Sandip Oza - Academia.edu (original) (raw)

Papers by Sandip Oza

Research paper thumbnail of Investigations of the inter-annual variations of polar Ice surface characteristics using altimetric observations

Research paper thumbnail of Understanding the spatial distribution and plausible genesis of supraglacial debris over the Himalaya-Karakoram region

Physical Geography, Apr 17, 2023

Research paper thumbnail of Bringing SAR capability to a safer ice navigation during Indian Antarctic Expedition in near real-time mode

Research paper thumbnail of Estimation of Sea Ice Concentration in the Arctic Using SARAL/AltiKa Data

IEEE Transactions on Geoscience and Remote Sensing

Research paper thumbnail of Estimation of sea ice freeboard from SARAL-AltiKa

Research paper thumbnail of Characterizing polar ice surface features using SARAL-AltiKa waveforms

Research paper thumbnail of Spatio-temporal analysis of melting onset dates of sea-ice in the Arctic

Present study aims at the investigation of long-term satellite derived images of Earliest Melting... more Present study aims at the investigation of long-term satellite derived images of Earliest Melting Onset Date (EMOD) and Latest Melting Onset Date (LMOD) to study the sea ice variability in the Arctic. By applying cluster classification technique on the images of EMOD and LMOD, clusters having similar tendency were retrieved. The locations of centroids of the clusters revealed a distinct pattern showing tendency of clusters towards the early/delayed onset of melting. It was observed that the clusters having larger differences between EMOD and LMOD fell within the ocean area that became ice-free in September 2007. This study indicates that similar analysis using information on the onset of melting over the recent past (1998-2009) may help to predict the ice-free vulnerable zones in the coming 6-8 years.

Research paper thumbnail of Multi source remote sensing spectral temporal data analysis for regional crop assessment

Research paper thumbnail of Establishment of SAR calibration site at Antarctica: Pre-NISAR calibration activity

Upcoming Synthetic Aperture Radar (SAR) missions with larger swath like NASA-ISRO Synthetic Apert... more Upcoming Synthetic Aperture Radar (SAR) missions with larger swath like NASA-ISRO Synthetic Aperture Radar (NISAR) (∼250 km) requires a large, flat and homogeneous low-background site, free from human-made structures for point targets deployment for calibration. Finding out such a large, flat, homogeneous area devoid of perceived sources of radar clutter is a challenging task. In this regard, Antarctica is a potential site for calibration as it fulfills many of the criteria required for the ideal calibration site and suitable for setting up a corner reflector (CR) network for SAR calibration. This network will help in the calibration study and aid the studies related to Interferometric SAR (InSAR) viz. ice velocity estimation. As a part of this activity, in-house designed and developed CRs were installed near Indian research base stations Maitri and Bharati at Antarctica during the 38th Indian Scientific Expedition to Antarctica (ISEA) during 2018-2019. Corner reflectors were design...

Research paper thumbnail of STUDY OF INTERANNUAL Ku-BAND BACKSCATTER VARIATIONS OF AMERY ICE SHELF , EAST ANTARCTICA

The widespread retreat of glaciers can be considered as response to the climate change. Being the... more The widespread retreat of glaciers can be considered as response to the climate change. Being the largest retreating glacier-ice shelf system in East Antarctica, the Amery Ice Shelf-Lambert Glacier system plays an important role in contributing to sea level rise as well as surrounding environment and climate. The present study is focused on the investigation of this ice shelf system using mid-month Ku-band scatterometer data from January 2000 to July 2009. The corresponding monthly weather data of Davis Station was obtained from the web site of Australian Antarctic Division. Average backscatter of all the pixels, within the selected sites, was generated and Microwave Polarization Difference Index (MPDI) was computed. It was observed that backscattering coefficients of Hand V-components increase from January 2000 to June 2006. A very prominent dip in the backscatter observed in the month of January is a distinct signature taking place due to physical process of large scale melting of...

Research paper thumbnail of Rice acreage estimation in Orissa using remotely sensed data. Status Report

Research paper thumbnail of Advances in Antarctic Sea Ice Studies in India

Sea ice cover plays a key role in regulating the Earth’s climate by influencing the global atmosp... more Sea ice cover plays a key role in regulating the Earth’s climate by influencing the global atmospheric and oceanic circulation through various feedback mechanisms. The only viable source for the continuous monitoring of sea ice cover, its variability and characterization in the vast and remote polr region is the utilization of data acquired by orbiting satellites supported by Ship based observations. India has been contributing significantly in the development of techniques for extraction of sea ice from state-of-art Indian sensors and other international missions. Significant progress has been made towards understanding sea ice variability in the Antarctic region. Based on various studies in polar regions, it has been observed that during last few decades, Arctic is showing the consistent decline of summer sea ice cover, in contrast to Antarctica which is showing regional anomalies with positive and negative trends. Role of sea ice concentration in Indian monsoon has also been exam...

