Spectral properties and geologic processes on Eros from combined NEAR NIS and MSI data sets

Abstract— From April 24 to May 14, 2000, the Near Earth Asteroid Rendezvous (NEAR) Shoemaker mission's near infrared spectrometer (NIS) obtained its highest resolution data of 433 Eros. High signal‐to‐noise ratio NIS reflectance spectra cover a wavelength range of 800–2400 nm, with footprint sizes from 213 times 427 m to 394 times 788 m. This paper describes improvement in instrument calibration by remediation of internally scattered light; derivation of a “pseudo channel” for NIS at 754 nm using Multispectral Imager (MSI) Eros approach maps at 951 and 754 nm; synthesis of a 3127‐spectrum high‐resolution data set with the improved calibration and expanded wavelength coverage; and investigation of global and localized spectral variation with respect to mineralogy, composition, and space weathering of Eros, comparing the findings with previous analyses. Scattered light removal reduces the “red” slope of Eros spectra, though not to the level seen by telescopic observations. The pseudo channel completes sampling of Eros' 1 micron (Band I) absorption feature, enabling direct comparison of NIS data with other asteroid and meteorite spectra without additional scaling or correction. Following scattered light removal and wavelength range extension, the spectral parameters of average Eros plot well inside the S(IV) field of Gaffey et al. (1993) and are consistent with the L6 chondrite meteorite fields of Gaffey and Gilbert (1998). Although Eros shows no evidence of mineralogical heterogeneity, modest spectral variations correlate with morphologically and geographically distinct areas of the asteroid. Eros bright‐to‐dark spectral ratios are largely consistent with laboratory “space weathering” experiment results and modeling of space weathering effects. Eros brightness variation unaccompanied by significant spectral variation departs from “lunar‐type”—where band depths, slopes, and albedoes all correlate—and “Ida‐type”—where significant spectral variation is unaccompanied by corresponding brightness variation. The brightest areas on Eros—steep crater walls—have lesser spectral slope and deeper Band I, consistent with exposure of “fresher,” less space weathered materials. Bright crater slope materials have opx/(opx + olv) of 0.24–0.29 and may be more representative of the subsurface mineralogy than “average” Eros, which is probably affected by space weathering. The floors of the large craters Psyche and Himeros have lower albedo and contain the most degraded or altered looking materials. NIS spectra retain a “red” spectral slope at greater than 2 microns. The recalibrated and expanded NIS spectra show better agreements with mixing models based on space weathering of chondritic mixtures.     

Spectrophotometric properties of surface water dissolved organic matter in an afforested upland peat catchment

Many upland catchments in the UK have undergone afforestation; their characteristic waterlogged soils require extensive pre‐plantation ground drainage to allow tree establishment. In peatland areas this can result in very highly coloured runoff and enhanced dissolved organic matter (DOM) export in rivers of naturally high concentrations. In 1966, the Coalburn Experimental Catchment, northern England, was established to investigate the impact of afforestation on an upland peat catchment. Here we report the variations in DOM spectrophotometric properties of streamflow in the catchment at canopy closure, especially with respect to potential carbon sources within the artificial drainage ditches. Drainage ditches are characterized by water that has higher absorption coefficients and which is more highly coloured than in the catchment tributaries. Ditched, afforested areas produce more highly‐coloured runoff waters that are more fluorescent and absorbent normalized to carbon concentration compared to ditches in open moorland. Ditches that had been experimentally re‐excavated have organic matter of different spectrophotometric character, with higher dissolved organic carbon concentration and less aromatic or lower molecular weight material. It is hypothesized that this is due to the exposure of bare peat faces within and adjacent to the ditches that are more susceptible to drying compared to vegetated areas. The large extent of this drainage network acts as both a rapid transport network increasing hydrological connectivity and a pool for the storage of DOM, which is of different spectrophotometric character under low flow conditions, depending on management conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

Geographical distribution of arsenic in sediments within the Rio Conchos Basin,Mexico

