Time filter

Source Type

Negi H.S.,Snow and Avalanche Study Establishment | Negi H.S.,University of Bremen | Kokhanovsky A.,University of Bremen
Cryosphere | Year: 2011

In the present paper, spectral reflectance measurements of Himalayan seasonal snow were carried out and analysed to retrieve the snow albedo and effective grain size. The asymptotic radiative transfer (ART) theory was applied to retrieve the plane and spherical albedo. The retrieved plane albedo was compared with the measured spectral albedo and a good agreement was observed with ±10% differences. Retrieved integrated albedo was found within ±6% difference with ground observed broadband albedo. The retrieved snow grain sizes using different models based on the ART theory were compared for various snow types and it was observed that the grain size model using two channel method (one in visible and another in NIR region) can work well for the Himalayan seasonal snow and it was found consistent with temporal changes in grain size. This method can work very well for clean, dry snow as in the upper Himalaya, but sometimes, due to the low reflectances (<20%) using wavelength 1.24 μm, the ART theory cannot be applied, which is common in lower and middle Himalayan old snow. This study is important for monitoring the Himalayan cryosphere using air-borne or space-borne sensors. © 2011 Author(s).

Negi H.S.,Snow and Avalanche Study Establishment | Negi H.S.,University of Bremen | Kokhanovsky A.,University of Bremen
Cryosphere | Year: 2011

In the present study we describe the retrievals of snow grain size and spectral albedo (plane and spherical albedo) for western Himalayan snow cover using Hyperion sensor data. The asymptotic radiative transfer (ART) theory was explored for the snow retrievals. To make the methodology operational only five spectral bands (440, 500, 1050, 1240 and 1650 nm) of Hyperion were used for snow parameters retrieval. The bi-spectral method (440 nm in the visible and 1050/1240 nm in the NIR region) was used to retrieve snow grain size. Spectral albedos were retrieved using satellite reflectances and estimated grain size. A good agreement was observed between retrieved snow parameters and ground observed snow-meteorological conditions. The satellite retrieved grain sizes were compared with field spectroradiometer retrieved grain sizes and close results were found for lower Himalayan snow. The wavelength 1240 nm was found to be more suitable compared to 1050 nm for grain size retrieval along the steep slopes. The methodology was able to retrieve the spatial variations in snow parameters in different parts of western Himalaya which are due to snow climatic and terrain conditions of Himalaya. This methodology is of importance for operational snow cover and glacier monitoring in Himalayan region using space-borne and air-borne sensors. © 2011 Author(s).

Negi H.S.,Snow and Avalanche Study Establishment | Singh S.K.,Space Applications Center | Kulkarni A.V.,Space Applications Center | Semwal B.S.,Hemwati Nandan Bahuguna Garhwal University
International Journal of Remote Sensing | Year: 2010

In the present study, spectroradiometer (350-2500 nm) experiments are carried out in the field to understand the influence of snow grain size, contamination, moisture, ageing, snow depth, slope / aspect on spectral reflectance and to determine the sensitive wavelengths for mapping of snow and estimation of snow characteristics using satellite data. The observations suggest that, due to ageing and grain-size variation, the maximum variations in reflectance are observed in the near-infrared region, i.e. around 1040-1050 nm. For varying contamination and snow depth, the maximum variations are observed in the visible region, i.e. around 470 and 590 nm, respectively. For the moisture changes, the maximum variations are observed around 980 and 1160 nm. Based on the spectral signatures of seasonal snow, the normalized difference snow index (NDSI) is studied, and snow indexes, such as grain and contamination indexes, are proposed. The study also suggests that the NDSI increases with ageing, grain size and moisture content. The NDSI values remain constant with variations in slope and aspect. Attempts are made to estimate seasonal snow characteristics using multispectral Advanced Wide Field Sensor (AWiFS) Indian Remote Sensing (IRS-P6) and Moderate Resolution Imaging Spectroradiometer (MODIS) Terra satellite data and validated with snow-meteorological observatory data of the study area. © 2010 Taylor & Francis.

