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Estimation of near surface soil moisture in a sloping terrain of a Himalayan watershed using ENVISAT ASAR multi‐incidence angle alternate polarisation data 
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下载免费PDF全文 Soil moisture is one of the important input variables in hydrological and water erosion models. The extraction of information on near surface soil moisture from synthetic aperture radar (SAR) is well established mostly for flat terrain and using low incidence angle single polarisation data. The ENVISAT advanced SAR (ASAR) data available in multiple incidence angles and alternate polarisation modes were investigated in this study for soil moisture estimation in sloping terrain. The test site was Sitla Rao watershed in the Lesser Himalayas of northern India. Empirical models were developed to estimate near surface soil moisture in bare agricultural fields using alternate polarisation ASAR data. Both soil moisture and surface roughness field measurements were performed during the satellite passes. Backscatter from medium incidence angle (IS‐4) and vertical‐vertical (VV) polarisation signal is correlated better with volumetric soil moisture content compared to other incidence angles. The model parameters were further improved, and soil moisture estimation was refined by combining medium incidence angle (IS4) vertical‐horizontal polarisation response as another variable along with VV polarisation response. The effect of slope on the radar backscatter was minimized by incorporating local incidence angles derived from an ASTER DEM. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Decadal prediction skill in a multi-model ensemble 总被引：4，自引：3，他引：1
Geert Jan van Oldenborgh Francisco J. Doblas-Reyes Bert Wouters Wilco Hazeleger 《Climate Dynamics》2012,38(7-8):1263-1280
Decadal climate predictions may have skill due to predictable components in boundary conditions (mainly greenhouse gas concentrations but also tropospheric and stratospheric aerosol distributions) and initial conditions (mainly the ocean state). We investigate the skill of temperature and precipitation hindcasts from a multi-model ensemble of four climate forecast systems based on coupled ocean-atmosphere models. Regional variations in skill with and without trend are compared with similarly analysed uninitialised experiments to separate the trend due to monotonically increasing forcings from fluctuations around the trend due to the ocean initial state and aerosol forcings. In temperature most of the skill in both multi-model ensembles comes from the externally forced trends. The rise of the global mean temperature is represented well in the initialised hindcasts, but variations around the trend show little skill beyond the first year due to the absence of volcanic aerosols in the hindcasts and the unpredictability of ENSO. The models have non-trivial skill in hindcasts of North Atlantic sea surface temperature beyond the trend. This skill is highest in the northern North Atlantic in initialised experiments and in the subtropical North Atlantic in uninitialised simulations. A similar result is found in the Pacific Ocean, although the signal is less clear. The uninitialised simulations have good skill beyond the trend in the western North Pacific. The initialised experiments show some skill in the decadal ENSO region in the eastern Pacific, in agreement with previous studies. However, the results in this study are not statistically significant (p?≈?0.1) by themselves. The initialised models also show some skill in forecasting 4-year mean Sahel rainfall at lead times of 1 and 5?years, in agreement with the observed teleconnection from the Atlantic Ocean. Again, the skill is not statistically significant (p?≈?0.2). Furthermore, uninitialised simulations that include volcanic aerosols have similar skill. It is therefore still an open question whether initialisation improves predictions of Sahel rainfall. We conclude that the main source of skill in forecasting temperature is the trend forced by rising greenhouse gas concentrations. The ocean initial state contributes to skill in some regions, but variations in boundary forcings such as aerosols are as important in decadal forecasting. 相似文献
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Michael Mueller Willem Jellema Bertrand Delforge David Teyssier Martin Eggens Robert Huisman Geert Keizer 《Experimental Astronomy》2014,37(2):369-379
HIFI is a heterodyne spectrometer aboard the Herschel Space Observatory, providing high-spectral-resolution capabilities. Of its seven frequency bands, four (bands 3, 4, 6, and 7) employ Martin-Puplett diplexers to combine sky signal and local oscillator at the two linear polarizations H and V, prior to feeding them into the mixers (receivers). The optical path difference in each of these 8 diplexers must be tuned to the observed frequency. The required actuator currents were determined in flight before the start of routine science observations. We here report on regular (roughly quarterly) engineering test observations to validate the repeatability of the HIFI diplexers during the routine phase of Herschel operations. We find the optical path difference to be stable to within 0.4 % of the relevant wavelength, typically at the sub-micron level. We conclude that the repeatability and precision of the diplexer tuning mechanism are so high that science data are in no way negatively affected. With the diplexer calibration established and validated, this line of reasoning can be reversed, and the diplexers can be used as relative spectrometers to measure the local-oscillator frequency, i.e., to check the spectral purity of the local oscillator across the diplexer bands. This was done from before launch out to the last months of cryogenic operations in space. 相似文献
