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- Accuracy
is a general term and is usually defined as closeness of agreement between a measured quantity value and a true quantity value. In most cases when we/customers mention accuracy we assume it is geospatial-positional accuracy or how close is the center of the hotspot to the actual hotspot on ground.
2. Acquisition Time
2. Acquisition Time
is the time when a satellite observed a patch on the ground. For hotspots, this represents the actual time when a potential fire was burning.
3. Detection Time
3. Detection Time
is the time when of one our algorithms detected the hotspot. This will always be later than the acquisition time since it also includes the time passed until the satellite product is made available by one of our external providers, and the time required to download and process the satellite product.
4. GEO
4. GEO
stands for Geostationary Orbit. Satellites in geostationary orbits circle Earth above the equator at an average altitude of 35,786 km. At this height satellites revolve around the Earth exactly once per 24 hours, thus they appear to be ‘stationary’ over a fixed position.
5. Ground Sampling Distance (GSD)
5. Ground Sampling Distance (GSD)
is the distance between the centers of the footprints on the ground of two adjacent pixels. It is often referred to as “resolution” or “spatial resolution” in conversations with users and professionals not in the Earth-observation field.
6. LEO
6. LEO
stands for Low Earth Orbit and describes orbits that are relatively close to Earth’s surface, at an average altitude of less than 1000 km above Earth.
7. Radiometric Resolution
7. Radiometric Resolution
describes the ability of a sensor to detect and represent various amounts of incoming light for each pixel. For example, a pixel with a radiometric resolution of 1 bit can only have the value 1 for all pixels that are brighter than a certain threshold and the value zero for all pixels darker than the threshold. On the other hand, a pixel with a radiometric resolution of 8 bit can use values between 0 and 255 to represent the gradually changing level of brightness between “dark” and “bright”.
8. Spectral Resolution
8. Spectral Resolution
refers to the spectral properties of the sensor. For a given spectral channel or band it describes the frequency range the sensor is sensitive to. An increased spectral resolution corresponds with a narrower frequency range. For example, the “green” band of Sentinel-2 is sensitive to light within ±17 nm around the center frequency 560 nm (“green”) whereas the “red” band is sensitive to light within ±15 nm around the center frequency of 665 nm (“red”). Thus, the spectral resolution of the “red” channel is slightly higher than for the “green” channel.
9. Temporal Resolution
9. Temporal Resolution
refers to how often data of the same area is collected by the same satellite. This is sometimes also referred to as “Revisit Time”.
10. Algorithms
10. Algorithms
11. Thermal channels used to detect wildfires
11. Thermal channels used to detect wildfires
Our Wildfire Solution leverages several algorithms to detect thermal anomalies (hotspots) in various satellite products:
OT-S (OroraTech-Sentinel) is a contextual thresholding algorithm developed in-house, based on the work of Wooster et al. (2012). The algorithm is applied to near-real-time data acquired by the SLSTR sensor onboard Sentinel-3 A/B, MERSI-2 sensor onboard Fengyun 3D, and AVHRR sensor onboard METOP-B/C.
OT-V (OroraTech-VIIRS) is a contextual thresholding algorithm developed in-house, based on the work described in the Visible Infrared Imaging Radiometer Suite (VIIRS) 750 m Active Fire Detection and Characterization Algorithm. The algorithm is applied to near-real-time VIIRS data with a 750m ground sampling distance (GSD).
OT-SWIR (OroraTech-Short Wave Infra Red) is a contextual thresholding algorithm developed in-house, based on the work of Schroeder et al. (2016). The algorithm is applied to data acquired by the MSI sensor onboard Sentinel-2 A/B and the OLI sensor onboard Landsat-8.
OT-AI (OroraTech-AI) is a deep learning algorithm developed in-house, based on the work of Pereira et al. (2021). The algorithm is applied to data acquired by Sentinel-2 A/B and Landsat-8/9.
In addition to applying the algorithms above, the Wildfire Solution provides also third-party fire products. These fire products contain a list of hotspots that were identified by the fire detection algorithm of the data provider. The following fire products are available in the system:
CSPP-VIIRS-Active-Fire-M-Band is the Visible Infrared Imaging Radiometer Suite (VIIRS) 750 m active firet derived from the VIIRS sensor onboard NOAA-21 satellite.
