¶ Overview of S1 Applications
Sentinel-1 delivers radar imagery for numerous applications. SAR images are the best way of tracking land subsidence and structural damage: systematic observations and enhanced interferometric capabilities make ground movement barely noticeable in everyday life detectable and closely monitorable. As well as being a valuable resource for urban planners, this kind of information is essential for monitoring shifts from earthquakes, landslides and volcanic uplift. Moreover it helps geohazard monitoring, mining, geology and city planning through subsidence risk assessment.
The mission’s dual polarimetric products benefit users interested in agriculture, forestry and land cover classification.
The SAR ability to provide observation in all weather, and in day or night time conditions, makes it ideal for maritime and Arctic monitoring. Images acquired over the ocean are essential for generating timely maps of sea ice for safe passage, for detecting and tracking oil spills and offer key information on wind and waves in the open sea for shipping and wave-energy applications.
Finally, Sentinel-1 is designed specifically to provide images for rapid response to disasters such as floods and earthquakes.
Through the products provided, security users can monitor major shipping routes to detect illegal activities, gather prosecution evidence in case of illegal discharges, detect unexpected building in remote areas, monitor deforestation and support search and rescue activities.
The mission’s main characteristics such as short revisit time and rapid data dissemination benefit emergency response users, such as the United Nations Home - International Disasters Charter , in emergency situations such as floods, earthquakes, volcanic eruptions and landslides.
Each application can be better served by specific acquisition modes and product types as shown in the table below. The Interferometric Wide swath mode is the primary operation mode for most applications over land. Description of each product type and format is available: Products.
Refer to the High-Level Operation Plan (HLOP) for a description of the acquisition strategy.
Table 1: Mapping of most common mode and application type used based on the processing baseline
| Applications | Acquisition Mode | Product Type | |||||||||||||||
| SM | IW | EW | WV | SLC | GRD | OCN | |||||||||||
| SH | SV | DH | DV | SH | SV | DH | DV | SH | SV | DH | DV | SH | SV | ||||
| Arctic Environment and Sea-Ice Zones Monitoring | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||||||||||
| Open Ocean Ship Surveillance | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||||||||||
| Oil Pollution Monitoring | ✔ | ✔ | ✔ | ✔ | ✔ | ||||||||||||
| Marine winds | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ||||||||||
| Forestry | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||||||||||
| Agriculture | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||||||||||
| Urban deformation mapping | ✔ | ✔ | ✔ | ✔ | ✔ | ||||||||||||
| Flood monitoring | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||||||||||
| Earthquake analysis | ✔ | ✔ | ✔ | ||||||||||||||
| Landslide and volcano monitoring | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ||||||||||
Note: for a number of small volcanic islands worldwide, from May 2015 onwards, the Stripmap mode (SM) is used for the regular coverage. This is implemented in the case a SM swath fully covers the island in one pass, and no maritime surveillance activities take place around the island. The SM mode features (at a comparable system resource consumption) a smaller swath w.r.t the IW mode (in the order of 80 km vs 250 km) but ensures a higher spatial resolution, of particular interest for volcano monitoring.
The user is addressed to the page Sentinels Toolboxes to verify the available processing tools for the Sentinel 1 mission.
¶ Land Monitoring
¶ Forestry
Sentinel-1 can play an important role in sustainable forest management with clear-cut and partial-cut detection, forest type classification, biomass estimation and disturbance detection. For climate change, mapping of forest fire scars can be an important part of mapping the carbon history of a forest and plays a critical role in the estimation of carbon emissions. Land cover maps can be used to support forest management and the monitoring of illegal timber harvesting worldwide.
For this application the most suitable product is the Interferometric Wide with dual polarisation. In fact, the cross -polarisation VH is more sensitive to change in vegetation density and structure while the polarisation ratio VH/VV is an important index for vegetation phenology or water content (European Wide Forest Classification Based on Sentinel-1 Data).
¶ Agriculture
Monitoring of crop conditions, soil properties and mapping tillage activities, help to assess land use, predict harvests, monitor seasonal changes and assist in implementing policy for sustainable development. Sentinel-1 can also be used for monitoring the changes of agricultural production and productivity of pastures caused by drought and monitoring the decline of land productivity and soil degradation due to excessive cultivation and pasturage and improper irrigation.
Agricultural maps enable provision of independent and objective estimates of the extent of cultivation in a given country or growing season, which can be used to support efforts to ensure food security in vulnerable areas.
Both SLC and GRD products can be used for crop monitoring, depending on the parameter of interest. Typically, if the SAR intensity is preferred, then the GRD is the only product needed. However, if more information are necessary, polarimetric parameters are requested so SLC product should be selected.
For both product types, double polarisation shall be selected as cross-polarised VH backscatter is highly sensitive to changes in vegetation densities and structure and polarisation ratio VH/VV is sensitive to vegetation phenology or water content.
