Geoid determination using adapted reference field, seismic Moho depths and variable density contrast   总被引：4，自引：0，他引：4  

H. A. Abd-Elmotaal  N. Kühtreiber 《Journal of Geodesy》2003,77(1-2):77-85

 The traditional remove-restore technique for geoid computation suffers from two main drawbacks. The first is the assumption of an isostatic hypothesis to compute the compensation masses. The second is the double consideration of the effect of the topographic–isostatic masses within the data window through removing the reference field and the terrain reduction process. To overcome the first disadvantage, the seismic Moho depths, representing, more or less, the actual compensating masses, have been used with variable density anomalies computed by employing the topographic–isostatic mass balance principle. In order to avoid the double consideration of the effect of the topographic–isostatic masses within the data window, the effect of these masses for the used fixed data window, in terms of potential coefficients, has been subtracted from the reference field, yielding an adapted reference field. This adapted reference field has been used for the remove–restore technique. The necessary harmonic analysis of the topographic–isostatic potential using seismic Moho depths with variable density anomalies is given. A wide comparison among geoids computed by the adapted reference field with both the Airy–Heiskanen isostatic model and seismic Moho depths with variable density anomaly and a geoid computed by the traditional remove–restore technique is made. The results show that using seismic Moho depths with variable density anomaly along with the adapted reference field gives the best relative geoid accuracy compared to the GPS/levelling geoid. Received: 3 October 2001 / Accepted: 20 September 2002 Correspondence to: H.A. Abd-Elmotaal  相似文献   

Dleineation and characterization of geomorphological features in a part of lower maharahstra metamorphic plateau using IRS-ID LISS-III Data     

G. P. Obi Reddy  A. K. Maji 《Journal of the Indian Society of Remote Sensing》2003,31(4):241-250

In the present study, an attempt has been made to delineate and characterize the different geomorphic units of Tundiya river catchment in a part of Lower Maharahstra Metamorphic Plateau, north-eastern part of Nagpur district, Maharashtra. The drainage, contour and delineated geological units have been overlaid on IRS-ID LISS III satellite imagery (bands 2,3 and 4) in EASI/PACE analysis system to delineate and characterize different geomorphological units and analysis of their processes based on the field observations. The study area is basically of metamorphic in origin with different geological formations and is influenced by the various fluvio-morphological processes. Based on the satellite data analysis, the distinct geomorphological units viz., table top summits, structural hills, subdued plateau, linear ridges, shallow, moderate and deeply buried foot slopes, shallow valley fills and deep valley fills have been delineated and characterized. The information generated from satellite data in the form of vector layers has been used in GIS to generate geological and geomorphological maps of the study area. The present study demonstrates that IRS-ID LISS-III data in conjunction with geology, drainage and contour parameters to enable detailed evaluation of different geomorphological units and analysis of their processes based on the field observations. The delineated geomorphological units can be utilized for evaluation and management of natural resources and geo-environment on sustainable basis at river catchment level.  相似文献   

Land damage assessment - a case study     

A. K. Soni  V. J. Loveson 《Journal of the Indian Society of Remote Sensing》2003,31(3):175-186

The paper discusses the land damage assessment and change detection analysis with reference to a mineral bearing zone in Manjhi, Manuni and Churan valleys. The area is located in environmentally sensitive and fragile region of Himalaya and constitutes of nearly 400 small-scale mines of slate, which were operative since last one hundred years and are stopped by court of law since 1995 on account of environment deterioration. The status of land degradation has been studied using IRS-1B satellite data of 1988,1992 and 1995. The geo-coded data on 1:50,000 scale has been interpreted and an increase in land degradation status was noticed. Finally, the management strategy for arresting the further land damage in a broader perspective is suggested.  相似文献   

Remote sensing and gis applications in the identification of aquaculture hotspots at village level     

K. Nageswara Rao  G. Murali Krishna  D. Ramprasad Naik  B. Hema Malini 《Journal of the Indian Society of Remote Sensing》2003,31(2):71-80

