Synthetic Aperture Radar

FS08 SAR

FS08: Synthetic Aperture Radar

Synthetic Aperture Radar (SAR) is a remote sensing technique typically used from satellites (e.g. Sentinel 1) to provide vegetation, biomass, moisture assessments and mapping of landscapes. The technological adaption for use working with drones allows a higher spatial resolution along with greater level of canopy and soil penetration which supports a much richer assessment of land condition with outcomes that include DTM/DSM/CHM, biomass, vegetation profile, soil moisture, soil types and even shallow buried objects. No one else in the UK has commercial access to this technology.

Background

The movement of the drone (or crewed aircraft) provides moving antennas (synthetic aperture) allowing smaller physical antennas and higher resolution. The process will use multiple pulsed electromagnetic frequencies with different wavelengths in combinations to build up images of the target survey area. The different frequencies can have the ability to penetrate vegetation/canopy and even soils.

SAR Survey

SAR is an emerging technology for use and application with uncrewed as well as crewed flights and can be applied to a range of interesting use cases and provide insights on land condition irrespective of the vegetation cover.

SAR surveys can provide good resolution data for Digital Surface and Terrain Models while supporting calculation of biomass, soil moisture, soil type, land deformation, vegetation health, voids/shallow objects. These outcomes are particularly valuable for agricultural, peatland restoration, forest management, rewilding, habitat assessment, coastal erosion, wild fires and slope stability.

Survey Processes

The data requirements govern the flight management approach. This includes the speed of the craft and its flight pattern which are both used to set the aperture and hence increase the resolution of the signals. The use of a ground base station working with further ground truthing is essential in developing accurate mapping and survey grade solutions. We also recommend using corroborating data from satellite or from further sensing solutions.

SAR has been used with rotary and fixed wing uncrewed systems as well as crewed craft. The selection is very much subject to resolution required and area of coverage.

Satellite SAR

Satellite SAR is well established and provides good coverage albeit with limited EM bands and low resolution. Nonetheless, there are commercial satellites with greater capability and increased resolution along with a proposed string a new satellite constellations which will offer even greater insights and most importantly a constant cycle of coverage providing ideal monitoring solutions for larger site areas.

Surveyar have been developing data fusion techniques, where the drone based SAR is used to 'calibrate' the satellite SAR via machine learning processes to increase the resolution and survey outcomes for specific use cases. Further, we are also developing triage solutions which use satellite based data to prioritise areas for aerial survey at higher resolution for 'areas of interest'.