DLR-MODIS-Active-Fire-Product is the MCD14DL MODIS Collection 6 NRT Hotspot / Active Fire Detections product derived from the MODIS sensor onboard Terra and Aqua satellites. Hotspots covering continental Europe are obtained through direct downlink of data via ground stations operated by the German Aerospace Center (DLR) and are uniquely provided to OroraTech, thus significantly reducing the detection latency
DLR-VIIRS-Active-Fire-I-Band is the Visible Infrared Imaging Radiometer Suite (VIIRS) 375 m active fire product derived from the VIIRS sensor onboard Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites. Hotspots covering continental Europe are obtained through direct downlink of data via ground stations operated by the German Aerospace Center (DLR) and are uniquely provided to OroraTech, thus significantly reducing the detection latency.
DLR-VIIRS-Active-Fire-M-Band is the Visible Infrared Imaging Radiometer Suite (VIIRS) 750 m active fire product derived from the VIIRS sensor onboard Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites. Hotspots covering continental Europe are obtained through direct downlink of data via ground stations operated by the German Aerospace Center (DLR) and are uniquely provided to OroraTech, thus significantly reducing the detection latency.
EUMETSAT_FIRG / EUMETSAT_FIRC is the Active Fire Monitoring (FIR) product derived from the SEVIRI sensor onboard Meteosat-8/9/10/11. The product is provided by EUMETSAT.
GA products are a group of products provided by Digital Earth Australia Hotspots product. Hotspots are derived from the AHI sensor onboard Himawari-8, VIIRS sensor onboard SUOMI-NPP and NOAA-20 and MODIS sensor onboard Terra and Aqua by applying an ensemble of algorithms:
GA-AHI-BNHCRC_BRIGHT is applied to Himawari 8/9 AHI data and is based on the BRIGHT algorithm (Engel et al., 2021a and Engel et al., 2021b).
GA-AHI-SRSS is applied to Himawari 8/9 AHI data and is based on a contextual fire detection algorithm (Lee and Tag, 1990, Flasse and Ceccato, 1996) with extra tests and thresholds modified to suit Australian conditions by Landgate.
GA-MODIS-SRSS is applied to MODIS data and is based on a combination of a contextual fire detection algorithm for nighttime data (Lee and Tag, 1990, Flasse and Ceccato, 1996) and NASA’s MOD14 and MYD14 fire products for daytime data (Justice et al., 2002) with extra tests for sunglint.
GA-VIIRS-Active-Fire-I-Band is applied to VIIRS 375m data and uses a multispectral contextual algorithm (Schroeder et al. 2014).
GA-VIIRS-SRSS is applied to VIIRS 375m data and is based on a combination of two contextual fire detection algorithms; Lee and Tag, 1990, Flasse and Ceccato, 1996 for nighttime data and Schroeder et al. 2014 for daytime data. Both algorithms were changed by adding extra tests and modifying thresholds to better suit Australian conditions.
GK2A-Active-Fire-Product is an active fire product derived from the AMI sensor onboard Geo-KOMPSAT-2A satellite. The product is provided by the Korean National Meterological Satellite Center (NMSC)
GOES is the ABI-L2-FDCF-M6 ABI Level 2 Fire/Hot Spot Characterization product derived from the ABI sensor onboard GOES-16 and GOES-17. The product is provided by NOAA.
MODIS-Collection6-Active-Fire-Product is the MCD14DL MODIS Collection 6 NRT Hotspot / Active Fire Detections product derived from the MODIS sensor onboard Terra and Aqua satellites. The product is provided by NASA.
SENTINEL-FRP is the SL_2_FRP Sentinel-3 NRT FRP product derived from the SLSTR sensor onboard Sentinel-3 A/B. The product is provided by EUMETSAT.
VIIRS-Active-Fire-I-Band is the Visible Infrared Imaging Radiometer Suite (VIIRS) 375 m active fire product derived from the VIIRS sensor onboard Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites.
*The nominal hotspot radius is the radius of a single hotspot on the ground (footprint) when observed from the nadir (when the sensor is directly above the hotspot). For sensors onboard geostationary satellites, the radius of hotspots further away from the nadir increases significantly and can reach a maximum of 4800 meters.
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