Lodging is a major yield-limiting factor in rice. Accurate assessment of rice lodging is essential for yield damage estimation, agricultural insurance claims settlement and subsequent management decisions. This study aims to explore the effect of lodging on backscatter/coherence and spectral reflectance derived from Sentinel-1 and Sentinel-2 data. Based on this, an extraction method of lodging rice distribution using multi-source remote sensing data was proposed. The results showed that: (a) The lodging area of rice could be effectively extracted from dual-polarization Sentinel-1 image data with an accuracy of 87.87%; (b) The vegetation indices (NDVI, DVI and LSWI) extracted by Sentinel-2 are sensitive to lodging rice. Based on a certain threshold, lodging rice can be effectively extracted with an accuracy of 87.5%. Our findings demonstrate the potential of Sentinel data for near real-time detection of the rice lodging.
Guest editors Shuisen Chen, Chandrasekar Nainarpandian, and Ayad M. Fadhil Al-Quraishi summarize the Special Section on Coastal Zone Remote Sensing for Environmental Sustainability.
Recent advancements in remote sensing facilitate the mapping of mineral occurrences but lack quantitative estimation of mineral abundances. In the present study, EO-1 Hyperion data are used for mapping and estimating beach placer minerals in the Cuddalore coastal stretch of Tamil Nadu, India, using spectral angle mapper (SAM) algorithm, continuum removed band depth analysis, and random forest (RF) regression. Strategic beach placer minerals are exposed in the image due to their specific spectral reflection/absorption characteristics; these unique settings are used to explore their spatial distribution from associated features. EO-1 Hyperion images are analyzed for (i) atmospheric correction; (ii) selection and transformation of optimum bands; (iii) fixing the input pixels from selected bands; (iv) generating n-D angle—for the preparation of end-members with unique spectra of mineral classes; (v) comparative analysis between true end-member and reference spectra of minerals using SAM, spectral feature fitting, and binary encoding algorithms; and (vi) image classification using SAM. The result of SAM shows the occurrence of placer mineral deposits such as zircon with an overall accuracy of 81.06% and Kappa coefficient of 0.71. The zircon shows strong absorption in spectral geometric parameters of EO-1 Hyperion data, such as band depth and band area at the spectral range of 1075 to 1150 nm. The positive correlation between geometric parameters of mineral spectra in its absorption characteristics and the mineral concentration of in situ samplings is used for developing an RF prediction model for estimating the placer minerals from beach sand deposits. Significantly, the lower RMSE values estimated at 0.082 and 0.156 for reference spectra (in situ) and image spectra respectively proved the ability of EO-1 Hyperion data for quantifying mineral resources.
We investigate the potential vulnerability to seawater intrusion into the aquifers along the Kozhikode coastal stretch using the modified GALDIT (GALDIT-U) model from an urbanization perspective. Urban growth impact (expansion of the impervious surface) was added as an additional input parameter in the GALDIT model, and the analyses were performed using GIS. The results indicated that the area of 16.84 km2, found within the proximity of urban settlements and eroded shorelines along with the Kozhikode, Beypore, Kadalundi, and Faroke, falls under very high vulnerability to seawater intrusion with vulnerability index values ranging 24.82 to 29.82. In the southern sector, the area of 16.84 km2 between Elathur and Beypore also falls within very high vulnerability zones. Similarly, the area of 37.01 km2 in Quilandi, Faroke, Puthiyankadi, Panniyankara, and the east sector of Kozhikode municipality is seen as high vulnerability zones with the vulnerability index values ranging 19.84 to 24.82. Seawater intrusion estimated under moderate vulnerability zones is found to occupy 47.85 km2 (vulnerability index values 14.88 to 19.84). The low and very low vulnerability zones cover 65.07 and 48.07 km2, with the vulnerability index values ranging 9.92 to 14.88 and 4.96 to 9.92, respectively. When cross-validated using major hydrochemical parameters, the results indicate a strong correlation between the vulnerability index classes and groundwater physicochemical parameters. The sensitivity analysis carried out indicated that the distance from the shoreline (D), impacts of urban growth (U), and depth to groundwater table above sea level (L) to be highly influencing parameters for seawater intrusion vulnerability in the coastal stretches. The modified GALDIT-U model shows reliable accuracy for estimating and demarcating seawater intrusion vulnerability zones and could act as an efficient tool in the sustainable management of coastal aquifers in an urban environment.
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