Terms and What They Mean

Each term as specialists use it, with a plain explanation.

Fire

Active Fire (Thermal Anomaly): A spot where a satellite saw something much hotter than its surroundings: almost always a fire burning at the moment it passed over.; Found by contextual algorithms on mid-infrared (about 3.7–4 µm) and thermal (11 µm) brightness temperatures: VIIRS I-band at 375 m (VNP14IMG), MODIS at 1 km (MOD14/MYD14). NASA FIRMS reports the pixel centers.
Fire Radiative PowerFRP: How much heat a fire gives off as radiation, in megawatts. A bigger number means a more intense fire.; Retrieved from the pixel's mid-infrared radiance above its background (Wooster et al., 2003). Integrated over time it gives fire radiative energy, proportional to the biomass burned.
Detection Confidence: How sure the algorithm is that a hot pixel is a real fire: low, nominal or high.; VIIRS: categorical (low, nominal, high) from the I4 and I5 tests with sun-glint and cloud context. MODIS: 0–100%, grouped here as 0–29 low, 30–79 nominal and 80–100 high.
Brightness Temperature: The temperature a satellite reads from the light a surface gives off in one band. Fires read far hotter than their surroundings.; The temperature of a blackbody emitting the observed spectral radiance (inverse Planck function). The VIIRS I4 band (3.74 µm) saturates near 367 K.
Shortwave-Infrared False ColorSWIR: An image made partly with infrared light we cannot see: burn scars look brown or red, active fires orange and vegetation green, even through thin smoke.; VIIRS M11 (2.25 µm), I2 (0.86 µm) and I1 (0.64 µm) as red, green and blue; MODIS bands 7-2-1. Shortwave infrared passes through fine smoke better than visible light.
Burned Area: The ground a fire has burned, mapped afterwards from the change it left. Not the same as where active fire was seen.; For example MODIS MCD64A1 (500 m, monthly), from daily surface-reflectance change seeded by active fires. Active-fire footprints miss burning between overpasses and under cloud or smoke.
Peat Fire: Fire in peat, a soil made of old plant matter. It can smoulder underground for weeks and makes thick smoke.; Smouldering, low-temperature combustion of organic soils: low FRP per unit area but high emission factors (PM2.5, CO). Widespread in drained tropical peatlands of Kalimantan and Sumatra.
PyrocumulonimbuspyroCb: A thunderstorm cloud made by the heat of a large fire. It can lift smoke very high.; Fire-triggered deep convection that can inject smoke into the upper troposphere and lower stratosphere, flagged by a high UV aerosol index (OMPS, OMI).
Fire Event (As Grouped Here): Detections close together over the 7 days, counted as one fire.; Connected components of 375 m cells within two cells (about 0.75 to 1.06 km) of each other over a 7-day window. See Methodology.
Rate of Spread: How fast a fire front moves forward. Earthasium shows how fast an event's outline grew instead, which is not the same thing.; The front-normal speed of the flaming front. Daily satellite outlines cannot resolve it; Earthasium reports the daily change in the equivalent radius of the cumulative detection hull.

