Journal papers

Geomorphic mapping and analysis of neotectonic structures in the piedmont alluvial zone of Haryana state, NW-India: a remote-sensing and GPR based approach


Harsh Kumar ,R. S. Chatterjee ,R. C. Patel ,Abhishek Rawat & Somalin Nath


The Himalayan Frontal Thrust (HFT) and the surrounding piedmont alluvial region represent a zone of active deformation in the Indo-Gangetic plains. We investigated the Piedmont zone between the Ghaggar and Yamuna River basins in Haryana, India, for geomorphic signatures of active tectonics using remotely sensed data and validated by Geophysical Ground Penetrating Radar (GPR) surveys. The possible locations and the types of active tectonic features such as sub-surface fault, ridges, lineaments and warps were identified based on the presence of geomorphic signatures such as drainage gradient anomalies, abrupt change in flow direction, river offset, compressed meanders, paleochannels and topographic breaks. We used various optical satellite imageries to detect and map the temporal changes in the flow pattern of rivers in the study area. GPR investigations were done at selected test sites to locate and verify the continuity of subsurface fault. The GPR profiles were taken in the North-South direction using the common midpoint technique with 40 and 100 MHz antennae. Low frequency bi-static GPR scanning confirmed a number of dipping reflectors due to fault planes and warp surfaces in the study area. It is concluded that the piedmont zone of Haryana is actively deforming and could become a future seismic hazard zone.

Favorable locations for new VGOS antennas in India depending on the assessment of geodetic parameters and environmental factors


Sujata Dhar,  Susanne Glaser, Robert Heinkelmann, Harald Schuh, Nagarajan Balasubramanian & Onkar Dikshit


VLBI simulation studies are carried out to investigate the impact of any proposed station or strategy on the geodetic parameters, such as Earth Orientation Parameters (EOP) and Terrestrial Reference Frame (TRF). In general, such studies are performed for making decisions on any new development in the existing VLBI network. Thus, for selecting the favorable locations for establishment of a VLBI antenna in India, simulation studies are performed on 42 potential locations to cover the whole Indian subcontinent. Furthermore, the simulation setup is divided into four scenarios that consider the current and future situations of the global VLBI network. Extensive simulation strategy is applied with optimized scheduling for each network geometry, Monte-Carlo simulations and analysis in the VieSched++ software. Since only the simulation results are thought to be insufficient for a thorough evaluation of the realistic performance of locations, environmental factors are also investigated in the current study. The environmental factors affecting the operation and vulnerability of the VLBI technique at the potential locations are also incorporated in the present study. For this, a weighted scoring model is developed with the scores and weights based on the probable impact and occurrence frequency of disrupting environmental events, respectively. This approach will avoid the possibility of new VLBI station ending up in an unfavorable location in India and, underperforming substantially in terms of the achieved improvement of geodetic parameters as determined from the simulation study. The VLBI Global Observing System (VGOS) network is being established at a global level to create a uniformly distributed network of the next generation VLBI system to meet the goals of the Global Geodetic Observing Systems (GGOS). India is planning to establish its first VGOS antenna, and therefore, this study helps to mark the high-performance favorable locations for VGOS. The improvements in geodetic parameters of favorable locations identified in the simulation study are 6.7–11.2% in the first scenario, 12.8–46.8% in second scenario, 9–20.5% in third scenario and 2.9–6.1% in fourth scenario. The favorable locations outperform other Indian locations by a factor of 1.1–5.8. In addition to that, the Indian locations having environmental factors that might affect the VGOS adversely are not portrayed as the favorable choice.

Comparative Analysis of NavIC Multipath Observables for Soil Moisture over Different Field Conditions


Sushant Shekhar, Rishi Prakash, Dharmendra K. Pandey, Anurag Vidyarthi, Deepak Putrevu, and Nilesh Desa


Studies of soil moisture with Global Navigation Satellite System (GNSS) have gained the attention of several researchers. Multipath amplitude, multipath phase, and multipath frequency are multipath observables that are utilized in the study of soil moisture. However, an inter-comparison of the performance of these parameters for soil moisture under different roughness and vegetation conditions is very much required to have a better insight so that more robust inversion algorithm for soil moisture retrieval with multipath observables can be designed. Therefore, this paper analyses the performance of these multipath observables for soil moisture over bare smooth soil, rough surface, and vegetated soil. Two different fields have been investigated to include the location variability. Navigation with Indian constellation (NavIC) multipath signal has been used in this study. Statistical parameters such as correlation coefficient (R), Root Mean Square Error (RMSE), and sensitivity have been determined to study the performance of multipath observable for soil moisture under different surface roughness and vegetation conditions.

National geospatial policy: status of the Indian geodetic data.


Goyal, Ropesh; Dikshit, Onkar; Tiwari, Ashutosh


The National Geospatial Policy has well communicated the need for sharing geospatial data, with an emphasis that these data must refer to the geodetic/topographic database of the Survey of India (SoI). SoI has been collecting, processing, archiving and disseminating geodetic data for over a century. Several stakeholders are using these datasets, viz. Government, academia, industry and researchers, for their respective applications. SoI also updated its database as and when required due to the introduction of sophisticated and precise instruments, accuracy requirements, or to improve the database scientifically. Although the results or policies involving the geodetic data are provided in the literature, there is limited discussion of the data themselves. This article provides comprehensive information about the geodetic data available to Indian users for various applications. The data discussed here are the horizontal and vertical positioning, gravity, geoid model and digital elevation models. Copyright of Current Science (00113891) is the property of Indian Academy of Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.