Research paper thumbnail of Analysis of Surface Weather Parameters and Energy Fluxes Over the Indian Antarctic Stations: Maitri and Bharati

Proceedings of the National Academy of Sciences, India Section A: Physical Sciences

Research paper thumbnail of Assessment of Cryospheric Parameters Over the Himalaya and Antarctic Regions using SCATSAT-1 Enhanced Resolution Data

Current Science

Antarctica is the focus of scientific studies considering the largest reservoir of terrestrial wa... more Antarctica is the focus of scientific studies considering the largest reservoir of terrestrial water in the form of ice and doubling of ice area during winter due to sea-ice growth. The third pole-Himalaya is equally important due to the large extent of snow and ice cover outside the polar regions, which is a major source of water for the Asian countries. At present, the Ku-band scatterometer observing global cryosphere is the SCATSAT-1 launched by India. This article describes the study carried out on different cryospheric parameters using high-resolution (~2.2 km) scatterometer data in the Antarctica and Himalaya. Impact of seasonal variations in snow/ice and ice calving on the backscatter over Antarctica is discussed in detail. A procedure developed for the estimation of sea-ice extent, which yielded overall accuracy of 89%, has been presented and successfully applied for daily monitoring of the Antarctic ice extent for 2017. Surface melting using backscatter and brightness temperature data has been discussed and the contrast between large-sized and small-sized Antarctic ice shelves during the austral summer period of summer 2017-18 is highlighted. The higher average surface melt observed around majority of east Antarctic ice shelves, particularly near the Indian station 'Maitri', is of particular interest. Typical surface melting patterns observed over the third largest Antarctic ice shelf, Amery, are discussed in detail. Over northwest Himalaya, derived changes in snow water equivalent (ΔSWE) shows a good correlation between observed and calculated SWE variations. The present study demonstrates that simultaneous availability of high-resolution brightness temperature and backscatter data from SCATSAT-1 provides a unique opportunity to study the polar and mountain cryosphere.

Research paper thumbnail of Estimation of Sea Ice Thickness from SARAL/AltiKa in Drifting Orbit Phase

Research paper thumbnail of SARAL/AltiKa Mission: Applications Using Ka-band Altimetry

Proceedings of the National Academy of Sciences, India Section A: Physical Sciences

Research paper thumbnail of Rift Assessment and Potential Calving Zone of Amery Ice Shelf, East Antarctica

Current Science

Ice shelves line the peripheries of Antarctica. Rift and crevasses are two main deformational str... more Ice shelves line the peripheries of Antarctica. Rift and crevasses are two main deformational structures affecting ice shelf stability. The present study deals with propagation-widening of five active rifts and future potential calving zones on Amery Ice Shelf (AIS), East Antarctica, between 2000 and 2017 using moderate resolution image spectroradiometer (MODIS) data. The widening and rift propagating rate, as well as advancement in AIS show abnormal behaviour. The expansion of AIS differs across the shelf. The highest rate of advancement was observed in 2012-2013 (~517 sq. km) and the lowest was observed in 2000-2001 (~35 sq. km). The rift system shows variability in its proportion and having poor relationship with environmental processes, which suggests heterogeneities in the AIS. The abnormal behaviour of rift propagation during the study period can be attributed to tsunamis, tide, current action, crevasses pattern and icequakes in the vicinity of the study region.

Research paper thumbnail of Volume loss of the Greenland ice sheet revealed by SARAL/AltiKa repeat passes radar altimetry

Journal of Earth System Science

The Greenland ice sheet (GrIS) is one of the drivers of global sea level rise and plays a crucial... more The Greenland ice sheet (GrIS) is one of the drivers of global sea level rise and plays a crucial role in understanding the global climate changes. Here, we have estimated and analysed the decadal (

Research paper thumbnail of Variability in the ice sheet elevations over Antarctica derived from repetitive SARAL/AltiKa radar altimeter data (2013–2016)

