Accuracy assessment of the MODIS snow products

A suite of Moderate‐Resolution Imaging Spectroradiometer (MODIS) snow products at various spatial and temporal resolutions from the Terra satellite has been available since February 2000. Standard products include daily and 8‐day composite 500 m resolution swath and tile products (which include fractional snow cover (FSC) and snow albedo), and 0·05° resolution products on a climate‐modelling grid (CMG) (which also include FSC). These snow products (from Collection 4 (C4) reprocessing) are mature and most have been validated to varying degrees and are available to order through the National Snow and Ice Data Center. The overall absolute accuracy of the well‐studied 500 m resolution swath (MOD10_L2) and daily tile (MOD10A1) products is ～93%, but varies by land‐cover type and snow condition. The most frequent errors are due to snow/cloud discrimination problems, however, improvements in the MODIS cloud mask, an input product, have occurred in ‘Collection 5’ reprocessing. Detection of very thin snow (<1 cm thick) can also be problematic. Validation of MOD10_L2 and MOD10A1 applies to all higher‐level products because all the higher‐level products are all created from these products. The composited products may have larger errors due, in part, to errors propagated from daily products. Recently, new products have been developed. A fractional snow cover algorithm for the 500 m resolution products was developed, and is part of the C5 daily swath and tile products; a monthly CMG snow product at 0·05° resolution and a daily 0·25° resolution CMG snow product are also now available. Similar, but not identical products are also produced from the MODIS on the Aqua satellite, launched in May 2002, but the accuracy of those products has not yet been assessed in detail. Published in 2007 by John Wiley & Sons, Ltd.     

Imprecise probabilities of climate change: aggregation of fuzzy scenarios and model uncertainties

Whilst the majority of the climate research community is now set upon the objective of generating probabilistic predictions of climate change, disconcerting reservations persist. Attempts to construct probability distributions over socio-economic scenarios are doggedly resisted. Variation between published probability distributions of climate sensitivity attests to incomplete knowledge of the prior distributions of critical parameters and structural uncertainties in climate models. In this paper we address these concerns by adopting an imprecise probability approach. We think of socio-economic scenarios as fuzzy linguistic constructs. Any precise emissions trajectory (which is required for climate modelling) can be thought of as having a degree of membership in a fuzzy scenario. Next, it is demonstrated how fuzzy scenarios can be propagated through a low-dimensional climate model, MAGICC. Fuzzy scenario uncertainties and imprecise probabilistic representation of climate model uncertainties are combined using random set theory to generate lower and upper cumulative probability distributions for Global Mean Temperature anomaly. Finally we illustrate how non-additive measures provide a flexible framework for aggregation of scenarios, which can represent some of the semantics of socio-economic scenarios that defy conventional probabilistic representation.     

Reduction in organic contaminant exposure and resultant hepatic hydropic vacuolation in winter flounder (Pseudopleuronectes americanus) following improved effluent quality and relocation of the Boston sewage outfall into Massachusetts Bay, USA: 1987-2003

Effluent upgrades for metropolitan Boston have included toxicant reduction, primary and secondary treatment and outfall extension. Between 1992 and 2003 winter flounder at five stations were surveyed annually for liver and muscle burden and chronic hepatic sub-lethal impacts of polynuclear and halogenated aromatic hydrocarbons, and metals. Trends in flounder availability and fin condition were also examined. In 1988 12% of the adult winter flounder in Boston Harbor exhibited hepatic neoplasms and up to 80% had hepatic hydropic vacuolation (HV). Tumor prevalence fell to 0-2% and HV to <50% by 1996. Since then tumors have been absent, while a steady prevalence of HV has persisted, consistent with lower hydrocarbon loading and tissue levels. Contaminants and HV also fell with distance from the Boston outfall. After the outfall extension was activated in 2000, there has been no significant change in flounder liver health at the new outfall site.     

