Application of Synthetic Aperture Radar (SAR) remote sensing in flood disaster management (Module 4)

Space based Disaster Management

Prepared by Venkata Sai Krishna Vanama, Ph.D. Research Scholar, CUSE, IITB. Email: [email protected] || Website: https://sites.google.com/view/venkata-sai-krishna flood monitoring (2018 flood event)

Venkata Sai Krishna Vanama, Mohamed Musthafa, Unmesh Khati, Gowtham R, Gulab Singh, Y. S. Rao. “Flood extent mapping of Kerala flood event in 2018 using ALOS-2 and temporal Sentinel-1 SAR images.” Current Science (In press)

2 Introduction Idamalayar , Ernakulam Kerala State: • In 1924: unprecedented rainfall (3,368 mm - 61 days) Source: BloombergQuint • In 2018: unprecedented rainfall (2,378 mm - 88 days) • Four times more than normal • 13 out 14 districts were severely affected. • Deaths reported: 400, people displaced: 1,50,000 • Heavy rainfall + Dam water release + Landslides

Periyar river flood Source: https://www.theatlantic.com/photo/2018/08/ devastating-monsoon-floods-in-kerala-/568171/

13 – 20 Aug 2018 Rainfall Source: https://www.youtube.com/watch?v=PaDiU7xQKj8 Source: https://www.indiatoday.in/india/story/why-kerala-floods-killed-so-many-destroyed-so-much-1319998-2018-08-21

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 3 Optical vs SAR images Sentinel-2 Sentinel-1 VV Pol

Images used: Pre-flood (Jan), Flood (Jun, Jul and Aug), Post-flood(Sep) Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 4 Datasets

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 5 Datasets

Apart from EO datasets ● Field survey data (Location, flood depth, photographs, land use) was also used.

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 6 Study Area

● Kottayam and Alappuzha districts ○ Rainfall during the period 01 Jun -22 Aug 2018 witnessed a departure of 51%and 29% respectively ○ Rich in ecologically sensitive land features such as wetlands and mangroves ○ The lake, a Ramsar site passes through the districts

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 7 Study Area

● Kottayam and Alappuzha districts ○ Rainfall during the period 01 Jun -22 Aug 2018 witnessed a departure of 51%and 29% respectively ○ Rich in ecologically sensitive land features such as wetlands and mangroves ○ The Vembanad lake, a Ramsar site passes through the districts ● Multiple land use land cover exists ○ Built-up (urban, semi-urban, transport) ○ Agricultural lands, plantations ○ Water bodies ○ Open land

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 8 Temporal S1 SAR backscatter (흈0) for high dense urban areas

system:time_start VV_Asc_Mean VH_Asc_Mean

21-Aug-18 -5.612 -12.612

27-Aug-18 -7.261 -14.112 Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 9 Temporal S1 SAR backscatter (흈0) for medium dense urban areas

system:time_start VV_Asc_Mean VH_Asc_Mean

21-Aug-18 -6.541 -15.391

27-Aug-18 -6.608 -16.359

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 10 Temporal S1 SAR backscatter (흈0) for low dense urban areas

system:time_start VV_Asc_Mean VH_Asc_Mean

21-Aug-18 -8.923 -16.347

27-Aug-18 -8.833 -16.45

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 11 Methodology

Flood image + manual thresholding ● Single pol (VH) – Multi-temporal Sentienl-1 images ● Dual pol (HH,HV) – Single date ALOS-2 image

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 12 Methodology

Flood image + manual thresholding ● Single pol (VH) – Multi-temporal Sentienl-1 images ● Dual pol (HH,HV) – Single date ALOS-2 image

Rule based classification (Dual pol VV+VH is used) ● RGB image is formed by before, during-flood image ● Red channel: 20*log10(|VVflood|) ● Green channel: 20*log10(|VHflood|) ● Blue channel: 20*log10(0.5*{|VVpre|+|VHpre|}) ● 05 May 2018 is used as pre-flood image

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 13 Results

ALOS-2 based flood map

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 14 Results

ALOS-2 based flood map Sentinel-1 based flood map

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 15 Results (Increased flood)

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 16 Results (Flood retreat)

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 17 Quantitative assessment of flood area

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 18 Ground truth database creation from optical images

● Two thematic indices (GNDVI, MNDWI) are created from the optical RS images. ● These indices are effectively useful to identify the permanent water bodies. ● The regions which are not affected by cloud cover are digitized and updated with the help of crowd-sourcing datasets.

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 19 Ground truth database creation from optical images 09 Jan 2018 12 Aug 2018 22 Aug 2018 27 Aug 2018 21 Jan 2018 01 Aug 2018 02 Sep 2018

Landsat-8 optical images optical Landsat-8 Sentinel-2 optical images optical Sentinel-2

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 20 Ground truth database creation from optical images

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 21 Ground truth database creation from optical images

Photos captured on 09th September 2018 by Prof. Harsha Rajan show the devastation caused by the floods in (a) Padanad , (b) Chengannur, (c) Kadapra and (d) Thiruvalla towns situated in Alappuza district. Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 22 Validation of results Ground Truth Flood Non-Flood

Algorithm Flood TP = 39204 FP = 1214 PPV = 0.97 output Non-Flood FN = 20119 TN = 58231 NPV = 0.74

TPR = 0.66 TNR = 0.98

Validation - Flood area obtained from SAR image acquired on 22 Aug 2019 ● An overall accuracy of 82.05 % for both classes ● F-Score of 78% for flood class alone.

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 23 Kerala flood analysis from secondary sources IIRS, ISRO

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 24 Kerala flood analysis from secondary sources

ESA Dept. of Disaster management, Govt. of Kerala NRSC, ISRO

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 25 Useful Resources

● Global Exposure Analysis on Floods/Drought and Poverty (Slides) ● Flood mapping by ESA. ● Flood mapping with Sentinel-1 data using SNAP and QGIS. ● SAR based Flood mapping tutorial by UN-SPIDER. ● How to Map Regional Inundation with Sentinel-1 using Sentinel-1 Toolbox (ASF DAAC) ● Flood mapping with Sentinel-1 data in Research and User Support (RUS) Service portal. ● Flood mapping tutorial by German Aerospace Center DLR. ● Lakes - Floods monitoring practical by Dr Yésou H. (4th ESA Advanced training course in Land Remote Sensing) ● Flood mapping by Herve Yesou, SERTIT, France. (PPT, tutorial) [8th Advanced Training Course on Land Remote Sensing] ● Advancing SAR and Optical Methods for Rapid Mapping (ASAPTERRA). ● Flood monitoring using Landsat-8 and Sentinel-2 in QGIS. ● Hazard: Flood mapping with Sentinel-1 (ESA EO College). ● 8th ESA Training Course on Radar and Optical Remote Sensing and tutorials.

https://sites.google.com/view/venkata-sai-krishna

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 26

Thank you

Flood mapping through SAR images || Prepared by Venkata Sai Krishna Vanama, email: [email protected] 27