Band-Limited Analysis of Current Satellite-to-Satellite Tracking, Gradiometry and Combined Earth Gravity Models     

Dimitrios Tsoulis  Konstantinos Patlakis 《Surveys in Geophysics》2013,34(4):375-394

Several satellite-only gravity models based on the analysis of satellite-to-satellite tracking (SST) data have become available in the course of the last decade. The realization of the satellite missions CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery And Climate Experiment (GRACE) enabled the practical implementation of two modes of the SST principle, namely the high–low and the low–low SST. Though similar in their fundamental idea, which is the indirect observation of the gravity field based on the position of two satellites orbiting the Earth, the different architecture and geometrical layout of these techniques capture different fingerprints of the observed field. In the last few years, satellite-only gravity models based on the analysis of satellite gravity gradiometry (SGG) data became available and led to a new insight into the gravity field. The implementation of the SGG principle became possible after the launch of Gravity field and steady-state Ocean Circulation Explorer (GOCE), the first gravitational gradiometry mission. Based on the principle of differential accelerometry, GOCE provides the gravitational gradients which can be used in gravity field retrieval as primary observations of the field at satellite altitude. In the present study, we consider some of the current satellite-only and combined gravity models based on the analysis of CHAMP, GRACE, GOCE, gravimetry and altimetry data. In order to perform a thorough analysis of the models, we present an overview of tools for their quality assessment both in an absolute and relative sense in terms of computing spectral quantities, such as correlation or smoothing coefficients per degree and per order, attempting to demonstrate possible non-isotropic features in the models. Furthermore, typical geodetic measures in computing second-order derivatives, such as degree and order variances and difference variances, have been also evaluated for the same models, using the combined model EGM2008 as reference. Apart from these standard spectral assessment quantities, a systematic spatial representation of the second derivatives at satellite altitude has been performed. The combination of the two analysis steps (spectral and spatial) permits a first detailed assessment of the models, focusing especially on the identification of characteristic interpretable bandwidths.  相似文献   

Integrated Use of Optical and Radar Satellite Data for Active Faults and Corresponding Displaced Landforms in Kozani Basin (Greece)     

Parcharidis Issaak  Nikolakopoulos Konstantinos  Serelis Konstantinos  Baskoutas Ioannis 《国际地球制图》2013,28(3):17-23

Abstract

The usefulness of integration of SAR (ERS-1) and Landsat TM data for study active faults and the corresponding displaced landforms in flat or almost flat areas has been demonstrated. The study area is the Kozani basin which in May 13, 1995 was affected by a strong earthquake (Ms=6.6). After co-registration and resampling the two data sets were merged to form a combined image. The combined image offers the spectral characteristics of the TM data with the spatial resolution and roughness sensitivity of SAR images. The merging method used was the IMS to RGB transform. The criteria and parameters examined were geomorphic features, drainage network analysis, slope processes, terrain analysis, and observations on spatial distribution of soil cover as well as linear features that correspond to fracture zones crossing the basin. The use of the combined image allowed us to identify tectonic terraces in the basin produced by activity of normal faults located in the adjacent relief zone.  相似文献   

Herbage Production and Species Richness in Sub-alpine Grasslands of Different Soil Parent Material in Northern Greece     

MPOKOS J.Panagiotis  YIAKOULAKI D.Maria  PAPAZAFEIRIOU Z.Agapi  SGARDELIS Stefanos  ALIFRAGIS Dimitrios  PAPANIKOLAOU Konstantinos 《山地科学学报》2014,(6):1579-1592

Several abiotic and biotic factors were investigated as possible predictors of local species richness in two sub-alpine grasslands of Jenna and Belles Mountains in Northern Greece.For species richness modelling a hierarchical modelling framework based on generalized additive models was adopted.The two sub-alpine grasslands differed in aspect,altitude and soil parent material（volcanic origin,mostly trachyte,and andesite（TA） for Jenna and metamorphic rocks,mostly gneiss（G） for Belles）.12 fenced squared plots,16 m2 each,were used per grassland,where soil properties,herbage production,species presence and cover of grasses,legumes and forbs were estimated.Mean herbage production was significantly affected by slope and altitude,soil K content and floristic composition as expressed by an ordination axis.Soil p H,floristic composition and average herbage production were significant predictors of forbs and total species richness.For the former,soil N content and for the latter the occurrence of Agrostis capillaris,were also included as significant terms in the predictive model.Thepredictors for grasses species richness were N content,having a positive effect,and average herbage production.In all cases higher species richness was predicted for intermediate values of average herbage production.Differential responses were found between forbs and grasses.The predictors of their species richness were different while for the case of the common predictor（N） the responses of the two groups were also different（grasses species numbers increase and forbs species numbers decreased with increasing N）.Maximum species richness of grasses was observed at relatively low production levels while forbs species richness maximized at relatively high production levels.  相似文献   