Journal of Earth System Science

Changes in surface elevations of polar ice sheets are the result of changes in ice dynamics and s... more Changes in surface elevations of polar ice sheets are the result of changes in ice dynamics and surface mass balance. Here, we present intra-and inter-annual elevation changes over the Antarctic ice sheet using the AltiKa radar altimeter's 40 Hz geophysical data record products for the period 2013-2016. Slope corrections were applied on the elevations using a digital elevation model (DEM) available from NASA's ice, cloud and land elevation satellite (ICESat). Comparison of elevations from AltiKa and ICESat's DEM yielded correlation, bias and root-mean-square-deviation values of the order of 0.99, −2.88 and 23.04 m, respectively, indicating the first-level accuracy of a former dataset. Further comparison of Airborne Topographic Mapper dataset with AltiKa derived elevation yielded 0.4 m root-mean-square-deviation over a part of Vostok subglacial lake. The intra-annual change indicates that for GY2 (glaciological year), GY3 and GY4, number of negative elevation change points exceeded the number of positive elevation change points during the Antarctic austral summer period (December-February). Inter-annual elevation changes were negative during 2013-2014 and positive during 2014-2015 over east Antarctica, whereas in west Antarctica negative elevation changes were observed for both periods.

Research paper thumbnail of Concurrent use of active and passive microwave remote sensing data for monitoring of rice crop

International Journal of Applied Earth Observation and Geoinformation

Estimation of crop area, growth and phenological information is very important for monitoring of ... more Estimation of crop area, growth and phenological information is very important for monitoring of agricultural crops. However, judicious combination of spatial and temporal data from different spectral regions is necessary to meet the requirement. This study highlights the use of active microwave QuikSCAT Ku-band scatterometer and Special Sensor Microwave/Imager (SSM/I) passive microwave radiometer data to derive information on important phenological phases of rice crop. The wetness index, a weekly composite product derived using brightness temperatures from 19, 37 and 85 GHz channels of SSM/I, was used to identify the puddling period. Ku-band scatterometer data provided the signal of transplanted rice seedlings since they acts as scatterers and increases the backscattering. Dual peak nature of temporal backscatter curve around the heading stage of rice crop was observed in Ku-band. The decrease of backscatter after first peak was associated with the threshold value of 60% crop canopy cover. The symmetric (Gaussian) and asymmetric (lognormal) curve fits were attempted to derive the date of initiation of the heading phase. The temporal signature from each of these sensors was found to complement each other in crop growth monitoring. Image showing pixel-wise timings of heading stage revealed the differences exists in various parts of the study area.

Research paper thumbnail of Investigations of the inter-annual variations of polar Ice surface characteristics using altimetric observations

Research paper thumbnail of Understanding the spatial distribution and plausible genesis of supraglacial debris over the Himalaya-Karakoram region

Physical Geography, Apr 17, 2023

Research paper thumbnail of Bringing SAR capability to a safer ice navigation during Indian Antarctic Expedition in near real-time mode

Research paper thumbnail of Estimation of Sea Ice Concentration in the Arctic Using SARAL/AltiKa Data

IEEE Transactions on Geoscience and Remote Sensing

Research paper thumbnail of Estimation of sea ice freeboard from SARAL-AltiKa

Research paper thumbnail of Characterizing polar ice surface features using SARAL-AltiKa waveforms

Research paper thumbnail of Spatio-temporal analysis of melting onset dates of sea-ice in the Arctic

Present study aims at the investigation of long-term satellite derived images of Earliest Melting... more Present study aims at the investigation of long-term satellite derived images of Earliest Melting Onset Date (EMOD) and Latest Melting Onset Date (LMOD) to study the sea ice variability in the Arctic. By applying cluster classification technique on the images of EMOD and LMOD, clusters having similar tendency were retrieved. The locations of centroids of the clusters revealed a distinct pattern showing tendency of clusters towards the early/delayed onset of melting. It was observed that the clusters having larger differences between EMOD and LMOD fell within the ocean area that became ice-free in September 2007. This study indicates that similar analysis using information on the onset of melting over the recent past (1998-2009) may help to predict the ice-free vulnerable zones in the coming 6-8 years.

Research paper thumbnail of Multi source remote sensing spectral temporal data analysis for regional crop assessment

Research paper thumbnail of Establishment of SAR calibration site at Antarctica: Pre-NISAR calibration activity

Upcoming Synthetic Aperture Radar (SAR) missions with larger swath like NASA-ISRO Synthetic Apert... more Upcoming Synthetic Aperture Radar (SAR) missions with larger swath like NASA-ISRO Synthetic Aperture Radar (NISAR) (∼250 km) requires a large, flat and homogeneous low-background site, free from human-made structures for point targets deployment for calibration. Finding out such a large, flat, homogeneous area devoid of perceived sources of radar clutter is a challenging task. In this regard, Antarctica is a potential site for calibration as it fulfills many of the criteria required for the ideal calibration site and suitable for setting up a corner reflector (CR) network for SAR calibration. This network will help in the calibration study and aid the studies related to Interferometric SAR (InSAR) viz. ice velocity estimation. As a part of this activity, in-house designed and developed CRs were installed near Indian research base stations Maitri and Bharati at Antarctica during the 38th Indian Scientific Expedition to Antarctica (ISEA) during 2018-2019. Corner reflectors were design...

