Glossary
Amplitude
A
The strength of the reflection received by the satellite.
Asc
Atmospheric Delay
Abbreviation of “ascending orbit”.
Ascending Orbit
The section of orbit where the satellite moves from the South to the North. For most satellites (right looking), this means that the radar signal is transmitted from roughly the West under an angle (the look angle) down to the earth’s surface.
Disturbances to the signal due to atmospheric conditions while the signal is travelling to and from the Earth’s surface, causing a delay in the signal. This atmospheric delay is a known source of noise in InSAR processing and needs to be accounted for.
Baseline
B
The difference between two satellite acquisitions in a specific parameter, such as time or orbit geometry. Common examples are temporal baseline and geometric baseline.
Coherence
C
A measure of how similar the radar signal remains between acquisitions. Higher coherence generally means a more reliable displacement estimate.
Coherent Scatterers
Pixels which reflect the incoming signal consistently, meaning change in observed phase differences mostly come from deformation. This makes them more reliable for estimating deformation through time.
CSK
Abbreviation of the COSMO-SkyMed satellite constellation (X-band). Operational since 2007.
Decomposition
D
A sequence of displacement over time at a specific location or in a specific area. It is used to understand how displacement evolves.
Descending orbit
The section of orbit where the satellite moves from the North to the South. For most satellites (right looking), this means that the radar signal is transmitted from roughly the East under an angle (the look angle) and measures displacement from the west and angled down to the earth’s surface.
Displacement rate
Displacement time series
Distributed Scatterers
DS
Dsc
Rate of change of the surface displacement. It is commonly expressed in mm or cm per year.
Pixels that contain many objects with similar reflectance properties which equally reflect the incoming signal. These areas can still provide useful deformation information when processed collectively.
Abbreviation of “Descending orbit”.
Digital Elevation Model. The generic term for a topographic model of the earth. Can be either a DTM or a DSM.
Digital Surface Model. A topographic model of the earth showing the elevation of the surface including objects.
Digital Terrain Model. This is a topographic model of the earth showing the elevation and terrain of the bare earth. It is used in processing and interpretation where ground elevation matters.
Abbreviation of “Distributed Scatterer”.
DEM
The process of estimating horizontal and vertical deformation components from multiple line of sight deformation measurements by the satellite. This combines measurements from different viewing geometries to separate movement components.
DSM
DTM
ENV
E
Abbreviation of the Envisat satellite (C-band). Operational from 2002 to 2012.
ERS
Abbreviation of the European Remote Sensing satellite, operational from 1994-2001 (ERS-1) and from 1995 to 2011 (ERS-2).
Epoch
Estimated models
The moment in time of an observation.
The types of functions used to estimate the displacement. Can be linear, quadratic or seasonal, or other relevant model components. These models help summarize the dominant pattern in the time-series.
F
Foreshortening
The appearance of compressed terrain features in the radar image caused by the shortened time delay between radar echoes due to topography.
Geostatistics
G
A branch of statistics regarding spatial data. It is often used to analyse patterns, variation and relationships across an area
High Points
H
High/low separation
The differentiation of displacement measurements taken on ground level, and those taken on infrastructure. Depending on the local geology and foundation types, this may help in distinguishing different deformation processes.
Hill shade
Histogram
Reflection points that have a high elevation, with respect to ground level. Most are reflected on buildings, or other tall built structures. Depending on the local geology and foundation types, they may represent a certain deformation process.
A terrain visualization created from elevation data that simulates illumination across the surface. It helps make slopes, ridges and other landforms easier to see and interpret.
A graph that shows the distribution of displacement estimates rate. It helps show whether values are concentrated, spread out or skewed.
InSAR
I
Interferometric Synthetic Aperture Radar. This is the technique used by SkyGeo to estimate surface deformation. It analyzes radar measurements through time to detect subtle surface movement.
Interferogram
The resulting image produced by applying InSAR, which involves subtracting two SAR images from different dates. The phase differences in the interferogram are used to estimate deformation.
Layover
L
Distortion in a radar image due to topography. In areas with very steep slopes, the radar echo from the bottom of the slope has a longer travel time than the echo from the top. This can cause topographic features to appear displaced, merged, or overlapping in the radar image. Surface movement cannot be assessed in areas affected by layover.
Line of Sight
The direction that the satellite signal reaches the surface at. Displacement is measured along this direction.
Linear fit
Low Points
One of the models used to estimate displacement behavior in a time series. It assumes a velocity model. This is useful where movement is broadly steady through time.
Reflection points on ground level. These are typically associated with measurements taken at the ground surface.
Metadata
M
Descriptive information about a dataset. It helps users understand the source, structure and properties of the data.
Measurement
The data is observed by the satellite. Displacement (rate) derived from these measurements are estimated / estimations.
NDMI
N
Abbreviation for Normalized Difference Moisture Index.
NDVI
Abbreviation for Normalized Difference Vegetation Index.
Normalized Difference Vegetation Index
NDWI
NISAR
Normalized Difference Moisture Index
Normalized Difference Water Index
Abbreviation for Normalized Difference Water Index.
Abbreviation of the NASA-ISRO Synthetic Aperture Radar mission (L-band). Operational since 2026.
