Land use indicators of a watershed in arid region, western Rajasthan using Remote Sensing and GIS

The vegetation dynamics and land use/land cover types of Birantiya Kalan watershed located in the arid tracts of western Rajasthan have been characterized and evaluated using Remote Sensing and Geographical Information System (GIS). The watershed under study falls in the transitional plain of Luni Basin and is characterized by Aravali ranges in the eastern half and vast alluvial plains in the west. The land use/land cover types, as identified are cropland, fallow, forest, land with scrub, land without scrub, sandy area and the water body. Land with scrub occupied maximum area (39% area of the watershed) in 1996 in place of crop land which was dominant (43% of total area) in the year 1988. During eight years period, seasonal fallow land increased significantly and the areal extent of water body decreased to almost half. Vegetation vigour types have been classified into very poor, poor. moderate, good and very good categories. Moderate vigour type reduced from 62 to 27% and poor type increased from 34 to 68% during the period 1988 to 1996. Other vegetation vigour types have not shown any significant changes. To quantify the changes over the years in both vegetation and land use/land cover, weightages have been given to each type and composite values of both vegetation vigour and land use types for 1996 and 1988 have been calculated. It has been observed that the ratio for vegetation vigour has been found to be 0.85 showing that the overall vegetation have not improved after the treatment. The ratio for land use is found to be 1.01, which indicates negligible change in land use.     

A Geographic Information System approach to evaluation of groundwater potentiality of Shamri micro-watershed in the Shimla Taluk, Himachal Pradesh

GIS. a potential tool for facilitating the generation and use of thematic information, has been applied to groundwater potentiality of the Shamri micro-watershed in Shimla Taluk. The role of various parameters, namely, drainage. lineament. lithology . slope and landuse have been emphasised for delineation of groundwater potential iones. IRS-I C IAN and LISS Ill FCC merged satellite images on 1:25000 scale and Topographic map no. 53L/4 SI together with field traverses have been used as the data source. A multi-criteria evaluation following probability weighted approach has been applied for overlay analysis that allows a linear combination of weights of each thematic map with the individual capability value. 1 he resultant map indicates a high groundwater potentiality in the flood plains, river terraces and river channels in the vicinity of the Shamri nala. Other sites of high potentiality include places showing break in slopes and criss-crossing of lineaments.     

Vening Meinesz inverse isostatic problem with local and global Bouguer anomalies

Inverse problems in isostasy will consist in making the isostatic anomalies to be zero under a certain isostatic hypothesis. In the case of the Vening Meinesz isostatic hypothesis, the density contrast is constant, while the Moho depth (depth of the Mohorovičić discontinuity) is variable. Hence, the Vening Meinesz inverse isostatic problem aims to determine a suitable variable Moho depth for a prescribed constant density contrast. The main idea is easy but the theoretical analysis is somewhat difficult. Moreover, the practical determination of the variable Moho depths based on the Vening Meinesz inverse problem is a laborious and time-consuming task. The formulas used for computing the inverse Vening Meinesz Moho depths are derived. The computational tricks essentially needed for computing the inverse Vening Meinesz Moho depths from a set of local and global Bouguer anomalies are described. The Moho depths for a test area are computed based on the inverse Vening Meinesz isostatic problem. These Moho depths fit the Moho depths derived from seismic observations with a good accuracy, in which the parameters used for the fitting agree well with those determined geophysically. Received: 4 February 1999 / Accepted: 4 October 1999     

Precise Real-Time Positioning in WADGPS Networks

In recent years the importance of real-time positioning and navigation with the Global Positioning System (GPS) has grown rapidly. Starting from the establishment of differential GPS (DGPS) reference stations for marine and land navigation, new users and applications have emerged that resulted in a high demand for the establishment of a high-density network of reference stations around the world. Many countries have established their own DGPS service, which is either governmentally or commercially owned. These services are referred to as Local Area DGPS Systems (LADGPS). However, the costs for the establishment and maintenance of a dense network of reference stations are very high. Therefore Wide Area DGPS Systems (WADGPS) are being developed to overcome the main drawbacks of LADGPS. In this case, only a few reference stations are used to cover a large area, such s a continent like Europe. To achieve high positioning accuracies, real-time modeling of the main error sources for long-range baselines is required as errors in the satellite orbit and ionospheric refraction do not cancel entirely in double differencing. In this article, a real-time correction model based on the Kalman filter for WADGPS and networked LADGPS services is discussed and results of field tests in a WADGPS network in Europe are presented. ? 2000 John Wiley & Sons, Inc.     

Evaluation of RADARSAT ScanSAR synthetic aperture radar data for rice crop inventory and monitoring

Radarsat ScanSAR Narrow (SN2) data acquired on July 24 and August 17, 1997 were used to analyse the signature of rice crop in West Bengal, India. The analysis showed that the lowland practice of cultivation gives a distinct signature to rice due to the initial water background. The relatively stable backscatter from water bodies in temporal data enhanced the separability of rice fields from water using two date data. Around 94 per cent classification accuracy was achieved for rice crop using two date data. It was feasible to discriminate rice sub-classes based on their planting period like early and late crop. The analysis indicates the suitability of ScanSAR data for large area rice crop monitoring as it has a wide swath of 300 km.     