Research paper thumbnail of STUDY OF INTERANNUAL Ku-BAND BACKSCATTER VARIATIONS OF AMERY ICE SHELF , EAST ANTARCTICA

The widespread retreat of glaciers can be considered as response to the climate change. Being the... more The widespread retreat of glaciers can be considered as response to the climate change. Being the largest retreating glacier-ice shelf system in East Antarctica, the Amery Ice Shelf-Lambert Glacier system plays an important role in contributing to sea level rise as well as surrounding environment and climate. The present study is focused on the investigation of this ice shelf system using mid-month Ku-band scatterometer data from January 2000 to July 2009. The corresponding monthly weather data of Davis Station was obtained from the web site of Australian Antarctic Division. Average backscatter of all the pixels, within the selected sites, was generated and Microwave Polarization Difference Index (MPDI) was computed. It was observed that backscattering coefficients of Hand V-components increase from January 2000 to June 2006. A very prominent dip in the backscatter observed in the month of January is a distinct signature taking place due to physical process of large scale melting of...

Research paper thumbnail of Rice acreage estimation in Orissa using remotely sensed data. Status Report

Research paper thumbnail of Advances in Antarctic Sea Ice Studies in India

Sea ice cover plays a key role in regulating the Earth’s climate by influencing the global atmosp... more Sea ice cover plays a key role in regulating the Earth’s climate by influencing the global atmospheric and oceanic circulation through various feedback mechanisms. The only viable source for the continuous monitoring of sea ice cover, its variability and characterization in the vast and remote polr region is the utilization of data acquired by orbiting satellites supported by Ship based observations. India has been contributing significantly in the development of techniques for extraction of sea ice from state-of-art Indian sensors and other international missions. Significant progress has been made towards understanding sea ice variability in the Antarctic region. Based on various studies in polar regions, it has been observed that during last few decades, Arctic is showing the consistent decline of summer sea ice cover, in contrast to Antarctica which is showing regional anomalies with positive and negative trends. Role of sea ice concentration in Indian monsoon has also been exam...

Research paper thumbnail of Analysis of Surface Weather Parameters and Energy Fluxes Over the Indian Antarctic Stations: Maitri and Bharati

Proceedings of the National Academy of Sciences, India Section A: Physical Sciences

Research paper thumbnail of Assessment of Cryospheric Parameters Over the Himalaya and Antarctic Regions using SCATSAT-1 Enhanced Resolution Data

Current Science

Antarctica is the focus of scientific studies considering the largest reservoir of terrestrial wa... more Antarctica is the focus of scientific studies considering the largest reservoir of terrestrial water in the form of ice and doubling of ice area during winter due to sea-ice growth. The third pole-Himalaya is equally important due to the large extent of snow and ice cover outside the polar regions, which is a major source of water for the Asian countries. At present, the Ku-band scatterometer observing global cryosphere is the SCATSAT-1 launched by India. This article describes the study carried out on different cryospheric parameters using high-resolution (~2.2 km) scatterometer data in the Antarctica and Himalaya. Impact of seasonal variations in snow/ice and ice calving on the backscatter over Antarctica is discussed in detail. A procedure developed for the estimation of sea-ice extent, which yielded overall accuracy of 89%, has been presented and successfully applied for daily monitoring of the Antarctic ice extent for 2017. Surface melting using backscatter and brightness temperature data has been discussed and the contrast between large-sized and small-sized Antarctic ice shelves during the austral summer period of summer 2017-18 is highlighted. The higher average surface melt observed around majority of east Antarctic ice shelves, particularly near the Indian station 'Maitri', is of particular interest. Typical surface melting patterns observed over the third largest Antarctic ice shelf, Amery, are discussed in detail. Over northwest Himalaya, derived changes in snow water equivalent (ΔSWE) shows a good correlation between observed and calculated SWE variations. The present study demonstrates that simultaneous availability of high-resolution brightness temperature and backscatter data from SCATSAT-1 provides a unique opportunity to study the polar and mountain cryosphere.