Investigating the Congruence between Gravimetric Geoid Models over India


 R. Goyal, S. J. Claessens, W. E. Featherstone, and O. Dikshit


A major motivation of precise geoid computation is to adopt it as a national vertical datum or as an alternative vertical reference surface to aid surveyors in calculating physical heights using the Global Navigation Satellite System (GNSS). There exist several methods of geoid computation, and only one particular method is generally used to calculate the national geoid model irrespective of the size and topographical landforms of the country. The validation of the developed geoid models is done with the complete GNSS-leveling data set. In such a case, it is hard to claim the consistency in the precision of the developed geoid model throughout the country. This study aims to identify the consistency of the geoid models over India computed using the three approaches primarily followed in Curtin University of Technology (CUT), the University of New Brunswick (UNB), and the Royal Institute of Technology (KTH). Three analyses have been done on the calculated geoid models: (1) clusterwise validation with the GNSS-leveling data, (2) intermodel comparison for the whole study area, and (3) intermodel comparison for Indian states and Union Territories (UT) only. The GNSS-leveling validation results show that the standard deviations of differences for all the methods are within a range of ±0.01  m with the exception of Uttar Pradesh West with the UNB method. However, inter-model comparison shows that the mean (meters) and standard deviation (meters) of the differences between the pairs (CUT-UNB), (CUT-KTH), and (KTH-UNB) are 0.241±0.854, −0.133±0.498, and 0.374±1.239, respectively, with maximum difference sometimes exceeding 5 m. There is only one UT and four states for which the mean value is within (−0.20  m, 0.20 m) and standard deviation ≤±0.05  m for all the three pairs. Therefore, the analysis shows that it is difficult to calculate a precise national geoid model using any one method alone and a strategy is required to merge various regional precise geoid models or methods to develop a consistently precise national geoid model.

Digitisation and analysis of historical vertical deflections in India


W. E. Featherstone & R. Goyal


We describe the [somewhat tedious] process of digitising from a 1955 report that lists over 1000 vertical deflections in India and some surrounding countries. It involved error-checking with closed-loop tests and resolution of an ambiguity surrounding the meridional vertical deflection at the Kalianpur origin of the datum. We transformed these Kalianpur coordinates to geodetic coordinates on geocentric datum to compute absolute vertical deflections. However, due to many changes to the Everest spheroid due to different feet to metre conversions and readjustments of the Kalianpur datum, we were restricted to using the abridged Molodensky transformation parameters for the 1975 Kalianpur datum and Everest 1956 spheroid based on only seven common points from the WGS84 technical manual. We compared these transformed absolute vertical deflections with EGM2008 and GGMplus (for both models: meridional standard deviation: ∼±2″; prime vertical standard deviation: ∼±3″), showing that the effort of digitisation and scrutiny of historical geodetic data is indeed worthwhile.

Draft National Geospatial Policy: a few salient observations


Ropesh Goyal, Onkar Dikshit and Ashutosh Tiwari


The new geospatial guidelines for acquiring and producing spatial data services issued vide the Department of Science and Technology (DST) F.No.SM/25/02/2020 (Part1) dated 15 February 2021 are appreciated unanimously by various experts, and considered a step forward towards boosting the geospatial industries in India1. The availability of comprehensive, highly accurate, granular and constantly updated geospatial data brings ample opportunities for the geospatial sector, including academia, industry and research, benefitting diverse sectors of the economy. The decision to maintain consistency and avoid duplication of geospatial data is a welcome step. However, it requires cooperation and unified execution of relevant ideas to bring tangible benefits to the community mentioned above. The geospatial guidelines were followed by a Draft Geospatial Policy2. This note aims to put forth some facets and views of the Draft Policy, which policymakers would like to consider before finalizing the National Geospatial Policy. We have summarized the key information from different clauses of the Policy in five broad points. We have presented views in our capacity as academicians/researchers in the geospatial domain.

Stable and upgraded horizontal datum for India


Sujata Dhar, Nagarajan Balasubramanian, Onkar Dikshit and Harald Schuh


A precise datum is significant as a starting or reference point for a multitude of activities like floodplain maps, property boundaries, civil surveys, precise agriculture, crustal deformation and climate studies, and works requiring consistent coordinates. A large nation like India, with almost its own tectonic plate, must have a well-defined network of horizontal datum for determining accurate and reliable 3D positioning for every user, anywhere and anytime. This article discusses the significance, methodology of realization and transformation, applications and static/dynamic coordinates for paving the way for a National Horizontal Datum in India.

The Role of Factors Affecting Flood Hazard Zoning Using Analytical Hierarchy Process: A Review


Nguyen Ba Dung, Nguyen Quoc Long, Ropesh Goyal, Dang Tran An & Dang Tuyet Minh


Flood hazard zoning is an important problem that has received much attention from environmental researchers. This problem requires complex spatial analysis; hence, numerous criteria have to be assessed. Factors contributing to the flood formation includes both natural and socioeconomic ones. However, the central question is what factors are important in creating a flood and how to quantify these factors. To answer this question, one of the popular approaches is the analytical hierarchy process (AHP) developed by Saaty. The usage of the AHP algorithm to calculate the weight of each factor is one of the main steps in the process of creating a flood hazard map. This paper will provide an overview of the factors that affect flood formation and analyze their weight by selecting and evaluating the degree of effect of factors in various research using the AHP algorithm. The results can be used as a reference for studies on flood risk zoning in different basins when selecting the impact criteria.

