Observation of Marine Atmospheric Boundary Layer (MABL) using RISAT-1 Data
Radar Imaging Satellite-1 (RISAT-1) was launched on April 26, 2012 by PSLV-C19 from Sriharikota. RISAT-1 is the India’s first Synthetic Aperture Radar (SAR) which enables imaging of the earth surface features during both day and night under all weather conditions. RISAT-1 was designed to image the Earth’s surface in different modes; 1.High Resolution Scanning - HRS (Spotlight scanning, resolution less than 2 m), 2. Fine Resolution Scanning - FRS-1 (Stripmap scanning, resolution 3 m), FRS-2 (Stripmap Scanning, resolution 6 m) 3. Medium Resolution Scanning - MRS (scanSAR scanning, resolution 25 m) and 4. Coarse Resolution Scanning - CRS (scanSAR scanning, resolution 50 m) with swath widths ranging from 30 to 220 km.
Active Microwave Remote Sensing provides cloud penetration and day-night imaging capability. These unique characteristics of SAR enable applications in agriculture, particularly paddy monitoring in kharif season and management of natural disasters like flood and cyclone. RISAT-1 also provides an opportunity to study the Marine Atmospheric Boundary Layer structures by detecting the changes in the sea surface roughness, which modulates the Normalised Radar Cross-Section (NRCS) of the sea surface.
A study was carried out recently by Space Applications Centre (SAC), ISRO Ahmedabad to understand the Marine Atmospheric Boundary Layer (MABL) using RISAT-1 data over the Indian Ocean, which exhibits marked spatio-temporal variability owing to Inter Tropical Convergence Zone (ITCZ) and proximity with land. Several fascinating atmospheric features like atmospheric fronts, convective cells, atmospheric rolls, convective rain cells and atmospheric gravity waves have been identified using SAR data, though it still remains a challenging task to decouple the MABL signature from the oceanic contribution. It is envisioned that this study will help in resolving the finer structures and wind pattern leading to better understanding of some interesting MABL phenomenon.