Radar imagery

WHAT IS THIS?

Radar imagery is an active remote sensing system which bounces microwave energy from a target and records the energy that returns to the sensor.

Radar data processing

Here are some examples of SAR satellite data analyzing methods and their applications:

Change detection analysis with the accuracy of several cm;
Structures deformation measurements with the accuracy of several mm;
Establishing trends and forecasting.

Interferometric synthetic aperture radar (InSAR)

Interferometric synthetic aperture radar (InSAR) techniques combine two or more SAR images over the same region to reveal surface topography or surface motion. If the combined SAR images originate from slightly different positions, the topography of the surface can be mapped. In contrast, if images from the same position but taken at different times are combined, the difference between them will show motion, or deformation, of the surface in the time between the two images.

Processing methods

Differential SAR Interferometry (DInSAR)

Basic method of SAR data interferometric processing. Differential interferometry (DInSAR) can detect movements in the radar look direction that are in the order of wavelength used, i.e. less than one centimetre

Permanent Scatterer Interferometry (PSInSAR)

This method accurately estimates the near vertical terrain deformation rates, of the order of ∼1 mm year-1, overcoming the physical and technical restrictions of classic InSAR.

Small baseline interferometry (SBAS)

SBAS technique is a time series analysis approach, which uses interferograms with small baselines to minimize geometrical decorrelation at the expense of spatial resolution.

PS/SBAS

Radar satellites perform multiple surveys of an area with a size of 40x40 km;
Between repeated surveys, the phase difference is calculated, proportional to the displacements of the earth's surface and the deformation of the structures;
Offsets are calculated for areas of the earth's surface and objects that consistently reflect the radar signal (areas of land without forest vegetation, buildings, structures, angular landforms;
The result is issued in the form of a file of points / map of displacements of the radar signal, indicating the displacement values for each point / pixel as of each date of the survey (the offsets are counted relative to the date of the first in the order of the survey);
The accuracy of measuring displacements reaches 2 - 4 mm - the first cm;
It is possible to measure vertical displacements and horizontal displacements in the direction "West-East".

PERSISTENT SCATTERERS INTERFEROMETRY (PSI)

PSI is a powerful remote sensing technique able to measure and monitor displacements of the Earth's surface over time with the highest possible accuracy of displacement estimation (2–4 mm in height). Input data should include at least 20-25 images of the same territory with different dates, made in the same geometry of the satellite radar survey.

Algorithm:
1. Selecting the original image
2. Co-registration of interferometric circuit pulses with an accuracy of 1/100 of a pixel
3. Building an interferogram for each pair of images
4. Estimation of the magnitude of coherence / standard deviations of the amplitude of each pair of measurements
5. Determination of points - stable scatterers of the radar signal
6. Evaluation of frequency differences and multi-time phase sweep for point targets by points, earlier
7. Application of an individual filter that removes the effect on the interferometric phase

The result of processing is a vector file of points with:

offsets for each shooting date;
average annual rate of displacement;
the total value of the displacements;
height above the WGS-84 ellipsoid.

Industry solutions

Agriculture

Satellite SAR imagery helps to monitor crops and fields remotely over time. Farmers can use imagery to get an aerial view of various fields and crops to look for changes or differences.

Water management

Satellite Synthetic Aperture Radar is a popular solution for mapping and monitoring surface water features, to distinguish water from non-water. It is important for sustainably managing this critical natural resource.

Forestry

Radar satellite technology with its capability to penetrate clouds is often used for investigating tropical forests as they are most of the time under clouds. Radar is also able to capture images through darkness which can be of great benefit for tracking nighttime illegal activities.

Terrain analysis

SAR imagery is perfectly used for monitoring critical areas for many branches of human activity: construction, industry, scientific research and geological exploration of territories.

Radar satellites

C-Band SAR

GaoFen-3

Gaofen 3 (GF3) is the first C- band high-resolution SAR satellite with a meter-level resolution from China. It's capable to provide Earth images from high-resolution (1 m) to large-swatch (650 km).

X-Band SAR

KOMPSAT-5

KOMPSAT-5 is part of the Korean National Development Plan of MEST (Ministry of Education, Science and Technology). The primary mission objective is to provide imagery for geographic information applications and to monitor environmental disasters.

C-band SAR

Sentinel-1A, 1B

Sentinel-1A and Sentinel-1B are European radar satellites. The first satellites launched under the European Space Agency's (ESA) Copernicus space program. While in the same orbit, both satellites can film the entire territory of the Earth within 6 days.

X-диапазон

COSMO-SKYMED 1-4

COSMO-SkyMed is an Italian Earth-imaging constellation consisting of four identical satellites. COSMO-SkyMed stands for 'COnstellation of small Satellites for the Mediterranean basin Observation'.

SAR (X-Band)

TerraSAR-X

TerraSAR-X is a satellite with a 1 meter resolution class radar satellite, which delivers Earth observation data for scientific, institutional and commercial users.

С-диапазон

Radarsat-2

RADARSAT-2 is a jointly-funded satellite mission of CSA (Canadian Space Agency) and MDA (MacDonald Dettwiler Associates Ltd. of Richmond, BC), representing a Canadian government/industry partnership [or PPP (Public Private Partnership)] in a commercial venture.

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