Department of Civil Engineering

Permanent URI for this collectionhttp://localhost:4000/handle/123456789/1927

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Subject: search.filters.subject.Remote sensing

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Now showing 1 - 10 of 13
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    An approach to the simulation of radar sounder radargrams based on geological analogs
    (IEEE, 2019-03) Thakur, Sanchari
    Simulation of radar sounder (RS) data is important for understanding the radar response of subsurface features to facilitate the interpretation of the real data. Conventional electromagnetic simulators require the definition of complex geoelectrical models of the investigated targets. They also involve time-complex solutions of Maxwell's equations for computing the received electric field, which leads to very high computation time. Furthermore, the simulated radargrams are often not realistic as it is very difficult to model all the variables involved in the data acquisition. In this paper, we propose a novel simulation approach that exploits the data available from existing RSs in geologically analogous terrains, to produce realistic simulations of the investigated RS target. This simulation strategy is based on minimizing the difference between the analog and the investigated acquisition scenarios. This is done by applying a series of corrections, which depend on the relation between the radargram characteristics and the physical variables describing the acquisition process. The aim is to produce radargrams that resemble the investigated scenario in terms of the echo magnitude, bandwidth, range resolution, and along-track resolution. Experimental results present three case studies for different possibilities of the analog and the investigated scenarios. The validation of the simulated radargrams with actual data demonstrates the effectiveness of the proposed approach. Finally, we also present a real application of this approach for the simulation of Radar for Icy Moon Exploration (RIME) radargrams for a combination of instrument and target parameters, using the SHAllow RADar (SHARAD) radargram acquired over the geological analog of a selected RIME target.
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    Analysis of subsurface hypotheses through simulation of rime radargrams based on available analogous data
    (IEEE, 2019) Thakur, Sanchari
    Radar for Icy Moon Exploration (RIME) is designed to characterize the subsurface geology of the Jovian icy moons. The RIME radargrams will show the combined response of a number of geophysical and geological characteristics of the ice-shells of these moons. Thus, radar sounder simulations are needed to understand the relationship between these target variables and the RIME response. In this paper, we use a computationally simple simulation approach that is based on reprocessing the radargrams available from the geological analogs of RIME targets. Moreover, we present a case study for a particular RIME target using this simulation technique for the generation of a database of RIME radar-grams, and a technique for analyzing this database. From the preliminary analysis of the simulated radargrams, we could derive important information regarding the underlying target variables. This confirms the usefulness of the presented approach to support the geological interpretation of the RIME radargrams.
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    Stratus: a new mission concept for monitoring the subsurface of polar and arid regions
    (IEEE, 2021) Thakur, Sanchari
    This paper presents the SaTellite RAdar sounder for earTh sUbsurface Sensing (STRATUS), which is a satellite mission for Earth Observation (EO) with an onboard instrument capable of probing the Earth's subsurface in polar and arid regions. STRATUS is based on an innovative distributed radar sounder (RS) with the unique capability to obtain continuous and large-scale subsurface measurements, with homogeneous and consistent quality in two of the least characterized and crucial frontiers of Earth: globally on the polar ice sheets, i.e., Greenland and Antarctica (primary objective), and regionally on the arid areas and deserts. STRATUS is a ground-breaking exploratory mission addressing crucial scientific questions. It provides new fundamental data that have not been acquired by any other past or present remote sensing mission on the Earth, with an expected high and genuine scientific return enabling the assessment of the climate change signature in the Earth subsurface.
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    An approach to the assessment of detectability of subsurface targets in polar ICE from satellite radar sounders
    (IEEE, 2021-10) Thakur, Sanchari
    A satellite mission onboard a radar sounder for the observation of the earth’s polar regions can greatly support the monitoring of the cryosphere and climate change analyses. Several studies are in progress proposing the design and demonstrating the performance of such an earth-orbiting radar sounder (EORS). However, one critical aspect of the cryospheric targets that are often ignored and simplified in these studies is the complex geoelectrical nature of the polar ice. In this article, we present a performance assessment of the polar ice target detectability by focusing on their realistic representation. This is obtained by simulating the orbital radargrams corresponding to different regions of the polar cryosphere by leveraging the data available from airborne campaigns in Antarctica and Greenland. We propose novel performance metrics to analyze the detectability of the internal reflecting horizons (IRHs), the basal interface, and to analyze the nature of the basal interface. This performance assessment strategy can be applied to guide the design of the signal-to-noise ratio (SNR) budget at the surface, which can further support the selection of the main orbital instrument parameters, such as the transmitted power, the two-way antenna gain, and the processing gains.