Interpretation of IRS LISS II and LISS III imagery has revealed the various landforms as well as land use/land cover features in a part of the Godavari delta coastal belt. A comparative analysis of geomorphological vs. land use/land cover maps suggested that the landforms exert a certain degree of control over human land use activities even in this monotonously plain area. Further, an analysis of the sequential imagery pertaining to 1992 and 2001 aimed at detecting the land use/land cover change has indicated that the aquaculture has phenomenally increased by 9,293.5 ha during the 9-year period. At the same time, the cropland which occupied about 29,104 ha in 1992 has been reduced to 19,153.9 ha by 2001 mainly due to the encroachment of aquaculture. Village level data on temporal variation in land use/land cover extracted through GIS analysis revealed that in 14 out of the total 39 villages in the area, the conversion of cropland into aquaculture ponds was more than 30% with the highest conversion rate of 89.8% in Gondi village. These fourteen villages, which are designated as ‘aquaculture hotspots’ are grouped into 4 priority classes based on the intensity of conversion.  相似文献   

Impact of waves on the sea drag: measurements in the Baltic sea and a model interpretation     

Xiaoli Guo Lars  n  Vladimir K. Makin  Ann-Sofi Smedman 《Journal of Atmospheric & Ocean Science》2003,9(3):97-120

Measurements from the Baltic Sea and a wind-over-wave coupled model are used to study the wave impact on the sea drag. The study has been carried out for different wave conditions, namely a pure wind-sea, following-swell/ mixed sea and cross-swell/ mixed sea. Measurements reveal the fact that the sea drag is dependent on the sea-state. In stationary conditions and in the absence of severe cross-swell, swell reduces drag compared to wind-sea at the same wind speed. The cross-swell enhances the drag as compared to the following-swell case and the magnitude of the drag coefficient is increased with increasing the angle of swell propagation to the wind. It is shown that the agreement between the model results and measurements is good for pure wind-sea and stationary mixed-sea cases. Discrepancies occur at light winds, where most of the data represent pure swell conditions. During these pure swell conditions the data are characterized by a large variation of the drag coefficient. The variation is caused by mesoscale variability in the stress co-spectra, wind-cross-swell effects and nonstationarity in the wave and wind fields not represented in the model.  相似文献   

A new approach to verify the model core with idealized experiments     

A. Chakraborty  H. C. Upadhyaya  O. P. Sharma  S. K. Deb 《Meteorology and Atmospheric Physics》2003,83(3-4):221-236

Summary ?A newly developed ocean general circulation model has been tested and verified with some idealized experiments. Generally two types of idealized experiments have been done here. First types are called as “symmetric experiments” and second types are called as “transport experiments”. The first types of experiment help to correct the model core and any deficiency from boundary conditions. The second types of experiment are the type of validation experiment. In both the experiments there are no continents, so in the first type of experiments where symmetric forcings are provided one can expect that model should maintain the symmetric nature. In the second type of experiments one can expect that model should respond correctly to the wind forcings, if no wind curl is present in the wind forcing there will be no circulation in the extratropics and if there is no wind the equator there will be no circulation. The model reproduces the possible envisaged results of these experiments and gives the confidence for performing the realistic integration. Received February 20, 2002; accepted July 7, 2002 Published online: February 20, 2003  相似文献   

Numerical simulation of a South China Sea typhoon Leo (1999)   总被引：6，自引：0，他引：6  

K.-H. Lau  Z.-F. Zhang  H.-Y. Lam  S.-J. Chen 《Meteorology and Atmospheric Physics》2003,83(3-4):147-161

