Application of drone-captured thermal imagery in aiding in the recovery of meteorites within a snow-covered strewn field     

Patrick J. A. Hill  Libby D. Tunney  Christopher D. K. Herd 《Meteoritics & planetary science》2023,58(3):421-432

The rapid recovery of meteorites mitigates the exposure of astromaterials to the terrestrial environment and subsequent contamination. Modern fireball observatories have enabled the more accurate triangulation of fireball trajectories, which has aided in the location of strewn fields, in the case of meteorite-producing events. Despite this advancement, most meteorite searches still use manual searching to locate any meteorite falls, which is often labor-intensive and has a slow coverage rate (km² day⁻¹). Recent work has begun exploring the application of drone technology to the recovery of meteorites; however, most of this work has focused on falls in arid environments. Our study examines the utilization of drones with thermal imaging technology to aid in the recovery of meteorites that have fallen on a snow-covered field. We created a simulated strewn field that included meteorite specimens as well as Earth rocks with similar properties (“meteowrongs”). Thermal imagery was utilized to determine whether the thermal contrast between meteorites and snow could aid in the identification of meteorites. We found that the thermal contrast was significant enough that meteorites were readily identifiable within thermal images; however, it was not significant enough to distinguish between the meteorites and the meteowrongs. The utilization of thermal imagery in conjunction with visible imagery has the potential to aid in the rapid recovery of meteorites in snow-covered landscapes.  相似文献   

Taxila LBM: a parallel,modular lattice Boltzmann framework for simulating pore-scale flow in porous media     

Ethan T. Coon  Mark L. Porter  Qinjun Kang 《Computational Geosciences》2014,18(1):17-27

The lattice Boltzmann method is a popular tool for pore-scale simulation of flow. This is likely due to the ease of including complex geometries such as porous media and representing multiphase and multifluid flows. Many advancements, including multiple relaxation times, increased isotropy, and others have improved the accuracy and physical fidelity of the method. Additionally, the lattice Bolzmann method is computationally very efficient, thanks to the explicit nature of the algorithm and relatively large amount of local work. The combination of many algorithmic options and efficiency means that a software framework enabling the usage and comparison of these advancements on computers from laptops to large clusters has much to offer. In this paper, we introduce Taxila LBM, an open-source software framework for lattice Boltzmann simulations. We discuss the design of the framework and lay out the features available, including both methods in the literature and a few new enhancements which generalize methods to complex geometries. We discuss the trade-off of accuracy and performance in various methods, noting how the Taxila LBM makes it easy to perform these comparisons for real problems. And finally, we demonstrate a few common applications in pore-scale simulation, including the characterization of permeability of a Berea sandstone and analysis of multifluid flow in heterogenous micromodels.  相似文献   

Receiver depth selection for passive sonar systems     

Ferla  C. Porter  M.B. 《Oceanic Engineering, IEEE Journal of》1991,16(3):267-278

Since tactical acoustic systems such as towed arrays can be deployed at various depths, the authors address the question of what depth is optimal. This question is considered principally from the point of view of optimum propagation conditions, employing two deep-water scenarios representing summer and winter conditions in the western Mediterranean. Two simple rules-of-thumb are derived from these results: first, if the source depth is known, then the best receiver depth is either the source depth or the conjugate depth (where the sound speed is the same as that at the source). Second, if the source depth is unknown, then a receiver depth where the ocean sound speed is as low as possible is optimal. These two rules are qualified with a few disclaimers. In the first place they are derived under the assumption of a range-invariant environment. In addition, a definition of optimality requires numerous assumptions that may not always be appropriate. Both these guidelines and their domain of applicability are discussed  相似文献   

Modeling techniques for marine-mammal risk assessment     

Siderius  M. Porter  M.B. 《Oceanic Engineering, IEEE Journal of》2006,31(1):49-60

Propagation modeling in the ocean may be said to be a fairly mature subject, with a number of reliable and efficient acoustic models freely distributed. However, acoustic modeling to predict effects of sound on marine mammals presents some particular challenges. Standard sonar models predict the mean power levels for static receivers. However, marine-mammal researchers have shown a strong interest in being able to predict the actual time series that a moving mammal would experience as it swims through an ensonified ocean. The time series can then be used to directly model auditory models of the mammalian ear. To do this properly requires attention to subtle Doppler effects. The authors present a Gaussian-beam-tracing method that handles all these issues. Another key element needed for such models is the ability to rapidly predict three-dimensional (3-D) acoustic fields for lots of source/receiver combinations. This problem arises in trying to choose optimal locations for navy exercises, considering also a variety of hypothesized mammal-migration patterns. The authors discuss a precomputation approach to solve this problem. Finally, they examine a technique to reduce the computation needed for the one-third octave transmission loss (TL) averages. The one-third octave average is often used as a metric for the assessment of risk to mammals. The brute-force solution to this problem requires propagation modeling at many frequencies in the band. Here, the authors develop a general relationship to replace those frequency averages with much more easily computed range averages. The novelty of this approach relative to the previous range-averaging techniques is that it extends those methods to the range-dependent conditions.  相似文献   

