GLOSSARY

A

Amplitude
The strength of the returned signal recorded by the satellite. This is depicted as the ‘height’ of the wave.

Ascending orbit
The section of the orbit where the satellite moves from south to north.

Atmosphere
Disturbances to the signal due to atmospheric conditions the signal encounters when travelling to and from the Earth’s surface, causing a delay in the signal.

B

C

Coherent reflectors
Pixels that reflect the incoming signal consistently over time in terms of strength.

D

Decomposition
The process of obtaining the horizontal and vertical deformation from the line of sight deformation measured by the satellite.

DEM
Digital Elevation Model. This is topographic model of the earth showing the elevation of the surface, including infrastructure.

Descending orbit
The section of the orbit where the satellite moves from north to south.

Distributed Scatterers
Pixels that contain multiple objects with similar, weaker, reflectance properties. By combing multiple similar neighboring Distributed Scatterers, the signal is trustworthy enough to show as deformation on the map.

DTM
Digital Terrain Model. This is a topographic model of the earth showing the elevation of the bare surface.

E

F

Factual report
A report produced by SkyGeo offering an overview of the processing steps taken to provide the customer with their products.

Fit
A mathematical function that models the actual deformation occurring within a time series.

G

Geostatistics
A branch of statistics regarding spatial data.

H

High/low separation
The differentiation of deformation measurements taken on ground level and those taken on higher infrastructure.

I

InSAR
Interferometric Synthetic Aperture Radar. This is the technique SkyGeo applies to SAR images to measure surface deformation.

Interferogram
The resulting image produced by applying Differential InSAR, which involves subtracting two SAR images from different dates. The image shows the phase differences between the two acquisitions.

J

K

L

Line of Sight
The angle that the satellite signal reaches the surface at, with respect to the vertical.

M

Metadata
Descriptive information about a dataset.

N

Noise
The part of a measurement that does not contain any information on the actual deformation. This unwanted modification of the signal comes from inaccuracies in the sensor or external factors like atmosphere.

O

P

Percentile
A statistical measure denoting the value that a certain percentage of the observations fall below.

Persistent scatterers
Pixels that contain objects with high reflectance properties and are time coherent.

Phase
The fraction of a complete wave cycle that is recorded by the satellite

Phase ambiguity
The uncertainty in the number of full wave cycles in the signal due to the cyclical nature of sinusoidal waves.

Phase difference
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.

Point density
The density of data points within a specified area.

Point Quality
A relative measure of the quality of one deformation point or cell, ranging from 0 to 1. See ‘Point Quality’ for more information.

Q

R

Reference point
The location where all deformation measurements are in reference to. The reference point is often assumed to be stable in time.

Reflection
The signal the satellite receives back from the earth’s surface after emitting a radar pulse.

Repeat Cycle
The number of days between consecutive observations of the same location on Earth by a certain satellite.

Resolution
The size of the area in which one measurement value can be obtained.

S

SAR
Synthetic Aperture Radar. The radar-based method that is used to acquire the images that form the basis for InSAR.

Sinusoidal wave
A wave with the form of a sinus. The signal is repeated after every wave cycle.

T

Time coherent
See ‘Coherent reflectors’

Time series
A graph showing deformation over time at a specific location or in a specific area.

U

Unwrapping
The process that is used to determine the number of completed wave cycles in the signal. By combining this information with the measured phase value, the deformation time series can be derived.

V

W

Wavelength
The distance between one peak or trough of a sinusoidal wave and the next peak or trough. This is the length of one wave cycle.

Wave cycle
One wave cycle includes one maximum value on a sinusoidal wave (peak) and one minimum value (trough). Wave cycles are repeated to create a wave.

Weighted averaging/span>
A technique which aggregates multiple data points to a virtual point on an asset of interest by using the relative distance of the data points to the asset.

WFS
Web Feature Service. This is a service for your local GIS viewer that allows you to display and access the values of the SkyGeo deformation data underlying the displayed image in SkyGeo Maps. See ‘Using WMS/WFS’.

WMS
Web Mapping Service. This is a service for your local GIS viewer to add SkyGeo data to your project as a static image. See ‘Using WMS/WFS’.

X

Y

Z