¶ Urban Deformation Mapping
Interferometric SAR can detect surface movements with an accuracy of a few millimetres per year and can provide an accurate tool for monitoring of land subsidence, structural damage and underground construction to improve safety and reduce economic loss.
https://dlmultimedia.esa.int/download/public/videos/2013/02/001/1302_001_AR_EN.mp4
Media 1 → Subsidence monitoring of Venice, Italy with Sentinel-1 (provides the means for continuous monitoring of ground movement with an accuracy of a few millimetres per year) [Credits: ESA]
¶ Maritime Monitoring
¶ Ice Monitoring
High-resolution ice charting services supply ice classification and iceberg data to national coast guards, navies and shipping companies, to assist in assuring safe year-round navigation in the ice-covered Arctic and sub-Arctic zones. For sea-ice, information on ice concentration, extent, type, thickness, albedo and drift velocity can be determined as well as the icebergs location, size and drift of icebergs. Copernicus Sentinel-1 dual polarisation data can significantly improve ice classification and discrimination.
Interaction of SAR with sea ice is a complex phenomenon that depends on
- radar parameters (frequency, polarisation, incident angle)
- ice characteristics (salinity, roughness, thickness, density, orientation, inclusions)
- properties of the overlying snow cover (moisture content, grain size, density, thickness)
The sea ice backscatter is not independent of incidence angle and the dependency changes for each ice type.
Dual polarisation (HH and HV) are a standard for operational ice classification: cross-polarisation (e.g. HV) is more sensitive than co-polarisation (e.g. HH).
Sentinel-1 has relatively high residual thermal noise contamination - especially in the cross-pol channel, therefore it needs for advanced correction algorithms (refer to RUS Webinar: Sea Ice Monitoring with Sentinel-1 - CRYO04)
Media 2: The evolution of damage to the Pine Island (boxes P1 and P2) and Thwaites (T1) Glaciers from October 2014 to July 2020, as seen by the https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-1 mission. [Credits: ESA]
Media 3: A-68A iceberg moving from July 2017 to December 2020. [Credits: ESA/ATG medialab]
¶ Ship Monitoring
Marine surveillance can be done using different methodologies. A first option consists of cooperative systems in which ships themselves report their identities and positions. The three most common options are Automatic Identification System (AIS), Long Range Identification and Tracking (LRIT) and Vessel Monitoring System (VMS). While the first one is in fact available continuously and globally, the two others are not. Another option is the non-cooperative systems which do not require cooperation on the side of the vessel. These systems most commonly use cameras and radars located on a variety of platforms (ships, airplanes, satellites, etc.).
Copernicus Sentinel-1 A and B spacecrafts' ship detection falls into the non-cooperative category and enables detection of vessels not carrying AIS or other tracking system on board such as smaller fishing ships or ships that are in the surveyed area illegally (illegal fishing, piracy etc.). An improvement will be introduced with Sentinel-1C (to be launched at the end of 2023) since the new satellite is equipped with the AIS signal antenna on board, allowing tracing and identifying the ships.
Data relevant to ship detection are transmitted by the satellite in real-time for reception by local collaborative ground stations supporting European and national services.
Product type useful for ship detection are typically EW and IW in L1 GRD product type, with dual polarisation.
In the below images the enormous Ever Given container ship, wedged in Egypt’s Suez Canal, is visible in new images captured by the Copernicus Sentinel-1 mission. The giant container ship ran aground in the canal on 23 March on its journey from China to the Netherlands. The image on the left, captured on 21 March, shows routine maritime traffic in the canal with vessels visible every 2 to 3 km. The image on the right, captured on 25 March, shows the 400 m-ship blocking the canal.
¶ Oil Pollution Monitoring
Oil detection applications are used for gathering evidence of illegal discharges, analysing the spread of oil spills and prospecting for oil reserves by highlighting naturally occurring seepage. Oil slicks are distinctly visible in SAR imagery as characteristically dark features. Most oil slicks are caused by ships emptying bilge before entering port. Detections can be correlated with Automatic Identification System (AIS) (Sentinel-1C only) information broadcasts from ships to determine sources and prosecute offenders. Data relevant to oil spill monitoring are transmitted by the satellite in real-time for reception by local collaborative ground stations supporting European and national services.
Likewise, detection of naturally occurring oil seepage from the ocean floor can provide clues for oil prospecting.
In this case it is useful to use IW, EW GRD products in dual polarisation.
Media 4 → Oil Spill Monitoring from Space Using SAR (old missions) [Credits: ESA]
¶ Marine Waves and Winds
SAR is sensitive to spatially varying surface roughness patterns caused by winds on the ocean surface. Copernicus Sentinel-1 ocean products, in conjunction with global ocean wave models, help determine the direction, wavelength and heights of waves on the open oceans and assist in weather prediction, ship transportation and wave energy applications. This is useful for understanding interactions between waves and currents and to visualise large-scale ocean currents, cold/warm water masses, coastal water currents and internal waves, improving efficiency for shipping and wave-energy applications, potentially producing economic benefits.