Evaluation of P-Band SAR Tomography for Mapping Tropical Forest Vertical Backscatter and Tree Height


Naveen Ramachandran, Sassan Saatchi, tefano Tebaldini, Mauro Mariotti d’Alessandro, and Onkar Dikshit


Low-frequency tomographic synthetic aperture radar (TomoSAR) techniques provide an opportunity for quantifying the dynamics of dense tropical forest vertical structures. Here, we compare the performance of different TomoSAR processing, Back-projection (BP), Capon beamforming (CB), and MUltiple SIgnal Classification (MUSIC), and compensation techniques for estimating forest height (FH) and forest vertical profile from the backscattered echoes. The study also examines how polarimetric measurements in linear, compact, hybrid, and dual circular modes influence parameter estimation. The tomographic analysis was carried out using P-band data acquired over the Paracou study site in French Guiana, and the quantitative evaluation was performed using LiDAR-based canopy height measurements taken during the 2009 TropiSAR campaign. Our results show that the relative root mean squared error (RMSE) of height was less than 10%, with negligible systematic errors across the range, with Capon and MUSIC performing better for height estimates. Radiometric compensation, such as slope correction, does not improve tree height estimation. Further, we compare and analyze the impact of the compensation approach on forest vertical profiles and tomographic metrics and the integrated backscattered power. It is observed that radiometric compensation increases the backscatter values of the vertical profile with a slight shift in local maxima of the canopy layer for both the Capon and the MUSIC estimators. Our results suggest that applying the proper processing and compensation techniques on P-band TomoSAR observations from space will allow the monitoring of forest vertical structure and biomass dynamics.

An experimental Indian gravimetric geoid model using Curtin University’s approach


Ropesh Goyal, Will E. Featherstone, Sten J. Claessens, Onkar Dikshit, and Nagarajan Balasubramanian


Over the past decade, numerous advantages of a gravimetric geoid model and its possible suitability for the Indian national vertical datum have been discussed and advocated by the Indian scientific community and national geodetic agencies. However, despite several regional efforts, a state-of-the-art gravimetric geoid model for the whole of India remains elusive due to a multitude of reasons. India encompasses one of the most diverse topographies on the planet, which includes the Gangetic plains, the Himalayas, the Thar desert, and a long peninsular coastline, among other topographic features. In the present study, we have developed the first national geoid and quasigeoid models for India using Curtin University’s approach. Terrain corrections were found to reach an extreme of 187 mGal, Faye gravity anomalies 617 mGal, and the geoid-quasigeoid separation 4.002 m. We have computed both geoid and quasigeoid models to analyse their representativeness of the Indian normal-orthometric heights from the 119 GNSS-levelling points that are available to us. A geoid model for India has been computed with an overall standard deviation of ±0.396 m but varying from ±0.03 to ±0.158 m in four test regions with GNSS-levelling data. The greatest challenge in developing a precise gravimetric geoid for the whole of India is data availability and its preparation. More densely surveyed precise gravity data and a larger number of GNSS/levelling data are required to further improve the models and their testing.

Landslide susceptibility mapping using MT-InSAR and AHP enabled GIS based multi-criteria decision analysis


M. Devara, A. Tiwari, R. Dwivedi


Landslide susceptibility maps (LSMs) are generally prepared by integrating multiple prominent thematic layers, including DEM derived products (elevation, slope, and aspect), and other parameters such as lithology, geomorphology, LULC, etc. These parameters can be assigned optimum weights using the analytic hierarchy process (AHP) method, followed by a GIS-based weighted overlay analysis. In recent years, multi-temporal interferometric synthetic aperture radar (MT-InSAR) techniques have been rigorously explored, for land deformation detection and monitoring, by extracting highly stable measurement pixels using tens of SAR acquisitions simultaneously. In this research work, a GIS-based multi-criteria decision analysis to prepare LSMs is proposed, with MT-InSAR derived displacement estimates used as a critical input parameter. An LSM is generated by processing 20 ERS-1/2 and Envisat ASAR images, acquired over ∼120 sq. km wide river basin, located in Uttarakhand, India. The generated LSM is found to be congruent with the susceptible maps made available by the Geological Survey of India (GSI) under the National Landslide Susceptibility Mapping (NLSM) program. Preliminary results indicate that the majority of the unstable zones along the Alaknanda River are correctly identified. The approach is further implemented to generate an updated susceptibility map using 60 scenes of freely available Sentinel-1A dataset, followed by validation through actual field survey. This resulted in the generation of an updated susceptibility map, which helped in the identification of 44.5% new landslide susceptible zones (LSZs). Furthermore, the status of previously identified zones is also quantified. The performance of the proposed approach suggests its usability in generating and updating near-real-time LSMs. 

