric turbulence channel. Then, for moderate to strong turbulence conditions, a novel closed-form statistical channel model is derived for Gamma-Gamma turbulence channel. The provided channel models, despite being simple and tractable, include the combined effects of atmospheric turbulence as well as the pointing errors. These also include the effects of receiver field-of-view limitation and inherent position, and orientation deviations of UAVs. Subsequently, for better performance analysis, the closed-form expressions for the outage probability and bit error rate (BER) are derived. Finally, the validity of the proposed novel channel models as well as the closed-form expressions for the outage probability and BER are confirmed by employing Monte-Carlo simulations. The developed results can therefore be applied as a benchmark for finding the optimal tunable parameters of UAV-based FSO links under different channel conditions and different levels of UAV instability without resorting to time-consuming Monte-Carlo simulations.

Clear-sky shortwave downward flux at the Earth's surface: Ground-based data vs. satellite-based data

The radiative flux data and other meteorological data in the BSRN archive start in 1992, but the RadFlux data, the clear-sky radiative fluxes at the BSRN sites empirically inferred through regression analyses of actually observed clear-sky fluxes, did not come into existence until the early 2000s, and at first, they were limited to the 7 NOAA SURFRAD and 4 DOE ARM sites, a subset of the BSRN sites. Recently, the RadFlux algorithm was applied more extensively to the BSRN sites for the production of clear-sky ground-based fluxes. At the time of this writing, there are 7119 site-months of clear-sky fluxes at 42 BSRN sites spanning from 1992 to late 2017. These data provide an unprecedented opportunity to validate the satellite-based clear-sky fluxes. In this paper, the GEWEX SRB GSW(V3.0) clear-sky shortwave downward fluxes spanning 24.5 years from July 1983 to December 2007, the CERES SYN1deg(Ed4A) and EBAF(Ed4.0) clear-sky shortwave fluxes spanning March 2000 to mid-2017 are compared with their RadFlux counterparts on the hourly, 3-hourly, daily and monthly time scales. All the three datasets show reasonable agreement with their ground-based counterparts. Comparison of the satellite-based surface shortwave clear-sky radiative fluxes to the BSRN RadFlux analysis shows negative biases (satellite-based minus RadFlux). Further analysis shows that the satellite-based atmosphere contains greater aerosol loading as well as more precipitable water than RadFlux analysis estimates.

A balloon-borne very long baseline interferometry experiment in the stratosphere: Systems design and developments

The balloon-borne very long baseline interferometry (VLBI) experiment is a technical feasibility study for performing radio interferometry in the stratosphere. The flight model has been developed. A balloon-borne VLBI station will be launched to establish interferometric fringes with ground-based VLBI stations distributed over the Japanese islands at an observing frequency of approximately 20 GHz as the first step. This paper describes the system design and development of a series of observing instruments and bus systems. In addition to the advantages of avoiding the atmospheric effects of absorption and fluctuation in high frequency radio observation, the mobility of a station can improve the sampling coverage (“uv-coverage”) by increasing the number of baselines by the number of ground-based counterparts for each observation day. This benefit cannot be obtained with conventional arrays that solely comprise ground-based stations. The balloon-borne VLBI can contribute to a future progress of research fields such as black holes by direct imaging.

Comparison of atmospheric CO2 mole fractions and source–sink characteristics at four WMO/GAW stations in China

As CO2 is a primary driving factor of climate change, the mole fraction and source–sink characteristics of atmospheric CO2 over China are constantly inferred from multi-source and multi-site data. In this paper, we compared ground-based CO2 measurements with satellite retrievals and investigated the source–sink regional representativeness at China's four WMO/GAW stations. The results indicate that, firstly, atmospheric CO2 mole fractions from ground-based sampling measurement and Greenhouse Gases Observing Satellite (GOSAT) products reveal similar seasonal variation. The seasonal amplitude of the column-averaged CO2 mole fractions is smaller than that of the ground-based CO2 at all stations. The extrema of the seasonal cycle of ground-based and column CO2 mole fractions are basically synchronous except a slight phase delay at Lin'an (LAN) station. For the two-year average, the column CO2 is lower than ground-based CO2, and both of them reveal the lowest CO2 mole fraction at Waliguan (WLG) station. The lowest (∼4 ppm) and largest (∼8 ppm) differences between the column and ground-based CO2 appear at WLG and Longfengshan (LFS) stations, respectively. The CO2 mole fraction and its difference between GOSAT and ground-based measurement are smaller in summer than in winter. The differences of summer column CO2 among these stations are also much smaller than their ground-based counterparts. In winter, the maximum of ground-based CO2 mole fractions and the greatest difference between the two (ground-based and column) datasets appear at the LFS station. Secondly, the representative areas of the monthly CO2 background mole fractions at each station were found by employing footprints and emissions. Smaller representative areas appeared at Shangdianzi (SDZ) and LFS, whereas larger ones were seen at WLG and LAN. The representative areas in summer are larger than those in winter at WLG and SDZ, but the situation is opposite at LAN and LFS. The representative areas for the stations are different in summer and winter, distributed in four typical regions. The CO2 net fluxes in these representative areas show obvious seasonal cycles with similar trends but different varying ranges and different time of the strongest sink. The intensities and uncertainties of the CO2 fluxes are different at different stations in different months and source-sink sectors. Overall, the WLG station is almost a carbon sink, but the other three stations present stronger carbon sources for most of the year. These findings could be conducive to the application of multi-source CO2 data and the understanding of regional CO2 source–sink characteristics and patterns over China.

