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Detection and analysis of growth of Sea - Ice using MSMR brightness temperature data Vinod Binyala, Sharad V. Oberoi Under Graduate Student, Department of Civil Engineering, Banaras Hindu University, Varanasi Dr. K. S. Rao Principal Research Scientist, CSRE, IIT Bombay
Introduction The polar ice, with its expansive maximum extent and large annual variability has a major influence on the global climate system. This is reflected by the fact that the global sea-ice has been rising about 2 mm a year over last century. Ice acts as insulating blanket between the relatively warm ocean and colder atmosphere. Sea-ice thickness determines the amounts of energy exchange between the air and the ocean by drastically modifying the transfer of heat, mass and momentum. Moreover, the feedback mechanism between sea-ice extent and atmospheric temperature tends to amplify climatic anomalies. The ice cover serves as a seasonal buffer between the atmosphere and ocean. In the winter, the growing ice releases cold dense brine into the ocean resulting in convective overturning, which causes the heat to be transported to the surface. In summer, the melting ice contributes to the fresh water surface layer, which affects deep-water convection. Thus the presence of sea-ice also affects the biological activities in the ocean. Ships navigating through high latitude seas are often faced with obstacles of pack ice and moving ice floes. Ice breakers are designed to facilitate travel in these areas, but they require knowledge about the most efficient and effective route through the ice. Satellite images give a large view of the area in front of a ship and will allow an experienced interpreter to estimate the age, type and concentration of the ice. With radar sensors, images can be acquired and sent to the ship by communications satellites, so the captain can see the most recent ice conditions in front of his ship. Thus, it is essential that our planet's snow and sea-ice be monitored on a global scale by remote sensing from satellites. Observations from MSMR data over polar region While analyzing the spatial and temporal variation of brightness temperature data obtained from IRS-P4 for Grid-1 (150 km resolution), an atypical trend was observed for a location in Beaufort and the Siberian Sea (near latitude 75° N and longitude 135°E). There was a sharp increase in brightness temperature (Tb) by an amount of 60-70 degrees for all frequencies and polarizations during a period of 15 days in the month of October 2000 [Figure 1a and Figure 1b]. Also, the polarization ratio changed by a considerably large amount [Figure 1c]. A monthly variation map for October 2000 was made using IRS-P4 data for Grid-3 (50 km resolution) to have a closer look [Figure 2]  (a) for Horizontal Polarization, H  (b) for Vertical Polarization, V  (c) for Horizontal/Vertical Polarization ratio, H/V Figure 1. Temporal Variation of Brightness temperature for location near latitude 75° N and longitude 135°E for frequencies 6.6, 10.65, 18 and 21 GHz
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