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    Analysis of earth’s ionosphere effects on englacial layering detectability in spaceborne radar sounders data
    (IEEE, 2022-06) Thakur, Sanchari
    Several studies are in progress for proposing an Earth-orbiting radar sounder (EORS) mission. Some of them consider as baseline system architecture a recently proposed distributed radar sounding array in formation flight with enhanced capabilities of clutter suppression. Besides clutter, the detectability of subsurface targets may also be affected by the propagation of the radar signal through Earth’s ionosphere. These effects include frequency-dependent phase dispersion and scintillations. In this letter, we present a subsurface detection performance assessment of an EORS with distributed architecture focusing on the ionospheric effects. The novel contributions of this work are: 1) simulation of the coherent radar response of a representative polar ice target (englacial layering) in the distributed radar sounding case; 2) inclusion of spatially dependent ionospheric scintillation effects on the distributed beam pattern; 3) inclusion of phase dispersion effects for different values of total electron content (TEC); and 4) analysis of the subsurface detection performance. Detectability analysis is performed after applying a state-of-the-art technique for compensating ionospheric phase-dispersion effects. The results show that the englacial layering is detectable by compensating for the dispersion effects in the range between 1 and 21 TECU in the ionosphere. The layering is also detectable at higher values of TEC by improving the accuracy of TEC estimation. Moreover, even without compensation, the worst case ionospheric phase scintillations of 25° produce a negligible effect on the detectability.
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    A range-doppler method for focusing radar sounder data generated by coherent electromagnetic simulators
    (IEEE, 2022-08) Thakur, Sanchari
    Radar sounders (RSs) are gaining importance in planetary missions thanks to their unique capability of providing direct measurements of subsurface (SS) structures. To support their design and data interpretation, several electromagnetic (e.m.) simulation techniques have been developed with enhanced capabilities for emulating the RS acquisition process. However, the raw simulated radargrams obtained from e.m. simulators are difficult to interpret and analyze without a focusing operation, which results in an underestimation of the RS detection performance. While frequency methods for range and azimuth compression of real RS data are well-established, their use on simulated data is not addressed in the literature and requires major modifications. This article presents a novel method that implements azimuth compression using unfocused and focused processing on simulated raw data. The proposed method is based on an adaptation of the range-Doppler algorithm to the case of raw data generated by a coherent RS simulator. The method is demonstrated in three case studies to show the similarity between simulated and real data processing: 1) simple geometries; 2) a simulated SHAllow RADar (SHARAD) radargram compared with the real data product; and 3) a real application scenario for supporting the design of a new RS instrument. The results indicate higher fidelity of the focused simulated data with the real data product and the target structure, confirming the usefulness of the proposed approach in obtaining realistic processing of simulated radargrams.
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    A multi-layer simulation technique for modeling large and small-scale scattering in radar sounder data
    (SPIE, 2022) Thakur, Sanchari
    Radar sounders (RS) provide information on subsurface targets for planetary investigations. Several simulation techniques have been developed to support the RS design and the data interpretation. Each technique has different properties and modeling capabilities, achieving different trade-offs between accuracy and computational requirements. The state-of-the-art RS simulation techniques include: i) numerical methods, such as the Finite- Difference Time-Domain (FDTD) technique, which allows the modelling of small-scale scattering phenomena at the cost of high computational requirements; ii) facet modeling and ray-tracing based methods, such as the multi-layered coherent RS (MCS) technique, which requires less computational resources than FDTD, allowing the modeling of large-scale scattering phenomena. Recently an integrated simulation methodology has been presented, for simulating small-scale scattering phenomena in large scenarios. However, this methodology was designed for modeling only surface scattering. In this paper, we propose a method that extends the capabilities of the integrated methodology to model both large and small-scale roughness in a multi-layer scenario. The proposed method uses the FDTD technique to evaluate the effects associated with small-scale roughness in terms of i) scattering phenomena associated with the layers and ii) power losses associated with the signal transmitted through a rough layer. To recursively apply scattering and transmission to multiple layers of the subsurface, a coherent ray-tracing method is used. We experimentally assessed the effectiveness of the proposed methodology on three-layer models by integrating the effect of roughness imposed on the layers and in transmission through them.
