Comparison between the Shkuratov and Hapke Scattering Theories for Solid Planetary Surfaces: Application to the Surface Composition of Two Centaurs

This project examines the different approaches which deal with the theory of radiative transfer on atmosphereless bodies. We present the relative merits of two scattering theories based on the equivalent slab model: the extensively used Hapke theory (Hapke 1981, J. Geophys. Res.86, 3039-3054) and the Shkuratov theory (Shkuratov et al. 1999, Icarus141, 132-155). We found that their main difference is the role of the phase function of individual particles of regolith, which is predicted (and generally forward directed) in the case of the Shkuratov model instead of being a free parameter as formulated in the Hapke model. We also emphasize that different assumptions as to the manner in which different constituents are physically mixed in either model have a substantial effect on the synthetic spectra inferred. This leads to a significant extension of the validity of Hapke's or similar practical approaches to areas where these approaches are valid.We used two objects (the Centaurs 5145 Pholus and 8405 Asbolus) as examples. Previous modeling of the spectra of these two bodies with the Hapke approach gave suspect results in terms of the derived grain sizes, which were smaller than the wavelength, violating key assumptions of the model (Cruikshank et al. 1998, Icarus135, 389-407 for Pholus; Barucci et al. 2000, Astron. Astrophys.357, L53-56 for Asbolus). We considered several different types of powdered surfaces to interpret the surface composition of these two Centaurs. The effect of fine-scale contamination of water ice grains by small amounts of carbon and/or tholins is also explored. We can explain the strong red color and the rich near-infrared spectral signatures of Pholus using a five-component surface (contaminated water ice, amorphous carbon, Titan tholin, olivine, and methanol ice) where the grain sizes are consistent with the model assumptions. These components are similar to those inferred by Cruikshank et al. (1998), but we obtain very different grain sizes and relative abundances. For example, we obtain a relative abundance of water ice on the surface of Pholus of about 40% instead of 6% found with the Hapke model. Organic and carbonaceous components change by similar amounts. In the case of Asbolus, a tholin and amorphous carbon areal mixture can reproduce the spectrum, with water remaining at 9% or less. Using the albedo published by Fernandez et al. (2002, Astron. J.123, 1050-1055) which is higher than most workers assume for Centaurs and Kuiper belt objects, a surface composition similar to that of Pholus is found. It appears that model-based uncertainties in relative compositions must be regarded with more attention.     

A deep Giant Metre-wave Radio Telescope 610-MHz survey of the 1HXMM–Newton/Chandra survey field

We present the results of a deep 610-MHz survey of the 1 ^H XMM–Newton / Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ∼7 arcsec and an rms noise limit of 60 μJy. To a 5σ detection limit of 300 μJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ∼2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of −0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e.  ' Q '= 2.45^+0.3_−0.4  ).     

Retrieval algorithm for atmospheric dust properties from Mars Global Surveyor Thermal Emission Spectrometer data during global dust storm 2001A

We present a new parameter retrieval algorithm for Mars Global Surveyor Thermal Emission Spectrometer data. The algorithm uses Newtonian first-order sensitivity functions of the infrared spectrum in response to variations in physical parameters to fit a model spectrum to the data at 499, 1099, and 1301 cm⁻¹. The algorithm iteratively fits the model spectrum to data to simultaneously retrieve dust extinction optical depth, effective radius, and surface temperature. There are several sources of uncertainty in the results. The assumed dust vertical distribution can introduce errors in retrieved optical depth of a few tens of percent. The assumed dust optical constants can introduce errors in both optical depth and effective radius, although the systematic nature of these errors will not affect retrieval of trends in these parameters. The algorithm does not include the spectral signature of water ice, and hence data needs to be filtered against this parameter before the algorithm is applied. The algorithm also needs sufficient dust spectral signature, and hence surface-to-atmosphere temperature contrast, to successfully retrieve the parameters. After the application of data filters the algorithm is both relatively accurate and very fast, successfully retrieving parameters, as well as meaningful parameter variability and trends from tens of thousands of individual spectra on a global scale (Elteto, A., Toon, O.B. [2010]. Icarus, this issue). Our results for optical depth compare well with TES archive values when corrected by the single scattering albedo. Our results are on average 1–4 K higher in surface temperatures from the TES archive values, with greater differences at higher optical depths. Our retrieval of dust effective radii compare well with the retrievals of Wolff and Clancy (Wolff, M.J., Clancy, R.T. [2003]. J. Geophys. Res. 108 (E9), 5097) for the corresponding data selections from the same orbits.     

Spatiotemporal variability in channel deformations on rivers of Russia

We assess the spatiotemporal changes in channel processes on rivers of Russia, determine the causes for vertical (incision or directional sediment accumulation) and horizontal (displacement of channel forms) deformations and show the distribution of stream channel of different morphodynamical types and with a different reconfiguration rate. The conditions are revealed, under which the channel types change over time. Particular emphasis is placed on the analysis of spatiotemporal changes in channels caused by anthropogenic disturbances and by direct technogenic interferences in the life of rivers (hydroelectric schemes, quarries in the river channels, and waterway dredging).     

Aluminum Consumption and Economic Growth: Evidence from Rich Countries

The article attempts to test the aluminum consumption–economic growth nexus for 20 rich economies for the period 1970–2009. Various panel data unit root and cointegration tests are applied. The series are found to be integrated of order one and cointegrated, especially after controlling for cross-sectional dependence. Moreover, the Blundell–Bond system generalized methods-of-moments is employed to conduct a panel causality test in a vector error-correction mechanism setting. Unidirectional causality running from aluminum consumption to real GDP is uncovered in the short-run, while real GDP is found to Granger-cause aluminum consumption in the long-run. Moreover, a 1% increase in real GDP generates an increase of 0.44% in aluminum consumption in the long-run for the whole panel.     

Automatic mapping of lunar landforms using DEM-derived geomorphometric parameters

Developing approaches to automate the analysis of the massive amounts of data sent back from the Moon will generate significant benefits for the field of lunar geomorphology. In this paper, we outline an automated method for mapping lunar landforms that is based on digital terrain analysis. An iterative self-organizing (ISO) cluster unsupervised classification enables the automatic mapping of landforms via a series of input raster bands that utilize six geomorphometric parameters. These parameters divide landforms into a number of spatially extended, topographically homogeneous segments that exhibit similar terrain attributes and neighborhood properties. To illustrate the applicability of our approach, we apply it to three representative test sites on the Moon, automatically presenting our results as a thematic landform map. We also quantitatively evaluated this approach using a series of confusion matrices, achieving overall accuracies as high as 83.34% and Kappa coefficients (K) as high as 0.77. An immediate version of our algorithm can also be applied for automatically mapping large-scale lunar landforms and for the quantitative comparison of lunar surface morphologies.     

Global temperature and monsoon activity

In this paper an attempt has been made to search a new parameter for the prediction of the Indian summer monsoon rainfall. For this purpose the relationship of the global surface-air temperature of four standard seasons viz., Winter (December-January-February), Spring (March-April-May), Summer (June-July-August), Autumn (September-October-November) with the Indian summer monsoon rainfall has been carried out. The same analysis is also carried out with surface-air temperature anomalies within the tropical belt (30°S to 30°N) and Indian summer monsoon rainfall. For the present study data for 30 years period from 1958 to 1988 have been used. The analysis reveals that there is a strong inverse relationship between the monsoon activity and the tropical belt temperature.     

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar?Cheliospheric?Cplanetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March??C?16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth??s mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.