NEC technology enables satellite radar to inspect urban infrastructure
Tokyo, July 20, 2018 - NEC Corporation (NEC; TSE: 6701) today announced the development of two-dimensional small displacement measurement technology that can enhance public safety through the analysis of aging roads, buildings and infrastructure in urban areas.
This new technology integrates displacement analysis using two satellite radars and precisely evaluates horizontal and vertical two-dimensional displacement. It enables the inspection of individual infrastructure and can be used to judge the need for costly detailed inspections, improving the efficiency of preventive infrastructure maintenance.
Currently, there is a great deal of promise for small displacement analysis technology (*1) using Synthetic Aperture Radar (SAR) (*2), which is being developed for practical use and implemented in the Cross-ministerial Strategic Innovation Promotion Program (SIP) led by Japan's Cabinet Office. However, this technology cannot reliably be used in urban areas, where there is a strong need for it, because it is very difficult to discern which infrastructure corresponds to the radar's reflection point in densely built-up areas.
NEC's new two-dimensional small displacement analysis technology can resolve this issue by determining reflection points and infrastructure using NEC's proprietary reflection point clustering technology (*3), enabling high-precision, individual displacement analysis.
NEC applied this technology to the analysis of land subsidence measurement in urban landfill areas and confirmed its high-precision analysis. The new technology reduced errors by 40% in flat (suburban) and urban areas when compared to land subsidence surveys (*4) done manually.
In the Mid-term Management Plan 2020, covering the three-year period through the fiscal year ending March 31, 2021, NEC positions the safety business as an engine for global growth. This technology accelerates and enhances the development of solutions and services to realize the NEC Safer Cities vision and contributes to the development of safe and secure cities.
Features of the two-dimensional small displacement analysis technology include the following:
- Reflection point clustering that enables displacement analysis of individual infrastructure
NEC developed a new method that enables horizontal and vertical two-dimensional displacement analysis of an individual structure by clustering radar reflection points that belong to the same structure. This new method recognizes a structure as an aggregate of rigid bodies (such as a mass of concrete). It is possible to separate and determine extracted reflection points for each rigid body by clustering the reflection points based on the similarities and positions of the fluctuations in the reflection characteristics.
- Correct mapping reflection point clusters based on map information that is suited to two-dimensional displacement analysis
By referring to the shape of reflection point clusters for each rigid body, it is possible to match this data with map information. This facilitates the correct associations with actual structures. Mapping between reflection point analysis results observed from multiple directions can also be accomplished.
- High-precision two-dimensional displacement analysis that facilitates screening
Two-dimensional analysis results based on associations improved the precision of displacement analysis. For example, the two-dimensional analysis results of the urban landfill area in figure 2 shows that in a case of forced mapping of reflection points using a conventional method, some of the reflection points look as though they are displaced upward, unlike the surrounding reflection points. Therefore, further study is required to discover whether detailed inspection is required. As a result of improved analytic precision due to correct mapping, the new method shows that all reflection points sink evenly; meaning that there is no abnormal displacement, making it easy to determine that there is no need for detailed inspection.
This technology improved precision in displacement analysis as seen above and the improved precision will make a great contribution to increased efficiency of the preventive maintenance of aging urban infrastructure by increasing the screening reliability and by streamlining determination of the need for more detailed inspection technology, which are based on IoT, robotic technology and laser measurement technology.
"NEC is working to demonstrate this technology and to practically apply it to displacement analysis in a variety of fields, including the diagnosis of aging infrastructure, monitoring of land subsidence caused by construction works and the monitoring of large-scale plants. Moving forward, NEC will continue to proactively engage in the development of infrastructure diagnostic technologies, including remote sensing technology," said Toshihiko Hiroaki, General Manager, NEC Corporation.
NEC will announce these results at IGARSS (International Geoscience and Remote Sensing Symposium), a remote sensing-related international academic conference from Sunday, July 22 to Friday, July 27; Valencia, Spain. URL: https://igarss2018.org/
- *1Small displacement analysis technology by SAR:
Displacement analytic technology using radar images consisting of reflection points (or scattered points) on the ground and infrastructure, such as roads, which are obtained when a periodically-orbiting radar observes terrain. It is capable of measuring micro-displacement down to the millimeter per year on the ground and roads by recognizing stable reflection points in dozens of radar images periodically observed to be originating from a single structure, analyzing them in chronological order. This technology is based on a single satellite and has been created for practical use as a high-precision, efficient technology to monitor the aging displacement of artificial structures using infrastructure maintenance controlling, updating and managing technology by the development technology team in the Cross-ministerial Strategic Innovation Promotion Program (SIP) led by Japan's Cabinet Office.
- *2Synthetic Aperture Radar (SAR):
Technology to achieve high-resolution radar images by enlarging the radar antenna (aperture length) virtually using satellite motion. For example, ASNARO2, NEC's small radar satellite, is capable of achieving high-definition images with a 1-m resolution from several hundred kilometers above ground. However, as radar only measures distance, the resulting images appear distorted in comparison with images obtained by an optical camera.
- *3Reflection point clustering technology:
Technology that classifies and brings together radar reflection points based on their features, for example, the location type where reflection points are found, which can be applied to estimations of land use.
- *4Land subsidence survey: Altitude observation of control points set and managed by the Geospatial Information Authority of Japan or local governments.
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