Advances in Radar Remote Sensing of Agricultural Crops: A Review

There are enormous advantages of a review article in the field of emerging technology like radar remote sensing applications in agriculture. This paper aims to report select recent advancements in the field of Synthetic Aperture Radar (SAR) remote sensing of crops. In order to make the paper comprehensive and more meaningful for the readers, an attempt has also been made to include discussion on various technologies of SAR sensors used for remote sensing of agricultural crops viz. basic SAR sensor, SAR interferometry (InSAR), SAR polarimetry (PolSAR) and polarimetric interferometry SAR (PolInSAR). The paper covers all the methodologies used for various agricultural applications like empirically based models, machine learning based models and radiative transfer theorem based models. A thorough literature review of more than 100 research papers indicates that SAR polarimetry can be used effectively for crop inventory and biophysical parameters estimation such are leaf area index, plant water content, and biomass but shown less sensitivity towards plant height as compared to SAR interferometry. Polarimetric SAR Interferometry is preferable for taking advantage of both SAR polarimetry and SAR interferometry. Numerous studies based upon multi-parametric SAR indicate that optimum selection of SAR sensor parameters enhances SAR sensitivity as a whole for various agricultural applications. It has been observed that researchers are widely using three models such are empirical, machine learning and radiative transfer theorem based models. Machine learning based models are identified as a better approach for crop monitoring using radar remote sensing data. It is expected that the review article will not only generate interest amongst the readers to explore and exploit radar remote sensing for various agricultural applications but also provide a ready reference to the researchers working in this field

Wheat leaf area index retrieval using RISAT-1 hybrid polarized SAR data

Leaf Area Index (LAI) is a key parameter to characterize the canopy–atmosphere interface, where most of the energy fluxes exchange. Space-borne satellite images have shown their relevance for various applications including LAI retrieval over large areas. Although optical data have been used for this purpose in previous studies, the constraints to acquire optical data during extreme weather conditions due to the presence of clouds, haze, smoke etc. hinders its use for uninterrupted monitoring. This study aims to analyze the relationships of C-band RISAT-1 hybrid polarized SAR data (σ˚RH and σ˚RV) with wheat LAI. The results have shown the correlation coefficient (|r|) of 0.57 and 0.73 for RH and RV backscatter, respectively, using non-linear regression approach. It is also observed that the accuracy of LAI retrieval has been significantly improved with |r| and RMSE of 0.81 and 0.54 (m2/m2), respectively, by considering both RH and RV backscatter as inputs for support vector machine-based model

Geomorphic assessment of active tectonics in Jaisalmer basin (Western Rajasthan, India)

The northwestern part of Indian plate consists of a number of sedimentary basins such as the Jaisalmer basin with Early Jurassic to Quaternary deposits. The NW-SE trending Kanoi fault and Ramgarh fault with Mari-Jaisalmer Arch in the basin are tectonically active. We delineate the tectonically active areas of the basin by considering watersheds, micro-scale basins and spot locations. Analytic Hierarchy Process (AHP) is applied to calculate the Index of Active Tectonics (IAT) for the watersheds. Basin asymmetry (AF), valley floor width to height ratio (Vf) and hypsometric curve are calculated/generated. Computed R2 values and the IAT identify watershed-4, Miajlai depression, to be tectonically most active. Three individual spots along the NW-trending Mari highland have tectonic control on drainage patters. The hydrocarbon fields are located in the Shahgarh and the Miajlar depression zones within watersheds 3 and 4, which are under tectonically moderate and high activities, respectively. Highlights Geomorphology of the Jaisalmer basin in response to active tectonics is investigated. Watershed 4 is tectonically active followed by watershed 3. Hydrocarbon fields are located in these two watersheds. The work will have far-reaching implication in petroleum geosciences of the area