Arsenic (As) content of sediments from the Rio Conchos and Rio San Pedro in northern Mexico were measured to determine if this toxic metalloid had accumulated to unsafe levels to humans and aquatic life. The spatial distribution of As in each of the six clusters of river and arroyo sediments was analyzed to determine variations with respect to background levels and to infer about potential As sources and sinks. In the northern part of the study area, background concentrations varied little throughout the area and concentrations in river sediments were close to background levels. In the southern part, however, the content of As in arroyo sediment contained a wider range of values and anomalous concentrations. The latter could be traced in part to the presence of mine tailings. As concentrations were below the limit in all studied river stretches and thus do not pose an immediate threat to the river environment, but As content in reservoir sediments exceeded the guideline values. Reservoirs seem to act as a sink for As, warranting closer observation and monitoring.     

Constraints on central uplift structure from the Manicouagan impact crater

Abstract— Recent drilling operations at the 90 km diameter, late Triassic Manicouagan impact crater of Quebec, Canada, have provided new insight into the internal structure of a complex crater's central region. Previous work had indicated that the impact event generated a ?55 km diameter sheet of molten rock of relatively consistent (originally ?400 m) thickness (Floran et al. 1978). The drilling data reveals melt sheet thicknesses of up to ?1500 m, with kilometer‐scale lateral and substantial vertical variations in the geometry of the crater floor beneath the melt sheet. The thickest melt section occurs in a 1500 m deep central trough encircled by a horseshoe‐shaped uplift of Precambrian basement. The uplift constitutes a modified central peak structure, at least part of which breached the melt sheet. Mineralogical and compositional segregation (differentiation) of the thicker melt sheet section, coupled with a lack of fractionation in the thinner units, shows that the footwall geometry and associated trough structure were in place prior to melt sheet solidification. Marked lateral changes in sub‐melt sheet (basement) relief support the existence of a castellated footwall that was created by high‐angle, impact‐related offsets of 100s to 1000s of meters. This indicates that deformation during the modification stage of the cratering process was primarily facilitated by large‐displacement fault systems. This work suggests that Manicouagan is a central peak basin with rings, which does not appear to fit with current complex crater classification schemes.     

Sedimentological and Geomorphological Impacts of The Jökulhlaup (Glacial Outburst Flood) In January 2002 At Kverkfjöll, Northern Iceland

Jökulhlaups (glacial outburst floods) are common hazards in many glaciated environments. However, research on the controls on the sedimentological and geomorphological impact of jökulhlaups is rare. Developing a more comprehensive understanding of flood impacts may be useful for hazard identification, prediction and mitigation. This study determines the controls on the sedimentological and geomorphological impact of a jökulhlaup in January 2002 at Kverkfjöll, northern Iceland. This jökulhlaup, caused by geothermal activity, reached a peak discharge of 490 m³s^?1 as recorded at a permanent gauging station 40 km downstream from the glacier snout. However, reconstructed peak discharges in the proximal part of the jökulhlaup channel near the glacier snout indicate a peak discharge of 2590 m³s^?1. The jökulhlaup hydrograph was characterized by a rapid rising stage and a more gradual falling stage. As a result, sedimentary and geomorphological impacts included poorly sorted, structureless, matrix‐supported deposits; massive sand units; clast‐supported units; ice‐proximal cobbles, rip‐up clasts and kettle‐holes; and steep‐sided kettle‐holes. These features are proposed to be characteristic of rapid rising stage deposition. Additionally, large‐scale gravel bars and bedload sheets prograded and migrated during the rapid rising stage. The development of these bedforms was facilitated by high bedload transport rates, due to high discharge acceleration rates during the rapid rising stage. During the more prolonged falling stage, there was sufficient time for sediment incision and erosion to occur, exhuming cobbles, ice blocks and rip‐up clasts, and creating well‐defined terrace surfaces. This study provides a clearer understanding of hydrological and sedimentological processes and mechanisms operating during jökulhlaups, and helps to identify flood hazards more accurately, which is fundamental for hazard management and minimizing risk.     

