Imaging the surface of Mercury using ground-based telescopes     

Michael Mendillo  Johan Warell  Sanjay S. Limaye  Jeffrey Baumgardner  Ann Sprague  Jody K. Wilson 《Planetary and Space Science》2001,49(14-15)

We describe and compare two methods of short-exposure, high-definition ground-based imaging of the planet Mercury. Two teams have recorded images of Mercury on different dates, from different locations, and with different observational and data reduction techniques. Both groups have achieved spatial resolutions of <250 km, and the same albedo features and contrast levels appear where the two datasets overlap (longitudes 270–360°). Dark albedo regions appear as mare and correlate well with smooth terrain radar signatures. Bright albedo features agree optically, but less well with radar data. Such confirmations of state-of-the-art optical techniques introduce a new era of ground-based exploration of Mercury's surface and its atmosphere. They offer opportunities for synergistic, cooperative observations before and during the upcoming Messenger and BepiColombo missions to Mercury.  相似文献   

Morphology and movements of polarizations features on Venus as seen in the pioneer Orbiter Cloud Photopolarimeter data     

Sanjay S. Limaye 《Icarus》1984,57(3):362-385

Polarization observations obtained from the Orbiter Cloud Photopolarimeter (OCPP) show local, organized features whose morphology is similar to that of the ultraviolet clouds. No obvious correlation between the observed amount of polarization and relative brightness was found, suggesting that the polarization features are not due to variations in the unpolarized intensity alone, but rather to other causes such are the existence of a haze. Many of the features that can be seen even at 935 nm wavelength are believed to be signatures of local variations in the haze of submicron-size particles that have been detected from the OCCP data (K. Kawabata, D. L/ Cooffeen, J. E. Hansen, W. A. Lane, M. Sato, and L. D. Travis (1980). J. Geophys. Res.85, 8129–8140). Substantial variations in the structure and visibility of the polarization features that are observed suggest that the haze amount mixed with and above the main cloud layer may not be constant by varies with time. Some of these features last for least a few days thus allowing measurements of their apparent motions. The small number of measurements possible from the available data shows movements similar to those of the ultraviolet clouds in both direction and speed. According to Kawabata et al. the haze extends well above the main cloud layer to about 5 mb pressure level while the optical depth unity at 365 nm (corresponding to the level of the ultraviolet clouds tracked to infer the cloud-top level circulation) occurs at about 30 mb pressure level. Thus, the rapid retrograde circulation suggested by the movements of haze features in the polarimetry data would indicate that the layer in which such rapid circulation exists is fairly deep.  相似文献   

Into the Untravelled Himalaya – Travel, treks and Climbs - by Harish Kapadia     

Sanjay K  Nepal 《The Geographical journal》2006,172(4):350-351

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Aftershock activity of Bhuj earthquake of january 26th, 2001     

Ashwani Kumar  S. C. Gupta  A. K. Jindal  Sanjay Jain  Vandana 《Journal of Earth System Science》2003,112(3):391-395

Following a large-sized Bhuj earthquake (M _s = 7.6) of January 26th, 2001, a small aperture 4-station temporary local network was deployed, in the epicentral area, for a period of about three weeks and resulted in the recording of more than 1800 aftershocks (-0.07 ≤M _L <5.0). Preliminary locations of epicenters of 297 aftershocks (2.0 ≤M _L <5.0) have brought out a dense cluster of aftershock activity, the center of which falls 20 km NW of Bhachau. Epicentral locations of after-shocks encompass a surface area of about 50 × 40 km² that seems to indicate the surface projection of the rupture area associated with the earthquake. The distribution of aftershock activity above magnitude 3, shows that aftershocks are nonuniformly distributed and are aligned in the north, northwest and northeast directions. The epicenter of the mainshock falls on the southern edge of the delineated zone of aftershock activity and the maximum clustering of activity occurs in close proximity of the mainshock. Well-constrained focal depths of 122 aftershocks show that 89% of the aftershocks occurred at depths ranging between 6 and 25 km and only 7% and 4% aftershocks occur at depths less than 5 and more than 25 km respectively. The Gutenberg-Richter (GR) relationship, logN = 4.52 - 0.89M_L, is fitted to the aftershock data (1.0<-M _L<5.0) and theb-value of 0.89 has been estimated for the aftershock activity.  相似文献   

TEC variation over an equatorial and anomaly crest region in India during 2012 and 2013     

