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 and from the University of Maryland VIIRS Active Fire Web page. 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.