For instance, NASA notes that a few VIIRS active fire hotspots are occasionally located outside the reported perimeter of a large fire. The data is not wrong but it is susceptible to errors and its interpretation is subject to multiple caveats. The VIIRS data complement the MODIS fire detections but the improved spatial resolution of the 375 m data provides a more accurate picture and has improved nighttime data-collection performance. Each VIIRS active fire or thermal hotspot location represents the centre of a 375 m x 375 m pixel. Technically, each MODIS active fire or thermal hotspot (red dot on the map) represents the center of a 1 km x 1 km pixel that is flagged by the algorithm as containing one or more fires within the pixel. VIIRS mechanism only differs in the size of the observation grid. Note: The mechanism described is for MODIS. How ground fires translate into map hotspots A red dot can be one single instance of fire or multiple fires, at times a single big fire can appear as a cluster of multiple red dots The number of red dots on FIRMS is not actually the real count of fires but an indication of the presence of fire(s) within a particular area (1 km x 1 km for MOIDS and 375 m x 375 m VIIRS). But it can be more than or even less than one fire. It uses a suite of tests for internal cloud masking and rejection of false alarms.Įach red dot or hotspot on the FIRMS map represents at least some fire. It uses a hybrid threshold and contextual algorithm that identifies thermal anomalies. In contrast, VIIRS uses radiometric signals from four micron, 11 micron and a few other bands for detection. The MODIS algorithm examines each pixel of the MODIS swath and ultimately assigns each to one of the following classes: Missing data, cloud, water, non-fire, fire or unknown. MODIS uses a contextual algorithm that exploits the strong emission of mid-infrared radiation from fires. FIRMS provides validated science-quality data as well, but with a two–three months lag from the time of satellite observation.īoth MODIS and VIIRS detect fire by processing thermal imaging of the Earth’s surface but use different technologies and algorithms. But due to time constraints, the raw data is not processed to the fullest and NASA recommends not using it for scientific enquiry. NRT data from both, MODIS and VIIRS, is useful for informing immediate disaster mitigation and management. FIRMS makes available Near Real-Time (NRT) active fire data within three hours of observation by these satellites on its online portal. VIIRS data is currently available from Januto the present. MODIS data is available from November 2000 (for Terra) and July 2002 (for Aqua) to the present. More specifically, they come from satellite observation of NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra and Aqua satellites and NASA’s Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi National Polar orbiting Partnership (Suomi NPP) and NOAA-20 satellites. The satellite images have been captured by the National Aeronautics and Space Administration (NASA) and made public under their Fire Information for Resource Management System (FIRMS). Given this, we at the Centre for Science and Environment’s Urban Data Analytic Lab (UDAL) have decided to analyse it in and determine if we are reading it correctly and moving in the right direction or need a course correction. Patients of COVID-19, living in areas with high air pollution, are more likely to die from the disease.ĭata accruing from the latest satellite images has acted as a springboard for action by civic authorities and the courts. Scientific evidence suggests that even short-term exposure to air pollution can significantly increase vulnerability to COVID-19. It is dangerous on its own but can combine with the novel coronavirus disease (COVID-19) to make one deadly concoction. This has triggered alarm bells about the possible return of winter smog. New satellite images have indicated an early onset of the stubble burning season this year in Punjab and Haryana (that usually starts in mid-October).
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