Spatial distribution of earthquake potential along the Himalayan arc


Y. Sharma, S. Pasari, K.-E. Ching, O. Dikshit, T. Kato, J.N. Malik, C.-P. Chang, and J.-Y. Yen


 To determine the spatial distribution of earthquake potential along the active Himalayan arc, we utilize GPS measurements and earthquake data. We derive horizontal velocity field and 2-D strain rates from a new set of 41 regional GPS stations along with 446 published velocities. We convert these strain rate tensors to geodetic moment rate build-up within 24 contiguous segments and compare to the seismic moment rate release derived from a reassessed earthquake catalog of 900 years. The geodetic to seismic moment rate ratio, an indicator of stored strain energy, varies from below unity to more than 50 in different segments. The estimated geodetic moment rate ranges from 1.7 × 1018 Nm/yr to 10.2 × 1018 Nm/yr, whereas the seismic moment rate ranges from 3.7 × 1016 Nm/yr to 5.1 × 1019 Nm/yr. This variation between the geodetic and seismic moment rate corresponds to a moment deficit rate of ~1.15×1017 Nm/yr to 7.97 × 1018 Nm/yr along various segments of the study region. The above moment deficit rate provides an equivalent earthquake potential of magnitude 5.7 − 8.2 in different segments. Specifically, the higher earthquake potential (Mw≥8.0) corresponds to the segments in the central seismic gap and the northeast part of Himalaya, whereas the lower earthquake potential (Mw<7.0) corresponds to the segments encompassing the rupture areas of recent large events. The present findings not only provide input constraints on the contemporary crustal deformation but also contributes to the time-dependent seismic hazard analysis along the Himalaya.

Contemporary Earthquake Hazards in the West-Northwest Himalaya: A Statistical Perspective through Natural Times


S.Pasari, Y. Sharma


 Himalayan earthquakes have deep societal and economic impact. In this article, we implement a surrogate method of nowcasting (Rundle et al., 2016) to determine the current state of seismic hazard from large earthquakes in a dozen populous cities from India and Pakistan that belong to the west‐northwest part of Himalayan orogeny. For this, we (1) perform statistical inference of natural times, intersperse counts of small‐magnitude events between pairs of succeeding large events, based on a set of eight probability distributions; (2) compute earthquake potential score (EPS) of 14 cities from the best‐fit cumulative distribution of natural times; and (3) carry out a sensitivity testing of parameters—threshold magnitude and area of city region. Formulation of natural time (Varostos et al., 2005) based on frequency–magnitude power‐law statistics essentially avoids the daunting need of seismicity declustering in hazard estimation. A retrospective analysis of natural time counts corresponding to M≥6 events for the Indian cities provides an EPS (%) as New Delhi (56), Chandigarh (86), Dehradun (83), Jammu (99), Ludhiana (89), Moradabad (84), and Shimla (87), whereas the cities in Pakistan observe an EPS (%) as Islamabad (99), Faisalabad (88), Gujranwala (99), Lahore (89), Multan (98), Peshawar (38), and Rawalpindi (99). The estimated nowcast values that range from 38% to as high as 99% lead to a rapid yet useful ranking of cities in terms of their present progression to the regional earthquake cycle of magnitude ≥6.0 events. The analysis inevitably encourages scientists and engineers from governments and industry to join hands for better policymaking toward land‐use planning, insurance, and disaster preparation in the west‐northwest part of active Himalayan belt.

Quantifying the current state of earthquake hazards in Nepal


S. Pasari, Y. Sharma, Neha


 Quantitative estimates of present-day earthquake hazard in major cities are essential for effective policymaking, community development, and seismic risk reduction. In this study, we develop a statistical analysis of natural times in Nepal to compute earthquake potential score (EPS) that describes the current level of seismic progression of a city through irregular repetitive cycle of regional earthquakes. The method, known as earthquake nowcasting (Rundle et al., 2016), uses a discrete time domain of natural times, cumulative counts of small interevent earthquakes, to characterize the present state of fault system by way of considering all earthquake events, including dependent, induced, or triggered seismicity. Data analysis and statistical inference of natural times corresponding to M ≥ 6 events assign EPS values between 59% and 99% to 24 major cities of Nepal, with the scores of metropolitan areas Kathmandu (95%), Pokhara (93%), Lalitpur (95%), Bharatpur (93%), Biratnagar (92%), and Birganj (93%). Physically, these nowcast scores, viewed as a way of tectonic stress accumulation since the last event, provide a realistic estimate on how far along is a city in its earthquake cycle of large sized events at current time. The proposed analysis and emanated results produce valuable information to the academia, industry, and public on the current dynamical state of seismic hazard in the highly earthquake prone Nepal region.

A synoptic view of the natural time distribution and contemporary earthquake hazards in Sumatra, Indonesia


S. Pasari, A.V.H. Simanjuntak, A. Mehta, Neha, Y. Sharma


 Tectonic plate interactions in Sumatra have caused a range of devastating earthquake events. In this study, we develop an analytical framework, known as earthquake nowcasting (Rundle et al. in Earth and Space Science 3:480–486, 2016. 10.1002/2016EA000185), to assess the current dynamical state of earthquake hazards in Sumatra and adjacent islands from the empirical distribution of natural times, the cumulative counts of “small” events (say, M ≥ 4) between two successive “large” earthquakes (say, M ≥ 6.5). Based on 50 years of instrumental earthquake data, the best fit Weibull distribution assigns earthquake potential score between 29 and 96% to 19 large cities in the study region with the values (%) of Aceh (72), Bengkulu (34), Binjai (81), Jambi (35), Lahat (29), Lampung (45), Lhoksuemawe (54), Medan (75), Mentawai (76), Meulaboh (71), Nias (95), Palembang (80), Padang (74), Pekanbaru (39), Sabang (72), Siantar (82), Sibolga (92), Sinabang (96), and Tanjung Balai (55). These areal-source based nowcast scores, analogous to the tectonic stress buildup since the last major event, essentially provides a unique characterization of the current level of seismic progression of a city through its repetitive cycle of regional earthquakes. Inclusion of dependent events with aftershocks being more common and the concept of natural times are some of the distinctive advantages of the proposed method. The resulting natural time statistics and consequent earthquake potential scores will facilitate seismic risk estimation, multistate decision-making, and community awareness, leading to an efficient seismic risk reduction strategy in the densely populated study region.