Energy in the urban environment: use of Terra/ASTER imagery as a tool in urban planning

In the present paper, Terra/ASTER imagery has been analysed together with in-situ spatial data to examine the potential of multi-spectral remote sensing to support urban planning. The potential of ASTER imagery to support energy budget estimation has been also examined by defining and mapping some microclimatic parameters for the centre of the city of Athens. Images in visible, near infrared and thermal infrared areas of the electromagnetic spectrum have been processed to define the urban land cover and topographic characteristics as well as to estimate the spatial distributions of vegetation, visible reflected radiation and brightness temperature. It has been found that ASTER multi-spectral imagery enables a better understanding of energy aspects, their causes and effects, providing an important addition to conventional methods of monitoring the urban environment.     

Atmospheric, oceanic and hydrological contributions to seasonal variations in length of day

 The annual and semiannual residuals derived in the axial angular momentum budget of the solid Earth–atmosphere system reflect significant signals. They must be caused by further excitation sources. Since, in particular, the contribution for the wind term from the atmospheric layer between the 10 and 0.3 hPa levels to the seasonal variations in length of day (LOD) is still missing, it is necessary to extend the top level into the upper stratosphere up to 0.3 hPa. Under the conservation of the total angular momentum of the entire Earth, variations in the oceanic angular momentum (OAM) and the hydrological angular momentum (HAM) are further significant excitation sources at seasonal time scales. Focusing on other contributions to the Earth's axial angular momentum budget, the following data are used in this study: axial atmospheric angular momentum (AAM) data derived for the 10–0.3 hPa layer from 1991 to 1997 for computing the missing wind effects; axial OAM functions as generated by oceanic general circulation models (GCMs), namely for the ECHAM3 and the MICOM models, available from 1975 to 1994 and from 1992 to 1994, respectively, for computing the oceanic contributions to LOD changes, and, concerning the HAM variations, the seasonal estimates of the hydrological contribution as derived by Chao and O'Connor [(1988) Geophys J 94: 263–270]. Using vector representation, it is shown that the vectors achieve a close balance in the global axial angular momentum budget within the estimated uncertainties of the momentum quantities on seasonal time scales. Received: 6 April 2000 / Accepted: 13 December 2000     

New analytical and numerical approaches for geopotential modeling

 The standard analytical approach which is applied for constructing geopotential models OSU86 and earlier ones, is based on reducing the boundary value equation to a sphere enveloping the Earth and then solving it directly with respect to the potential coefficients _n,m . In an alternative procedure, developed by Jekeli and used for constructing the models OSU91 and EGM96, at first an ellipsoidal harmonic series is developed for the geopotential and then its coefficients _n,m ^e are transformed to the unknown _n,m . The second solution is more exact, but much more complicated. The standard procedure is modified and a new simple integral formula is derived for evaluating the potential coefficients. The efficiency of the standard and new procedures is studied numerically. In these solutions the same input data are used as for constructing high-degree parts of the EGM96 models. From two sets of _n,m (n≤360,|m|≤n), derived by the standard and new approaches, different spectral characteristics of the gravity anomaly and the geoid undulation are estimated and then compared with similar characteristics evaluated by Jekeli's approach (`etalon' solution). The new solution appears to be very close to Jekeli's, as opposed to the standard solution. The discrepancies between all the characteristics of the new and `etalon' solutions are smaller than the corresponding discrepancies between two versions of the final geopotential model EGM96, one of them (HDM190) constructed by the block-diagonal least squares (LS) adjustment and the other one (V068) by using Jekeli's approach. On the basis of the derived analytical solution a new simple mathematical model is developed to apply the LS technique for evaluating geopotential coefficients. Received: 12 December 2000 / Accepted: 21 June 2001     

The stochastic estimation of satellite clock correction information in WADGPS

1 IntroductionChnventional DGPS is limited by the range overwhich the differential corrections are valid due tothe rapid decorrelation of the error sources with in-creasing distance from the reference station to user.In wide area differential GPS (WWPS) errorsources in GPS measurements are medeled sepa-rately,on the basis of a limited number of referencestaitOns, to overcome this drawback. The main er-ror sources are regarded as broadcast ephemeris er-ror,atmospheric refraction and satel…     

The geochemical coherence of Pu and Nd and the 244Pu238U ratio of the early solar system

Two very different sets of ${}^{244}\text{Pu}{}^{238}\text{U}$ ratios have been reported for early solar system materials. One group of samples yields high (0.015–0.016) ratios (Podosek, 1970a, 1972; Drozd et al., 1977) and calculations based on another group of analyses yield low ratios (~0.004) (Marti et al., 1977). Recently measured partition coefficients for Pu and Sm are used to evaluate the data of Marti et al. and $\text{sol}{}^{244}\text{Pu}{}^{238}\text{U}$ ratios from other sources are also considered. A low $\text{sol}{}^{244}\text{Pu}{}^{238}\text{U}$ ratio (~0.005) is favored, and some implications of this low ratio to galactic nucleosynthesis and meteorite age dating are briefly discussed.