Human activity and related land use change are the primary cause of accelerated soil erosion, which has substantial implications for nutrient and carbon cycling, land productivity and in turn, worldwide socio-economic conditions. Here we present an unprecedentedly high resolution (250 × 250 m) global potential soil erosion model, using a combination of remote sensing, GIS modelling and census data. We challenge the previous annual soil erosion reference values as our estimate, of 35.9 Pg yr−1 of soil eroded in 2012, is at least two times lower. Moreover, we estimate the spatial and temporal effects of land use change between 2001 and 2012 and the potential offset of the global application of conservation practices. Our findings indicate a potential overall increase in global soil erosion driven by cropland expansion. The greatest increases are predicted to occur in Sub-Saharan Africa, South America and Southeast Asia. The least developed economies have been found to experience the highest estimates of soil erosion rates.

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Over the oceans, approximately 90% of net radiation produces evaporation (Budyko, 1974), primarily in the tropics. Over continents, net radiation heats the surface, evaporates water from water bodies or moist soils, or provides plants with energy to remove water from soils (Pitman, 2003; Istanbulluoglu and Bras, ANALYSISAt the watershed scale, soil moisture is the major control for rainfall-runoff response, especially where saturation excess runoff processes dominate. From the ecological point of view, the pools of soil moisture are fundamental ecosystem resources providing the transpirable water for plants. In drylands particularly, soil moisture is one of the major controls on the structure, function, and diversity in ecosystems. In terms of the global hydrological cycle, the overall quantity of soil moisture is small, ∼0.05%; however, its importance to the global energy balance and the distribution of precipitation far outweighs its physical amount. In soils it governs microbial activity that aff ects important biogeochemical processes such as nitrifi cation and CO 2 production via respiration. During the past 20 years, technology has advanced considerably, with the development of diff erent electrical sensors for determining soil moisture at a point. However, modeling of watersheds requires areal averages. As a result, point measurements and modeling grid cell data requirements are generally incommensurate. We review advances in sensor technology, particularly emerging geophysical methods and distributed sensors, aimed at bridging this gap. We consider some of the data analysis methods for upscaling from a point to give an areal average. Finally, we conclude by off ering a vision for future research, listing many of the current scientifi c and technical challenges.

In the investigation of oculomotor systems and especially in the mathematical descriptions of them as pursuit, tracking and stabilizing systems, the need arises for a more exact knowledge of the mechanics of the eyeball, the extraocular muscles and the supporting tissues of the orbit, particularly of the way in which these factors permit the globe to respond to the efferent discharges arising in the oculomotor nuclei. In 1954 Westheimer proposed that the eye moved in a saccade by the application of a step function of net muscular force. He further proposed that the mechanical system was of second order, slightly underdamped and had a natural resonant frequency of about 120 radians per second (19 c/s). Alpern (1962) has discussed the inadequacy of this picture in view of the large burst of activity during a saccade recorded by extraocular electromyography (Bj6rk, 1955; Miller, 1958).The development of the suction contact lens has made practicable a closer investigation of the mechanics of the saccade, for it provides a simple method of applying known forces and loads to the eye while measuring subsequent rotations without fear of lens slippage. The evidence presented here will demonstrate that the system of eyeball and orbital tissues is heavily overdamped, has no resonant frequency and is little affected by the mass of the eyeball. It has an upper mechanical frequency response of only 1 c/s and it succeeds in making quick saccadic movements only under the impetus of a large, briefly applied, excess force delivered by the extraocular muscles. For example, in maintaining the eye 100 horizontally from the primary position the horizontal recti need apply a net force of only 15 g but during the saccade to reach that position they apply about 43 g during the first 40 msec of movement. METHODSThe experiments involved four procedures with the intact human eye and one with the lateral rectus of the cat. Three human, normal, adult, male subjects were used. The human experiments were conducted with normal room lighting illuminating a horizontal row of black dots spaced 50 apart on a white spherical background 1 m from the subject.

constant) of a material emerged as an elegant method of estimating water content in porous materials. For the Substantial advances in the measurement of water content and first time the same physical property (permittivity) could bulk soil electrical conductivity (EC) using time domain reflectometry be measured for a range of scales and used to estimate (TDR) have been made in the last two decades. The key to TDR's success is its ability to accurately measure the permittivity of a material water content. Electromagnetic methods, whether TDR and the fact that there is a good relationship between the permittivity (localized measurement), ground penetrating radar of a material and its water content. A further advantage is the ability (two-dimensional profile), or active microwave remote to estimate water content and measure bulk soil EC simultaneously sensing (land surface), all estimate water content based using TDR. The aim of this review is to summarize and examine on the permittivity of the target medium. A further advances that have been made in terms of measuring permittivity and advance was the development of analysis methods using bulk EC. The review examines issues such as the effective frequency TDR. Time domain reflectometry was adapted to estiof the TDR measurement and waveform analysis in dispersive dielecmate both soil water content (Hoekstra and Delaney, trics. The growing importance of both waveform simulation and in-1974; Topp et al., 1980) and soil bulk EC simultaneously verse analysis of waveforms is highlighted. Such methods hold great (Dalton et al., 1984). In spite of decades of research, potential for obtaining far more information from TDR waveform analysis. Probe design is considered in some detail and practical guid-we are only beginning to efficiently utilize electrical ance is given for probe construction. The importance of TDR measuretechnology that ranges from satellite and airborne radar ment sampling volume is considered and the relative energy storage to ground penetrating radar and localized sensors such density is modeled for a range of probe designs. Tables are provided as TDR and impedance probes. that compare some of the different aspects of commercial TDR equip-The underlying success of these techniques can be ment, and the units are discussed in terms of their performance and considered in two parts, the first of which is the equiptheir advantages and disadvantages. It is hoped that the review will ment's ability to accurately measure the bulk dielectric provide an informative guide to the more technical aspects of permitpermittivity and EC of a material. The second is the close tivity and EC measurement using TDR for the novice and expert alike.relationship between the measured permittivity and the volumetric water content, or the ionic concentration and the bulk EC of the material. This review concentrates