Empirical comparison between stochastic and deterministic modifiers over the French Auvergne geoid computation test-bed


R. Goyal, J. Ågren, W.E. Featherstone, L.E. Sjöberg, O. Dikshit, N. Balasubramanian


Since 2006, several different groups have computed geoid and/or quasigeoid (quasi/geoid) models for the Auvergne test area in central France using various approaches. In this contribution, we compute and compare quasigeoid models for Auvergne using Curtin University of Technology’s and the Swedish Royal Institute of Technology’s approaches. These approaches differ in many ways, such as their treatment of the input data, choice of type of spherical harmonic model (combined or satellite-only), form and sequence of correction terms applied, and different modified Stokes’s kernels (deterministic or stochastic). We have also compared our results with most of the previously reported studies over Auvergne in order to seek any improvements with respect to time [exceptions are when different subsets of data have been used]. All studies considered here compare the computed quasigeoid models with the same 75 GPS-levelling heights over Auvergne. The standard deviation for almost all of the computations (without any fitting) is of the order of 30–40 mm, so there is not yet any clear indication whether any approach is necessarily better than any other nor improving over time. We also recommend more standardisation on the presentation of quasi/geoid comparisons with GPS-levelling data so that results from different approaches over the same areas can be compared more objectively.

Comparison and Validation of Satellite-Derived Digital Surface/Elevation Models over India


R. Goyal, W.E. Featherstone, O. Dikshit, N. Balasubramanian


India presents among the world’s most topographically complex geomorphologies, with land elevations ranging from –2 m to + 8586 m and terrain gradients sometimes exceeding 45°. Here, we present an evaluation of four freely available digital surface models (DSMs) on a model-to-model basis, as well as a validation using independent ground-truth data from levelled benchmarks in India. The DSMs tested comprise SRTM1″, SRTM3″, ASTER1″ and Cartodem1″ [an India-only model]. Along with these four DSMs, the MERIT3″ digital elevation model (DEM) is also tested with the ground-truth data. Our results for India indicate some mismatch of these DEMs/DSMs from their claimed accuracies/precisions. All DSMs/DEMs (except for ASTER) have > 90% of pixels satisfying ± 16 m at the one-sigma level, but only in the low-lying (< 500 m) parts of India, i.e. the Gangetic plains and the Thar desert.

Spatial-spectral computation of local planar gravimetric terrain corrections from high-resolution digital elevation models


R. Goyal, W.E. Featherstone, D. Tsoulis, O. Dikshit


Computation of gravimetric terrain corrections (TCs) is a numerical challenge, especially when using very high-resolution (say, ∼30 m or less) digital elevation models (DEMs). TC computations can use spatial or/and spectral techniques: Spatial domain methods are more exact but can be very time-consuming; the discrete/fast Fourier transform (D/FFT) implementation of a binomial expansion is efficient, but fails to achieve a convergent solution for terrain slopes >45°. We show that this condition must be satisfied for each and every computation-roving point pair in the whole integration domain, not just at or near the computation points. A combination of spatial and spectral methods has been advocated by some through dividing the integration domain into inner and outer zones, where the TC is computed from the superposition of analytical mass-prism integration and the D/FFT. However, there remain two unresolved issues with this combined approach: (1) deciding upon a radius that best separates the inner and outer zones and (2) analytical mass-prism integration in the inner zone remains time-consuming, particularly for high-resolution DEMs. This paper provides a solution by proposing: (1) three methods to define the radius separating the inner and outer zones and (2) a numerical solution for near-zone TC computations based on the trapezoidal and Simpson's rules that is sufficiently accurate w.r.t. the exact analytical solution, but which can reduce the computation time by almost 50 per cent.

Signal contribution of the polar and the inclined pairs in a Bender configuration


A. Yadav, B. Devaraju, M. Weigelt


The Bender configuration comprises of two GRACE-like pairs, one in a polar orbit and the other in an inclined orbit. While the polar pair covers the entire globe, the inclined pair does not cover the higher latitudes. Similarly, the polar orbit due to its north-south orientation is able to capture features that are predominantly oriented in the east-west direction, but the inclined pair does not have any such issues. In this scenario, we would like to know the signal contribution of the polar and inclined pairs to the different spherical harmonic coefficients. Furthermore, this contribution analysis will enable us to understand the strengths and weaknesses of the GRACE(-FO) mission. In this study we use simulated data for analysing the signal contribution of the two pairs of satellites.

