We have constructed a new high resolution solar reference spectrum in the spectral range between 250 and 550 nm. The primary
use of this spectrum is for the calibration of the Dutch – Finnish Ozone Monitoring Instrument (OMI), but other applications
are mentioned. The incentive for deriving a new high resolution solar reference spectrum is that available spectra do not
meet our requirements on radiometric accuracy or spectral resolution. In this paper we explain the steps involved in constructing
the new spectrum, based on available low and high resolution spectra and discuss the main sources of uncertainty. We compare
the result with solar measurements obtained with the OMI as well as with other UV-VIS space-borne spectrometers with a similar
spectral resolution. We obtain excellent agreement with the OMI measurements, which indicates that both the newly derived
solar reference spectrum and our characterization of the OMI instrument are well understood. We also find good agreement with
previously published low resolution spectra. The absolute intensity scale, wavelength calibration and representation of the
strength of the Fraunhofer lines have been investigated and optimized to obtain the resulting high resolution solar reference
spectrum. 相似文献
NASA’s Meteoroid Environment Office has implemented a program to monitor the Moon for meteoroid impacts from the Marshall
Space Flight Center. Using off-the-shelf telescopes and video equipment, the Moon is monitored for as many as 10 nights per
month, depending on weather. Custom software automatically detects flashes which are confirmed by a second telescope, photometrically
calibrated using background stars, and published on a website for correlation with other observations. Hypervelocity impact
tests at the Ames Vertical Gun Range facility have begun to determine the luminous efficiency and ejecta characteristics.
The purpose of this research is to define the impact ejecta environment for use by lunar spacecraft designers of the Constellation
manned lunar program. The observational techniques and preliminary results will be discussed.
The U.S. Government's right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged. 相似文献
The Canadian Meteor Orbit Radar is a multi-frequency backscatter radar which has been in routine operation since 1999, with
an orbit measurement capability since 2002. In total, CMOR has measured over 2 million orbits of meteoroids with masses greater
than 10 μg, while recording more than 18 million meteor echoes in total. We have applied a two stage comparative technique
for identifying meteor streams in this dataset by making use of clustering in radiants and velocities without employing orbital
element comparisons directly. From the large dataset of single station echoes, combined radiant activity maps have been constructed
by binning and then stacking each years data per degree of solar longitude. Using the single-station mapping technique described
in Jones and Jones (Mon Not R Astron Soc 367:1050–1056, 2006) we have identified probable streams from these single station
observations. Additionally, using individual radiant and velocity data from the multi-station velocity determination routines,
we have utilized a wavelet search algorithm in radiant and velocity space to construct a list of probable streams. These two
lists were then compared and only streams detected by both techniques, on multiple frequencies and in multiple years were
assigned stream status. From this analysis we have identified 45 annual minor and major streams with high reliability. 相似文献
The Mars Reconnaissance Orbiter observes Mars from a nearly circular, polar orbit. From this vantage point, the Mars Color Imager extends the ∼5 Mars years record of Mars Global Surveyor global, visible-wavelength multi-color observations of meteorological events and adds measurements at three additional visible and two ultraviolet wavelengths. Observations of the global distribution of ozone (which anti-correlates with water vapor) and water ice and dust clouds allow tracking of atmospheric circulation. Regional and local observations emphasize smaller scale atmospheric dynamics, especially those related to dust lifting and subsequent motion. Polar observations detail variations related to the polar heat budget, including changes in polar frosts and ices, and storms generated at high thermal contrast boundaries. 相似文献
Fine-resolution (500 m/pixel) Cassini Visual and Infrared Mapping Spectrometer (VIMS) T20 observations of Titan resolve that moon's sand dunes. The spectral variability in some dune regions shows that there are sand-free interdune areas, wherein VIMS spectra reveal the exposed dune substrate. The interdunes from T20 are, variously, materials that correspond to the equatorial bright, 5-μm-bright, and dark blue spectral units. Our observations show that an enigmatic “dark red” spectral unit seen in T5 in fact represents a macroscopic mixture with 5-μm-bright material and dunes as its spectral endmembers. Looking more broadly, similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes. The presence of interdunes indicates that Titan's dunefields are both mature and recently active. The spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of Titan; various organics are consistent with the dunes' measured reflectivity. We measure a mean dune spacing of 2.1 km, and find that the dunes are oriented on the average in an east-west direction, but angling up to 10° from parallel to the equator in specific cases. Where no interdunes are present, we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m. These results pave the way for future exploration and interpretation of Titan's sand dunes. 相似文献
Straddling the south polar region of Saturn's moon Enceladus, the four principal “tiger stripe” fractures are a likely source of tectonic activity and plume generation. Here we investigate tidally driven stress conditions at the tiger stripe fractures through a combined analysis of shear and normal diurnal tidal stresses and accounting for additional stress at depth due to the overburden pressure. We compute Coulomb failure conditions to assess failure location, timing, and direction (right- vs left-lateral slip) throughout the Enceladus orbital cycle and explore a suite of model parameters that inhibit or promote shear failure at the tiger stripes. We find that low coefficients of friction (μf=0.1-0.2) and shallow overburden depths (z=2-4 km) permit shear failure along the tiger stripe faults, and that right- and/or left-lateral slip responses are possible. We integrate these conditions into a 3D time-dependent fault dislocation model to evaluate tectonic displacements and stress variations at depth during a tiger stripe orbital cycle. Depending on the sequence of stress accumulation and subsequent fault slip, which varies as a function of fault location and orientation, frictional coefficient, and fault depth, we estimate resolved shear stress accumulation of ∼70 kPa prior to fault failure, which produces modeled strike-slip displacements on the order of ∼0.5 m in the horizontal direction and ∼5 mm in the vertical direction per slip event. Our models also indicate that net displacements on the order of 0.1 m per orbital cycle, in both right- and left-lateral directions, are possible for particular fault geometries and frictional parameters. Tectonic activity inferred from these analyses correlates with observed plume activity and temperature anomalies at Enceladus's south polar region. Moreover, these analyses provide important details of stress accumulation and the faulting cycle for icy satellites subjected to diurnal tidal stress. 相似文献
Catastrophic disasters can change the course of urban development and challenge the long-run sustainability of cities and regions. How to rapidly reconstruct communities impaired by catastrophic disaster is a world-wide challenge. The reconstruction after the 2008 Wenchuan earthquake in China was an unusual case of very rapid reconstruction after a catastrophic disaster. Over US$147 billion was invested to rebuild the damaged areas within 3 years. The reconstruction was not simply building back what was destroyed, but was used as an opportunity to advance national goals for urbanization, rural transformation, and poverty reduction. In this article, we review how the reconstruction was planned, budgeted, and financed in the sociopolitical context of 2008 China. Particularly, we discuss two innovative programs, namely pair assistance and land-based financing. Despite the unique circumstances of China, lessons can be learned to speed up post-disaster reconstruction and urban development in other countries. Conversely, this case illustrates that a narrow focus on physical reconstruction may overlook broader economic and social issues.