Research paper thumbnail of Estimation of Sea Ice Thickness from SARAL/AltiKa in Drifting Orbit Phase

Research paper thumbnail of SARAL/AltiKa Mission: Applications Using Ka-band Altimetry

Proceedings of the National Academy of Sciences, India Section A: Physical Sciences

Research paper thumbnail of Rift Assessment and Potential Calving Zone of Amery Ice Shelf, East Antarctica

Current Science

Ice shelves line the peripheries of Antarctica. Rift and crevasses are two main deformational str... more Ice shelves line the peripheries of Antarctica. Rift and crevasses are two main deformational structures affecting ice shelf stability. The present study deals with propagation-widening of five active rifts and future potential calving zones on Amery Ice Shelf (AIS), East Antarctica, between 2000 and 2017 using moderate resolution image spectroradiometer (MODIS) data. The widening and rift propagating rate, as well as advancement in AIS show abnormal behaviour. The expansion of AIS differs across the shelf. The highest rate of advancement was observed in 2012-2013 (~517 sq. km) and the lowest was observed in 2000-2001 (~35 sq. km). The rift system shows variability in its proportion and having poor relationship with environmental processes, which suggests heterogeneities in the AIS. The abnormal behaviour of rift propagation during the study period can be attributed to tsunamis, tide, current action, crevasses pattern and icequakes in the vicinity of the study region.

Research paper thumbnail of Volume loss of the Greenland ice sheet revealed by SARAL/AltiKa repeat passes radar altimetry

Journal of Earth System Science

The Greenland ice sheet (GrIS) is one of the drivers of global sea level rise and plays a crucial... more The Greenland ice sheet (GrIS) is one of the drivers of global sea level rise and plays a crucial role in understanding the global climate changes. Here, we have estimated and analysed the decadal (

Research paper thumbnail of Variability in the ice sheet elevations over Antarctica derived from repetitive SARAL/AltiKa radar altimeter data (2013–2016)

Journal of Earth System Science

Changes in surface elevations of polar ice sheets are the result of changes in ice dynamics and s... more Changes in surface elevations of polar ice sheets are the result of changes in ice dynamics and surface mass balance. Here, we present intra-and inter-annual elevation changes over the Antarctic ice sheet using the AltiKa radar altimeter's 40 Hz geophysical data record products for the period 2013-2016. Slope corrections were applied on the elevations using a digital elevation model (DEM) available from NASA's ice, cloud and land elevation satellite (ICESat). Comparison of elevations from AltiKa and ICESat's DEM yielded correlation, bias and root-mean-square-deviation values of the order of 0.99, −2.88 and 23.04 m, respectively, indicating the first-level accuracy of a former dataset. Further comparison of Airborne Topographic Mapper dataset with AltiKa derived elevation yielded 0.4 m root-mean-square-deviation over a part of Vostok subglacial lake. The intra-annual change indicates that for GY2 (glaciological year), GY3 and GY4, number of negative elevation change points exceeded the number of positive elevation change points during the Antarctic austral summer period (December-February). Inter-annual elevation changes were negative during 2013-2014 and positive during 2014-2015 over east Antarctica, whereas in west Antarctica negative elevation changes were observed for both periods.

Research paper thumbnail of Concurrent use of active and passive microwave remote sensing data for monitoring of rice crop

International Journal of Applied Earth Observation and Geoinformation

Estimation of crop area, growth and phenological information is very important for monitoring of ... more Estimation of crop area, growth and phenological information is very important for monitoring of agricultural crops. However, judicious combination of spatial and temporal data from different spectral regions is necessary to meet the requirement. This study highlights the use of active microwave QuikSCAT Ku-band scatterometer and Special Sensor Microwave/Imager (SSM/I) passive microwave radiometer data to derive information on important phenological phases of rice crop. The wetness index, a weekly composite product derived using brightness temperatures from 19, 37 and 85 GHz channels of SSM/I, was used to identify the puddling period. Ku-band scatterometer data provided the signal of transplanted rice seedlings since they acts as scatterers and increases the backscattering. Dual peak nature of temporal backscatter curve around the heading stage of rice crop was observed in Ku-band. The decrease of backscatter after first peak was associated with the threshold value of 60% crop canopy cover. The symmetric (Gaussian) and asymmetric (lognormal) curve fits were attempted to derive the date of initiation of the heading phase. The temporal signature from each of these sensors was found to complement each other in crop growth monitoring. Image showing pixel-wise timings of heading stage revealed the differences exists in various parts of the study area.