Negi H.S.,Snow and Avalanche Study Establishment | Thakur N.K.,Snow and Avalanche Study Establishment | Ganju A.,Snow and Avalanche Study Establishment | Snehmani,Snow and Avalanche Study Establishment
Journal of Earth System Science | Year: 2012

In this study, Gangotri glacier was monitored using Indian Remote Sensing (IRS) LISS-III sensor data in combination with field collected snow-meteorological data for a period of seven years (2001-2008). An overall decreasing trend in the areal extent of seasonal snow cover area (SCA) was observed. An upward shifting trend of wet snow line was observed in the beginning of melt period, i.e., in May and dominant wet snow conditions were observed between May and October. Snow meteorological parameters collected in the Gangotri sub-basin suggest reduction in fresh snowfall amount during winter, increase in rainfall amount during summer, decrease in snowfall days, increase in rainfall days and rising trend of average temperature. The prevailing wet snow condition on glacier has caused scouring of slopes which led the excessive soil/debris deposition on the glacier surface. This was observed as one of the major factor for activating fast melting and affecting the glacier health significantly. Apart from climatic conditions, terrain factors were observed for changing the glacio-morphology. The significant changes on the glacier surface were observed in the regions of abrupt slope change. The above factors affecting the Gangotri glacier health were also validated using high resolution satellite imageries and field visit. A deglaciation of 6% in overall area of Gangotri glacier was observed between the years 1962 and 2006. © Indian Academy of Sciences.

Gusain H.S.,Snow and Avalanche Study Establishment | Mishra V.D.,Snow and Avalanche Study Establishment | Arora M.K.,Indian Institute of Technology Roorkee
Antarctic Science | Year: 2014

Surface energy fluxes of the ice sheet close to oases (ice-free land regions) are crucial in the case of retreating ice sheet and growing oasis areas. This study presents a four-year record of the meteorological parameters, radiative and turbulent energy fluxes at the edge of the Antarctic ice sheet, close to Schirmacher Oasis in Dronning Maud Land, East Antarctica from March 2007-February 2011. The energy fluxes were analysed for summer season, winter season and transition periods. High katabatic winds were observed during winter (seasonal mean 9.3 m s-1) as compared to other seasons. A high correlation (r 2 = 0.89) was observed between the glacier surface temperature and air temperature, and regression relations were obtained for summer, winter and transition periods. The net radiative flux was the main heat source to the glacier during summer (46.8 W m-2) and heat sink during winter (-42.2 W m-2). Sensible heat flux (annual mean 32 W m -2) was the heat source and latent heat flux (annual mean -61 W m-2) was the heat sink to the glacier surface, averaged over all seasons. Comparison with other coastal or dry valley locations in Antarctica show that low humidity (50%), high katabatic winds (8.3 m s-1) and mild surface (-11.4°C) and air temperature (-10.2°C) contribute to high latent heat flux at the present study location. © Antarctic Science Ltd 2013.

Sharma V.,Snow and Avalanche Study Establishment | Mishra V.D.,Snow and Avalanche Study Establishment | Joshi P.K.,TERI University
International Journal of Remote Sensing | Year: 2014

The present study deals with spatio-temporal snow cover distribution in Northwest Himalaya (NWH) in a discourse on regional topography and prevalent climatology. Snow cover variation during 2001-2012 in NWH and eight major river basins was examined using MODIS data on board the Terra satellite. Slope match topographic correction was applied to eliminate the differential illumination effect on satellite imagery. The impact of cloud cover was removed by generating a 10-day maximum snow cover product. Annual and seasonal analysis shows a decreasing trend in snow cover area (SCA) over the entire NWH. Maximal SCA was observed in the windward river basins of the Lower and the Middle Himalayan zones and in the highly glaciated Shyok river basin of the Upper Himalaya. Monthly snow cover duration (SCD) maps revealed the effect of longitudinal variation as well as the strong influence of regional climatology and topography. The relationship of SCA with altitude and aspect was studied in all the river basins of NWH. The study shows a linear increment of SCA/D with increasing respect to elevation in all river basins. The maximum rate of SCA/D change with elevation was observed in the Jhelum river basin. In the Middle Himalayan Zone, an effect of basin orientation in regard to elevation was observed. Mean annual SCA at altitudes of up to 4500 m shows a decreasing trend. Seasonal analysis of aspect-wise snow cover shows that southern slopes have lower SCA during winter months. The difference in SCA between northern and southern slopes is even higher in summer and the monsoon period. © 2014 Taylor & Francis.

Satyawali P.K.,Snow and Avalanche Study Establishment | Schneebeli M.,Institute for Snow and Avalanche Research
Annals of Glaciology | Year: 2010

A method for automated and fast classification of snow texture would be useful for applications where snow structure must be quantified. Large numbers of field measurements were carried out on natural snow in order to investigate small-scale variations of the micro-penetration force. Snow characterization was done for snow from the Himalaya and the Alps, using a high-resolution snow penetrometer (SnowMicroPen). Measurements of snow resistance at equal intervals of 4 mm were geostatistically evaluated. The range parameter (correlation length, or CL) of penetration force was estimated for all major snow classes from the sample semivariogram. Average CL was lowest for new snow and highest for melt-freeze snow. For major snow classes, CL was found to increase with snow density. Ground-perpendicular and ground-parallel snow profiles were also obtained for homogeneous snow, and CL was estimated along these directions. New snow showed larger CL in the ground-parallel direction, and depth-hoar snow showed larger CL in the ground-perpendicular direction. Based on CL, the directional anisotropy was calculated. An attempt was also made to show the relationship between CL and texture index. The semivariogram was used to estimate the fractal dimension. Both CL and fractal dimension were found to be potential parameters to describe snow.