A BME solution of the stochastic three-dimensional Laplace equation representing a geothermal field subject to site-specific information     

George Papantonopoulos  Konstantinos Modis 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(1-2):23-32

This work develops a model of the geothermal field in the Nea Kessani region (Greece) by means of the Bayesian maximum entropy (BME) method, which describes the temperature variations across space in the underground geological formations. The geothermal field is formed by a thermal reservoir consisting of arcosic sandstones. The temperature distribution vs depth was first investigated by the Greek Institute of Geology and Mineral Exploration (IGME) using measurements in a set of vertical drill holes. These measurements showed that hot fluids rising from the deep enter the reservoir in a restricted area of the field and flow towards local thermal springs. The field modelling, which was based on the powerful BME concept, involves the solution of a stochastic partial differential equation that assimilates important site-specific information. The stochastic three-dimensional steady-state Laplace equation was considered as general knowledge and the drilling exploration data were used to construct the specificatory knowledge base in the BME terminology. The produced map is more informative and, in general, it gives higher temperature estimates compared to previous studies of the same region. This is also in agreement with the quartz geothermometry analysis carried out by IGME.  相似文献   

Assimilating remotely sensed snow observations into a macroscale hydrology model   总被引：1，自引：0，他引：1  

Konstantinos M. Andreadis  Dennis P. Lettenmaier 《Advances in water resources》2006

Accurate forecasting of snow properties is important for effective water resources management, especially in mountainous areas like the western United States. Current model-based forecasting approaches are limited by model biases and input data uncertainties. Remote sensing offers an opportunity for observation of snow properties, like areal extent and water equivalent, over larger areas. Data assimilation provides a framework for optimally merging information from remotely sensed observations and hydrologic model predictions. An ensemble Kalman filter (EnKF) was used to assimilate remotely sensed snow observations into the variable infiltration capacity (VIC) macroscale hydrologic model over the Snake River basin. The snow cover extent (SCE) product from the moderate resolution imaging spectroradiometer (MODIS) flown on the NASA Terra satellite was used to update VIC snow water equivalent (SWE), for a period of four consecutive winters (1999–2003). A simple snow depletion curve model was used for the necessary SWE–SCE inversion. The results showed that the EnKF is an effective and operationally feasible solution; the filter successfully updated model SCE predictions to better agree with the MODIS observations and ground surface measurements. Comparisons of the VIC SWE estimates following updating with surface SWE observations (from the NRCS SNOTEL network) indicated that the filter performance was a modest improvement over the open-loop (un-updated) simulations. This improvement was more evident for lower to middle elevations, and during snowmelt, while during accumulation the filter and open-loop estimates were very close on average. Subsequently, a preliminary assessment of the potential for assimilating the SWE product from the advanced microwave scanning radiometer (AMSR-E, flown on board the NASA Aqua satellite) was conducted. The results were not encouraging, and appeared to reflect large errors in the AMSR-E SWE product, which were also apparent in comparisons with SNOTEL data.  相似文献   

Seismicity characteristics of a potentially active Quaternary volcano: The Tatun Volcano Group, northern Taiwan     

Konstantinos I. Konstantinou  Cheng-Horng Lin  Wen-Tzong Liang 《Journal of Volcanology and Geothermal Research》2007,160(3-4):300-318

