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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesSatellites detect many wildfires by sensing unusually strong heat in mid-infrared wavelengths, not by photographing flames. That lets thermal instruments detect fires in darkness and often through smoke—but clouds can weaken or hide the signal. A detection is a pixel-scale alert, not a mapped fire perimeter, so it is useful for awareness and planning, not as stand-alone confirmation for tactical response or evacuation.
What a satellite fire detection actually represents
An active-fire product flags a satellite pixel whose measured energy is unusually consistent with a hot source. The fire may cover only a fraction of that pixel; the algorithm uses measurements from several spectral channels and surrounding pixels to identify small, hot sources within a larger footprint. A flagged pixel therefore does not mean the whole footprint is burning, nor does it trace the fire’s boundary.
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Other sources of heat or misleading surface signals can also trigger detections. NASA FIRMS cautions that points may represent fire, hot smoke, agriculture, or other sources, while NOAA lists possible false alarms such as gas flares, steel mills, structural fires, sun glint, reflective surfaces, fresh burn scars, and sandy soils. Conversely, weak fires and obscuring conditions can prevent a detection.
How satellites sense heat in daylight and darkness
Flames and smoldering material emit strongly in mid-infrared wavelengths. The VIIRS active-fire algorithm uses its 375 m I-band observations as primary inputs. Its 750 m M-band observations, including the mid-infrared M13 channel, help estimate fire radiative power for fires smaller than a pixel and screen noise. The instrument specifications in NASA’s VIIRS algorithm documentation include five 375 m I-bands, 16 750 m M-bands, and a 750 m Day-Night Band.
Mid-infrared measurements do not require sunlight, so thermal fire detection can operate on both day and night observations. The Day-Night Band is a separate low-light measurement: NOAA says it can register faint visible emissions from small or newly developing fires at night. Not every fire product uses that band, and night does not remove limits caused by cloud, resolution, or detection thresholds.
What clouds and smoke do to the signal
Clouds can weaken or block detection
Clouds are a major source of missing observations. Thin cloud can reduce the apparent fire-intensity value; thick cloud may be masked by a product’s cloud screen or obscure the fire altogether. A blank spot on a satellite fire map is therefore not proof that no fire is present: the source may be hidden or too weak to meet the product’s detection conditions.
Smoke is often less of a barrier to thermal sensing
Smoke is usually transparent in the mid-infrared bands used for thermal fire detection. However, dense, tall, or pyrocumulus-like plumes can resemble cloud in daytime imagery and be classified as cloud, causing an omission. Detecting the heat source and mapping the smoke plume are related but distinct tasks.
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For smoke over cloud, NASA’s April 2025 FIRMS Q&A describes the S-NPP OMPS Aerosol Index layer as a way to help identify and track smoke. It distinguishes 2 km imagery from the instrument’s underlying 50 km OMPS resolution. The same Q&A said NOAA-20 and NOAA-21 layers were being incorporated at that time; that dated statement does not establish their current availability.
VIIRS and GOES answer different monitoring needs
Polar-orbiting and geostationary satellites make different trade-offs. VIIRS passes over different parts of Earth on discrete orbits and supplies relatively fine fire-sensitive imagery. NOAA describes its high-resolution imager band as 375 m. NASA’s algorithm documentation describes a 3,060 km swath and global wall-to-wall coverage every 12 hours or less, depending on latitude; those are instrument coverage characteristics, not a guarantee of a particular product’s delivery time.
Geostationary GOES instruments repeatedly observe the same region, making them useful for following changes in fire behavior and smoke between polar-orbiting overpasses. Their repeat viewing comes with coarser spatial detail than VIIRS. Which source is more useful depends on whether the immediate need is finer spatial detail or frequent updates, as well as coverage, latency, and product quality information.
| Characteristic | Polar-orbiting VIIRS | Geostationary GOES |
|---|---|---|
| Viewing pattern | Discrete overpasses; broad swath coverage | Repeated observations of the same region |
| Fire detail | 375 m fire-sensitive I-band imagery, as described by NOAA and NASA | Coarser spatial detail than VIIRS; the reviewed sources do not state a single GOES resolution for this comparison |
| Useful for | Sharper imagery and detecting smaller fires, subject to conditions | Following change in fire behavior and smoke over time |
| Important limitation | Discrete overpasses leave intervals between observations | Spatial resolution and product maturity or quality can affect interpretation; check current product documentation |
In its April 2025 Q&A, NASA described geostationary active-fire products in FIRMS as Beta, citing the relatively new application of these sensors to active-fire detection, ongoing algorithm refinement, and sensor and spatial-resolution characteristics. It also noted commission, omission, and geolocation issues. That is a dated status description, not confirmation of the current label; consult live product documentation before relying on a status designation.
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Why a fire can be missed, appear displaced, or trigger a false alarm
There is no single minimum fire size that guarantees a satellite detection. NOAA’s conditional rule of thumb for traditional MODIS, VIIRS, and GOES algorithms is that they begin to respond when active fire occupies at least 0.01% of a pixel footprint and the average fire temperature is at least 800 K. At an effective 1 km pixel resolution, NOAA gives 100 m² as an example of that fraction. This is an illustrative response threshold, not an operational promise; at larger view angles the ground footprint grows and the required fire area rises.
Detection also depends on fire temperature and strength, the satellite’s view angle, clouds, terrain, forest canopy, and plume geometry. At high view angles, a tall, hot plume can be detected away from the ground perimeter because of parallax. NOAA notes this can occur at night over large, rapidly growing fires. A nearby-in-time observation closer to nadir may help assess a suspicious displaced point.
Fire Radiative Power (FRP) describes radiative energy release and can help characterize relative activity or support emissions calculations, but its absolute value depends on fuel, weather, and observation conditions. NOAA gives a 50 MW example that could describe either the most active part of a small grassland burn or the least intense part of a large wildfire; the number is not a direct measure of fire area.
How to use a satellite detection safely
NOAA says fire positions should be treated as general guidance for strategic planning. Tactical response and evacuation decisions require corroboration; a satellite point alone is not enough. When reviewing a detection, check:
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- The observation time and whether it represents a new look or a repeated display of an earlier observation.
- Any confidence or quality attributes supplied with the product.
- Nearby observations, including whether another pass closer to nadir supports a point that appears displaced.
- Cloud conditions and whether a gap could reflect obscuration rather than absence of fire.
- Official incident information and ground reports where available.
Remember that the pixel is an observation footprint, not an estimate of the burned perimeter. NOAA warns that using pixel area as fire size can grossly overestimate the perimeter because only rarely does a fire occupy an entire pixel.
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