Integration of SAR and multi-spectral imagery in flood inundation mapping – a case study on Kerala floods 2018

ABSTRACT

Torrential floods had placed a record in the history of Kerala, the state on the south-western coast of India, in 2018. This study focusses primarily on the assessment of flood inundation mapping using the Sentinel-1 SAR imagery applying the Otsu’s thresholding algorithm for the Alappuzha region. Though the pre-processing of SAR imagery is difficult, the availability of software and enhanced hardware facilitates efficacy in image processing. Normalized Difference Water Index (NDWI) was computed to aid in differentiating the permanent waterbody from the flooded region. The results implicate the spread of flood-inundated zones has considerably increased in August, thereby indicating the devastating effect of the flood in August. Based on the results obtained, 13.86% area of the region has been covered by flood in August, excluding the permanent water bodies, which is comparatively high compared to the previous months. It is necessary to note that, extreme rainfall accompanied by the full reservoir level of the dams in the region served to be the key to the disaster in August. The resultant flood inundation map could be utilized quite effectively for relief measures and damage assessment.

KEYWORDS:

• Kerala floods
• flood inundation mapping
• NDWI
• sentinel-1
• thresholding technique

Acknowledgments

We are much grateful to the European Space Agency’s Copernicus Open Access Hub for providing us with Sentinel-1 and Sentinel-2 images freely.

Author contributions statements

The authors have contributed substantially towards the research work and the preparation of the manuscript. The first author (JJJ) has carried out the background study of the research idea and implemented it assessing the delineation of the flood-inundated areas using microwave remotely sensed imagery. The third author (AD) contributed to the collection of field data and preparation of figures. The results and manuscript were reviewed and corrected by the corresponding author (Dr.SS).

Data availability

Data sharing does not apply to this article, as no new data were created or analysed in this study.

Disclosure statement

No potential conflict of interest was reported by the authors.