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Papers by prem datt
International Journal of Climatology, 2016
This study presents the spatio‐temporal winter snow albedo analysis over different mountain range... more This study presents the spatio‐temporal winter snow albedo analysis over different mountain ranges of north‐west Himalaya (NWH) for a period of approximately 24 years. Here we assess the temporal albedo variations in past two decades (1991–2010) in comparison to the recent 14 years (2000–2014). The field collected manual data of two representative observatories of Lower Himalaya (LH) and Great Himalaya (GH), and six automatic weather stations in LH, GH and Karakoram Himalaya (KH) were analysed. Satellite derived MODIS albedo data (MOD10A1) over these stations between 2001 and 2014 were analysed. A good correlation (r = 0.59) was observed between monthly average MODIS retrieved albedo and field collected albedo for GH with a relative error of 11%. In past two decades, a statistically significant (99%) decreasing rate of −0.011 per year in winter snow albedo was observed over GH (1993–2010), while in recent decade (2001 onward), no statistically significant increasing trend was observed. The change in albedo of GH is attributed to winter mean air temperature, which shows a significant rise in the past two decades, but there has been a hiatus in winter mean air temperature rise in recent decade. The higher winter mean air temperature above 0 °C since beginning of the study period (1991 onward) kept albedo of moist/wet snow approximately stable in LH. Further, insignificant increasing trend of albedo was observed over KH range in recent decade, and it is attributed to persistent very low temperatures and an increase in the frequency of snowfall days. This albedo study over NWH supports the recently reported findings on Himalayan snow cover and glacier variations during different durations.
Encyclopedia of Earth Sciences Series, 2011
Microelectronics Reliability, 1976
Structural Control and Health Monitoring
Cold Regions Science and Technology
Current Science, 2015
Snow depth is an important parameter for avalanche forecast and hydrological studies. In the Hima... more Snow depth is an important parameter for avalanche forecast and hydrological studies. In the Himalaya, manual snow depth data collection is difficult due to remote and rugged terrain and the severe weather conditions. However, microwave-based sensors in various satellites have the capability to estimate snow depth in all weather conditions. In the present study, experiments were performed to establish an algorithm for snow depth estimation using ground-based passive microwave radiometer with 6.9, 18.7 and 37 GHz antenna frequencies at Dhundhi and Patseo, Himachal Pradesh, India. Different layers in the snowpack were identified and layer properties, i.e. thickness, density, moisture content, etc. were measured manually and using a snow fork. Brightness temperature ( T B ) of the entire snowpack and of the individual snow layers was measured using passive microwave radiometer. It was observed that T B of the snow is affected by various snow properties such as depth, density, physical ...
Journal of the Geological Society of India, 2015
Sub-surface heat flux plays an important role in the energy balance of snow cover, glaciers and i... more Sub-surface heat flux plays an important role in the energy balance of snow cover, glaciers and ice sheets, and varies with the density of snow/ice media. In this paper, we report experimental observations of the sub-surface heat flux conducted in different snow and ice media in Antarctica. Experiments were conducted on low density fresh snowpack, wind compacted high density snowpack, and blue ice area in east Dronning Maud Land, Antarctica, in a radius of 10 km from Indian research station Maitri (70°46′03.98″ S and 11°41′40.72″ E). Direct measurements of net subsurface heat flux were carried out using an experimental setup consisting of heat flux plates. Two heat flux plates along with two temperature sensors were placed horizontally inside the snowpack / ice sheet at a depth of approximately 10 cm from the surface during summer season between December 2011and February 2012. The mean diurnal net subsurface heat fluxes for low density snow (location 1), high density wind compacted snow (location 2), and blue ice area (location 3) observed were 7.36±9.39 W m-2, -0.12±7.6 W m-2 and 3.20±13.32 W m-2, respectively, during the measurements periods. The amplitudes of the mean diurnal variations of net sub-surface heat flux were 14.23 W m-2, 11.42W m-2 and 18.55 W m-2 at location 1, location 2 and location 3, respectively. Mean net sub-surface heat flux was observed to be comparatively lower for wind compacted high density snow.
