Estimating surface ice velocity on Chhota Shigri glacier from satellite data using Particle Image Velocimetry (PIV) technique     

Akansha Patel  Jaydeo K. Dharpure  Snehmani  Ashwagosha Ganju 《国际地球制图》2019,34(4):335-347

Information about the surface ice velocity is one of the important parameters for Mass balance and Glacier dynamics. This study estimates the surface ice velocity of Chhota Shigri glacier using Landsat (TM/ETM+) and ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) temporal data-sets from a period of 2009 to 2016 and 2006 to 2007, respectively. A correlation based Particle Image Velocimetry (PIV) technique has been used for the estimation of surface ice velocity. This technique uses multiple window sizes in the same data-set. Four window sizes (low, medium, high, very high) are used for each image pair. Estimated results have been compared with the published data. The outcomes attained from the medium window size closely matches with the published results. The estimated mean surface ice velocities of medium window size are 24 and 28.5 myr^?1 for 2009/2010 and 2006/2007 images pair. Highest velocity is observed in middle part of the glacier while lowest in the accumulation zone of the glacier.  相似文献   

Heavy metals in the Bombay harbour area     

B. Patel  Vasanti S. Bangera  Shakunt Patel  M.C. Balani 《Marine pollution bulletin》1985,16(1):22-28

Bombay harbour is one of the major sinks, on the western peninsula of the Indian subcontinent, receiving anthropogenic pollutants including heavy metals, radionuclides and hydrocarbons in addition to sewage. To evaluate possible impacts of a few heavy metals on the harbour ecosystem, the distribution patterns of Zn, Mn, Cu, Fe, Co, Ni, Cd, Cr, Pb and Sr in water, sediment and two benthic species, the blood clam Anadara granosa and gobiid mudskipper Boleophthalmus boddaerti were studied over the period 1976–1980. The present levels of the ten elements in biotic and abiotic matrices were found to be far below those that are known to affect adversely the life and quality of benthic communities. Furthermore, the concentrations of these elements in various compartments neither revealed any systematic temporal or spatial fluctuations nor reflected the substantial incease in the total budget over the past 8–12 years. Also these levels were within the range reported in the nearshore and oceanic environs along the west coast. In view of this, the poor growth and high percentage mortality observed in the clam Anadara granosa fished from the Sewri clam bed compared to that of the stock harvested from the Trombay region in the harbour may well be due to anoxic conditions caused by organic pollutants present in the domestic sewage and industrial wastes released in the vicinity of the Sewri clam bed.  相似文献   

Results of optical, thermomagnetic and electron microprobe analyses of titanomagnetite grains     

J. P. Patel  H. C. Palmer 《Physics of the Earth and Planetary Interiors》1982,30(4):373

This paper presents results of a study of titanomagnetite from specimens of ten different rock units. The rock units comprise trachytes, basalts, ignimbrites, nephelinites, olivine melanephelinites and welded tuffs from Kenya, with ages ranging from recent to Precambrian. The correlations of the stability index with opaque petrology and with thermomagnetic analyses of the titanomagnetite and titanomaghemite bearing specimens appear to be significant. Electron microprobe analyses of the titanomagnetite grains indicate a high percentage of “impurities” in the low stability index specimens and elevation of the Curie point in the high stability index specimens.  相似文献   

Simulation and evaluation of satellite scanner stereo images     

Vijay K. Agarwal  R. Ramani  R. M. Patel  Meoss Project 《Journal of the Indian Society of Remote Sensing》1987,15(1):55-65

During 1986–1996, several satellite missions on Stereoscopy are planned. This paper sumarises an attempt in evaluating these stereoscopic images for cartographic purposes. For the purpose, we have taken into account a proposed Indian experiment on satellite stereoscopy, which will be based on push-broom type scanning and a ground resolution of 70m×70m. *** DIRECT SUPPORT *** A04KF003 00004  相似文献   

