Since we post the VIIRS map all the time, here is some infi about it...
Questions about VIIRS active fire data
The Visible Infrared Imaging Radiometer Suite (VIIRS) is an instrument aboard the Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 weather satellites. VIIRS was launched on Suomi NPP on October 28, 2011 and again on NOAA-20 (formally known as Joint Polar Satellite System-1 (JPSS-1)) on November 18, 2017. The VIIRS instrument will be launched on JPSS-2 in 2022 and join NOAA-20 and Suomi NPP in the same orbit.
If you wish to view the VIIRS reflectance imagery that corresponds to the active fire detections, you can display this in FIRMS Fire Map or Worldview.
What is the VIIRS 375 m Active Fire Product?
The VIIRS 375 m (VNP14IMGTDL_NRT) active fire product is the latest product to be added to FIRMS. It provides data from the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor aboard the joint NASA/NOAA Suomi-National Polar-orbiting Partnership (Suomi-NPP) and NOAA-20 satellites. The 375 m data complements MODIS fire detections; 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.
What is the temporal frequency of the VIIRS 375 m fire data?
The VIIRS instrument aboard the Suomi-NPP and NOAA-20 satellites acquire data continuously. The 3,040 km VIIRS swath enables ≈15% image overlap between consecutive orbits at the equator, thereby providing full global coverage every 12 hours. Suomi-NPP has a nominal (equator-crossing) observation times at 1:30pm and 1:30am. NOAA-20 operates about 50 minutes ahead of Suomi NPP. Thanks to its polar orbit, mid-latitudes will experience 3-4 looks a day.
What is the spatial resolution of the data?
The 375 m data describe the nominal resolution after native data are spatially aggregated (See figure below).
Spatial resolution of VIIRS imagery data as a function of scan angle. The three distinct regions represent unique data aggregation zones extending from nadir to the edge of swath.
Spatial resolution of VIIRS imagery data as a function of scan angle. The three distinct regions represent unique data aggregation zones extending from nadir to the edge of swath.
The aggregation scheme changes across three distinct image regions. In the first region (nadir to 31.59° scan angle), three native pixels are aggregated in the along scan (cross-track) direction to form one data sample in the Level 1 image. In the second region (31.59° to 44.68° scan angle), two native pixels are aggregated to form one data sample. Finally in the third and last region (44.68° to 56.06° - edge of swath) one native pixel will result in one data sample. All five 375 m channels are aggregated onboard the spacecraft before the data are transmitted to the ground stations, whereas a subset of the VIIRS 750 m data (dual-gain channels only) are aggregated on the ground.
What is the main difference between the VIIRS 375 m and 750 m active fire data?
The two data products use similar methodologies to detect active fire pixels although differences in the spectral characteristics of the VIIRS channels used in each case led to unique algorithms. Because of its improved spatial resolution, the 375 m algorithm will tend to detect more fire pixels compared to the 750 m data set. That difference is particularly pronounced during the nighttime part of the orbit when the occurrence of smaller/cooler fires will favor the 375 m product.
Will the VIIRS 375 m fire detection algorithm always outperform the 750 m one?
Generally speaking, the higher resolution product will achieve higher probability of fire detection in both day and nighttime scenes. However, areas subject to strong solar reflectance associated with sun glint could see a few 750 m fire pixels without a corresponding 375 m fire detection. This is attributed to the relatively shorter wavelength of the 375 m mid-infrared channel used in the fire algorithm, which will experience greater influence of the solar component. In order to minimize the associated consequences, namely the occurrence of false alarms over bright/reflective surfaces (e.g., metallic factory rooftops), the 375 m algorithm uses slightly more conservative tests to avoid the effects of sun glint over those areas.
Are those few isolated fire pixels in the middle of the South Atlantic Ocean real?
Those occurrences are typically associated with spurious fire detections due to the South Atlantic Magnetic Anomaly. The 375 m active fire algorithm contains a specific filter to flag those occurrences as low confidence detections. However, in some cases (average 2-3 pixels every night) the spurious signal generated in the input Level 1 data is confused for a regular fire pixel and therefore assigned a nominal confidence flag. Note that verified true positives can also be found over South Atlantic Ocean waters along the southeast coast of Brazil and the west coast of Africa where oil rigs normally operate.
Are the VIIRS 375 m (and 750 m) active fire data science-ready?
The VIIRS active fire data have been extensively tested since routine production of the mission’s data record started in 19 January 2012. Numerous bad scan episodes (i.e., pixel clusters containing spurious radiances extending across the swath) were found in the Level 1 input data during the initial 18-24 months of the time series [Csiszar et al., 2014]. Those anomalies were gradually addressed by the VIIRS science team and their occurrence have dropped to virtually zero with the implementation of revised Level 1 data processing packages in 2015. Initial assessment of both VIIRS 375 m and 750 m was implemented over a few experimental sites indicating consistent fire detection and characterization performance. Additional data comparison analyses were implemented using near coincident Aqua/MODIS and TET-1 (German Aerospace Center) active fire data, which again showed consistent performance of the VIIRS active fire products across different observation conditions. Consequently, we consider the current data of good enough quality for use in fire management applications and scientific studies. However, users must be aware of the data quality limitations involving the archived data. NASA will be spearheading future data reprocessing efforts in order to generate a consistent time series for the VIIRS Level 1 and 2 data.
Is the VIIRS 375 m product still being refined?
Absolutely. The current suite represents the second release of the VNP14IMG and VNP14 active fire algorithms; data imperfections can – and likely will – occur. As with other satellite data products, the VIIRS active fire algorithm development undergoes routine quality control during which data issues such as omission errors, false alarms and other anomalies are investigated and addressed. New versions of the products will be released once algorithm revisions are implemented and tested. Users are encouraged to report back to the science team when encountering potential data discrepancies.
Where do I go for more information?
Schroeder, W., Oliva, P., Giglio, L., & Csiszar, I. a. (2014). The New VIIRS 375m active fire detection data product: Algorithm description and initial assessment. Remote Sensing of Environment, 143, 85–96.
https://doi.org/10.1016/j.rse.2013.12.008
https://earthdata.nasa.gov/earth-observ ... -fire-data
http://viirsfire.geog.umd.edu/
https://earthdata.nasa.gov/earth-observ ... -vnp14imgt