Deep learning networks for selection of measurement pixels in multi-temporal SAR interferometric processing


A. Tiwari, A.B. Narayan, O. Dikshit


In multi-temporal SAR interferometry (MT-InSAR), persistent scatterer (PS) pixels are used to estimate geophysical parameters, essentially deformation. Conventionally, PS pixels are selected based on the estimated noise present in the spatially uncorrelated phase component along with look-angle error in a temporal interferometric stack. In this study, two deep learning architectures, namely convolutional neural network for interferometric semantic segmentation (CNN-ISS) and convolutional long short term memory network for interferometric semantic segmentation (CLSTM-ISS), based on learning spatial and spatio-temporal behaviour, respectively, were proposed for selection of PS pixels. These networks were trained to relate the interferometric phase history to its classification into phase stable (PS pixels) and phase unstable (non-PS pixels) measurement pixels using ~10,000 real world interferometric patch images of different study sites containing man-made objects, forests, vegetation, uncropped land, water bodies, and areas affected by lengthening, foreshortening, layover and shadowing. The networks were trained using training labels obtained from the Stanford method for Persistent Scatterer Interferometry (StaMPS) algorithm. However, pixel selection results, evaluated using a combination of R-index, Similar Time Series Interferometric Pixel (STIP) maps and a classified image of the test dataset, reveal that CLSTM-ISS estimates improved the classification of PS and non-PS pixels as compared to those of StaMPS and CNN-ISS. The predicted results show that CLSTM-ISS reached an accuracy of 93.50%, higher than that of CNN-ISS (89.21%). CLSTM-ISS also improved the density of reliable PS pixels compared to StaMPS and CNN-ISS. Further, the architecture outperformed StaMPS, and is expected to compete with other MT-InSAR algorithms in terms of computational efficiency.

Estimation of Snow Depth in the Hindu Kush Himalayas of Afghanistan During Peak Winter and Early Melt Season


A.B. Mahmoodzada, D. Varade and S. Shimada


The Pamir ranges of the Hindu Kush regions in Afghanistan play a substantial role in regulating the water resource for the middle eastern countries. Particularly, the snowmelt runoff in the Khanabad watershed is one of the critical drivers for the Amu River, since it is a primary source of available water in several middle eastern countries in the off monsoon season. The purpose of this study is to devise strategies based on active microwave remote sensing for the monitoring of snow depth during the winter and the melt season. For the estimation of snow depth, we utilized a multi-temporal C-band (5.405 GHz) Sentinel-1 dual polarimetric synthetic aperture radar (SAR) with a differential interferometric SAR (DInSAR)-based framework. In the proposed approach, the estimated snowpack displacements in the VV and the VH channels were improved by incorporating modeled information of snow permittivity, and the scale was enhanced by utilizing snow depth information from the available ground stations. Two seasonal datasets were considered for the experiments corresponding to peak winter season (February 2019) and early melt season (March 2019). The results were validated with the available nearest field measurements. A good correlation determined by the coefficient of determination of 0.82 and 0.57, with root mean square errors of 2.33 and 1.44 m, for the peak winter and the early melt season, respectively, was observed between the snow depth estimates and the field measurements. Further, the snow depth estimates from the proposed approach were observed to be significantly better than the DInSAR displacements based on the correlation with respect to the field measurements.

A framework for automatic classification of mobile LiDAR data using multiple regions and 3D CNN architecture


B. Kumar, G. Pandey, B. Lohani, S.C. Misra


This paper proposes a framework for automatic classification of mobile laser scanner (MLS) point cloud using multi-faceted multi-object convolutional neural network (MMCN). The proposed method takes a full three-dimensional (3D) point cloud as input and outputs a class label for each point. Unlike other existing classification methods for MLS data, the proposed method is not dependent on any parameter or its tuning. The proposed MMCN uses multiple objects of a sample, defined by different sizes of the sample, in addition to the different facets obtained by rotating about the various axes, thus adding more information during the training and testing stages.


Conference publications

Validation of sea surface heights from satellite altimetry along the Indian coast


M. Murshan, B. Devaraju, N. Balasubramanian, O. Dikshit


 Satellite altimetry provides measurements of sea surface height of centimeter-level accuracy over open oceans. However, its accuracy reduces when approaching the coastal areas and over land regions. Despite this downside, altimetric measurements are still applied successfully in these areas through altimeter retracking processes. This study aims to calibrate and validate retracted sea level data of Envisat, ERS-2, Topex/Poseidon, Jason-1, 2, SARAL/AltiKa, Cryosat-2 altimetric missions near the Indian coastline. We assessed the reliability, quality, and performance of these missions by comparing eight tide gauge (TG) stations along the Indian coast. These are Okha, Mumbai, Karwar, and Cochin stations in the Arabian Sea, and Nagapattinam, Chennai, Visakhapatnam, and Paradip in the Bay of Bengal. To compare the satellite altimetry and TG sea level time series, both datasets are transformed to the same reference datum. Before the calculation of the bias between the altimetry and TG sea level time series, TG data are corrected for Inverted Barometer (IB) and Dynamic Atmospheric Correction (DAC). Since there are no prior VLM measurements in our study area, VLM is calculated from TG records using the same procedure as in the Technical Report NOS organization CO-OPS 065.

Forest Fire Risk Assessment for Sikkim using Earth Observation (EO) Datasets and Multi Criteria Decision Making Technique.


  A. Laha, R. Sinha, B. Nagarajan.


 Forest fires significantly influence the whole ecosystem by increasing the mortality rate of vegetation and by regulating the exchange of carbon, water, and other particulate matter between land and atmosphere. Recent climate change and anthropogenic activities are increasing the incidents of forest fires, degrading rich forest biodiversity and, their functioning. It is therefore of paramount importance to design effective strategies for protecting the forest areas. Understanding the spatial distribution of forest fires and identification of the Forest Fire Risk (FFR) zones is urgently needed to propose effective forest fire management strategies by advising efficient and practical mitigation measures.

