Estimation of regional evapotranspiration over the North China Plain using geostationary satellite data     

Yunqiao Shu  Simon Stisen  Karsten H. Jensen  Inge Sandholt 《International Journal of Applied Earth Observation and Geoinformation》2011

Data from the first operational Chinese geostationary satellite Fengyun-2C (FY-2C) satellite are applied in combination with Moderate Resolution Imaging Spectroradiometer (MODIS) satellite products for the assessment of regional evapotranspiration over the North China Plain. The approach is based on the improved triangle method, where the temperature–vegetation index space includes thermal inertia. Two thermal infrared channels from FY-2C are used to estimate surface temperature (Ts) based on a split window algorithm originally proposed for the MSG-SEVIRI sensor. Subsequently the high temporal resolution of FY-2C data is exploited to give the morning rise in Ts. Combined with the 16 days composite MODIS vegetation indices product (MOD13) at a spatial resolution of 5 km, evaporative fraction (EF) is estimated by interpolation in the ΔTs–NDVI triangular-shaped scatter space. Finally, regional actual evapotranspiration (ET) is derived from the evaporative fraction and available energy estimated from MODIS surface albedo products MCD43. Spatial variations of estimated surface variables (Ts, EF and ET) corresponded well to land cover patterns and farmland management practices. Estimated ET and EF also compared well to lysimeter data collected for the period June 2005–September 2007. The improved triangle method was also applied to MODIS products for comparison. Estimates based on FY-2C products proved to provide slightly better results than those based on MODIS products. The consistency of the estimated spatial variation with other spatial data supports the use of FY-2C data for ET estimation using the improved triangle method. Of particular value is the high temporal frequency of image acquisitions from FY-2C which improves the likelihood of obtaining cloud free image acquisitions as compared to polar orbiting sensors like MODIS.  相似文献   

Invasion genetics of Pacific oyster Crassostrea gigas shaped by aquaculture stocking practices     

Jenny Moehler  K. Mathias Wegner  Karsten Reise  Sabine Jacobsen 《Journal of Sea Research》2011,66(3):256-262

As a result of aquaculture activities Pacific oysters Crassostrea gigas (Thunberg, 1793) have invaded the European Wadden Sea. Using a variable noncoding mitochondrial marker, we show that the invaded range is the result of two independent invasions. Haplotype frequencies point towards two separate groups, one in the southern and the other in the northern Wadden Sea. We found virtually no genetic differentiation throughout the southern range and the putative source from British Columbia, Canada, suggesting that the Southern region can be considered as a closed population. In the North, mismatch distributions, haplotype ordination and isolation-by-distance analysis suggest a stronger, persistent impact of aquaculture on invasive populations. Due to the ongoing supply of new genetic material from hatchery production the northern invasive populations can therefore be considered as an open population highlighting the importance of aquaculture practice on the genetics of this keystone invader in the Wadden Sea.  相似文献   

Measuring Thermo-Mechanical Properties of Cometary Surfaces: In Situ Methods     

Kömle  Norbert I.  Kargl  Günter  Seiferlin  Karsten  Marczewski  Wojiech 《Earth, Moon, and Planets》2002,90(1-4):269-282

Thermal and mechanical properties of cometary ices are closely associated with eachother. Both are largely determined by the texture (porosity, grain size distribution,grade of sintering) of the material. The surface probe of the Rosetta mission to comet46P/Wirtanen (Rosetta Lander) will for the first time measure these thermo-mechanical keyparameters in situ, using a hammering device, a drill, and anchors to be shot intothe ground by pyrotechnical means. Several of these components are associated to theexperiment MUPUS (MUlti-PUrpose-Sensors forsurface and sub-surface science). The development of this instrument has now reached amature state, as the flight model is already delivered and integrated with thespacecraft. We describe the main aspects of the experiment, outline the evaluationmethods, and show representative results from test measurements.  相似文献   

Rift processes and crustal structure of the Amundsen Sea Embayment,West Antarctica,from 3D potential field modelling     

Thomas Kalberg  Karsten Gohl  Graeme Eagles  Cornelia Spiegel 《Marine Geophysical Researches》2015,36(4):263-279

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A three-dimensional model study on processes of stratification and de-stratification in the Limfjord     

Richard Hofmeister  Hans Burchard  Karsten Bolding 《Continental Shelf Research》2009,29(11-12):1515-1524

Investigations on stratifying and de-stratifying processes in the Limfjord in Denmark, stretching from the North Sea at the western end to the Kattegat at the eastern end, were carried out. The forcing of the Limfjord is dominated by mean sea surface elevation and salinity gradients, diffuse freshwater supply, as well as episodic saline inflow events from the North Sea boundary. The physical regime of the Limfjord switches periodically from stratified to mixed conditions. In order to investigate the complexity of the system, a realistic three-dimensional high-resolution numerical model study was conducted for the year 2003. The results are based on, and compared to, available field data. A central subject of this study is the anomaly of potential energy as a measure for stratification. The stratifying and de-stratifying processes are identified as contributing terms in a dynamic equation for the potential energy anomaly. The comparison of model results and observations shows that the model has the capability of reproducing the observed physical regimes. Changes in the simulated stratification turn out to be a complex interaction of differential advection, heating and turbulent mixing in the central Limfjord.  相似文献   

A geophysical survey of the De Gerlache Seamounts: preliminary results     

Rick A. Hagen  Karsten Gohl  Rainer Gersonde  Gehard Kuhn  David Völker  V. N. Kodagali 《Geo-Marine Letters》1998,18(1):19-25