Comparison of MODIS and VIIRS cloud properties with ARM ground-based observations over Finland

Abstract. Cloud retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard the satellites Terra and Aqua and the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the Suomi-NPP satellite are evaluated using a combination of ground-based instruments providing vertical profiles of clouds. The ground-based measurements are obtained from the Atmospheric Radiation Measurement (ARM) programme mobile facility, which was deployed in Hyytiälä, Finland, between February and September 2014 for the Biogenic Aerosols – Effects on Clouds and Climate (BAECC) campaign. The satellite cloud parameters cloud top height (CTH) and liquid water path (LWP) are compared with ground-based CTH obtained from a cloud mask created using lidar and radar data and LWP acquired from a multi-channel microwave radiometer. Clouds from all altitudes in the atmosphere are investigated. The clouds are diagnosed as single or multiple layer using the ground-based cloud mask. For single-layer clouds, satellites overestimated CTH by 326 m (14 %) on average. When including multilayer clouds, satellites underestimated CTH by on average 169 m (5.8 %). MODIS collection 6 overestimated LWP by on average 13 g m−2 (11 %). Interestingly, LWP for MODIS collection 5.1 is slightly overestimated by Aqua (4.56 %) but is underestimated by Terra (14.3 %). This underestimation may be attributed to a known issue with a drift in the reflectance bands of the MODIS instrument on Terra. This evaluation indicates that the satellite cloud parameters selected show reasonable agreement with their ground-based counterparts over Finland, with minimal influence from the large solar zenith angle experienced by the satellites in this high-latitude location.

Investigation of Self-Reported Musculoskeletal Injuries on Post-Deployment Health Assessment Forms for Aeromedical Evacuation Personnel.

Musculoskeletal injuries (MSIs) are a concern for the military community because of medical expenses, possible disability, and separation from the military. This study investigated the prevalence of MSIs in deployed aeromedical evacuation (AE) populations reported on Post-Deployment Health Assessment (PDHA) forms. A secondary aim was to examine the relationship between the occurrence of self-reported MSIs on PDHAs and a subsequent medical diagnosis. Flight nurses (Air Force Specialty Code [AFSC] 46F) and AE technicians (AETs) (AFSC 4N0 with a flight duty badge) who completed a PDHA during 2008-2010 were investigated. Data from the test population were compared with a control group of deployed ground-based counterparts. During this time period, 1,366 and 1,959 PDHAs were completed by the AE nursing and AET groups, respectively. At least 1 MSI was reported by 18% of AE nurse and 19% of AET compared with 23% of non-AE nurse and 25% of non-AET PDHAs. Of these individuals with reported MSIs, 35% and 44% of AE nurse and AET PDHAs, respectively, had a diagnosis matching their MSIs. Identifying the prevalence of MSIs in the unique AE environment can lead to the development of preventative and ergonomic solutions, minimizing the risk of MSIs and improving mission success.

Using cosmic voids to distinguishf(R) gravity in future galaxy surveys

We use properties of void populations identified in N-body simulations to forecast the ability of upcoming galaxy surveys to differentiate models of f (R) gravity from cold dark matter cosmology. We analyse multiple simulation realizations, which were designed to mimic the expected number densities, volumes, and redshifts of the upcoming Euclid satellite and a lower-redshift ground-based counterpart survey, using the public VIDE toolkit. We examine void abundances, ellipicities, radial density profiles, and radial velocity profiles at redshifts 1.0 and 0.43. We find that stronger f (R) coupling strengths eliminates small voids and produces voids up to ∼20 per cent larger in radius, leading to a significant tilt in the void number function. Additionally, under the influence of modified gravity, voids at all scales tend to be measurably emptier with correspondingly higher compensation walls. The velocity profiles reflect this, showing increased outflows inside voids and increased inflows outside voids. Using the void number function as an example, we forecast that future surveys can constrain the modified gravity coupling strength to ∼3 × 10−5 using voids.

