What is the VIIRS 375 m Active Fire Product?
The Visible Infrared Imaging Radiometer Suite (VIIRS) 375 m thermal anomalies / active fire product provides data from the VIIRS sensor aboard the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites. The 375 m data complements Moderate Resolution Imaging Spectroradiometer (MODIS) fire detection; they both show good agreement in hotspot detection but the improved spatial resolution of the 375 m data provides a greater response over fires of relatively small areas and provides improved mapping of large fire perimeters. The 375 m data also has improved nighttime performance. Consequently, these data are well suited for use in support of fire management (e.g., near real-time alert systems), as well as other science applications requiring improved fire mapping fidelity.
Fire products from VIIRS: A complementary VIIRS M-Band 750 m active fire data product is available in HDF format from NASA's Earthdata Search. FIRMS has opted to distribute the 375 m product rather than the 750 m product as the increased spatial resolution and increased number of fires detected is of interest to the to the broader fire management community.
Attribute fields for NRT VIIRS 375 m active fire data distributed by FIRMS
|Latitude||Latitude||Center of nominal 375 m fire pixel|
|Longitude||Longitude||Center of nominal 375 m fire pixel|
|Bright_ti4||Brightness temperature I-4||VIIRS I-4 channel brightness temperature of the fire pixel measured in Kelvin.|
|Scan||Along Scan pixel size||The algorithm produces approximately 375 m pixels at nadir. Scan and track reflect actual pixel size.|
|Track||Along Track pixel size||The algorithm produces approximately 375 m pixels at nadir. Scan and track reflect actual pixel size.|
|Acq_Date||Acquisition Date||Date of VIIRS acquisition.|
|Acq_Time||Acquisition Time||Time of acquisition/overpass of the satellite (in UTC).|
|Satellite||Satellite||N= Suomi National Polar-orbiting Partnership (Suomi NPP), 1=NOAA-20 (designated JPSS-1 prior to launch)|
This value is based on a collection of intermediate algorithm quantities used in the detection process. It is intended to help users gauge the quality of individual hotspot/fire pixels. Confidence values are set to low, nominal and high. Low confidence daytime fire pixels are typically associated with areas of sun glint and lower relative temperature anomaly (<15K) in the mid-infrared channel I4. Nominal confidence pixels are those free of potential sun glint contamination during the day and marked by strong (>15K) temperature anomaly in either day or nighttime data. High confidence fire pixels are associated with day or nighttime saturated pixels.
Please note: Low confidence nighttime pixels occur only over the geographic area extending from 11deg E to 110 deg W and 7 deg N to 55 deg S. This area describes the region of influence of the South Atlantic Magnetic Anomaly which can cause spurious brightness temperatures in the mid-infrared channel I4 leading to potential false positive alarms. These have been removed from the NRT data distributed by FIRMS.
|Version||Version (Collection and source)||Version identifies the collection (e.g. VIIRS Collection 1) and source of data processing: Near Real-Time (NRT suffix added to collection) or Standard Processing (collection only).
"1.0NRT" - Collection 1 NRT processing.
"1.0" - Collection 1 Standard processing
|Bright_ti5||Brightness temperature I-5||I-5 Channel brightness temperature of the fire pixel measured in Kelvin.|
|FRP||Fire Radiative Power||
FRP depicts the pixel-integrated fire radiative power in MW (megawatts). FRP depicts the pixel-integrated fire radiative power in MW (megawatts). Given the unique spatial and spectral resolution of the data, the VIIRS 375 m fire detection algorithm was customized and tuned in order to optimize its response over small fires while balancing the occurrence of false alarms. Frequent saturation of the mid-infrared I4 channel (3.55-3.93 µm) driving the detection of active fires requires additional tests and procedures to avoid pixel classification errors. As a result, sub-pixel fire characterization (e.g., fire radiative power [FRP] retrieval) is only viable across small and/or low-intensity fires. Systematic FRP retrievals are based on a hybrid approach combining 375 and 750 m data. In fact, starting in 2015 the algorithm incorporated additional VIIRS channel M13 (3.973-4.128 µm) 750 m data in both aggregated and unaggregated format.
|DayNight||Day or Night||
D= Daytime fire, N= Nighttime fire
The VIIRS I-Band 375 m Active Fire Product Algorithm
The VIIRS 375 m active fire product is described in Schroeder et al (2014). The product builds on the MODIS fire product heritage [Kaufman et al., 1998; Giglio et al., 2003 et al.], using a multi-spectral contextual algorithm to identify sub-pixel fire activity and other thermal anomalies in the Level 1 (swath) input data. The algorithm uses all five 375 m VIIRS channels to detect fires and separate land, water, and cloud pixels in the image. Additional 750 m channels complement the available VIIRS multispectral data. Those channels are used as input to the baseline active fire detection product, which provides continuity to the EOS/MODIS 1km Fire and Thermal Anomalies product.
Some Key information about VIIRS
- The VIIRS sensor aboard the Suomi NPP satellite, crosses the equator at approximately 13:30 PM (ascending node) and 1:30 AM (descending node).
- The VIIRS sensor aboard the NOAA-20 satellite, crosses the equator approximately 50 minutes prior to Suomi NPP, at approximately 12:40 PM (ascending node) and 12:40 AM (descending node).
- The 3,040 km VIIRS swath enables ~15% image overlap between consecutive orbits at the equator, thereby providing full global coverage every 12 hours and mid-latitudes will experience 3-4 looks a day.
- VIIRS has 5 high resolution Imagery channels (I-bands), 16 moderate resolution channels (M-bands) and a Day/Night Band (DNB).
- The VIIRS detectors have a constant angular resolution that results in an increasing pixel footprint size as the scan is further from nadir (see figure 1 below). This means the actual area of each scan has the shape of a bow-tie, as consecutive scans overlap away from nadir. The bow-tie effect is reduced during processing through a combination of aggregation and deletion of overlapping pixels.
For more information on VIIRS Active data: University of Maryland VIIRS Active Fire Web page.