All SAR satellites orbit the Earth on a near-polar orbit at an altitude ranging from 500 to 800 km above the Earth’s surface

InSAR satellite list

The time taken for a satellite to re-pass over the same area is called the ‘revisiting time’. Since the launch of ERS satellites in 1992, numerous satellites have been orbiting the Earth, providing higher resolution images, faster repeat times and data redundancy for many parts of the world.

SAR satellites

Synthetic Aperture Radar (SAR) satellites acquire images of the Earth’s surface by emitting electromagnetic waves and analysing the reflected signals.

All SAR satellites travel from the north pole towards the south pole for half of their trajectory (descending orbit) and from the south towards the north pole for the other half (ascending orbit). As a consequence, the same area of interest is revisited along the two orbits with ascending and descending imageries collected over it through time.

SAR satellites
SAR signal

SAR signal

Each SAR image incorporates two fundamental properties: phase and amplitude.

The phase contains information of the sensor-to-target distance that is used in interferometric applications (InSAR or SAR Interferometry) to measure ground surface motion over time. The amplitude instead is related to the energy of the backscattered signal and it used in speckle/pixel tracking applications and ground change detection.

No ground equipment is needed. SAR satellites detect targets already existing on the ground (e.g. buildings, linear structures, rocky outcrops, uncultivated lands, debris, etc.) and register their backscattered signals.

Techniques

By exploiting both the phase and amplitude properties of SAR imagery, TRE ALTAMIRA has developed different techniques to extract surface displacement measurements and to detect information about surface characteristics and variations.

 

Measure

Detect

InSAR
Displacement Map
SqueeSAR™Rapid Motion Tracking (RMT)InterferogramAmplitude MapsChange Detection Maps
Range of movementDisplacement > few cmDisplacement rate < few cm/yearDisplacement rate > few cm/year---
Minimum # SAR images215-2010212
Max measurement precisionCentimetricRate: lower than 1 mm/year

Single measure: lower than 5 mm
1/10 SAR image pixel (from few to tens cm)---
Spatial resolutionTens of pixels (tens of metres)One-point target50-100 pixels (hundreds of metres)Tens of pixels (tens of metres)Few pixels (few metres)Few pixels (few metres)
Movement components1D (LOS)

2D (Vertical, East-West)
1D (LOS)

2D (Vertical and East-West)
2D (LOS and Azimuth)

3D (Vertical, North-South, East-West)
---
OutputGeotiff raster map, kmzSet of georeferenced points with displacement Time Series (shapefile or other database)Sets of georeferenced points with displacement Time Series (shapefile or other database)Geotiff raster map, kmzGeotiff raster map, kmzGeotiff raster map, kmz
ApplicabilityDisplacement rate > few cm between two acquisitions

Areas not affected by
decorrelation or strong atmospheric noise
Displacement rate between mm/year and few cm/year

Coherent radar
targets over time
Displacement rate > cm/year

Areas with a good
and persistent reflectivity
Detection of areas affected by surface motion between two acquisitions

Areas not affected by
decorrelation or strong atmospheric noise
Detection of surface reflectivity characteristicsDetectection of surface reflectivity variations
TRE ALTAMIRA's data center

Our processing infrastructure

An in-house data centre, designed to cope with the high demand of SAR imagery processing and storage.

The architecture consists of a Linux-based parallel processing system, made up of approximately 100 servers and 276 cores for data processing and 10 CPUs for interactive session management. The system has also a storage capacity of 200 TByte accessed via a high-performance parallel file system.