The Tatun Volcano Group (TVG) is located at the northern tip of Taiwan, near the capital Taipei and close to two nuclear power plants. Because of lack of any activity in historical times it has been classified as an extinct volcano, even though more recent studies suggest that TVG might have been active during the last 20 ka. In May 2003 a seismic monitoring project at the TVG area was initiated by deploying eight three-component seismic stations some of them equipped with both short-period and broadband sensors. During the 18 months observation period local seismicity mainly consisted of high frequency earthquakes either occurring as isolated events, or as a continuous sequence in the form of spasmodic bursts. Mixed and low frequency events were also present during the same period, even though they occurred only rarely. Arrival times from events with clear P-/S-wave phases were inverted in order to obtain a minimum 1D velocity model with station corrections. Probabilistic nonlinear earthquake locations were calculated for all these events using the newly derived velocity model. Most high frequency seismicity appeared to be concentrated near the areas of hydrothermal activity, forming tight clusters at depths shallower than 4 km. Relative locations, calculated using the double-difference method and utilising catalogue and cross-correlation differential traveltimes, showed insignificant differences when compared to the nonlinear probabilistic locations. In general, seismicity in the TVG area seems to be primarily driven by circulation of hydrothermal fluids as indicated by the occurrence of spasmodic bursts, mixed/low frequency events and a b-value (1.17 ± 0.1) higher than in any other part of Taiwan. These observations, that are similar to those reported in other dormant Quaternary volcanoes, indicate that a magma chamber may still exist beneath TVG and that a future eruption or period of unrest should not be considered unlikely.  相似文献   

Analysis of broad-band regional waveforms of the 1996 September 29 earthquake at Bárdarbunga volcano, central Iceland: investigation of the magma injection hypothesis     

Konstantinos I. Konstantinou  Honn Kao  Cheng-Horng Lin  Wen-Tzong Liang 《Geophysical Journal International》2003,154(1):134-145

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Climatic variability and the anchovy/sardine ratio in Hellenic waters     

I. Konstantinos Stergiou  Alex Lascaratos 《GeoJournal》1997,41(3):245-254

In the present work, the monthly anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) commercial catches, the anchovy/sardine commercial catch ratio as well as different climatic parameters in Hellenic waters (air and sea surface temperature AIRT and SST, sea level pressure SLP, N-S wind component NSW, and wind speed cubed WISC) over the 1964 to 1989 period were analyzed using spectral and cross-spectral analyses. The monthly anchovy and sardine catches as well as the anchovy/sardine catch ratio all exhibited a pronounced seasonal cycle that is related to the behaviour of sardine and anchovy and the nature of the purse seine fishery. Spectral analysis of the monthly sardine catches and anchovy/sardine catch ratio in the Hellenic waters also revealed cycles of 2.7 yr whereas that of anchovy catches revealed a prominent peak at 4.6 yr and secondary ones at 3.6 and 1.9 yr. Cross-spectral analysis resolved significant coherence between the anchovy/sardine ratio and SLP at 2.7 yr and marginally with NSW and WISC at 2.7 and 5.3 yr, respectively. The corresponding phase spectra showed that increased SLP and NSW over the north Aegean Sea proceed and are associated with decreased anchovy/sardine ratio with a lag of about 2.5 months for SLP and 6 months for NSW whereas increased WISC over the north Aegean proceed and are associated with increased anchovy/sardine ratio with a lag of 28 months. Cross-spectral analysis also resolved significant coherence between the anchovy catches and AIRT and SLP at 2.7 yr, NSW at 1.8 yr and WISC at 5.3 yr. The corresponding phase spectra showed that increased SLP, AIRT and NSW over the north Aegean Sea proceed and are associated with decreased anchovy catches with a lag of about 2 months for SLP, 16 months for AIRT and 6 months for NSW whereas increased WISC over the same area proceed and are associated with increased anchovy catches with a lag of 30 months. In contrast, cross-spectral analysis resolved no significant coherence between sardine catches and all five climatic variables. Possible mechanisms underlying such patterns are discussed.  相似文献   

Influence of spatial scales of observation on temporal change in diversity and trophic structure of fine-sand communities from the English Channel and the southern North Sea   总被引：2，自引：0，他引：2  

Ghertsos  Konstantinos; Luczak  Christophe; Dewarumez  Jean-Marie; Dauvin  Jean-Claude 《ICES Journal of Marine Science》2000,57(5):1481-1487

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Nutrient relationships of Greek lakes: Water eutrophication monitoring,assessment and forecasting     

Alexis Conides  Theodore Koussouris  L Gritzalis  Konstantinos  Alkistis Parpoura  George Fotis 《GeoJournal》1995,36(4):383-390

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