![]() MODIS and VIIRS combined data are the default option in the Fire Activity overlay and are displayed on the map together. Similar to MODIS, it provides multiple passes around the Earth every 24hrs with several satellites and is a major part of the current fire activity layer. The VIIRS program has a nominal resolution of 375m. Furthermore, that resolution is only when the satellite is "looking straight down." At the edges of the satellite's view path, the resolution will be less. MODIS satellites have a nominal resolution of 1km, which means that they can differentiate down to a 1km square but within that km x km box the satellite cannot further differentiate where heat and/or smoke are. The MODIS program consists of two satellites, Aqua and Terra, that pass around the Earth, covering the entire Earth at least once every 24hrs. As you zoom in on maps additional information is revealed. Each option provides a slightly different dataset or view. There is a drop down menu for the Current Fire Activity overlay that allows selection from MODIS and VIIRS, GOES Heat and GOES Detections, All Satellites, VIIRS 375m, VIIRS Progression, and Perimeters. However, a lot of smart people have worked on this and have developed algorithms to mitigate this known potential for error, so the data is still remarkably accurate.ĬalTopo’s Fire Activity overlay combines data from 4 main sources: three satellite platforms, MODIS, VIIRS, and GOES, and the National Interagency Fire Center. This can result in fire detection being perceived in a different place than it actually is at, show the wrong intensity, or just miss a spot because it's hidden by a steep mountain. For all of the satellites, the angle from which they are viewing the earth ranges from straight above to somewhat oblique (off to the side.)įor example, if the satellite passes straight over San Francisco, but is recording data from 150 miles to the east and west of its location, then data it is picking up from Lake Tahoe is at an oblique angle. Some satellites stay in the same place above the earth at all times (geostationary), while others orbit the earth continuously. Some things to keep in mind when looking at this satellite data: ![]() ![]() These features have been added over the years, unfortunately usually as a result of fire activity.īelow we’ll take a look at the different types of fire data available in CalTopo, and pluses and minuses are inherent in each. Introduction to CalTopo Fire Dataįire Activity is a checkbox in the Map Overlays section.ĬalTopo aggregates data from a large number of sources that provide insights for fire fighters, fire managers, and the general public. To say that again - the more often the data updates, the less reliable it is as to where that fire is at on the ground. The more "real time" that the data is, the less accurate it is. Fire history is usually not updated until after the new year for the previous year.įire data generally comes from satellite sources to provide data in near real-time.Premium base layers Sentinel and GOES live provide imagery data.GOES Live is not accurate, but very up-to-the-minute.MODIS and VIIRS and Perimeters are the most accurate, but slightly older data.Fire activity overlays show fire activity on top of base maps.This page contains a LOT of information about imaging, data sources, and methods, some of which was previously covered in blog posts in 2017, 2018, and 2020 but is updated here. With the increase in wildfires across the Western US in the last few years we’ve seen a huge spike in usage on CalTopo as well as numerous questions. Above all things, please stay safe and healthy. While maps provide valuable insights into fire behavior and areas affected, a map is always just a representation of the best available data. ![]() First and foremost: If you’re in an area near a wildfire, follow your local authorities for evacuation notices and up-to-the-minute information.
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