Air Quality and Smoke

Aerosol Optical DepthAOD: How much haze, smoke or dust dims the sunlight. 0.1 is clear; above 1 is heavy haze.; Column extinction (scattering plus absorption) at 550 nm, without units. Dark Target and Deep Blue retrievals (MODIS, VIIRS) and the CAMS analysis.
UV Aerosol IndexUVAI: Shows smoke and dust that absorb ultraviolet light, even above clouds. Higher means more absorbing particles.; The residual of the near-UV radiance ratio (for example 340/378 nm) against a pure-Rayleigh atmosphere: positive for absorbing aerosols and sensitive to the layer's height.
Fine Particulate MatterPM2.5: Tiny particles in the air, smaller than 2.5 thousandths of a millimeter: smoke and soot that reach deep into the lungs.; Mass concentration (µg/m³) of particles with an aerodynamic diameter up to 2.5 µm. WHO 2021 guideline: 15 µg/m³ as a 24-hour mean, 5 µg/m³ as an annual mean.
Coarse Particulate MatterPM10: Particles smaller than 10 thousandths of a millimeter: dust, smoke and pollen.; Mass concentration of particles up to 10 µm. WHO 2021 guideline: 45 µg/m³ as a 24-hour mean.
Carbon MonoxideCO: A gas from incomplete burning. On satellite maps it traces fire smoke as it travels.; Retrieved in the mid-troposphere by AIRS (4.7 µm) and as a total column by TROPOMI. Its lifetime of about two months makes it a tracer of long-range transport.
Nitrogen DioxideNO₂: A gas from burning fuel: traffic, power plants, industry and fires.; Tropospheric vertical column from TROPOMI's DOAS retrieval. Its short lifetime keeps it close to its sources.
Sulfur DioxideSO₂: A gas from volcanoes and from burning coal and oil.; Total vertical column in Dobson units from TROPOMI; the value depends on the plume height assumed.
Total Column Ozone: All the ozone above a place, from the ground to space: mostly the ozone layer that screens ultraviolet light.; Vertically integrated ozone in Dobson units (1 DU = 2.687 × 10²⁰ molecules per m²). About 300 DU is typical; under 220 DU marks the Antarctic ozone hole.
Air Quality IndexAQI: One number for how polluted the air is, from several pollutants, with named bands from Good to Hazardous.; US EPA AQI: the highest of piecewise-linear sub-indices for PM2.5, PM10, O₃, NO₂, SO₂ and CO, on a 0–500 scale. The European AQI (EEA) uses 0–100+ bands. Computed here by Open-Meteo from CAMS.

Weather

Air Temperature (2 m): How warm the air is at head height, 2 m above the ground, as weather stations measure it.; The model's diagnostic air temperature 2 m above the surface; not the land surface (skin) temperature.
Apparent Temperature: How hot or cold it feels, with humidity, wind and sunshine taken into account.; Open-Meteo's apparent temperature after Steadman (1984), from air temperature, humidity, wind speed and radiation.
Dew Point: The temperature at which dew would form. The higher it is, the more humid the air feels.; The temperature to which air must cool, at constant pressure and moisture, to reach saturation.
Relative Humidity: How close the air is to holding all the water vapor it can, in percent.; The ratio of actual to saturation vapor pressure at the air temperature, times 100.
Precipitation: Rain, snow and hail reaching the ground, in millimeters: 1 mm is 1 liter of water on each square meter.; Liquid-water-equivalent depth over an interval; rates in mm per hour.
Probability of Precipitation: The chance, in percent, of at least 0.1 mm falling in that hour or day.; From the share of ensemble members exceeding 0.1 mm (Open-Meteo); the daily value is the highest hourly probability.
Wind Speed (10 m): How fast the air moves 10 m above the ground, the standard height for wind. Direction is where it blows from.; The 10-minute mean horizontal wind at 10 m, as WMO standardizes it.
Wind Gust: The strongest short burst of wind, well above the average.; The highest 3-second wind at 10 m within the interval.
Beaufort ScaleBft: Wind strength from 0 (calm) to 12 (hurricane force), named after what the wind does to sea and land.; WMO Beaufort numbers from 10 m mean-wind thresholds; force 6, for example, is 10.8 to 13.8 m/s.
Mean Sea Level PressureMSLP: Air pressure adjusted to sea level, in hectopascals. Low pressure often brings clouds and rain.; Surface pressure reduced to mean sea level; the standard atmosphere is 1013.25 hPa.
Cloud Cover: How much of the sky is covered by cloud, in percent.; Total cloud fraction over all levels, from the model.
Cloud Top Height: How high the tops of clouds reach. Tall tops mean strong storms.; From CO₂-slicing and infrared-window brightness temperatures (MODIS).
UV Index: How strong the sun's ultraviolet light is: 3 to 5 moderate, 6 to 7 high, 8 and above very high.; WHO and WMO's erythemally weighted UV irradiance times 40 m²/W.
Reference EvapotranspirationET₀: How much water the air would draw from well-watered grass in a day: a measure of how fast things dry.; FAO-56 Penman–Monteith reference evapotranspiration, in mm per day.