Mary Anning, Alfred Nicholson Leeds and Steve Etches form part of a long line of individuals who furnished a substantial addition to our understanding of marine and terrestrial ecosystems through collecting significant numbers of superb fossils. For all three collectors, fossils became a factor that dominated their lives, and their fossil collecting led to the discovery of numerous taxa new to science. Extensive collecting was made possible by the fortunate circumstances of living ‘in the right place at the right time’, close to fine-grained UK Jurassic deposits (Lagerstätten) with well-preserved large Jurassic marine reptiles. All three were highly-motivated and developed a considerable skill sets for discovering, collecting, preparing, conserving and displaying fossils. They developed personal and professional interactions with family and friends, and university and museum professionals, although their collecting resulted in variable recognition of their work. Each collector can be considered a complex mix of amateur and professional: Mary Anning, a professional fossil collector and amateur palaeontologist; Alfred Leeds transitioned from amateur to professional fossil collector, but remained an amateur palaeontologist; and Steve Etches has remained an amateur fossil collector and palaeontologist. However, all three exhibited an entirely professional outlook to collecting, and should be considered professionals of the highest degree. The impact of Mary Anning, Alfred Nicholson Leeds and Steve Etches has been critical for the development of Palaeontology as a science, and without whom palaeontology, with all its associated benefits to a wide scientific and non-scientific audience, would not be as rich as we currently know it. 相似文献
Active wildfire seasons in the western U.S. warrant the evaluation of post-fire forest management strategies. Ground-based salvage logging is often used to recover economic loss of burned timber. In unburned forests, ground-based logging often follows best management practices by leaving undisturbed areas near streams called stream buffers. However, the effectiveness of these buffers has not been tested in a post-wildfire setting. This experiment tested buffer width effectiveness with a novel field-simulated rill experiment using sediment-laden runoff (25 g/L) released over 40 min at evenly timed flow rates (50, 100 and 150 L/min) to measure surface runoff travel length and sediment concentration under unburned and high and low soil burn severity conditions at 2-, 10- and 22-month post-fire. High severity areas 2-month post-fire had rill lengths of up to 100 m. Rill length significantly decreased over time as vegetation regrowth provided ground cover. Sediment concentration and sediment dropout rate also varied significantly by soil burn severity. Sediment concentrations were 19 g/L for the highest flow 2-month post-fire and reduced to 6.9–14 g/L 10-month post-fire due to abundant vegetation recovery. The amount of sediment dropping out of the flow consistently increased over the study period with the low burn severity rate of 1.15 g L−1 m−1 approaching the unburned rate of 1.29 g L−1 m−1 by 2-year post-fire. These results suggest that an often-used standard, 15 m buffer, was sufficient to contain surface runoff and reduce sediment concentration on unburned sites, however buffers on high burn severity sites need to be eight times greater (120 m) immediately after wildfire and four times greater (60 m) 1-year post-fire. Low burn severity areas 1-year post-fire may need to be only twice the width of an unburned buffer (30 m), and 2-year post-fire these could return to unburned widths. 相似文献
Karst areas and their catchments pose a great challenge for protection because fast conduit flow results in low natural attenuation of anthropogenic contaminants. Studies of the hydrochemistry of karst sources and river solutes are an important tool for securing and managing water resources. A study of the geochemical downriver evolution of the Wiesent River and its tributaries, located in a typical karst terrain, revealed unexpected downstream decreases of nitrate with maximum mean values of 30 mg/L at the source to minimum values of 18 mg/L near the river mouth. This trend persisted over the length of the river even though increased agricultural activities are evident in the downstream section of the catchment. This pattern is caused by fertilizer inputs via diffusive and fast conduits flow from karst lithology in the upstream area that may have reached the river's source even from beyond the hydrological catchment boundaries. Further downstream, these influences became diluted by tributary inputs that drain subcatchments dominated by claystone and sandstone lithologies that increased potassium and sulphate concentrations. Our findings indicate that bedrock geology remains the dominant control on the major ion chemistry of the Wiesent River and that agricultural influences are strongest near the headwaters despite increased land use further downstream, due to long‐term storage and accumulation in karst aquifers. This feature may not be unique to the Wiesent River system, as carbonates cover significant portions of the Earth's surface and subsequent work in other river systems could establish whether such patterns are ubiquitous worldwide. 相似文献