A proxy for moisture content in a region of soil.
A proxy for vegetation health.
A proxy for the presence of surface water.
PAZ
P
Spanish SAR satellite (X-band), in the same orbit as and compatible with the TerraSAR-X and Tandem-X satellites. Operational since 2018.
Persistent scatterers
Percentile
Phase
PS
Perpendicular Baseline
The number of detected points within a specified area. Higher point density generally provides more detail across an area or asset.
Phase ambiguity
Phase difference
Point height
Point Scattering
Point density
A statistical measure denoting the value below which a certain percentage of the observations falls.
The distance between two satellite positions for a given image pair, measured relative to the line of sight. It affects sensitivity to topography and the quality of the interferometric measurement.
Conventional term to indicate a continuously coherent point scatterer. These are pixels which contain a dominant and continuous scatterer from a single object.
The fraction of a complete wavelength, as received at the satellite. This is the signal we use to estimate displacement.
The unknown number of full phase cycles accompanying a phase value due to the cyclical nature of phase. These phase ambiguities are estimated to allow the proper retrieval of the displacement.
The change in phase between two consecutive measurements at the same location. This indicates the change in distance from the surface to the satellite and ultimately the amount of deformation. It is one of the core inputs used to calculate line-of-sight deformation.
The estimated height of the InSAR point. It is crucial for the geolocation of the point. Furthermore, It helps distinguish whether a point is likely on the ground or on an elevated object.
A relative measure of the quality of one displacement measurement, ranging from 0-1. Higher values indicate greater confidence in the measurement.
Abbreviation of “Point Scattering”.
R
Reference point
The location of the Point Scatterer which all other displacement measurements are in reference to. All reported displacement is relative to this chosen location.
Reflection
Resolution
Repeat cycle
The mirroring or casting back of the emitted radar signal off of Earth’s surface. The character of that returned signal influences the quality of the measurement.
The number of days between successive observations of the same area on Earth from the same satellite orbit position . This affects how often displacement can be observed in a time-series.
The distance at which objects can be distinguished by the radar, hence, higher resolution generally allows smaller features to be distinguished.
RSAT2
Abbreviation for the RadarSAT-2 SAR satellite (C-band). Operational since 2008.
S1
S
Abbreviation of the Sentinel-1 SAR satellite mission (C-band). Operational since 2014.
S2
Abbreviation of the Sentinel-2 multispectral satellite mission. Operational since 2015. See Sentinel-2 Satellite.
SAOCOM
Sentinel-2 Satellite
Scattering noise
Abbreviation for Shortwave Infrared.
SAR
SBAS
Spatial coherence
SWIR False Color Images (SFCI)
SWIR
Abbreviation of the Satélite Argentino de Observación Con Microondas satellite mission (L-band). Operational since 2019.
Synthetic Aperture Radar. This is the radar imaging technique used to obtain high resolution by integrating observations along the orbit.
Abbreviation for Small Baseline Subset. An InSAR processing method used to capture dynamic displacements. It requires a spatial estimation of phase ambiguities. Therefore, the spatial smoothness of the displacement signal and the surface cover (level of decorrelation) should allow this approach.
Fluctuations in the reflected signal that can obscure the deformation data. It can reduce confidence in a measurement if not separated from the deformation signal.
An optical, multi-spectral satellite that can be used to monitor various dynamic changes to surface conditions at each acquisition. Although it does not measure deformation directly, it provides useful surface context alongside InSAR.
spatial measure of how similar the radar signal remains between acquisitions. Higher coherence generally means a more reliable displacement estimate.
Images used to distinguish water from snow and ice. This combination can make moisture and snow or ice boundaries easier to interpret.
T
True Color Images (TCI)
An image that offers a natural color rendition; combining each of these color band wavelengths in an image mimic how a human eye would observe an object. It is useful for visual context because it resembles natural human vision.
TSX
Abbreviation of the TerraSAR-X satellite constellation (X-band), in the same orbit as and compatible with the Tandem-X and PAZ satellites. Operational since 2008.
Unwrapping
U
The process done by SkyGeo to estimate the number of completed phase cycles that accompanies each phase value. This converts wrapped phase values into a continuous displacement signal.
Vegetation False Color Images (VFCI)
V
Multi-band images for which the combination of wavelengths is sensitive to vegetation coverage. It can help highlight differences in vegetation condition and extent.This combination of wavelengths is sensitive to vegetation coverage. It can help highlight differences in vegetation condition and extent.
Wave cycle
W
One wave cycle includes one maximum value on a wave (peak) and one minimum value (trough). Wave cycles are repeated to create a wave. The repetition of these cycles defines the wave pattern.
Wavelength
The length over which the radar wave makes a complete cycle, i.e. goes up, down, up and returns to the same point. It is a fundamental property of the radar signal and influences how it interacts with surfaces.
WMS
WFS
Web Feature Service. This is a service for your local GIS viewer that allows you to display and access the SkyGeo deformation data which lays behind the displayed image. It is useful when you want to query or style the underlying vector data locally.
Web Mapping Service. This is a service for your local GIS viewer to add SkyGeo data as a background image to your project. It is useful when you want a visual layer without downloading the underlying data.