Securing underwater wireless communication networks

Underwater wireless communication networks are particularly vulnerable to malicious attacks due to the high bit error rates, large and variable propagation delays, and low bandwidth of acoustic channels. The unique characteristics of the underwater acoustic communication channel, and the differences between underwater sensor networks and their ground-based counterparts require the development of efficient and reliable security mechanisms. In this article, a complete survey of security for UWCNs is presented, and the research challenges for secure communication in this environment are outlined.

PROTECTION OF NAVAL SYSTEMS AGAINST ELECTROMAGNETIC EFFECTS DUE TO LIGHTNING

This study investigates possible lightning threats to naval crafts, especially those sailing in the shallow waters of tropical oceans where thunderstorms prevail throughout the year and Far-East Asian region where dangerous positive lightning is a signiflcant characteristic in winter thunderstorms. It is empathized that sea water acts as nearly a perfect conductor thus lightning electromagnetic transients propagate over the sea with almost zero attenuation of amplitude and high frequency components intact. The ratio between the peak electric flelds at 5km from the lightning channel, after flelds propagate over dry soil and over sea water is 0.75. The ratio between the peak electric fleld derivatives under the same conditions is 0.1. Such small ratios are observed in the magnetic flelds and their time derivatives as well. Apart from the conductivity, the topological irregularities of the plane over which propagation takes place also contribute to further attenuation of flelds and their time derivatives. This makes marine naval systems more vulnerable to lightning induced efiects than their ground-based counterparts. The paper discusses in detail the lapses of existing naval standards in the defense of electrical and electronic systems against both direct lightning currents and induced efiects of nearby lightning. Consequently we propose the development of a dedicated standard for the lightning protection of naval systems, with the inclusion of several signiflcant recommendations specifled in this paper.

Computational Model of a Novel, Two-Cup Horizontal Wind-Turbine System

Typical wind turbine systems are sufficiently large so as to require extensive physical space for their installa- tion and operation. These requirements preclude the use of turbines in crowded, urban environments. On the other hand, smaller turbine systems may find practical application as rooftop units, installed atop tall buildings. Such rooftop units must be much smaller than their ground-based counter parts. In this paper, a new, vertical-axis wind turbine has been ana- lyzed by using a two-step numerical procedure. The design consists of two turbine cups that are positioned with 180 o separation. In the first step of the analysis, a complete numerical simulation of the wind-flow patterns across the cup with wind impacting angles spanning 360 o was completed. From these calculations, it was possible to determine the functional relationship between rotational forces, relative wind speed, and the relative angle of wind approach. The second stage of numerical procedure was a time-wise integration of the instantaneous angular velocity of the wind turbine. These calcula- tions were carried out until the turbine had achieved quasi-steady motion. The corresponding cycle-averaged angular ve- locity (terminal angular velocity) was then determined. This second stage was completed for a wide range of wind speeds so that a functional dependence of the turbine rotational velocity on the wind speed could be found. This functional rela- tionship enables a user to predict the operational response of the wind turbine based on a known and steady wind velocity.

The ground-based counterpart of the CoRoT asteroseismic observations from space

Inhalt (u.a.): M. BREGER: Delta Scuti stars: Observational aspects; M.S. Cunha: Theory of rapidly oscillating Ap stars; M. SACHKOV et al.: Vertical structure of pulsations in roAp stars; G. HOUDEK: Theoretical asteroseismology of solar-like oscillations; B.L. POPIELSKI: Core modes as a seismic probe of mixing beyond the convective core; M. GODART: Temperature gradients in the core overshooting region; W.A. DZIEMBOWSKI – J. DASZYŃSKA-DASZKIEWICZ – A.A. PAMYATNYKH: Interpretation of the Be star HD 163868 oscillation spectrum based on the MOST observations; D. KILKENNY: Pulsating Hot Subdwarfs – An Observational Review; M.H. MONTGOMERY: Mapping Convection using Pulsating White Dwarf Stars; M. ROTH: The Network Activities in HELAS; I. KUDZEJ et al.: A New Slovak Observatory 500 km from Vienna; W.W. WEISS: Microsatellites; G. KOPACKI – S. FRANDSEN: RR Lyrae stars in M4

New generation atmospheric Cherenkov detectors

High energy γ-ray astronomy has been established during the last decade through the launch of the Compton Gamma Ray Observatory (CGRO) and the success of its ground-based counterpart, the imaging atmospheric Cherenkov technique. In the aftermath of their important and surprising scientific results a worldwide effort developing and designing new generation atmospheric Cherenkov detectors is underway. These novel instruments will have higher sensitivity at E > 250 GeV, but most importantly, will be able to close the unexplored energy gap between 20 GeV and 250 GeV. Several ground-based detectors are proposed or under construction. Aspects of the techniques used and sensitivity are discussed in this overview paper. The instruments cover largely complementary energy ranges and together are expected to explore the γ-ray sky between 20 GeV and 100 TeV with unprecedented sensitivity.