Summary ?A South China Sea typhoon, Leo (1999), was simulated using the Penn State/NCAR mesoscale model MM5 with the Betts-Miller convective parameterization scheme (BMEX). The simulation had two nested domains with resolutions at 54 and 18 km, and the forecast duration was 36 hours. The model was quite successful in predicting the track, the rapid deepening, the central pressure, and the maximum wind speed of typhoon Leo as verified with reports from the Hong Kong Observatory (HKO). The structure of the eye, the eye wall, and the spiral convective cloud band simulated in the model are found to be comparable to corresponding features identified in satellite images for the storm, and also with those reported by other authors. A trajectory analysis was performed. Three kinds of trajectory were found: (1) spirally rising trajectories near the eye wall; (2) spirally rising/descending trajectories in the convective/cloud free belt; (3) straight and fast rising trajectories in a heavy convection zone along one of the cloud bands on the periphery of the tropical cyclone. Both the HKO and the U.S. Joint Typhoon Warning Center (JTWC) reported the rapid deepening of Leo started around 00 UTC 29 April. In the model, the eye was first formed in the lower troposphere, and it extended to the upper troposphere within a few hours. We speculate that the spin-up of cyclonic rotation in the low-level eye enhanced the positive vorticity along the low-level eye wall. The positive vorticity was then transported to the upper troposphere by convection, leading to an extension and growth of the eye into the upper troposphere. To examine the impact of convective parameterization scheme (CPS) on the simulation, the Grell scheme (GLEX) was also tested. The GLEX predicted a weaker typhoon with a wilder eye that extended not as high up in the upper troposphere as BMEX. The different structures of the eye between the BMEX and GLEX suggest that the mesoscale features of the eye are dependent on the convection. In other words, the vertical and horizontal distribution of convective heating is essential to the development and structure of the eye. Received December 18, 2001; accepted May 7, 2002 Published online: March 20, 2003  相似文献   

A Laboratory and Theoretical Study on the Uptake of SO2 Gas by Large and Small Water Drops Containing Heavy Metal Ions     

A. Heusel-Waltrop  K. Diehl  S. K. Mitra  H. R. Pruppacher 《Journal of Atmospheric Chemistry》2003,44(2):211-223

Laboratory experiments have been carried out to investigate the uptake of sulfur dioxide by water drops containing heavy metal ions where the metal ions serve as catalysts to oxidise the taken up S(IV) into S(VI). During the gas uptake the drops were freely suspended at their terminal velocity in the airstream of the Mainz vertical wind tunnel. Two series of experiments were carried out, one with large millimeter size water drops containing manganese or iron ions, and the other with small water drops containing manganese ions and having radii in hundreds of micron size range. The experimental results were compared against model computations using the Kronig–Brink model and the fully mixed model, modified for the case that heavy metal ions present in the liquid phase act as catalysts for the oxidising process. The results of the model calculations show that there are only small differences between the predicted gas uptake according to the two models. In addition it was found that the experimental obtained results from the uptake of SO₂ by water drops containing heavy metal ions for both, large and small water drops did agree with the model results.  相似文献   

Influence of Changes in the Prevailing Synoptic Conditions on the Response of Aerosol Characteristics to Land- and Sea-Breeze Circulations at a Coastal Station     

K. Krishna Moorthy  Preetha S. Pillai  S. Suresh Babu 《Boundary-Layer Meteorology》2003,108(1):145-161

The changes in the response of near surfaceaerosol properties to land- and sea-breezecirculations, associated with the changes in the prevailing synoptic meteorological conditions, are examined for a tropical coastal station. Aerosol properties are nearly similar in both the breeze regimes (land and sea) during seasons of marine airmass while they are distinct during seasons of continental airmass. As the prevailing winds shift from continental to marine and the ambient weather changes from winter conditions to the humid monsoon season, the submicron mode, which dominated the aerosol mass-size distribution, is largely suppressed and the dominance of the super micron mode increases. During periods of continental air mass (winter), the aerosol loading is significantly higher in the land-breeze regime, (particularly in the submicron range) but as the winds shift to marine, the loading initially becomes insensitive to the breeze regimes and later becomes higher in the sea-breeze regime, particularly in the super micron range.  相似文献   

Simple indices of global climate variability and change: Part I – variability and correlation structure     

K. Braganza  D. Karoly  A. Hirst  M. Mann  P. Stott  R. Stouffer  S. Tett 《Climate Dynamics》2003,20(5):491-502

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