On the binarity of Herbig Ae/Be stars     

Deborah Baines  René D. Oudmaijer  John M. Porter †  Monica Pozzo 《Monthly notices of the Royal Astronomical Society》2006,367(2):737-753

We present high-resolution spectro-astrometry of a sample of 28 Herbig Ae/Be and three F-type pre-main-sequence stars. The spectro-astrometry, which is essentially the study of unresolved features in long-slit spectra, is shown from both empirical and simulated data to be capable of detecting binary companions that are fainter by up to 6 mag at separations larger than ∼0.1 arcsec. The nine targets that were previously known to be binary are all detected. In addition, we report the discovery of six new binaries and present five further possible binaries. The resulting binary fraction is 68 ± 11 per cent. This overall binary fraction is the largest reported for any observed sample of Herbig Ae/Be stars, presumably because of the exquisite sensitivity of spectro-astrometry for detecting binary systems. The data hint that the binary frequency of the Herbig Be stars is larger than that of the Herbig Ae stars. The Appendix presents model simulations to assess the capabilities of spectro-astrometry and reinforces the empirical findings. Most spectro-astrometric signatures in this sample of Herbig Ae/Be stars can be explained by the presence of a binary system. Two objects, HD 87643 and Z CMa, display evidence for asymmetric outflows. Finally, the position angles of the binary systems have been compared with available orientations of the circumprimary disc and these appear to be coplanar. The alignment between the circumprimary discs and the binary systems strongly suggests that the formation of binaries with intermediate-mass primaries is due to fragmentation as the alternative, stellar capture, does not naturally predict aligned discs. The alignment extends to the most massive B-type stars in our sample. This leads us to conclude that formation mechanisms that do result in massive stars, but predict random angles between the binaries and the circumprimary discs, such as stellar collisions, are also ruled out for the same reason.  相似文献   

Dissociative recombination contributions to I(5577) and I(6300) [OI] and N_mF2 enhancements resulting from moderate proton PCA events     

H.S. Porter  B.C. Edgar  A.E.S. Green 《Planetary and Space Science》1975,23(6):935-944

We investigate the dissociative recombination contribution to I(5577) and I(6300) of [OI] as a function of low energy cutoff for two measured solar proton spectra. The volume ionization rate profiles used in the calculation are obtained using a detailed atomic cross section approach in the continuous slowing down approximation. The ratio of the dissociative recombination contribution to the direct impact contribution for both the 5577 Å and 6300 Å [OI] emissions is found to be dependent upon the low energy cutoff. This ratio has a nominal value of ～2.0 for the 5577 Å [OI] emission and ～0.25 for the 6300 Å [OI] emission. The I(5577)/I(3914) and I(6300)/I(3914) ratios including the direct and dissociative recombination contributions are strongly dependent upon the low energy cutoff of the spectrum. We have also investigated F-layer enhancements resulting from the low energy spectrum component. For the Mizera et al. (1972) spectrum with a low energy cutoff of 12.4 keV, we find an N_mF2 of ～4.5 × 10³ electrons/cm³ or about 10 per cent of the ionization required to maintain the dip pole at a value of 5 × 10⁴ electrons/cm³. Extension of the cutoff to 1 keV results in ～1 × 10⁴ electrons/cm³, or about 20 per cent of the required maintenance ionization.  相似文献   

Determination of HBCD, PBDEs and MeO-BDEs in California sea lions (Zalophus californianus) stranded between 1993 and 2003   总被引：1，自引：0，他引：1  

Stapleton HM  Dodder NG  Kucklick JR  Reddy CM  Schantz MM  Becker PR  Gulland F  Porter BJ  Wise SA 《Marine pollution bulletin》2006,52(5):522-531