Land and Water

Normalized Difference Vegetation IndexNDVI: How green and dense the plants are: near 1 for dense forest, near 0 for bare ground.; (NIR − Red) / (NIR + Red) from surface reflectance. It saturates over dense canopy, where EVI keeps its range.
Enhanced Vegetation IndexEVI: A vegetation index that keeps working over dense tropical forest.; 2.5 × (NIR − Red) / (NIR + 6 Red − 7.5 Blue + 1); reduces the influence of soil and atmosphere.
Land Surface TemperatureLST: How hot the ground surface itself is, not the air. Bare ground in the sun can be far hotter than the air above it.; Radiometric skin temperature from thermal-infrared split-window or TES algorithms (MODIS MOD11, MOD21).
Soil Moisture: How much water the soil holds. Dry peat burns more easily.; Volumetric water content (m³/m³). SMAP L-band brightness temperatures assimilated into a land model for the root zone (0–100 cm).
River Discharge: How much water flows past a point on a river, in cubic meters per second.; Simulated by GloFAS (the LISFLOOD model) at about 0.05°, driven by ECMWF forecasts.
Flood Extent: Where water covers land that is usually dry.; MODIS and VIIRS near-real-time flood products (2-day composites) and OPERA DSWx (optical and radar, 30 m).
Digital Elevation ModelDEM: A map of ground heights. Earthasium draws its 3D terrain from one.; Copernicus DEM GLO-30 (TanDEM-X, 30 m) via Mapterhorn's Terrarium tiles. A surface model: it includes the forest canopy and buildings.

Ocean

Sea Surface TemperatureSST: How warm the top of the ocean is.; Foundation SST analysis (GHRSST L4 MUR, 0.01°) from infrared and microwave sensors.
Sea Surface Temperature Anomaly: How much warmer or cooler the sea is than its usual for the date.; SST minus a daily climatology; for MUR, the 2003–2014 mean.
Chlorophyll-a Concentration: How much microscopic plant life (phytoplankton) the water holds: the base of the ocean's food web.; mg/m³ from ocean-color band-ratio algorithms (OC3, OCI) on PACE OCI and MODIS Aqua.
Sea Surface SalinitySSS: How salty the surface water is.; Practical salinity (PSU) from L-band radiometry (SMAP), as an 8-day running mean.
Significant Wave HeightHs: The average height of the highest third of the waves: about what a sailor would report.; Four times the square root of the zeroth moment of the wave spectrum, from wave models (ECMWF WAM and others).

Climate Drivers

Temperature Anomaly: How much warmer or cooler the air is than its 1991–2020 average for the date and place.; Here, the 24-hour mean of GFS 2 m air temperature minus NCEP–DOE Reanalysis 2's 1991–2020 monthly mean, read between month middles for the date and moved to GFS's ground height at 6.5 °C per km over land.
Climate Normal: The average weather of a place over 30 years. The standard period now is 1991–2020.; WMO's standard 30-year reference period is 1991–2020. Monthly means, read for a date between the middles of the two nearest months.
El Niño–Southern OscillationENSO: A natural swing of the tropical Pacific between warm (El Niño) and cool (La Niña) phases. El Niño tends to bring drought and fire to Indonesia.; A coupled ocean–atmosphere mode. El Niño suppresses convection over the Maritime Continent and lengthens its dry season.
Oceanic Niño IndexONI: NOAA's measure of El Niño: how much warmer or cooler than normal the central Pacific has been over three months.; The 3-month running mean SST anomaly in the Niño 3.4 region (5° N–5° S, 170°–120° W) from ERSSTv5, against centered 30-year base periods; ±0.5 °C for five overlapping seasons makes an episode.
Indian Ocean DipoleIOD: A swing in sea temperatures across the Indian Ocean. Its positive phase tends to dry Indonesia.; Dipole Mode Index: the SST anomaly of the western tropical Indian Ocean (50°–70° E, 10° S–10° N) minus that of the south-east (90°–110° E, 10° S–0°).