 The De Gerlache Seamounts actually consist of two medium-sized guyots, with summits at depths of 350–600 m. Acoustic profiler data show no significant sediment on these guyots. Alkaline basalts dredged from the summit of the eastern guyot yield K/Ar ages between 20.1±1.0 and 23.2±1.2 Ma. Basement ridges and sediment-filled troughs between the guyots are associated with the prominent gravity anomaly extending north from the Antarctic margin. This structure possibly played a role in the guyot formation, however, the question of how the De Gerlache Seamounts are related to this gravity anomaly remains uncertain. Received: 13 February 1997 / Revision received: 30 September 1997  相似文献   

Documentation of Istanbul Historic Peninsula by Kinematic Terrestrial Laser Scanning     

Thomas P.  Kersten  Gürcan  Büyüksal&#;h  &#;brah&#;m  Baz  Karsten  Jacobsen 《The Photogrammetric Record》2009,24(126):122-138

Although the Historic Peninsula of old Istanbul was added to the UNESCO World Heritage List in 1985, complete documentation of this important area has not yet been carried out. In 2006 the Istanbul Metropolitan Municipality's Historical Environment Protection Directorate initiated the "Historic Peninsula Project", which covers an area of 1500 ha and includes approximately 48 000 buildings in crowded and frequently narrow streets. BİMTAŞ, a company owned by the Municipality, immediately started the documentation of all buildings in the project area using terrestrial laser scanning. This created the challenge of building up an efficient production environment with new high-end technology to fulfil the requirements of this project in a very short timeframe of 2 years. This paper describes the entire production environment for documentation of all buildings, detailing the frequent adaptations of the process resulting from learning on the job. Although the data acquisition and mapping environment was established in the course of production, it was always essential to optimise the technical solutions in order to meet the requirements for data quality and delivery deadlines. Only 80 ha of the required 1500 ha was completed using static scanning during the first 6 months, thus requiring a change from static to mobile terrestrial laser scanning in order to accelerate the work and to conclude the scanning phase for the remaining major area within 3 months.  相似文献   

Multi-Constrained Catchment Scale Optimization of Groundwater Abstraction Using Linear Programming     

Mehrdis Danapour  Michael N. Fienen  Anker Lajer Højberg  Karsten Høgh Jensen  Simon Stisen 《Ground water》2021,59(4):503-516

Due to increasing water demands globally, freshwater ecosystems are under constant pressure. Groundwater resources, as the main source of accessible freshwater, are crucially important for irrigation worldwide. Over-abstraction of groundwater leads to declines in groundwater levels; consequently, the groundwater inflow to streams decreases. The reduction in baseflow and alteration of the streamflow regime can potentially have an adverse effect on groundwater-dependent ecosystems. A spatially distributed, coupled groundwater–surface water model can simulate the impacts of groundwater abstraction on aquatic ecosystems. A constrained optimization algorithm and a simulation model in combination can provide an objective tool for the water practitioner to evaluate the interplay between economic benefits of groundwater abstractions and requirements to environmental flow. In this study, a holistic catchment-scale groundwater abstraction optimization framework has been developed that allows for a spatially explicit optimization of groundwater abstraction, while fulfilling a predefined maximum allowed reduction of streamflow (baseflow [Q95] or median flow [Q50]) as constraint criteria for 1484 stream locations across the catchment. A balanced K-Means clustering method was implemented to reduce the computational burden of the optimization. The model parameters and observation uncertainties calculated based on Bayesian linear theory allow for a risk assessment on the optimized groundwater abstraction values. The results from different optimization scenarios indicated that using the linear programming optimization algorithm in conjunction with integrated models provides valuable information for guiding the water practitioners in designing an effective groundwater abstraction plan with the consideration of environmental flow criteria important for the ecological status of the entire system.  相似文献   

Six circumpolar currents—on the forcing of the Antarctic Circumpolar Current by wind and mixing     

Dirk Olbers  Karsten Lettmann  Ralph Timmermann 《Ocean Dynamics》2007,57(1):12-31

The transport of the Antarctic Circumpolar Current (ACC) is influenced by a variety of processes and parameters. A proper implementation of basin geometry, ocean topography and baroclinicity is known to be a fundamental requisite for a realistic simulation of the circulation and transport. Other, more subtle parameters are those of eddy-induced transports and diapycnal mixing of thermohaline tracers or buoyancy, either treated by eddy resolution or by a proper parameterization. Quite a number of realistic numerical simulations of the circulation in the Southern Ocean have recently been published. Many concepts on relations of the ACC transport to model parameters and forcing function are in discussion, however, without much generality and little success. We present a series of numerical simulations of circumpolar flow with a simplified numerical model, ranging from flat-bottom wind-driven flow to baroclinic flow with realistic topography and wind and buoyancy forcing. Analysis of the balances of momentum, vorticity, and baroclinic potential energy enables us to develop a new transport theory, which combines the most important mechanisms driving the circulation of the ACC and determining its zonal transport. The theory is based on the importance of the bottom vertical velocity in generating vorticity and shaping the baroclinic potential energy of the ACC. It explains the breaking of the -constraint by baroclinicity and brings together in one equation the wind and buoyancy forcing of the current. The theory emphasizes the role of Ekman pumping and eddy diffusion of buoyancy to determine the transport. It also demonstrates that eddy viscosity effects are irrelevant in the barotropic vorticity balance and that friction arises via eddy diffusion of density. In this regime, the classical Stommel model of vorticity balance is revived where the bottom friction coefficient is replaced by (with the Gent–McWilliams coefficient and the baroclinic Rossby radius ) and a modified wind curl forcing appears.  相似文献   

International viewpoint and news     

Karsten Gohl  Alan Haywood 《Environmental Geology》2009,56(6):1249-1250

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