Blubber samples from male California sea lions (Zalphophus californianus) stranded between 1993 and 2003 were analyzed for 27 polybrominated diphenyl ether (PBDE) congeners, three isomers of hexabromocyclododecane (HBCD) and 14 methoxylated polybrominated diphenyl ether (MeO-BDE) congeners. Total PBDEs ranged from 450 ng/g to 4740 ng/g wet mass and total HBCD ranged from < 0.3 ng/g to 12 ng/g wet mass. The concentration of HBCD increased from 0.7 ng/g to12.0 ng/g wet mass in sea lion blubber between 1993 and 2003. However, no significant temporal trend was observed for any of the other brominated compounds over this 10 year period. Only one of the 14 MeO-BDE congeners was detected in the blubber samples, 6-methoxy-2,2',4,4'-tetrabromodiphenyl ether (6-MeO-BDE 47), and concentrations ranged from < 0.2 ng/g to 12 ng/g wet mass. A bromo-, chloro-heterocyclic compound, 1,1'-dimethyl-tetrabromo-dichloro-2,2'-bipyrrole (DBP-Br4Cl2), previously reported in marine species along the Pacific coast, was also identified in the sea lion blubber. DBP-Br4Cl2 ranged from 44 ng/g wet mass to 660 ng/g wet mass and was present at concentrations rivaling the dominant PBDE congener, BDE 47 (2,2',4,4'-tetrabromodiphenyl ether). Concentrations of DBP-Br4Cl2 were positively correlated with 6-MeO-BDE 47 (r = 0.7; p < 0.05). Both of these compounds have been identified in marine algae and sponges, and studies suggest they are both produced from natural sources. This study demonstrates that brominated compounds from both anthropogenic and biogenic sources can accumulate to similar levels in marine mammals. In addition, HBCD concentrations appear to be increasing in California sea lion populations, whereas PBDE concentrations, between 1993 and 2003, were highly variable.  相似文献   

Physical properties of trans-neptunian binaries (120347) Salacia–Actaea and (42355) Typhon–Echidna     

J.A. Stansberry  W.M. Grundy  M. Mueller  S.D. Benecchi  G.H. Rieke  K.S. Noll  M.W. Buie  H.F. Levison  S.B. Porter  H.G. Roe 《Icarus》2012,219(2):676-688

  相似文献   

The politics of greening unceded lands in the settler city     

Libby Porter  Julia Hurst  Tina Grandinetti 《The Australian geographer》2020,51(2):221-238

ABSTRACT

Urban greening is a buzz term in urban policy and research settings in Australia and elsewhere. In a context of settler colonial urbanism, like Australia, a first fact becomes clear: urban greening is always being practiced on unceded Indigenous lands. Recognising this requires some honest reckoning with how this latest urban policy response perpetuates dispossessory settler-colonial structures. In this paper, we listen to the place-based ontologies of the peoples and lands from where we write to inform understanding the city as an always already Indigenous place – a sovereign Aboriginal City. In so doing, the paper tries to practice a way of creating more truthful and response-able urban knowledge practices. We analyse three distinct areas of scholarly research that are present in the contemporary literature: urban greening and green infrastructure; urban political ecology; and more-than-human cities. When placed in relationship of learning with the sovereign Aboriginal City, our analysis finds that these scholarly domains of urban greening work to re-organise colonial power relations. The paper considers what work the practice and scholarship of ‘urban greening’ might need to do in order to become response-able and learn to learn with Indigenous sovereignties and ontologies.  相似文献   

Near‐surface hydraulic conductivity of northern hemisphere glaciers          下载免费PDF全文

Ian T. Stevens  Tristram D.L. Irvine‐Fynn  Philip R. Porter  Joseph M. Cook  Arwyn Edwards  Martin Smart  Brian J. Moorman  Andy J. Hodson  Andrew C. Mitchell 《水文研究》2018,32(7):850-865

The hydrology of near‐surface glacier ice remains a neglected aspect of glacier hydrology despite its role in modulating meltwater delivery to downstream environments. To elucidate the hydrological characteristics of this near‐surface glacial weathering crust, we describe the design and operation of a capacitance‐based piezometer that enables rapid, economical deployment across multiple sites and provides an accurate, high‐resolution record of near‐surface water‐level fluctuations. Piezometers were employed at 10 northern hemisphere glaciers, and through the application of standard bail–recharge techniques, we derive hydraulic conductivity (K) values from 0.003 to 3.519 m day^?1, with a mean of 0.185 ± 0.019 m day^?1. These results are comparable to those obtained in other discrete studies of glacier near‐surface ice, and for firn, and indicate that the weathering crust represents a hydrologically inefficient aquifer. Hydraulic conductivity correlated positively with water table height but negatively with altitude and cumulative short‐wave radiation since the last synoptic period of either negative air temperatures or turbulent energy flux dominance. The large range of K observed suggests complex interactions between meteorological influences and differences arising from variability in ice structure and crystallography. Our data demonstrate a greater complexity of near‐surface ice hydrology than hitherto appreciated and support the notion that the weathering crust can regulate the supraglacial discharge response to melt production. The conductivities reported here, coupled with typical supraglacial channel spacing, suggest that meltwater can be retained within the weathering crust for at least several days. Not only does this have implications for the accuracy of predictive meltwater run‐off models, but we also argue for biogeochemical processes and transfers that are strongly conditioned by water residence time and the efficacy of the cascade of sediments, impurities, microbes, and nutrients to downstream ecosystems. Because continued atmospheric warming will incur rising snowline elevations and glacier thinning, the supraglacial hydrological system may assume greater importance in many mountainous regions, and consequently, detailing weathering crust hydraulics represents a research priority because the flow path it represents remains poorly constrained.  相似文献