In the below picture an example of a multi-temporal image combining two radar acquisitions from the Copernicus Sentinel-1 mission taken one month apart to show changes over time. The first image was captured on 29 December 2019, while the second was taken on 22 January 2020. Here, the main changes between acquisitions occurred in the open ocean, with the bright red colours showing wavy waters in December 2019. This image is also featured on the Earth from Space video program (image credit: ESA, the image contains modified Copernicus Sentinel data (2019-20), processed by ESA, CC BY-SA 3.0 IGO)
Sea Surface Wind (SSW), i.e., speed and direction, is a physical Essential Climate Variable (ECV), which crucially contributes to the characterisation of Earth’s climate system and its changes. SSW measurements may be provided by several different sources, such as in situ stations, space-borne active microwave sensors (i.e., scatterometers and radar altimeters), and numerical weather prediction (NWP) models.
In situ stations are unfortunately costly and sparse, and not deployable in areas that are difficult to access. They are typically used for in situ validation of wind estimates, derived from other techniques such as modelling and other sources. Satellite scatterometers and radar altimeters, on the other hand, are suitable for synoptic and mesoscale observations of the ocean wind.
However, the main weaknesses of scatterometers and altimeters are a lack of accurate data near the shore and the temporal sampling. As a consequence, wind estimates from those space-borne systems are not useful for studies focused on near-shore processes. Furthermore, NWP models (mainly global or at scales of an EU sea basin) may suffer from problems of precision and accuracy in marine coastal areas, and so would not be adequate for lower scale coastal dynamics.
Synthetic Aperture Radar (SAR) systems, like those on the Sentinel-1 satellites, can provide wind speed and direction measurements in the ocean, especially in marine coastal areas. In particular, the estimation is derived from the Ocean Wind Field (OWI) and Ocean Radial Velocity (RVL) component level-2 Ocean products.
The importance of SAR derived SSW retrievals is recognised, at both global and local scale, in a wide range of applications such as marine meteorology, oceanography, oil spill monitoring and in view of wind resources assessment for renewable energy plant operations and coastal dynamics modelling.
Wind field estimates also play an important part in oil spill monitoring to help discriminate look-alike from actual spills.
¶ Emergency Management
¶ Flood Monitoring
Over 75% of natural disasters that occur worldwide involve flooding. SAR's inherent capability to observe during cloud cover and Sentinel-1's frequent revisits makes it ideal for flood monitoring. It can be used to assess the extent of flooded areas and the impact on human, economic and environmental loss. Furthermore, high-resolution digital elevation models (DEMs) generated through Sentinel-1's interferometric modes can be used to conduct run-off and inundation analysis in areas previously lacking elevation data.
Calm open water surfaces appear flat when being hit by C-band SAR radiation, and the radiation is scattered away from the satellite’s sensor. Consequently, the received energy (measured as backscatter) is low and shows high contrast to general land surfaces. Generally, the underlying principle of the SAR-based flood mapping methods is to identify low backscatter measurements where land is expected under normal conditions. Two SAR polarisations (VV and VH) are required to allow a detection of flooded vegetation.
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¶ Earthquake Analysis
InSAR provides the unique ability to produce medium and high-resolution maps of earthquake deformations. Through the persistent monitoring of earthquake-prone areas, active fault lines can be discovered and potential risks can be studied. The Interferometric Wide swath mode will make it easier to monitor very large scale earthquakes. Since the phase information is necessary for interferometric images, SLC product type is the one to be considered.
¶ Landslide and Volcano Monitoring
SAR interferometry can locate areas prone to landslides and monitor surface deformation to provide early warning of potential disasters and monitoring of critical infrastructure. Pre-eruption uplift and post eruption volcanic shrinkage can be monitored with similar interferometric techniques and can complement in-situ networks from volcano observatories. InSAR monitoring can help detect first signs of increasing levels of volcanic activity, preceding earthquakes and other precursors that may signal eruptions.
In the following images SAR interferometry has been used to quantify quantify the ground deformation with millimetric precision due to the volcanic event on La Palma in September 2021.
Two images were used: one from September 10 (1 day before the anomalous seismic activity began) and another from September 22 (last image available at the time of this study). The interferogram resulting from the comparison is shown on the left: The fringe pattern shows a huge lobe along Cumbre Vieja that indicates a major deformation of the terrain. To interpret an interferogram, a color palette is assigned to the phase difference values. As a result, a fringe pattern appears in the areas of ground deformation (Left image). To better understand the results, on the right the displacement map is presented: the blue color is interpreted as uplift (Cumbre Vieja zone), and the red color as subsidence (La Bombilla zone). The displacement values are given in the satellite line of sight (LOS). The interferometry fringes in the background are shown for reference.