玄武岩内非均质性对地震资料的影响:印度德干圈闭的一个研究实例

Hydrocarbon exploration interests have renewed the need for developing new sub basalt imaging techniques. One of the most important problems encountered today is seismic imaging below basalt. In recent years, this problem appears to have been overcome partly by using long offset seismic data. However near offset data are yet to be fully utilised due to the complex waveform caused by the surface as well as internal heterogeneity of the basalts. The near normal incidence data, which influence the sub-basalt imaging, are highly useful to understand the internal structure within a basalt layer. The use of converted waves for such targets has been proposed as an alternative in a rather homogeneous basalt layer. With a few synthetic modelling exercises here we highlight the practical difficulties in dealing with more realistic and heterogeneous basalt flow. Full waveform seismograms are computed to understand the effects of intra-trappean sediments on the seismic data. A case study from the Deccan Traps of India is presented in this paper. First, we discuss the effects of intercalated sediments on the overall seismic image. Later, the sonic log data from the field are used to compute the full wave-field response using the reflectivity method and compared with the field data. The feasibility of using mode converted waves （P to S and vice-versa at the top and bottom basalt interfaces） for sub-basalt imaging in Kutch region is discussed through a series of velocity-depth profiles. By comparing with the field data we demonstrate that the effects of multiple thin layering within the basalt can strongly deteriorate the image we seek to interpret and exploit.     

Seismic anisotropy of upper mantle in eastern Tibetan Plateau and related crust-mantle coupling pattern

By using the polarization analysis of teleseismic SKS waveform data recorded at 116 seismic stations which respectively involved in China National Digital Seismograph Network, and Yunnan, Sichuan, Gansu and Qinghai regional digital networks, and portable broadband seismic networks deployed in Sichuan, Yunnan and Tibet, we obtained the SKS fast-wave direction and the delay time between fast and slow waves of each station by use of the stacking analysis method, and finally acquired the fine image of upper mantle anisotropy in the eastern Tibetan Plateau and its adjacent regions. We analyzed the crust-mantle coupling deformation on the basis of combining the GPS observation results and the upper mantle anisotropy distribution in the study area. The Yunnan region out of the plateau has dif-ferent features of crust-mantle deformation from the inside plateau. There exists a lateral transitional zone of crust-mantle coupling in the eastern edge of the Tibetan Plateau, which is located in the region between 26° and 27°N in the west of Sichuan and Yunnan. To the south of transitional zone, the fast-wave direction is gradually turned from S60°―70°E in southwestern Yunnan to near EW in south-eastern Yunnan. To the north of transitional zone in northwestern Yunnan and the south of western Sichuan, the fast-wave direction is nearly NS. From crust to upper mantle, the geophysical parameters (e.g. the crustal thickness, the Bouguer gravity anomaly, and tectonic stress direction) show the feature of lateral variation in the transitional zone, although the fault trend on the ground surface is inconsis-tent with the fast-wave direction. This transitional zone is close by the eastern Himalayan syntaxis, and it may play an important role in the plate boundary dynamics.     

Small towns as ‘sub-poles’ in English rural development: Investigating rural–urban linkages using sub-regional social accounting matrices

This paper uses spatial economic data from four small English towns to measure the strength of economic integration between town and hinterland and to estimate the magnitude of town–hinterland spill-over effects. Following estimation of local integration indicators and inter-locale flows, sub-regional social accounting matrices (SAMs) are developed to estimate the strength of local employment and output multipliers for various economic sectors. The potential value of a town as a ‘sub-pole’ in local economic development is shown to be dependent on structural differences in the local economy, such as the particular mix of firms within towns. Although the multipliers are generally small, indicating a low level of local linkages, some sectors, particularly financial services and banking, show consistently higher multipliers for both output and employment.