 A protocol has been developed in this work to produce the FFR maps for the entire Sikkim state using the earth observation datasets and multi-criteria decision-making technique, i.e., AHP (Analytical Hierarchy Process) in a GIS (Geographic Information System) framework. We selected 9 different parameters (vegetation type, vegetation density, land surface temperature, elevation, slope, aspect, and distance from settlements, river, and roads) based on the understanding of the factors influencing the spatial distribution of forest fires in the region. Our results show that more than 50% area of all the districts is under high risk zones except North Sikkim, which lies at an altitude of 500m to 8056m and is mostly covered with snow. The model showed an accuracy of 82.36%, which implies that a large number of past forest fire incidence overlay the high risk zone of the state. Further analysis concluded that moderate dense forest of this region is more prone to fire, whereas aspect and human density differentiate very high and high risk zones. This model has provided a geographical representation of fire ignition probability and identifies high-risk areas in different regions.

Indian Plate Motion Revealed by GPS Observations: Preliminary Results.


 Neha, Y. Sharma, S. Pasari


 In this study, we present a brief summary of the motion of the Indian plate and its interior deformation. An analysis of four GPS stations across the Indian subcontinent provides evidence of convergence towards the Eurasian plate at a velocity of about 50 mm/yr in the northeast direction. Our analysis shows that the internal deformation of the Indian plate is very low (~1±3 mm/yr) and the whole Indian plate interior behaves like a solid rigid plate. In addition, we observe that the Indian subcontinent is subsiding at a rate of ~3±1 mm/yr. Along the Himalayan arc, we find high velocity gradient which conforms to the rapid deformation along the plate boundary. Finally, we argue that the past earthquakes and possible future earthquakes along the plate interior depend either upon the internal lithospheric stress or on the stress from the plate boundary (i.e. Himalaya).

Towards the derivation of Multiple Representation Database.


 J. Boodala, O. Dikshit, N. Balasubramanian


 This paper presents the background study carried out to design the derivation process of the Multiple Representation Database (MRDB). A topographic feature, for example, a building, is represented differently at different levels of detail (LoDs). When these different representations of a topographic feature are stored and linked, then it forms MRDB. In the proposed design, MRDB is created automatically by the model generalization process. The flowline of the model generalization is designed by studying various existing data specifications, data models, and data products of different scales. The ScaleMaster diagram is used to represent the knowledge that drives the automatic model generalization. The generalization engine discussed in this paper is currently being implemented using the selection criteria, constraints, and model generalization operators tabulated in the ScaleMaster diagram. The results of this generalization engine will be used to maintain the link between different LoDs, thus creating MRDB.


Book Chapter(s)

Spatial Data Infrastructure and Generalization.


 J. Boodala, O. Dikshit, N. Balasubramanian





A deep learning approach for efficient multi-temporal interferometric synthetic aperture radar (MT-InSAR) processing


 A.Tiwari, A.B. Narayan, O. Dikshit


 Multi-temporal interferometric synthetic aperture radar (MT-InSAR) technique has been effectively used to monitor deformation events over the last two decades. The processing steps generally involve pixel selection, phase unwrapping and displacement estimation. The pixel selection step takes most of the processing time, while a reliable method for phase unwrapping is still not available. This study demonstrates the effect of using deep learning (DL) architectures for MT-InSAR processing. The architectures are applied to reduce time computations and further to improve the quality of pixel selection. Some promising results for pixel selection have been shown earlier with the proposed architecture. In this study, we investigate the performance of the proposed architectures on newer datasets with larger temporal interval. To achieve this objective, the models are retrained with interferometric stacks covering larger temporal period and large time steps (for better estimation of interferometric phase components). Pixel selection results are compared with those obtained using open access algorithms used for MT-InSAR processing.

Establishment of State-of-the-Art Geodesy Village in India: Current status and Outlook


 S. Dhar, A. Tiwari, B. Nagarajan, B. Devaraju, O. Dikshit, J. Prakash, P. Mishra, D. Agarwal, V. Sharma, D. Varade, A. Laha, A. Kumar, S. Singh, A.B. Narayan, R. Goyal, V. Kumar


 National Centre for Geodesy (NCG) has been established in IIT Kanpur, India with the vision of acting as a hub of excellence in geodetic research at the National and International level. Working towards its mission, it has initiated this state-of-the- art establishment for improving the space geodetic infrastructure of the country and encouraging more researches in the geodesy field. The presentation will discuss the current status of the planned core site and its future establishments. It will provide detailed description of all the facilities installed in the site right now, and the future extensions. This new core-site will house facilities for three technologies – Space, Time and Earth gravity domain. The main purpose of establishing this site is for improving the realization of terrestrial and celestial reference frames, Earth Orientation Parameters (EOPs) and other data products essential for understanding the Earth’s environment. This co-located site with four space geodetic techniques will help in the International campaign for determination of TRF with 1mm accuracy and 0.1 mm/yr. stability. Moreover, this site location will improve the uniformity in geographical distribution of the ITRF observatories and the necessity of this station has been confirmed by simulation modelling.

Comparison of spectral methods for the evaluation of Stokes integral


 A.B. Narayan, A. Tiwari, G. Sharma, B. Devaraju, O. Dikshit


 The spherical approximation of the fundamental equation of geodesy defines the boundary value problems. Stokes’s integral provides the solution of boundary value problems that enables the computation of geoid from the properly reduced gravity measurements to the geoid. The stokes integral can be evaluated by brute-force numerical integration, spectral methods, and least-squares collocation. There is a trade-off between computation time and accuracy when we chose numerical integration technique or any spectral method. This research will compare time complexity and the accuracy of different spectral methods (1D-FFT, 2D-FFT, Multi-band FFT) and numerical integration technique for the region in the lower Himalaya, around Nainital, Uttarakhand, India.

