EARTH OBSERVATION - Rail Technical Strategy

Earth observation

What is earth observation?

The UK Space Agency defines Earth Observation (EO) as “the collection, analysis and presentation of information about planet Earth’s physical, chemical and biological systems via remote sensing technologies”. The European EO programme – Copernicus – is operated by the European Space Agency and EUMETSAT, and collects information and data about the Earth through its seven present Sentinel satellites. Current technology is sufficiently mature for applications that are relevant to a range of railway challenges, such as better monitoring of vegetation and floods. The scope of future applications is likely to grow as more satellites are launched and the resolution, latency and associated analytics improve.

How is earth observation relevant to the rail industry?

EO offers capabilities that are relevant to multiple sectors including rail now and in the future. A summary of EO capabilities and their potential applicability to rail follows:

Directly applicable to rail

Management of asset and infrastructure deformations
EO can be used to monitor and manage deformations and structural changes in critical structure. This includes detecting and assessing movement or damage in buildings, bridges and roads.
Identification of land use changes
EO can identify urban expansion, deforestation, illegal activities and track biodiversity by mapping habitats and monitoring vegetation health, including distinguishing healthy and diseased plants. Also, EO can assist with land cover classification, land use mapping and monitoring and analysis of land degradation.
Detection of intruders
Through high-resolution imagery, EO can provide visual evidence of unauthorised activities or intruders within a defined, enclosed area, and thus enhance security systems.

Indirectly applicable to rail

Monitoring and assessment of the impact of severe weather
EO is able to monitor and assess the impact from severe weather such as hurricanes, floods, storms and droughts, and in the atmosphere can:
o Determine cloud temperature and the chance of rain
o Determine speed and direction of winds
o Estimate sea surface temperature
o Detect and monitor fog, dust storms, pollution, and volcanic ash.

What are the capabilities of EO?

Currently there are five levels of spatial resolution: low (above 300m), medium (300m – 30m), high (30m – 5m), very high (below 5m) and more recently very very high (below 1m). To obtain spatial data with very high, and very very high spatial resolution, individuals and organisations typically must purchase it from commercial providers.

There are two methods to collect imagery from space. Active imagery is captured relying on instruments with their own source of ‘light’, while passive ones rely on reflected signal/light. So, passive imagery allows easier interpretation of images as it portrays the Earth the same way as the human eye views it. On the other hand, active imagery is able to detect extremely small changes and anomalies, but the data needs to be processed before it’s visible to the human eye. Another key advantage of active imagery is that it is indifferent to the day/night cycle and most weather conditions, except for heavy rain.

Space data acquired from different space assets has unique characteristics, such as revisit time (the time elapsed between observations of the same point on Earth by a satellite, measured in days), spatial resolution (the level of detail captured by a given image, measured in m) and swath (the size of the observed area, measured in km), which directly impact the quality of the received data.

Imagery from a large number of passive sensors are freely available to the public such as the Copernicus Sentinel 2 and the U.S. Geological Survey’s Landsat system. They are typically used to measure land and sea surface, temperature, vegetation properties, cloud and aerosol properties, along with other physical attributes (NASA, 2023).

Sentinel 2 has the following capabilities: revisit time is approximately 5 days; spatial resolution ranging from 1.5m and 6m, and swath area of 290km.

Active sensors such as Copernicus Sentinel 1 use synthetic aperture radar imaging (SAR), which increases the overall spatial resolution by expanding the antenna length of a radar sensor. They are typically used to measure vertical profiles of aerosols, forest structure, precipitation and winds, sea surface topography and ice, etc.. They have the following characteristics: revisit time is 12 days, spatial resolution in 9-50m, and swath area is 80 – 400km.

To access more information about EO capabilities, please see the technology brief.