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Journal of the Geological Society of India
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Cold Regions Science and Technology, 2014
Abstract The efficient detection of acoustic emission (AE) activity from snow having porous and f... more Abstract The efficient detection of acoustic emission (AE) activity from snow having porous and fragile character is hindered by the fact that the AE signals have small amplitudes and are typically attenuated within a short distance from the source. We therefore tested seven different types of highly sensitive resonant AE sensors and a multi-channel AE system in a wide frequency range of 1 kHz–400 kHz to evaluate the performance of multi-sensor coupler and waveguides with varying displacement rates. The AE generated during small fracturing of a natural snowpack, caused by a ram penetrometer, were detected using a cylindrical waveguide and a detection range of up to 16 m with detection efficiency of 38 dB AE were observed in snow. The AE activities produced by the snowpack were continuously recorded using a 2D-arrestor for AE in relation with the natural melt-freeze process. Prominent AE activity was observed near the phase-transition temperature of snow. Furthermore, spectral analysis of the AE signals generated by snow was carried out using the Short-time Fast Fourier Transform (ST-FFT) method. The AE behavior of snow was observed at different states of stress by varying from low to high, corresponding to different frequency ranges and grain sizes and an empirical relation was established for peak AE rates as a function of displacement rate. Apart from it, an attempt was made to monitor the real time failure of snow sample vis-a-vis AE energy with the help of an AE system and a high-speed camera. Our results are quite encouraging towards application of AE technique in the direction of slope stability evaluation and AE-based non-destructive evaluation of snow under various physical processes. The network of acoustic arrestors and waveguides can be crucial towards prediction of slope stability in view of avalanche release.
CURRENT …, 2011
Ground Penetrating Radar (GPR) of antenna frequency 1000 MHz was used for snow depth estimation a... more Ground Penetrating Radar (GPR) of antenna frequency 1000 MHz was used for snow depth estimation and snow stratigraphic studies in the Pir Panjal and Greater Himalayan range of NW Himalayas. GPR profiles were acquired at a selected site near Solang observatory (Himachal Pradesh (HP), India) for snow depth estimation. It was observed that the estimated snow depth correlates well with ground measurements taken using snow stakes. Based on these snow depth measurements with GPR and manual density measurement at different locations within the sampling area, the snow water equivalent was also estimated. Experiments were also conducted at Patseo (HP) for snow depth estimation and snowpack layer identification. By analysing the profiles we were able to capture the prominent snow layers present within the snowpack at Patseo. Manual stratigraphy was also performed along with the GPR profiles, and it was found that layer positions in the radargram correspond fairly well with the stratigraphic layer positions. Dielectric constant of snow, which is an important parameter for acquisition/interpretation of GPR profiles was also measured using snow fork.
Applied Acoustics, 2016
Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with ... more Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with air (+water vapour) saturated pores. Investigation of snow acoustic properties is useful to understand the interaction between snow structure and sound waves, which can be further used to devise non-destructive way for exploring physical (non-acoustic) properties of snow. The present paper discusses the experimental measurements of various acoustical properties of snow such as acoustic absorption coefficient, surface impedance and transmission losses across different snow samples, followed by inverse characterization of different geometrical parameters of snow. The snow samples were extracted from a natural snowpack and transported to a nearby controlled environmental facility at Patsio, located in the Great Himalayan range of India. An impedance tube system (ITS), working in the frequency range 63-6300 Hz, was used for acoustic measurements of these snow samples. The acoustic behaviour of snow was observed strongly dependent upon the incident acoustic frequency; for frequencies smaller than 1 kHz, the average acoustic absorption coefficient was found below than 0.4, however, for the frequencies more than 1 kHz it was found to be 0.85. The average acoustic transmission loss was observed from 1.45 dB cm À1 to 3.77 dB cm À1 for the entire frequency range. The real and imaginary components of normalized surface impedance of snow samples varied from 0.02 to 7.77 and À6.05 to 5.69, respectively. Further, the measured acoustic properties of snow were used for inverse characterization of non-acoustic geometrical parameters such as porosity, flow resistivity, tortuosity, viscous and thermal characteristic lengths using the equivalent fluid model proposed by Johnson, Champoux and Allard (JCA). Acoustically derived porosity and flow resistivity were also compared with experimentally measured values and good agreement was observed between them.
Journal of Earth System Science, 2012
Wind caused snow drifting plays a dominant role in the redistribution of snow mass that restructu... more Wind caused snow drifting plays a dominant role in the redistribution of snow mass that restructures a snowpack. Strong wind activity at the mountain tops results in uneven distribution of snow with erosion on windward side and deposition on leeward areas. Such snowdrift events are responsible for the formation of cornices, increase in the loading of avalanche release zones on the leeward side and consequent increase in the level of avalanche hazard. In this paper, we present the results of snowdrift measurement using an acoustic snowdrift meter, the FlowCapt, built by IAV Engineering, which was used during winter seasons of 2007-2010 at a field research station of Snow and Avalanche Study Establishment (SASE) in the western Himalayas. The aim of the study was to evaluate the suitability of the instrument in measuring snowdrift in the Himalayan weather conditions. Results proved the utility of the instrument as a useful tool to study drifting snow in remote areas. However, in the absence of conventional snow gauges for validation, the quality of the absolute snow flux data could not be ascertained.