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The anthropogenic changes during boreal winter in the thermal and zonal flow structure over Eastern Atlantic and Western Europe (EAWE) have been investigated using an ensemble of CMIP3 and CMIP5 models. The ensemble mean change in the zonal wind at 500 hPa over this region is characterized by an eastward extension of the belt of zonal winds. Using the thermal wind relation these wind changes are found to be consistent with the changes in the tropospheric temperature profile. An enhanced warming is simulated in the subtropical upper troposphere and a relative surface cooling in the mid-latitudes. The subtropical upper tropospheric warming is related to the downward branch of the mean meridional circulation, whereas the mid-latitude lower tropospheric relative cooling is linked to the ocean processes that govern changes in its surface temperatures. Inter-model differences in the simulated change of the zonal wind over the EAWE by the CMIP3 and CMIP5 models relate well with differences in the upper tropospheric subtropical warming and the mid-latitude lower tropospheric relative cooling. The simulated change of the zonal wind over the EAWE region by the CMIP3 and CMIP5 models correlates well with changes in the meridional SST gradient. We conclude that uncertainties in the projected changes of the zonal flow over Europe are at least partly due to uncertainties in the response of the North Atlantic Ocean to increased levels of greenhouse gases. 相似文献
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Li Xiao-Feng Blenkinsop Stephen Barbero Renaud Yu Jingjing Lewis Elizabeth Lenderink Geert Guerreiro Selma Chan Steven Li Yafei Ali Haider Villalobos Herrera Roberto Kendon Elizabeth Fowler Hayley J. 《Climate Dynamics》2020,54(11):4823-4839
Climate Dynamics - We investigate the global distribution of hourly precipitation and its connections with the El Niño–Southern Oscillation (ENSO) using both satellite precipitation... 相似文献
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An overview is presented on possible mechanisms that control the leaching behaviour of the oxyanion forming elements As, Cr, Mo, Sb, Se, V and W in cementituous systems and alkaline solid wastes, such as municipal solid waste incinerator bottom ash, fly ash and air pollution control residues, coal fly ash and metallurgical slags. Although the leachability of these elements generally depends on their redox state, speciation measurements are not common. Therefore, experimental observations available in the literature are combined with a summary of the thermal behaviour of these elements to assess possible redox states in freshly produced alkaline wastes, given their origin at high temperature. Possible redox reactions occurring at room temperature, on the other hand, are reviewed because these may alter the initial redox state in alkaline wastes and their leachates. In many cases, precipitation of oxyanions as a pure metalate cannot provide a satisfactory explanation for their leaching behaviour. It is therefore highly likely that adsorption and solid solution formation with common minerals in alkaline waste and cement reduce the leachate concentration of oxyanions below pure-phase solubility. 相似文献
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Els Hannes Diana Kusumastuti Maikel León Espinosa Davy Janssens Koen Vanhoof Geert Wets 《Journal of Geographical Systems》2012,14(2):143-165
In this paper, the “mental map” concept is positioned with regard to individual travel behaviour to start with. Based on Ogden and Richards’ triangle of
meaning (The meaning of meaning: a study of the influence of language upon thought and of the science of symbolism. International
library of psychology, philosophy and scientific method. Routledge and Kegan Paul, London, 1966) distinct thoughts, referents and symbols originating from different scientific disciplines are identified and explained
in order to clear up the notion’s fuzziness. Next, the use of this concept in two major areas of research relevant to travel
demand modelling is indicated and discussed in detail: spatial cognition and decision-making. The relevance of these constructs
to understand and model individual travel behaviour is explained and current research efforts to implement these concepts
in travel demand models are addressed. Furthermore, these mental map notions are specified in two types of computational models,
i.e. a Bayesian Inference Network (BIN) and a Fuzzy Cognitive Map (FCM). Both models are explained, and a numerical and a
real-life example are provided. Both approaches yield a detailed quantitative representation of the mental map of decision-making
problems in travel behaviour. 相似文献
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Harald Geiger Ian Barnes Karl H. Becker Birger Bohn Theo Brauers Birgit Donner Hans-Peter Dorn Manfred Elend Carlos M. Freitas Dinis Dirk Grossmann Heinz Hass Holger Hein Axel Hoffmann Lars Hoppe Frank Hülsemann Dieter Kley Björn Klotz Hans G. Libuda Tobias Maurer Djuro Mihelcic Geert K. Moortgat Romeo Olariu Peter Neeb Dirk Poppe Lars Ruppert Claudia G. Sauer Oleg Shestakov Holger Somnitz William R. Stockwell Lars P. Thüner Andreas Wahner Peter Wiesen Friedhelm Zabel Reinhard Zellner Cornelius Zetzsch 《Journal of Atmospheric Chemistry》2002,42(1):323-357
Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere. 相似文献
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Andreas Sterl Geert Jan van Oldenborgh Wilco Hazeleger Gerrit Burgers 《Climate Dynamics》2007,29(5):469-485
Using observations covering the last 128 years we show that apparent changes in El Niño-Southern Oscillation (ENSO) teleconnections can be explained by chance and stem from sampling variability. This result is backed by experiments in which an atmosphere model is driven by 123 years of observed sea surface temperature. The possibility of ENSO teleconnection changes in a warming climate is further investigated using coupled GCMs driven by past and projected future greenhouse gas concentrations. These runs do not exclude physical changes in the teleconnection strength but do not agree on their magnitude and location. If existing at all, changes in the strength of ENSO teleconnection, other than obtained by chance, are small and will only be detectable on centennial time scales. 相似文献