ANNOUNCEMENTS
Heavy rainfall and related disasters see a frequent occurrence in a tropical monsoon country like India. Landslides are one such. These are the result of heavy downpour as well as human intervention. Identifying these immediately after the occurrence to take necessary steps has been difficult to the scientific community. Optical data has been a useful tool for the researchers over years, but various disadvantages such as cloud cover, lack of continuous data acquisition etc have lead the researchers to opt different wavelengths of the spectrum for analyzing various features on earth surface. This thesis concentrates on identifying a methodology to identify landslides (during heavy rainfall period) on microwave data. The cloud burst on the Indian state of Kerala during the year 2019 resulted in wide spread landslides which caused heavy loss of lives as well as property and this was the reason for opting this year as the period of study. SAR and optical images of pre and post event were acquired to observe the changes. Sentinel-1 for microwave data and Sentinel- 2 for optical data were used. Optical data was used to find the landslide locations using visual interpretation due to lack of ground points. The first methodology that was adopted mainly concentrates on identifying landslides using amplitude data. A total of 57 landslides were identified using optical data out of which maximum are in the district of Wayanad (43) and the rest were identified in the district of Calicut (14). Major landslides include Pachakkadu, Chembaonoda and few other places, which observed heavy human loss and authorities were not able to recover the dead bodies from the disaster site. Backscatter coefficient value derived from the landslide points of September 2019 for VH polarization ranged between -7 dB to -22 dB for Wayanad region, whereas for Calicut, it ranged between -8 dB to -18 dB. For VV polarization, the coefficient values ranged between -1 dB to -20 dB for Wayanad and -1 dB to -12 dB for Calicut respectively. Backscatter coefficient values derived for the month of July of VH polarization for Wayanad region ranged between -5dB to -20 dB and from -8 dB to -19 dB for Calicut region. The values for VV polarization for Wayand ranged between -3 dB to -16 dB and for Calicut between -3 dB to -12 dB. A slightly distinguished signature was found on the VV polarized image but not on VH polarized image. The signature of one large slide was visible and the rest were not.
Keywords: Landslide, SAR Amplitude, Visual interpretation method, Backscatter coefficient.