Methods and Maps

Geostationary Satellite: A satellite that stays over one spot, 35,786 km up, imaging the same half of Earth every 10 minutes.; GOES-19 and GOES-18 (ABI), Himawari-9 (AHI), Meteosat-12 (FCI): full disk every 10 minutes at 0.5–2 km at nadir, coarser toward the edge of the disk.
Polar-Orbiting Satellite: A satellite that circles from pole to pole about 830 km up, seeing each place about twice a day, in more detail.; Sun-synchronous orbits: NOAA-20, NOAA-21 and Suomi NPP cross the equator near 13:30 local time, Terra near 10:30 and Aqua near 13:30. VIIRS swaths are about 3,000 km wide.
Reanalysis: A consistent record of past weather, made by running a weather model through years of observations.; Historical observations assimilated into a fixed model: ERA5 at 0.25°, MERRA-2 at 0.5° × 0.625°, NCEP–DOE Reanalysis 2 at about 1.9°.
Numerical Weather PredictionNWP: Forecasting the weather by computing how the atmosphere will change, starting from today's observations.; Global models such as ECMWF IFS (9 km), NOAA GFS (13 km) and DWD ICON (13 km); Open-Meteo picks the best available for each place.
Ensemble Forecast: Many runs of a forecast from slightly different starts, to show how certain it is.; Perturbed initial conditions and physics (ECMWF ENS has 51 members); probabilities from the share of members.
Back-Trajectory: The path the air took to reach a place, traced backwards through a weather model's winds.; Kinematic trajectories integrated backward from the arrival point on GFS winds at 925 hPa, in 15-minute steps over 72 hours. A model, not a measurement.
Vertical Exaggeration: Stretching heights on a 3D map so gentle relief can be seen. ×1 is true to scale.; A multiplier on elevation relative to the horizontal scale, applied to the terrain's displacement in the vertex stage.
Eye Altitude: How high the camera is above the ground.; The camera's height above the WGS84 ellipsoid, shown in your distance unit.
Decimal Degrees and DMSDD, DMS, DDM: Ways to write latitude and longitude: 2.21° S, 2° 12′ 36″ S, or 2° 12.600′ S.; Geographic coordinates on WGS84 (EPSG:4326).
Universal Transverse MercatorUTM: A grid of 60 zones that gives positions in meters east and north.; Transverse Mercator per 6° zone: scale factor 0.9996, false easting 500,000 m, false northing 10,000,000 m in the south; zone exceptions for Norway and Svalbard.
Military Grid Reference SystemMGRS: The grid NATO and many emergency services use: a zone, a 100 km square, then meters, as in 49M GT 12345 67890.; UTM zone and band, two letters for the 100 km square, then easting and northing to the chosen precision (5 digits: 1 m). Polar areas use UPS, not shown here.
Earthquake Magnitude: The size of an earthquake. Each step up is about 32 times more energy.; Moment magnitude (Mw) from the seismic moment where available; USGS reports its preferred type (mb, ML, Mww and others).
Hypocenter Depth: How deep underground an earthquake began. Shallow ones shake the surface hardest.; The depth where rupture began. USGS classes: shallow under 70 km, intermediate 70–300 km, deep below 300 km.
GDACS Alert Level: An automatic estimate of how serious a disaster may be for people: green, orange or red.; From the Global Disaster Alert and Coordination System (United Nations and European Commission), combining hazard severity with exposed population and vulnerability. Not an official warning.

Evidence Grades

Seen: Detected by a satellite: a measurement.; A direct remote-sensing observation, such as a VIIRS active-fire detection.
Mapped: Inside an area drawn on a public map, as of that map's date.; A spatial intersection with a published dataset, cited with its date.
Recorded: In an official record: a court decision, an enforcement action, a government dataset.; Primary documentation from a public authority.
Reported: Reported by news media or an NGO, with the source named.; Secondary reporting: cited, not independently verified.
Model: Estimated by a named model, not measured: forecasts, air-quality fields, trajectories.; Output of numerical models (NWP, CAMS, GloFAS, reanalysis), with their uncertainties.