International Journal of Climatology, 2016
This study presents the spatio‐temporal winter snow albedo analysis over different mountain range... more This study presents the spatio‐temporal winter snow albedo analysis over different mountain ranges of north‐west Himalaya (NWH) for a period of approximately 24 years. Here we assess the temporal albedo variations in past two decades (1991–2010) in comparison to the recent 14 years (2000–2014). The field collected manual data of two representative observatories of Lower Himalaya (LH) and Great Himalaya (GH), and six automatic weather stations in LH, GH and Karakoram Himalaya (KH) were analysed. Satellite derived MODIS albedo data (MOD10A1) over these stations between 2001 and 2014 were analysed. A good correlation (r = 0.59) was observed between monthly average MODIS retrieved albedo and field collected albedo for GH with a relative error of 11%. In past two decades, a statistically significant (99%) decreasing rate of −0.011 per year in winter snow albedo was observed over GH (1993–2010), while in recent decade (2001 onward), no statistically significant increasing trend was observed. The change in albedo of GH is attributed to winter mean air temperature, which shows a significant rise in the past two decades, but there has been a hiatus in winter mean air temperature rise in recent decade. The higher winter mean air temperature above 0 °C since beginning of the study period (1991 onward) kept albedo of moist/wet snow approximately stable in LH. Further, insignificant increasing trend of albedo was observed over KH range in recent decade, and it is attributed to persistent very low temperatures and an increase in the frequency of snowfall days. This albedo study over NWH supports the recently reported findings on Himalayan snow cover and glacier variations during different durations.
Encyclopedia of Earth Sciences Series, 2011
Microelectronics Reliability, 1976
Structural Control and Health Monitoring
Cold Regions Science and Technology
Current Science, 2015
Snow depth is an important parameter for avalanche forecast and hydrological studies. In the Hima... more Snow depth is an important parameter for avalanche forecast and hydrological studies. In the Himalaya, manual snow depth data collection is difficult due to remote and rugged terrain and the severe weather conditions. However, microwave-based sensors in various satellites have the capability to estimate snow depth in all weather conditions. In the present study, experiments were performed to establish an algorithm for snow depth estimation using ground-based passive microwave radiometer with 6.9, 18.7 and 37 GHz antenna frequencies at Dhundhi and Patseo, Himachal Pradesh, India. Different layers in the snowpack were identified and layer properties, i.e. thickness, density, moisture content, etc. were measured manually and using a snow fork. Brightness temperature ( T B ) of the entire snowpack and of the individual snow layers was measured using passive microwave radiometer. It was observed that T B of the snow is affected by various snow properties such as depth, density, physical ...
Journal of the Geological Society of India, 2015
Sub-surface heat flux plays an important role in the energy balance of snow cover, glaciers and i... more Sub-surface heat flux plays an important role in the energy balance of snow cover, glaciers and ice sheets, and varies with the density of snow/ice media. In this paper, we report experimental observations of the sub-surface heat flux conducted in different snow and ice media in Antarctica. Experiments were conducted on low density fresh snowpack, wind compacted high density snowpack, and blue ice area in east Dronning Maud Land, Antarctica, in a radius of 10 km from Indian research station Maitri (70°46′03.98″ S and 11°41′40.72″ E). Direct measurements of net subsurface heat flux were carried out using an experimental setup consisting of heat flux plates. Two heat flux plates along with two temperature sensors were placed horizontally inside the snowpack / ice sheet at a depth of approximately 10 cm from the surface during summer season between December 2011and February 2012. The mean diurnal net subsurface heat fluxes for low density snow (location 1), high density wind compacted snow (location 2), and blue ice area (location 3) observed were 7.36±9.39 W m-2, -0.12±7.6 W m-2 and 3.20±13.32 W m-2, respectively, during the measurements periods. The amplitudes of the mean diurnal variations of net sub-surface heat flux were 14.23 W m-2, 11.42W m-2 and 18.55 W m-2 at location 1, location 2 and location 3, respectively. Mean net sub-surface heat flux was observed to be comparatively lower for wind compacted high density snow.