Sanjay Kumar  Kalpana Patel  Abhay Kumar Singh 《GPS Solutions》2016,20(4):617-626

Using the global positioning system (GPS) measurements, the total electron content (TEC) at station Bangalore (13.02°N, 77.57°E geographic; 04.44°N, 150.84°E geomagnetic), lying at the equatorial region, and station Lucknow (26.91°N, 80.95°E geographic; 17.96°N, 155.24°E geomagnetic), lying at equatorial ionospheric anomaly (EIA) crest region, have been estimated for the year 2012–2013. In order to evaluate the International Reference Ionosphere (IRI) model regarding simulation/modeling of ionospheric studies specially at equatorial and EIA crest regions, we have compared the TEC derived from the recent version of the IRI-2012 model and the older IRI-2007 with its three topside options, namely IRI-NeQuick (IRI-NeQ), IRI-2001, and IRI01-corr, with that of GPS-TEC over Bangalore and Lucknow. For the EIA station Lucknow, the IRI-2012 model with IRI-NeQ and IRI01-corr topside is found in good agreement with GPS-TEC during summer and equinox season, while the IRI-2012 model for all three topside options significantly overestimates the GPS-TEC during winter season. The IRI-2001 topside overestimates the GPS-TEC over both the stations during all seasons. The anomalous difference between the IRI-2012 model prediction and ground-based GPS-TEC in daytime hours during the winter season observed at Lucknow could be attributed to discrepancies in the slab thickness predicted by the model, which is more during the winter season as compared to summer and equinox. These large discrepancies in the slab thickness predicted by the IRI-2012 as well as the IRI-2007 model during the winter season have been supported by using the foF2 data from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation-based measurements. We also observed that the discrepancies in the recent IRI-2012 model with respect to GPS-TEC are found to be slightly larger than those with the older IRI-2007 model over the EIA region Lucknow. However, over the equatorial region Bangalore, the discrepancy with the older model IRI-2007 was found to be larger than with the recent IRI-2012 model. This suggests that the performance of the IRI-2012 model is poorer than the IRI-2007 model at the EIA region while better at equatorial region, and that further improvements in the IRI-2012 models are required particularly in the low-latitude and EIA regions. The GPS-TEC showed disappearance of the winter anomaly during 2012–2013, while the IRI model failed to predict the disappearance of winter anomaly.  相似文献   

Estimation of the source parameters of the Nepal earthquake from strong motion data     

A. Joshi  Monu Tomer  Sohan Lal  Sumer Chopra  Sandeep Singh  Sanjay Prajapati  M. L. Sharma  Sandeep 《Natural Hazards》2016,83(2):867-883

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Wind-wave prediction equations for probabilistic offshore hurricane hazard analysis     

Vahid Valamanesh  Andrew T. Myers  Sanjay R. Arwade  Jerome F. Hajjar  Eric Hines  Weichiang Pang 《Natural Hazards》2016,83(1):541-562

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Discussion of the Technical Note “Seismic Passive Earth Thrust on Retaining Walls with Cohesive Backfills using Pseudo-Dynamic Approach” by A.H. Shafiee, A. Eskandarinejad, M. Jahanandish: Geotechnical and Geological Engineering, DOI 10.1007/s10706-010-9327-3     

Sanjay Kumar Shukla 《Geotechnical and Geological Engineering》2010,28(6):929-930

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Integrated approach for demarcating the fracture zone for well site location : A case study near Gumla and Lohardaga,Bihar     

B. K. Sinha  Ashok Kumar  Deepak Shrivastava  Sanjay Srivastava 《Journal of the Indian Society of Remote Sensing》1990,18(3):1-8

In recent years satellite remote sensing techniques have greatly aided identification of fractures/joints/faults in connection with groundwater exploration. However, due to some constraints in filtering out the type of fracture i.e. shear fracture, tensional fracture, mineralised fracture etc. as to their “open or closed” nature from groundwater aspects, there is need of adding geophysical survey, particularly resistivity survey to further enhance the accuracy, and hence minimise drilling failures. The area under study is a part of Ranchi plateau and lithologically comprising of granite-gneiss. The present paper lays stress on an integrated approach for localising well sites through satellite data analysis and resistivity profiling along with vertical electrical sounding which is based on fracture patterns. With this combined effort i.e. firstly considering the surfacial features like drainage, geomorpho-logy, lithology and lineaments, and secondly taking into account geophysical survey aspects, i.e. depth and thickness of fracture zone, lateral extent, different layer parameter, etc., fairly accurate results are achieved. In the presnt study this type of an integrated survey has been carried out in Lohardaga and Gumla districts in Bihar, the results of which are highlighted in the paper.  相似文献   

Experimental superensemble forecasts of tropical cyclones over the Bay of Bengal   总被引：2，自引：1，他引：2  

T. S. V. Vijaya Kumar  J. Sanjay  B. K. Basu  A. K. Mitra  D. V. Bhaskar Rao  O. P. Sharma  P. K. Pal  T. N. Krishnamurti 《Natural Hazards》2007,41(3):471-485

This study entails the implementation of an experimental real time forecast capability for tropical cyclones over the Bay of Bengal basin of North Indian Ocean. This work is being built on the experience gained from a number of recent studies using the concept of superensemble developed at the Florida State University (FSU). Real time hurricane forecasts are one of the major components of superensemble modeling at FSU. The superensemble approach of training followed by real time forecasts produces the best forecasts for tracks and intensity (up to 5 days) of Atlantic hurricanes and Pacific typhoons. Improvements in track forecasts of about 25–35% compared to current operational forecast models has been noted over the Atlantic Ocean basin. The intensity forecasts for hurricanes are only marginally better than the best models. In this paper, we address tropical cyclone forecasts over the Bay of Bengal for the years 1996–2000. The main result from this study is that the position and intensity errors for tropical cyclone forecasts over the Bay of Bengal from the multimodel superensemble are generally less than those of all of the participating models during 1- to 3-day forecasts. Some of the major tropical cyclones, such as the November 1996 Andhra Pradesh cyclone and October 1999 Orissa super cyclone were well handled by this superensemble approach. A conclusion from this study is that the proposed approach may be a viable way to construct improved forecasts of Bay of Bengal tropical cyclone positions and intensity.  相似文献