Importance of Shared Vocabularies in Deriving Geographic Data of Varying Levels of Detail.


 J. Boodala, O. Dikshit, N. Balasubramanian,



Optimal choice of the number and configuration of VLBI global observing system in India.


 S. Singh, R. Goyal, N. Balasubramanian, B. Devaraju, O. Dikshit


 The need of the geodetic VLBI stations in South Asia region has been discussed and suggested for decades to have a uniform global VLBI network and relatively more accurate realisation of ITRF. With the recent initiative of National Centre for Geodesy, India, setting up of a few VLBI stations in the country is being proposed. India spans from latitude 8.4º N to 37.6º N and longitude 68.7º E to 97.25º E and encompasses a diversified topography with a plethora of geodynamical activities. Along with contributions to the international geodetic campaigns, we would like to choose the locations of these VGOS stations so that these can be an aid to the Indian geodetic infrastructure along with several other studies of national importance. For multitude of reasons, the prospective sites for establishing VGOS stations in India are: 1) IIST Ponmudi campus, 2) Mt. Abu Observatory, PRL, 3) IIT Kanpur and 4) NE-SAC, Shillong. The approximate longitudinal extent of 20º and latitudinal extent of 18º between these prospective sites are worth exploiting for determining the angle of the Earth rotation (dUT1) and polar motion, respectively. In this study, we present the comparison results of the solutions with and without additional VGOS station in India. For this, we first generated an optimised schedule for a classical VGOS/R1 session, using VieVS, with existing stations using the comparatively more important optimisation criteria (duration, sky-coverage, number of observations and idle time) and corresponding weight factors. The simulation result of the best schedule is kept as our reference solution. With respect to this reference network, we further generated optimised schedules by including the prospective stations from India (different combinations of the four proposed stations). We present our analysis due to change in network geometry, and therefore, we compare the variations in the repeatability values of the estimated EOPs with the addition of VGOS station(s) in India.

Subtleties in spherical harmonic synthesis of the gravity field.


  R. Goyal, S.J. Claessens, W.E. Featherstone, O. Dikshit


 Spherical harmonic synthesis (SHS) can be used to compute various gravity functions (e.g., geoid undulations, height anomalies, deflections of vertical, gravity disturbances, gravity anomalies, etc.) using the 4pi fully normalised Stokes coefficients from the many freely available Global Geopotential Models (GGMs). This requires a normal ellipsoid and its gravity field, which are defined by four parameters comprising (i) the second-degree even zonal Stokes coefficient (J2) (aka dynamic form factor), (ii) the product of the mass of the Earth and universal gravitational constant (GM) (aka geocentric gravitational constant), (iii) the Earth's angular rate of rotation (ω), and (iv) the length of the semi-major axis (a). GGMs are also accompanied by numerical values for GM and a, which are not necessarily identical to those of the normal ellipsoid. In addition, the value of W0, the potential of the geoid from a GGM, needs to be defined for the SHS of many gravity functions. W0 may not be identical to U0, the potential on the surface of the normal ellipsoid, which follows from the four defining parameters of the normal ellipsoid. If W0 and U0 are equal and if the normal ellipsoid and GGM use the same value for GM, then some terms cancel when computing the disturbing gravity potential. However, this is not always the case, which results in a zero-degree term (bias) when the masses and potentials are different. There is also a latitude-dependent term when the geometries of the GGM and normal ellipsoids differ. We demonstrate these effects for some GGMs, some values of W0, and the GRS80, WGS84 and TOPEX/Poseidon ellipsoids and comment on its omission from some public domain codes and services (isGraflab.m, harmonic_synth.f and ICGEM). In terms of geoid heights, the effect of neglecting these parameters can reach nearly one metre, which is significant when one goal of modern physical geodesy is to compute the geoid with centimetric accuracy. It is also important to clarify these effects for all (non-specialist) users of GGMs.

Indian gravimetric geoid model


 R. Goyal, W.E. Featherstone, S.J. Claessens, O. Dikshit, N. Balasubramanian



Geodetic monitoring of the hydrological changes in Nepal Himalaya.


  J.D. Ray, B. Devaraju, M.S.M. Vijayan, W. Godah


 Mass of the Earth's system although remains constant, it gets transported between various Earth's system components. These mass transports are found to induce deformations of the Earth's surface known as surface mass loading and are driven by climate patterns. Therefore, temporal mass variations within the Earth's system and hence surface mass loading is the direct impact of climate change. One of the major sources of mass transport in the Indian subcontinent is the monsoon. This subcontinent receives a significant amount of rainfall during the monsoon period. The mass transports caused by the Indian monsoon deform the Earth's surface which can be detected with space geodetic techniques such as Global Navigational Satellite Systems (GNSS) and dedicated gravity satellite missions, in particular, the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow on (GRACE-FO) satellite missions. The overarching objective of this study is to monitor the hydrological changes in Nepal Himalaya using geodetic data. In particular, it is aimed at investigating the contribution of mass transports from various catchments in the Nepal Himalaya and its surrounding areas to the hydrological signal observed by the continuously operating GPS (Global Positioning System) stations. GRACE/GRACE-FO satellite missions' data, hydrological models and spatio-temporal modelling techniques have been used to ascertain the aforementioned contribution. The results obtained were presented, analysed and discussed.