Order a new survey. High resolution satellite images

Spatial resolution is the size of the smallest terrain detail reproduced on the image. It is defined by pixel size: for an image with 1 m spatial resolution one pixel corresponds to a 1 × 1 m area of the Earth's surface.

There is no single unified classification of spatial resolution. The following grading is used in the service materials:

• very low — worse than 100 m;
• low — 15–100 m;
• medium — 5–15 m;
• high — 1–2.5 m;
• very high — 0.5–1 m;
• extra-extra-high — 0.15–0.5 m.

The choice of resolution depends on the objects to be distinguished, the area of the territory, the observation frequency and the processing result. For photogrammetry the source content gives the following guides: for scale 1:5,000 — resolution 0.25 m; for 1:10,000 — 0.5 m; for 1:25,000 — 1.25 m; for 1:50,000 — 2.5 m. The main criteria of image suitability for orthophotomaps are spatial resolution, georeferencing accuracy and other parameters of the terms of reference.

By coverage, images are divided into global, large-regional, regional and local. Global images cover the planet, large-regional — continents and large regions, regional — individual regions and their parts, local — cities, industrial complexes and small areas. The more detailed the image, the smaller, as a rule, the area of one frame, and the more important it is to define the area of interest correctly.

For extra-high-detail tasks, data from the following spacecraft may be considered WorldView-1, WorldView-2, WorldView-3, GeoEye-1. For archive analysis over long periods, data from Landsat-7. The specific source is selected after checking the archive, parameters and licence terms.

Satellite imagery differs by scale, spatial resolution, coverage and spectral characteristics. These parameters determine the possibilities of object interpretation and the range of tasks that can be solved from the images.

By the nature of coverage of the Earth's surface, four main types of satellite imagery are distinguished:

1. Single, or selective, photography. Performed for individual areas; images may be oblique and have significant tilt angles.
2. Strip survey. Performed along the satellite's orbital flight. Strip width depends on flight altitude and the viewing angle of the imaging system. Fan imaging with several systems may be used to widen the swath.
3. Targeted survey. Intended to acquire images of specially designated areas off the satellite track.
4. Global survey. Performed from geostationary and polar-orbiting satellites and provides regular overview images of large territories.

The order also specifies the survey mode: mono or stereo. A mono image is suitable for visual analysis and many kinds of thematic processing. Stereo survey is required when a digital elevation model, height measurement or photogrammetric processing is needed. The mode affects the source-data composition, cost, order area and operator requirements.

GEO Innoter works with the main operators of remote sensing spacecraft and supplies images from both optical and radar satellites. Materials with various characteristics are available: from extra-high-detail imagery with 30 cm spatial resolution to medium-resolution overview images for regional-scale tasks.

Optical images are close in visual properties to human perception of the surroundings: colour, shape, structure and relative position of objects are analysed on them. They are used for visual and automated interpretation, mapping, construction monitoring, land use, forests, farmland and the environment.

The request can specify panchromatic, multispectral or hyperspectral imagery. Several spectral bands make it possible to detect vegetation condition, plant diseases and the vegetation phase, and to analyse water bodies, soils, geological features and pollution sources.

Radar images are formed by a different physical principle and provide an image of the Earth's surface regardless of cloud cover and time of day. Their interpretation requires specialised knowledge. Radar data are used, for example, to detect oil films, analyse ice structure, perform geodynamic monitoring and operational control of emergencies.

The quality of satellite photography depends on the imaging system, orbital altitude, spatial resolution, georeferencing accuracy, off-nadir angle, sun angle, cloud cover, snow cover and the survey period. When selecting materials these parameters are checked together, because high detail alone does not guarantee that an image is suitable for a specific task.

Remote sensing data processing is divided into preliminary and thematic. Preliminary processing transforms the source information received by a ground station into standard remote sensing products suitable for archiving and further use. It usually includes radiometric correction, geographic referencing and geometric correction of the image.

After incoming quality control, satellite images may undergo photogrammetric and thematic processing, orthorectification, colour and lighting correction, mosaicking, interpretation and preparation of derived materials. You can order photogrammetric processing, remote sensing imagery interpretation, orthophotomap creation, maps, digital models and analytical materials.

Satellite images can be combined with ready vector or raster data in GIS after geometric and perspective distortions are removed, after alignment, scaling and conversion to an agreed coordinate system.

Archive data are suitable when an image of the required territory, date and characteristics is already held by the operator. They can be obtained faster, and the cost is usually lower than a new survey. A new survey is ordered if the current state of the territory, a given season or period, specific angles, cloud cover, spectral characteristics are required, or archives have no suitable coverage.

The advantage of high- and very-high-resolution satellite imagery is speed and large coverage. An archive image may be available immediately, and a new satellite survey does not require flight clearance from government authorities. One satellite image covers a substantially larger area than a frame from an aircraft or UAV. Satellite photography is especially effective for hard-to-reach territories where field work is costly.

Medium-spatial-resolution images are widely used to monitor crops, inventory land, support precision agriculture, search for minerals, control water bodies, emergencies, forests and the environment. They are used as a backdrop for large territories and to create and update maps at scale 1:100,000 and smaller.

High-spatial-resolution images are used to create and update topographic and special maps up to a scale of 1:25,000, build digital elevation models, control construction and oil-and-gas infrastructure, perform environmental monitoring, territorial planning, forest inventory, crop-condition assessment, and monitoring of waterlogging, desertification, salinisation, karst, erosion and fires.

Modern applications of satellite imagery include meteorology, oceanology, geology and geomorphology, studies of glaciers, wetlands, deserts and forests, land accounting, natural and economic zoning, and creation and updating of thematic and general geographic maps.