Glossary

Analysis ready data (ARD) is imagery processed so it can be used directly for analysis with consistent geometry, metadata, and quality information.

Cadence is how often a processed product is delivered, which can differ from sensor revisit time.

A composite is a mosaic built over a time window, often selecting the “best” pixel per location.

A DEM is a raster representing elevation, used for terrain correction, hydrology, and orthorectification.

Georeferencing links pixels or coordinates in a dataset to real-world locations on Earth.

Latency is the delay between when data is acquired and when a usable product is delivered to the user.

A mosaic combines multiple scenes into one continuous image covering a larger area or time window.

NoData is a special value that means a pixel has no valid measurement, for example due to clouds or missing coverage.

Orthorectification corrects geometric distortion so imagery aligns properly with the ground, using terrain and sensor geometry.

A quality mask is a layer that flags pixels with issues such as clouds, shadows, saturation, or low confidence.

Radiometry is the measurement and calibration of electromagnetic energy recorded by a sensor.

Reprocessing means older data is processed again with updated algorithms or calibration, which can change values for the same date.

Reprojection converts data from one coordinate reference system (CRS) to another.

Resampling changes the pixel grid of a raster, for example when reprojecting or changing resolution.

Revisit time is the typical time between observations of the same location by a sensor or constellation.

UTM is a projected coordinate system that divides Earth into zones, allowing measurements in meters.

An AOI is the geographic area you want to analyze or request data for, defined by a boundary such as a polygon or bounding box.

A bounding box is a rectangle defined by minimum and maximum coordinates, commonly used to specify an AOI.

A CRS defines how coordinates map to locations on Earth, including the projection and datum.

An EPSG code is a numeric identifier for a CRS, such as EPSG:4326 for WGS84 latitude/longitude.

Geospatial data is any data tied to a location on Earth, such as maps, satellite imagery, or field boundaries.

A polygon is a closed boundary used to represent an area such as a field, region, or administrative unit.

WGS84 is a global geographic coordinate system commonly used for latitude and longitude.

An API key is a credential used to authenticate requests and associate them with an account or application.

A rate limit restricts how many requests an API accepts in a time window to protect stability and fairness.

Atmospheric correction removes or reduces atmospheric effects so scenes are more comparable across time and space.

BRDF describes how reflectance changes with viewing and illumination geometry, affecting apparent brightness across scenes.

A cloud mask labels pixels likely affected by clouds so they can be excluded or handled differently.

Cloud shadow is the darkening of the surface caused by clouds blocking sunlight, often mistaken for real change.

Haze is atmospheric scattering from aerosols that reduces contrast and shifts reflectance, especially in blue bands.

Optical imagery measures reflected sunlight, providing rich spectral information but being sensitive to clouds and illumination.

Radiance is the raw physical quantity measured by optical sensors, representing energy reaching the sensor.

Reflectance is the fraction of incoming light that a surface reflects, commonly used for analysis and comparison.

Surface reflectance estimates what reflectance would be at the ground after removing atmospheric effects.

TOA reflectance is reflectance at the top of the atmosphere, before full atmospheric correction to the surface.

Backscatter is the amount of radar signal returned to the sensor, influenced by roughness, moisture, and structure.

Incidence angle is the angle between the radar beam and the surface; it affects SAR backscatter and comparability.

Polarization describes the transmit and receive orientation of radar waves; different polarizations respond to different surface properties.

SAR is an active radar sensor that works day or night and can see through clouds, measuring surface scattering rather than reflected sunlight.

Speckle is a grainy noise pattern in SAR imagery caused by coherent interference, typically reduced by filtering or multi-looking.

A band is a single spectral channel in an image, measuring energy within a specific wavelength range.

A digital number (DN) is the raw pixel value recorded by a sensor before it is converted to physical units like radiance or reflectance.

Earth observation is the use of satellites, aircraft, or drones to measure and monitor the planet’s surface and atmosphere.

A pixel is the smallest unit in a raster; it represents the sensor’s measurement over a ground area.

A raster is a grid of pixels where each pixel stores a value, commonly used for satellite imagery and elevation models.

Remote sensing measures Earth from a distance using sensors that record reflected or emitted energy.

Spatial resolution describes the ground detail an image can represent, commonly expressed as meters per pixel.

Spectral resolution describes how finely a sensor samples wavelengths and how narrow its bands are.

Temporal resolution describes how often a location is observed, such as a 5-day revisit.

Vector data represents geometry as points, lines, and polygons, typically used for boundaries, roads, and field parcels.

Change detection identifies meaningful differences between dates, such as harvest, flooding, deforestation, or construction.

Data fusion combines multiple data sources or sensors to create a more complete or consistent product.

Gap filling estimates missing values in time series caused by clouds, shadows, or data dropouts.

Harmonization reduces differences between scenes or sensors so values are more comparable across time.

NDVI is a vegetation index that uses red and near-infrared reflectance to approximate vegetation greenness and vigor.

Temporal integrity means an output for a given date is built only from information available on or before that date.

A time series is a sequence of observations over time for the same location, used for monitoring and change detection.

Zonal statistics summarize raster values inside a polygon, such as average NDVI per field.

A COG is a GeoTIFF organized for fast partial reads over HTTP, enabling streaming access without downloading the full file.

GeoTIFF is a raster image format that embeds georeferencing metadata so pixels map to real-world coordinates.

STAC is a standard for describing geospatial data assets so they can be discovered and accessed consistently.

Ground truth is reference information about real conditions on the ground used to train or validate models.

Training data is the labeled examples used to fit a machine learning model.

Validation tests model performance on data not used for training, to estimate how well it will generalize.

Sentinel-1 is an ESA SAR mission providing radar observations that work through clouds and at night.

Sentinel-2 is an ESA optical multispectral mission widely used for land monitoring at 10–60 m resolution.