Study of fractional vegetation cover using high spectral resolution data     

N. K. Patel  R. K. Saxena  Ajay Shiwalkar 《Journal of the Indian Society of Remote Sensing》2007,35(1):73-79

A field experiment was conducted to study the effect of vegetation cover on soil spectra and relationship of spectral indices with vegetation cover. Multi-date spectral measurements were carried out on twelve wheat fields. Five sets of measurements were taken during the growth period of wheat crop. Field reflectance data were collected in the range 350 to 1800 nm using ASD spectroradiometer. Analysis of data was done to select narrow spectral bands for estimation of ground cover. The ratio of reflectance from vegetation covered soil and reflectance from bare soil indicated that spectral reflectance at 670 and 710 nm are the most sensitive bands. Two bands in visible (670 and 560 nm), three bands in near infrared (710, 870 and 1100 nm) and three bands in middle infrared (1480, 1700 and 1800 nm) were found highly correlated with fractional cover. Vegetation indices developed using narrow band spectral data have been found to be better than those developed using broad- band data for estimation of ground cover.  相似文献   

Characteristic of plasma bubbles observed by DMSP in the topside ionosphere during the year 2005     

K. Patel  A. K. Singh 《Journal of Earth System Science》2010,119(2):211-220

To study the characteristic of plasma bubbles in the topside ionosphere during the solar minima, we have analyzed a large database of post-sunset plasma density measurement acquired during ∼5104 equatorial crossings made by Defense Meteorological Satellite Program (DMSP) F14 in 2005. On 675 of these crossings, equatorial plasma bubbles (EPBs) events were observed as intervals of depleted and irregular plasma densities that degrade communication and navigation signals. We have analyzed these EPB events to study their distributions with month, season and longitude. To test for possible dependence of EPB occurrence at topside altitudes on the level of magnetic activity, we compared the distributions of one year database with those of Kp index at the time of equatorial crossings by the DMSP satellites. We also examined the response of the evening sector, low-latitude ionosphere during eight magnetic storms with minimum Dst ≤ −100 nT. We observed that EPBs occurred regularly during geomagnetic storms, especially in the initial and main phases but can be suppressed sometimes for days, after prolonged activity during recovery phases. These results are discussed according to the other reported results.  相似文献   

Comparative Analysis of a Transition Region Bright Point with a Blinker and Coronal Bright Point Using Multiple EIS Emission Lines     

N. Brice Orange  Hakeem M. Oluseyi  David L. Chesny  Maulik Patel  Katie Hesterly  Lauren Preuss  Chantale Neira  Niescja E. Turner 《Solar physics》2014,289(5):1557-1584

Since their discovery 20 year ago, transition region bright points have never been observed spectroscopically. Bright point properties have not been compared with similar transition region and coronal structures. In this work we have investigated three transient quiet Sun brightenings including a transition region bright point (TR BP), a coronal bright point (CBP) and a blinker. We use time-series observations of the extreme-ultraviolet emission lines of a wide range of temperature T (logT=5.3?–?6.4) from the EUV Imaging Spectrometer (EIS) onboard the Hinode satellite. We present the EIS temperature maps and Doppler maps, which are compared with magnetograms from the Michelson Doppler Imager (MDI) onboard the SOHO satellite. Doppler velocities of the TR BP and blinker are ≤?25 km?s^?1, which is typical of transient TR phenomena. The Doppler velocities of the CBP were found to be ≤?20 km?s^?1 with exception of those measured at logT=6.2 where a distinct bi-directional jet is observed. From an EM loci analysis we find evidence of single and double isothermal components in the TR BP and CBP, respectively. TR BP and CBP loci curves are characterized by broad distributions suggesting the existence of unresolved structure. By comparing and contrasting the physical characteristics of the events we find that the BP phenomena are an indication of multi-scaled self-similarity, given the similarities in both their underlying magnetic field configuration and evolution in relation to EUV flux changes. In contrast, the blinker phenomena and the TR BP are sufficiently dissimilar in their observed properties as to constitute different event classes. Our work is an indication that the measurement of similar characteristics across multiple event types holds class-predictive power, and is a significant step towards automated solar atmospheric multi-class classification of unresolved transient EUV sources. Finally, the analysis performed here establishes a connection between solar quiet region CBPs and jets.  相似文献   

