SAR imagery (Radar satellite data)

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SAR imagery (Radar satellite data) is a special type of space imaging in which microwave radiation with wavelengths ranging from 1 cm to 1 m is used to obtain information by illuminating the Earth's surface and detecting the reflected signals. Radar aerial and space imaging is one of the methods of remote sensing of the Earth's surface, allowing for the acquisition of images of the terrain in the microwave range of the electromagnetic spectrum. Radar images enable the visualization of the Earth's surface and objects regardless of weather conditions, in both day and night time, by emitting and receiving reflected signals from the Earth's surface, followed by the conversion of these signals into images or extraction of phase difference information between the transmitted and reflected signals. The data obtained from radar sensors, similar to optical satellite images, have different spatial resolutions and the ability to capture information in various electromagnetic bands. Radar satellite data consist of two components: the phase component and the amplitude component. The differential interferometric processing of the phase component allows for the measurement of surface displacements, while the processing of the amplitude component enables differentiation of the reflecting surface based on roughness characteristics and volumetric scattering, i.e., object decryption. The technology of differential interferometric processing involves the formation of an interferogram, which, in simplified terms, is the result of multiplying a pair of complex-valued radar images of the same area acquired by identical SAR (Synthetic Aperture Radar) systems from closely located points of the orbit. The phase cycle differences within each pixel in the interferogram represent the relative change in distance between the radar antenna and the reflector (probed surface).

Space imagery allows:

analyze socio-economic development of territories;
to track the dynamics of changes in the area
acquisition of information regardless of the object of interest location
use both archived and fresh information;
detect objects and events with high accuracy;

Satellite imagery / satellite data received from an airplane or a UAV has high visual informative capacity and excellent measurement properties, but requires longer time for surveying, as it requires time for coordinating permission for flight, movement of aircraft (UAV with operators) to the survey area and higher (multiples) cost of data per 1 km2.

Another indisputable advantage of space imagery is its objectivity (the human factor is minimized).

The image of the Earth is constantly changing and any map is gradually aging. Space images contain up-to-date and reliable terrain data and are successfully used for updating maps not only at small, but at large scales as well. They allow correcting maps of large territories of the world. Space imagery is especially efficient in hard-to-reach areas where fieldwork is very labor- and cost-consuming.

Applications of SAR imagery/Sar images (Radar satellite data)

SAR imagery/SAR Images (Radar satellite data) is indispensable compared to other observation methods in challenging weather conditions. It offers the ability to obtain images at any time of day and in any weather, precise measurement of coordinates and geometric characteristics of objects, detection of objects invisible in the optical or infrared range of the electromagnetic spectrum, hidden under snow or vegetation cover, or located beneath the Earth's surface.

Purposes and Objectives of SAR imagery/SAR images
(Radar satellite data)

The purpose of space radar imaging is to obtain timely and relevant information about the terrain and water surface, which is necessary for solving numerous tasks in various fields of activity. The main objectives of radar imaging include:

Creation and updating of topographic maps and plans, as well as other cartographic products;
Creation of engineering-geological maps for geological surveys;
Land management and cadastral work;
Generation of digital terrain models for planning and development of telecommunication networks;
Agricultural research, detection of plant diseases, determination of vegetation phase;
Monitoring of emergencies and their consequences, control of emergency restoration work;
Forest inventory (forest assessment, determination of age, height, and diameter of growing trees, wood reserves, annual growth, etc.);
Detection of oil spills;
Detection of fuel dumping from ships;
Information support for the prevention and elimination of oil and petroleum product spills;
Monitoring of deformation and displacement of the Earth's surface in mining areas;
Monitoring of structural deformations in urban areas;
Monitoring of critical industrial facilities;
Pipeline monitoring;
Monitoring of roads and railways and other objects;
Monitoring of ice conditions and ship movements;
Monitoring of natural and man-made hazardous processes, including earthquakes, landslides, avalanches, sinkholes, flooding, karst, suffusion, river erosion, coastal erosion, and changes in sea and reservoir coastlines.

Initially, the tasks of radar imaging were limited to the study of the ocean surface. However, the scope of radar imaging has expanded, and it now allows for obtaining data on millimeter-level displacements of objects on the Earth's surface, tracking oil pollution and maritime situations in water areas, as well as creating digital terrain models (the well-known SRTM DTM is based on radar data processing).

Advantages of Radar Imaging/SAR Images

Radar imaging offers several advantages compared to other observation methods. It provides high precision in measuring the coordinates and geometric characteristics of objects and the ability to obtain radar images at any time of day and in any weather conditions (microwave radiation easily penetrates through clouds and does not rely on daylight, unlike visible and infrared imagery).

Ability to conduct radar imaging in any weather conditions (including strong cloud cover) and at any time of day (including nighttime);
High level of detail due to the high spatial resolution of radar imagery;
Cost-effective alternative to GPS monitoring of ground displacements.

Innovative processing techniques open up new areas of radar imaging utilization, including:

The ability to conduct radar imaging regardless of weather conditions makes it particularly valuable for mapping remote regions in the Far East of Russia and other countries, where snow hinders imaging during the winter and continuous cloud cover occurs during the rainy season throughout the imaging season. Another advantage of radar imaging for cartography is its relatively high spatial resolution, which enables the creation and updating of maps up to a scale of 1:50,000.
By using the phase information of radar signals, digital elevation models and terrain models can be created through interferometric processing. These models can be used in various areas of society.
Temporal radar images provide information on ground surface displacements. This helps detect ground subsidence in mining areas, deviations of infrastructure objects from their normal positions, and track landslide processes.
SAR images of water surfaces enables the detection of oil spills. Due to the specific characteristics of oil, which result in a smoother surface and different reflectivity compared to natural water, oil spills can be easily identified on radar images.
SAR images allows for the detection of ships that have intentionally disabled their tracking signals or have lost signal due to accidents. Radar signals are well reflected by metallic surfaces, enabling the automatic detection of ships even on medium-resolution radar images. Moreover, radar images can be obtained just an hour after acquisition, providing more precise information to the relevant authorities.
The varying reflectivity of radar imaging allows for the detection of forest fires and deforestation in forest areas, as well as monitoring the condition of agricultural crops.

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