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    Detecting near-surface melt-water and basal ice-water interfaces by VHF radar sounder data
    (IEEE, 2024-07) Thakur, Sanchari
    Very high-frequency (VHF) radar sounding from an orbital platform is a promising mission concept for subsurface observations of the Earth’s polar caps for mapping the ice sheets and ice shelves from the surface to the base. Previous feasibility studies have analyzed the detectability of the basal interface, the internal layers and the subglacial lakes in simulated VHF radargrams. However, there are few studies on the detection of near-surface melt-water and the ice-ocean interface, which are important for predicting the stability of the polar ice. This paper both presents a novel semi-supervised basal ice-water detection algorithm and exploits a state-of-the-art dielectric inversion technique to detect surface melt for the analysis of simulated VHF radargrams. Results show that about 90% of the ice-ocean interfaces are correctly detected with the proposed detection algorithm and that the dielectric inversion revealed a pool of melt-water in the Antarctic peninsula.
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    Development of a web application through a mobilized crowdsourcing platform to enable participatory risk sensitive urban development
    (AARS, 2025) Goonetilleke, Ashantha
    Flooding is the most frequent and destructive natural disaster currently facing Sri Lanka. Rapid urbanization and changing precipitation patterns are exacerbating the situation, leading to extensive socio-economic damage and disrupting countless lives. Despite the availability of technology-based applications that can raise disaster awareness and improve management, these tools are not fully utilized in Sri Lankan communities. The study addresses the critical issue of insufficient awareness and the lack of formal early flood alert mechanisms within Sri Lankan. Although, recent technological advancements offer opportunities for community to engage in sharing early disaster warnings among their networks, they remain underutilized. The community engagement in disaster management is still minimal, reducing the preparedness and resilience of vulnerable communities. To address this, a platform integrating a crowdsourcing-based mobile application with a web application was developed, aiming to make disaster management and response inclusive through community involvement and advanced remote sensing technologies. A flood vulnerability assessment model was created using 30 years of historical flood data and nine conditioning factors, including topographic features, weather-related variables, hydrological networks, land cover, and soil type, with Sentinel-2 satellite imagery for the Kelaniya watershed area enhancing the model's accuracy. The mobile application facilitates real-time data collection from individuals in flood-prone areas, who can report on flood levels, affected locations, and other critical information. This crowdsourced data undergoes rigorous verification to ensure accuracy. Once validated, the information is visualized on a web application, serving as a vital communication tool for both the community and disaster response authorities. The methodology includes developing the vulnerability assessment model, creating the mobile application with integrated crowdsourcing techniques, and conducting trial workshops to engage the community and validate the platform with the contribution of relevant authorities. Mobilization strategies are proposed based on insights from these community interactions. By prioritizing community participation and utilizing cutting-edge geo-information technologies, this research significantly contributes to building resilient and proactive urban communities in Sri Lanka. The findings demonstrate the substantial potential of combining crowdsourced data with remote sensing to enhance disaster management and community resilience.
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    Spatiotemporal change analysis of urbanization in Gurugram district of Haryana, India, using a geospatial technique
    (Springer, 2024-07) Singh, Ajit Pratap
    Remote sensing and GIS play a very important role in monitoring, managing, and mapping the operation of natural resources. This study includes the Landsat 5 and Landsat 8 satellite imagery for the analysis of urban sprawl for the years 1999 and 2019, respectively, in the Gurugram (previously known as Gurgaon) district of Haryana, India. The methodology of the study follows by calculating the NDBI (normalized built-up index) spectral indices for extracting the built-up feature class from the Landsat time series data sets of 1999 and 2019. The aim of this study is to: (i). find out urbanization patterns in the area of interest and (ii). temporal change analysis, in particular, urban feature class from 1999–2019. The outcomes of the study illustrate a rapid urban sprawl in the region by the percent increase of 293%. In conclusion, the study findings suggest to secure a livable and resilient future for the residents of the region; policymakers and urban planners must embrace sustainable and integrated approaches to urban development that balance economic growth with environmental protection.