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Journal of the Geological Society of India
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Encyclopedia of Earth Sciences Series, 2011
Cold Regions Science and Technology, 2014
Abstract The efficient detection of acoustic emission (AE) activity from snow having porous and f... more Abstract The efficient detection of acoustic emission (AE) activity from snow having porous and fragile character is hindered by the fact that the AE signals have small amplitudes and are typically attenuated within a short distance from the source. We therefore tested seven different types of highly sensitive resonant AE sensors and a multi-channel AE system in a wide frequency range of 1 kHz–400 kHz to evaluate the performance of multi-sensor coupler and waveguides with varying displacement rates. The AE generated during small fracturing of a natural snowpack, caused by a ram penetrometer, were detected using a cylindrical waveguide and a detection range of up to 16 m with detection efficiency of 38 dB AE were observed in snow. The AE activities produced by the snowpack were continuously recorded using a 2D-arrestor for AE in relation with the natural melt-freeze process. Prominent AE activity was observed near the phase-transition temperature of snow. Furthermore, spectral analysis of the AE signals generated by snow was carried out using the Short-time Fast Fourier Transform (ST-FFT) method. The AE behavior of snow was observed at different states of stress by varying from low to high, corresponding to different frequency ranges and grain sizes and an empirical relation was established for peak AE rates as a function of displacement rate. Apart from it, an attempt was made to monitor the real time failure of snow sample vis-a-vis AE energy with the help of an AE system and a high-speed camera. Our results are quite encouraging towards application of AE technique in the direction of slope stability evaluation and AE-based non-destructive evaluation of snow under various physical processes. The network of acoustic arrestors and waveguides can be crucial towards prediction of slope stability in view of avalanche release.
CURRENT …, 2011
Ground Penetrating Radar (GPR) of antenna frequency 1000 MHz was used for snow depth estimation a... more Ground Penetrating Radar (GPR) of antenna frequency 1000 MHz was used for snow depth estimation and snow stratigraphic studies in the Pir Panjal and Greater Himalayan range of NW Himalayas. GPR profiles were acquired at a selected site near Solang observatory (Himachal Pradesh (HP), India) for snow depth estimation. It was observed that the estimated snow depth correlates well with ground measurements taken using snow stakes. Based on these snow depth measurements with GPR and manual density measurement at different locations within the sampling area, the snow water equivalent was also estimated. Experiments were also conducted at Patseo (HP) for snow depth estimation and snowpack layer identification. By analysing the profiles we were able to capture the prominent snow layers present within the snowpack at Patseo. Manual stratigraphy was also performed along with the GPR profiles, and it was found that layer positions in the radargram correspond fairly well with the stratigraphic layer positions. Dielectric constant of snow, which is an important parameter for acquisition/interpretation of GPR profiles was also measured using snow fork.
Applied Acoustics, 2016
Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with ... more Snow is a sound absorbing porous sintered material composed of solid matrix of ice skeleton with air (+water vapour) saturated pores. Investigation of snow acoustic properties is useful to understand the interaction between snow structure and sound waves, which can be further used to devise non-destructive way for exploring physical (non-acoustic) properties of snow. The present paper discusses the experimental measurements of various acoustical properties of snow such as acoustic absorption coefficient, surface impedance and transmission losses across different snow samples, followed by inverse characterization of different geometrical parameters of snow. The snow samples were extracted from a natural snowpack and transported to a nearby controlled environmental facility at Patsio, located in the Great Himalayan range of India. An impedance tube system (ITS), working in the frequency range 63-6300 Hz, was used for acoustic measurements of these snow samples. The acoustic behaviour of snow was observed strongly dependent upon the incident acoustic frequency; for frequencies smaller than 1 kHz, the average acoustic absorption coefficient was found below than 0.4, however, for the frequencies more than 1 kHz it was found to be 0.85. The average acoustic transmission loss was observed from 1.45 dB cm À1 to 3.77 dB cm À1 for the entire frequency range. The real and imaginary components of normalized surface impedance of snow samples varied from 0.02 to 7.77 and À6.05 to 5.69, respectively. Further, the measured acoustic properties of snow were used for inverse characterization of non-acoustic geometrical parameters such as porosity, flow resistivity, tortuosity, viscous and thermal characteristic lengths using the equivalent fluid model proposed by Johnson, Champoux and Allard (JCA). Acoustically derived porosity and flow resistivity were also compared with experimentally measured values and good agreement was observed between them.
Journal of Earth System Science, 2012
Wind caused snow drifting plays a dominant role in the redistribution of snow mass that restructu... more Wind caused snow drifting plays a dominant role in the redistribution of snow mass that restructures a snowpack. Strong wind activity at the mountain tops results in uneven distribution of snow with erosion on windward side and deposition on leeward areas. Such snowdrift events are responsible for the formation of cornices, increase in the loading of avalanche release zones on the leeward side and consequent increase in the level of avalanche hazard. In this paper, we present the results of snowdrift measurement using an acoustic snowdrift meter, the FlowCapt, built by IAV Engineering, which was used during winter seasons of 2007-2010 at a field research station of Snow and Avalanche Study Establishment (SASE) in the western Himalayas. The aim of the study was to evaluate the suitability of the instrument in measuring snowdrift in the Himalayan weather conditions. Results proved the utility of the instrument as a useful tool to study drifting snow in remote areas. However, in the absence of conventional snow gauges for validation, the quality of the absolute snow flux data could not be ascertained.