Temporal Pointing Variations of the Solar Dynamics Observatory’s HMI and AIA Instruments on Subweekly Time Scales     

N. Brice Orange  Hakeem M. Oluseyi  David L. Chesny  Maulik Patel  Patrick Champey  Katie Hesterly  Dylan Anthony  Robert Treen 《Solar physics》2014,289(5):1901-1915

Achieving subarcsecond co-registration across varying time-lines of multi-wavelength and instrument images is difficult and requires an accurate characterization of the instrument pointing jitter. We investigated the internal pointing errors on daily and yearly time-scales that occur across the Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI). Using cross-correlation techniques on the AIA 1700 Å passband and the HMI line-of-sight magnetograms from three years of observational image pairs at approximately three-day intervals, internal pointing errors were quantified. Pointing variations of ±?0.26″ (jitter-limited) and ±?0.50″ in the solar East–West (x) and North–South (y) directions, respectively, were measured. AIA observations of the Venus transit in June 2012 were used to measure existing coalignment offsets in all passbands. We found that the AIA passband pointing variations are 〈ΔX _CO〉=1.10″±1.41″ and 〈ΔY _CO〉=1.25″±1.24″ when aligned to the HMI nominal image center, referred to here as the CutOut technique. Minimal long-term pointing variations found between limb and correlation derived pointings provide evidence that the image-center positions provided by the instrument teams achieve single-pixel accuracy on time scales shorter than their characterization. However, daily AIA passband pointing variations of ??1.18″ indicate that autonomous subarcsecond co-registration is not fully achieved yet.  相似文献   

Photometric and polarimetric studies of three W UMa-type binaries: FZ Ori,V407 Peg and LP UMa     

Vinod Prasad  J. C. Pandey  M. K. Patel  D. C. Srivastava 《Astrophysics and Space Science》2014,353(2):575-594

We present analyses of new optical photometric observations of three W UMa-type contact binaries FZ Ori, V407 Peg and LP UMa. Results from the first polarimetric observations of the FZ Ori and V407 Peg are also presented. The periods of FZ Ori, V407 Peg and LP UMa are derived to be 0.399986, 0.636884 and 0.309898 d, respectively. The O?C analyses indicate that the orbital periods of FZ Ori and LP UMa have increased with the rate of 2.28×10^?8 and 1.25×10^?6 d?yr^?1, respectively and which is explained by transfer of mass between the components. In addition to the secularly increasing rate of orbital period, it was found that the period of FZ Ori has varied in sinusoidal way with oscillation period of ～30.1 yr. The period of oscillations are most likely to be explained by the light-time effect due to the presence of a tertiary companion. Small asymmetries have been seen around the primary and secondary maxima of light curves of all three systems, which is probably due to the presence of cool/hot spots on the components. The light curves of all three systems are analysed by using Wilson-Devinney code (WD) and the fundamental parameters of these systems have been derived. The present analyses show that FZ Ori is a W-subtype, and V407 Peg and LP UMa are A-subtype of the W UMa-type contact binary systems. The polarimetric observations in B, V, R and I bands, yield average values of polarization to be 0.26±0.03, 0.22±0.02, 0.22±0.03 and 0.22±0.05 per cent for FZ Ori and 0.21±0.02, 0.29±0.03, 0.31±0.01 and 0.31±0.04 per cent for V407 Peg, respectively.  相似文献   

X-Ray Line Transfer in Plasmas with Large Velocity Gradients     

F. M. Kerr  A. Gouveia  R. W. Lee  P. K. Patel  O. Renner  S. J. Rose  H. A. Scott  J. S. Wark 《Astrophysics and Space Science》2005,298(1-2):171-176

An astrophysically relevant experiment is compared to the output of a multidimensional radiation transfer code in which populations and radiation are self-consistently treated. Experimental Al Ly α spectra obtained with a very high-resolution spectrometer are presented as quantitative evidence of dot plasma non-planar expansion. Analysis of these spectra using the code is performed, in particular examining the effects of velocity gradients in directions other than that of the primary expansion. These calculations are found to be in good agreement with the experimental results. Usage of the Ly α doublet as a planarity diagnostic is discussed.  相似文献