Upadhyay A.,Snow and Avalanche Study Establishment | Kumar A.,Snow and Avalanche Study Establishment | Chaudhary A.,Snow and Avalanche Study Establishment
Annals of Glaciology | Year: 2010

Wet snow avalanches in India are common during the mid-and late winter in the Pir Panjal Range (2000-3000 ma.s.l.) and during the late winter in the Great Himalayan Range (3000 ma.s.l. and above). Although it is well known that the presence of liquid water in snow makes the flow behaviour of wet snow avalanches different from that of dry snow avalanches, there exist few actual flow measurements with wet snow. The aim of this investigation is to understand the dynamics of wet snow avalanches by conducting medium-scale experiments (volumes of 3, 6 and 11m3) on the Dhundi snow chute in Himachal Pradesh, India. We measured flow velocities using video data, as well as optical velocity sensors installed on the side walls and running surface. Measurement results relating to the slip velocity of the front and tail of the moving snow mass, as well as the average slip velocity, are presented. In addition, we use the results of the vertical velocity profile measurements to calculate the effective viscosity of snow at two locations within the flow. We identified a shear thinning type of behaviour, suggesting that a single avalanche rheology cannot describe wet snow avalanche behaviour.

Srivastava P.K.,Snow and Avalanche Study Establishment | Mahajan P.,Indian Institute of Technology Delhi | Satyawali P.K.,Snow and Avalanche Study Establishment | Kumar V.,Snow and Avalanche Study Establishment
Annals of Glaciology | Year: 2010

The process of temperature gradient metamorphism in snow strongly affects the microstructure and associated mechanical properties of the snow. The purpose of this study was to: (1) examine the temporal variations in three-dimensional snow microstructure under the influence of a strong temperature gradient for 6 days using X-ray computed microtomography (mCT); and (2) numerically simulate the linear elastic properties of snow from microtomographic data using a voxel-based finite-element technique. The temporal changes in the snow structure were analyzed in terms of density, specific surface area (SSA), thickness distribution of ice matrix and pores, structure model index and mean intercept length (MIL) fabric tensor. The structural indices and orthotropic elastic compliance matrix were computed over several sub-volumes within the reconstructed volume to account for statistical uncertainties. The mean density increased by about 14% on day 1 and no significant trend was observed thereafter. The SSA decreased by 22%, whereas both the ice and pore thickness distributions widened with time. The computed Young's moduli were 1.5-4 times larger than previously published dynamic measurements and found to be significantly correlated with ice volume fraction and MIL fabric measures. The increasing trend in computed moduli during the experiment is consistent with the observed development of thicker vertical ice structures. Multiple linear regression models of elastic compliances using fabric tensor formulation and ice volume fraction could explain 89.9-93.0% of the variance. Our results suggest a strong dependence of elastic properties on both density and microstructural fabric.

Joshi J.C.,Snow and Avalanche Study Establishment | Ganju A.,Snow and Avalanche Study Establishment
Journal of Earth System Science | Year: 2010

Temperature and fresh snow are essential inputs in an avalanche forecasting model. Without these parameters, prediction of avalanche occurrence for a region would be very difficult. In the complex terrain of Himalaya, nonavailability of snow and meteorological data of the remote locations during snow storms in the winter is a common occurrence. In view of this persistent problem present study estimates maximum temperature, minimum temperature, ambient temperature and precipitation intensity on different regions of Indian western Himalaya by using similar parameters of the neighbouring regions. The location at which parameters are required and its neighbouring locations should all fall in the same snow climatic zone. Initial step to estimate the parameters at a location, is to shift the parameters of neighbouring regions at a reference height corresponding to the altitude of the location at which parameters are to be estimated. The parameters at this reference height are then spatially interpolated by using Barnes objective analysis. The parameters estimated on different locations are compared with the observed one and the Root Mean Square Errors (RMSE) of the observed and estimated values of the parameters are discussed for the winters of 2007-2008. © Indian Academy of Sciences.

Loading Snow and Avalanche Study Establishment collaborators
Loading Snow and Avalanche Study Establishment collaborators