Comet 81P/Wild 2 was observed in the thermal infrared over 6 months during its 1997 perihelion passage. The comet was most active in late February, about 3 months preperihelion; dust production declined by a factor of 3 between February and August. For the GIOTTO Halley dust size distribution, maximum dust production rate was ∼2 × 106 g/s. The comet displayed a 10-μm silicate feature about 25% above the continuum, similar to several other Jupiter-family comets, but much lower than that seen in a number of Oort cloud comets.NASA’s STARDUST sample return mission will encounter P/Wild 2 98 days postperihelion in January 2004. Based on our observations at a similar point in the orbit and the Halley size distribution, we predict that the mass fluence on the spacecraft for a 150 km miss distance will be about 8 × 10−6 g/cm2 for particles up to 1 cm in radius. The corresponding areal coverage will be about 10−4. 相似文献
Reflectance spectra of Mercury, covering the spectral range of ~0.3–1.1 μm obtained during 1963–1976, were examined for any correlations with surface terrain. Mercury's 6.1385°/day rotational rate, the phases of the planet around maximum elongations, and bidirectional reflectance spectroscopy theory were used to identify the surface area associated with each spectrum. Data from 1974–1975, re-reduced with improved standard star flux ratios, show a weak absorption band in the near infrared not see in earlier analyses. Older spectra suggest that the western longitudes of the unimaged side of Mercury are similar to the rest of the planet. Spectra of the intercrater plains in the 0–90° quadrant suggest a possible absorption band. Spectra of areas dominated by Caloris Basin with the encompassing smooth plains may show Fe2+ abundances in the soil comparable to lunar highlands soil. No striking differences between spectra of intercrater plains and spectra of smooth plains are found. The absorption features seen in spectra of Mercury are generally weaker than features seen in lunar spectra. 相似文献
We have developed an artificial neural net detector for use on board Mars rovers that correctly identifies calcite under Mars analogue dust (JSC Mars-1 regolith simulant) layers up to ∼100 μm thickness and 80% aerial coverage. Both the detector output and the band depth of the ∼2300 nm CO=3 absorption are linearly related to the surface area of exposed calcite. This detector provides a means for rapid and robust automated recognition of calcite on Mars in areas of active aeolian erosion. 相似文献
We explored the utilization of Landsat-8 Operational Land Imager (OLI) data for mapping of hydrothermal alteration zones. The region in and around the cities of Dungarpur and Udaipur of Rajasthan state in India was selected for this study. The rock types of Dungarpur and Udaipur are serpentinites, talc-carbonate, talc-schist, and quartzite of the Aravalli Supergroup. Hydrothermally altered zones and resultant hydrous minerals play an important role in the genesis of these rocks. We aimed to identify possible locations of hydrothermally altered zones in regional context around Dungarpur and Udaipur using Landsat-8 OLI data. False-color composite maps and band ratios were prepared from Landsat-8 bands. Band ratios such as band 6/band 7 (short-wave infrared 1 (SWIR1)/short wave infrared 2 (SWIR2)), band 4/band 3 (red/green), and band 5/band 6 (near infrared (NIR)/SWIR1) and visual interpretation techniques were used to identify the hydrothermally altered zones. Spectroscopic analyses of field rock samples were done to validate the hydrothermal alteration zones delineated from the analysis of Landsat-8 data. We present the combined results of Landsat-8 and field spectroradiometer analysis which brings out the hydrothermal alteration zones associated with hydrous minerals (antigorite, lizardite, montmorillonite, vermiculite, talc, and saponite). The study demonstrates the utility Landsat-8 OLI (with field spectroradiometer data) in the mapping of hydrothermally altered zones as a key in understanding geological processes. 相似文献
Landslide susceptibility is the likelihood of a landslide occurrence in an area predicted on the basis of local terrain conditions. Since last few years, researchers have attempted to analyse the probability of landslide occurrences and introduced different methods of landslide susceptibility assessment. The objective of this paper is to assess the landslide susceptibility in parts of the Darjeeling Himalayas using a relatively simple bivariate statistical technique. Seven factor layers with 24 categories, responsible for landslide occurrences in this area, are prepared from Cartosat and Resourcesat — 1 LISS-IV MX data. Each category was given a weight using the Information Value Method. Weighted sum of these values were used to prepare a landslide susceptibility map. The result shows that 8% area was predicted for high, 32% for moderate and remaining 60% for low landslide susceptibility zones. The high value (0.89) of the area under the receiver operating characteristic curve showed the high accuracy of the prediction model. 相似文献
The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change.Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time. 相似文献
Among the activities developed under the framework of the Global Earthquake Model, the development of a global consequences database was included. This was defined with the objective of serving as public repository of damages and losses, occurred on different types of elements because of a selected list of earthquakes with epicentres at varying locations around the globe, but also to be used as a benchmark for the development of vulnerability models that capture specific characteristics of the building typologies in each country. The online earthquakes consequences’ database has information on 71 events where 16 of them occurred in the Latin America and the Caribbean Region. A complete and comprehensive review and data gathering process were developed for these selected earthquakes accounting for different aspects and dimensions that were considered of interest, besides the physical damage, such as casualties, socio-economic implications, damages and disruptions in critical facilities and infrastructures, together with the occurrence of secondary events triggered by the ground shaking such as landslides and tsunamis. When possible, the damage and casualties were geo-located using a standardized approach and included in the database. The contributions of the Latin America and Caribbean Region to the database were at the same time a challenge and an opportunity to collect, review, put together and standardize, up to a certain point, damage data of previous earthquakes additionally of being a step forward in the field of open data.