Monsoon was active over different regions of India especially in Gujarat, Eastern Uttar Pradesh, Western Bihar, Assam and lately in West Bengal during mid July 2017. Heavy rains have created severe floods in these regions with extreme flood in parts of Gujarat and neighboring areas. Districts namely Banaskantha, Ahmedabad, Gandhinagar, Mehsana, Patan, Sabarkantha etc., recorded more than 300% rainfall above average level during July 20, 2017 to July 26, 2017.
Satellite plays important role in detection and monitoring of flood situations over large regions. Optical remote sensing from geostationary platform (INSAT-3D/3DR) provides rapid and valuable information on cloud patterns and meteorological parameters (rainfall); however, unable to image the surface water conditions in presence of cloud. Microwave remote sensing techniques have unique advantage in which electromagnetic radiation penetrate the clouds and senses the surface hydrological characteristics. The data from SCATSAT-1 (launched by PSLV-C35 on September 26, 2016) was used for the detection of the flood situations over India.
SCATSAT-1 is a continuity mission for Oceansat-2 Scatterometer for Ocean weather forecasting, cyclone detection and tracking. The satellite carries Ku-band Scatterometer and scans in a conical fashion in HH and VV polarizations and allows developing high-resolution datasets due to high overlapping areas. SCATSAT-1 observations in Ku-band for backscattering and brightness temperatures have been analyzed for flood detection and monitoring over India with special emphasis in Gujarat and southern parts of Rajasthan.
Merging of backscattering and brightness temperature data helped to delineate the regions, which were flooded, partially submerged or existed in different soil wetness conditions (saturated or dry). Inundated areas have been obtained during second week of July over Ganga (Kanpur to Patna and Kosi river) and Brahmaputra flood plains. Extreme flooding conditions were observed in Ahmedabad, Mehsana, Kheda, Banskantha, Bhavnagar as compared to relatively dry conditions in Bharuch during fourth week of July along with moderate inundation in parts of West Bengal.
Sentinel-1A, a C-band SAR imaging satellite high resolution data on July 24, 2017 helped to compare inundated regions over parts of Gujarat. Observations on flooding conditions were well correlated in SCATSAT-1 and Sentinel-1A data.
Analysis showed the usefulness of SCATSAT-1 mission in detecting and monitoring extreme events such as flood with high temporal resolution (daily). Further details can be obtained from VYOM and VEDAS web portal of Space Applications Centre.