Seasonal changes in the distribution and exchange of inorganic nitrogen between sediment and water in the Northern Baltic (Gulf of Bothnia)

The concentration profiles of nitrate plus nitrite, ammonium, and redox potential in sediment and water column were determined in late winter and summer at a sampling site off Norrbyn, northern Sweden, in the Gulf of Bothnia. The sediment had an oxidized surface layer during winter and spring, and nitrification occurred. Nitrate but not ammonium was present in the water column at this time. During summer a layer of planktonic detritus was deposited onto the sediment and led to its deoxygenation and reduction. Ammonium was then the predominant form of inorganic nitrogen in the water column.Laboratory experiments confirmed that nitrification in the surface layer of sediment prevented ammonium export during winter. Enhanced temperature or organic detritus deoxygenated the surface sediment and inhibited nitrification, and export of ammonium from the sediment increased. Although nitrification was important in determining the flow of nitrogen in the sediment it accounted for at most only 5% of the total oxygen uptake by the sediment.     

Sensitivity,responsivity, stability and irreversibility as multiple objectives in civil systems

This paper recommends the consideration of sensitivity, stability, risk, and irreversibility as objective functions in water resource management models within the framework of multiobjective analysis. Six major sources of uncertainties and errors in systems modeling are identified. They are associated with the following model characteristics: model structure (topology), model parameters, model scope or focus, data, optimization technique, and human subjectivity. In particular, the major objective of this paper is to set the stage for the development of an analytical and operational multiobjective framework which will provide decision-makers and plamers with alternatives that consider systems' sensitivity, responsivity, stability and irreversibility along with cost and other performance indices as multiple objectives. This type of a framework should have a very wide spectrum of applications in water and related land resources, environmental studies, energy, and others. The Surrogate Worth Trade-off method is proposed for the solution of the resulting multiobjective optimization problem.     

The British Tertiary igneous province: palaeomagnetism of the Arran dykes

Summary. Five hundred and sixteen sites in Arran were sampled. After cleaning by heating and/or alternating fields 87 per cent yielded directions with α₉₅ < 10°, comprising 435 dykes, 12 sills and one granite; polarities could be determined for some of the remainder. Directions are thought to be primary and on average are shallower than corresponds to the mean centred axial dipole, with many shallow reversely-magnetized dykes present.
Seventeen per cent of the dykes are normally magnetized, 5 per cent have intermediate directions. Polarity does not correlate with petrography, thickness or trend, but does depend upon location. In particular, on the NE coast up to 70 per cent are normal, and possibly belong to a different swarm.
Normal polarities were found for both sites in the Northern Granite, for Holy Island and for some of the sills. In conjunction with the known stratigraphy this shows that the rocks were formed during an R-N-R sequence of polarities, or more probably R-N-R-N. Using the radiometric age of 58 Ma for the Northern Granite and the best estimate of the polarity time-scale the duration of activity was probably in the range 0.5 to 3.4 Ma if three polarity periods were involved, and 3.4 to 4.4 Ma if four were involved.     

The prospects for life on Mars: A pre-Viking assessment

Mariner 9 has provided a refutation or reinterpretation of several historical claims for Martian biology, and has permitted an important further characterization of the environmental constraints on possible Martian organisms. Four classes of conceivable Martian organisms are identified, depending on the environmental temperature, T, and water activity, a_w: Class I, high T, high a_w; Class II, low T, high a_w; Class III, high T, low a_w; and Class IV, low T, low a_w. The Viking lander biology experiments are essentially oriented toward Class I organisms, although arguments are given for the conceivable presence on Mars of organisms in any of the four classes. Organisms which extract their water requirements from hydrated minerals or from ice are considered possible on Mars, and the high ultraviolet flux and low oxygen partial pressure are considered to be negligible impediments to Martian biology. Large organisms, possibly detectable by the Viking lander cameras, are not only possible on Mars; they may be favored. The surface distribution of Martian organisms and future search strategies for life on Mars are discussed.     

Symmetries in the Optimal Control of Solar Sail Spacecraft

The theory of optimal control is applied to obtain minimum-time trajectories for solar sail spacecraft for interplanetary missions. We consider the gravitational and solar radiation forces due to the Sun. The spacecraft is modelled as a flat sail of mass m and surface area A and is treated dynamically as a point mass. Coplanar circular orbits are assumed for the planets. We obtain optimal trajectories for several interrelated problem families and develop symmetry properties that can be used to simplify the solution-finding process. For the minimum-time planet rendezvous problem we identify different solution branches resulting in multiple solutions to the associated boundary value problem. We solve the optimal control problem via an indirect method using an efficient cascaded computational scheme. The global optimizer uses a technique called Adaptive Simulated Annealing. Newton and Quasi-Newton Methods perform the terminal fine tuning of the optimization parameters.