News of Marine Surveillance in Cuba with SAR technology from the e-GEOS_INSMET collaboration

2.1 SAR technology applied to marine meteorology

SAR radars are capable of observing the ocean surface in high spatial resolution in all weather conditions. In recent years, the potential of SAR images to detect oil slicks and wave parameters such as wave direction, period and height has been demonstrated (Nieto et al., 2006). SAR images at sea provide evidence of a large set of geophysical phenomena in addition to oceanographic features related to waves and ocean currents (Li et al., 2022Li, Q., Zhang, Y., Wang, Y., Bai, Y., Zhang, Y., & Li, X. (2022). Numerical Simulation of SAR Image for Sea Surface. Remote Sensing, 14(3), 439. https://doi.org/10.3390/rs14030439).

With its day-night acquisitions not dependent on weather, SAR is currently experiencing tremendous growth. In addition to operating at different frequencies, they are characterized by the availability of different operating modes, which provides the possibility of balancing resolution and coverage (Zamparelli et al., 2016Zamparelli, V., Jackson, G., Cucco, A., Fornaro, G., & Zecchetto, S. (2016). SAR based sea current estimation in the Naples coastal area. In IGARSS 2016—2016 IEEE International Geoscience and Remote Sensing Symposium (pp. 4665–4668). IEEE. https://doi.org/10.1109/IGARSS.2016.7730217).

Natural disasters such as floods take place all over the world and can be analyzed using SAR technology (Abreu Del Sol & Rodriguez, 2023Abreu Del Sol, M., & Rodriguez, A. (2023). Aplicación de Detección de Cambios De Imágenes SAR en las inundaciones costeras [Tesis de Diploma, Universidad de La Habana, InSTEC]. https://doi.org/10.13140/RG.2.2.32291.02089). The effects of these include urban areas, coasts and agricultural areas; one of its main causes being extreme weather phenomena (Pelich et al., 2022Pelich, R., La, T. V., Chini, M., & Matgen, P. (2022). Retrieval and multi-temporal characterization of oil spills from multi-sensor earth observation imagery. In 2022 IEEE International Workshop on Metrology for the Sea; Learning to Measure Sea Health Parameters (MetroSea) (pp. 388–392). IEEE. https://doi.org/10.1109/MetroSea55331.2022.9950927). The well-known inSAR techniques can be used for the evaluation of disasters and also to verify the outputs of forecast models.

In Cuba, coastal flooding is caused by tropical cyclones, cold fronts and southern winds associated with extratropical lows. These phenomena generate the most intense winds in the region with a significant increase in sea level in the coastal area (Mitrani, 2017Mitrani, I. (2017). Meteorologia Marina. CITMA℡.). The most severe floods in Cuba are generated by tropical cyclones where the storm surge effect also appears (Perez et al., 2019Pérez-Bello, A., Mitrani-Arenal, I., Díaz-Rodríguez, O. O., Wettre, C., & Hole, L. R. (2019). A numerical prediction system combining ocean, waves and atmosphere models in the Inter-American Seas and Cuba. Revista Cubana De Meteorología, 25(1), 109–120. http://rcm.insmet.cu/index.php/rcm/article/view/459).

2.2 SAR technology in the detection of oil slicks in the sea

Oil particles are described in SAR images by long dark tails protruding from the sea surface. The operability of SAR for oil slick discovery is restricted by wind speed. Low wind speeds (less than 3 m/s) do not reflect the complexity of the marine environment contaminated by the absence of waves; while, in conditions of intense wind (more than 12 m/s), the roughness on the surface of the contaminant decreases due to the increase in waves and emulsification (Gee et al., 2016Gee, D., Sowter, A., Novellino, A., Marsh, S., & Gluyas, J. (2016). Monitoring land motion due to natural gas extraction: Validation of the Intermittent SBAS (ISBAS) DInSAR algorithm over gas fields of North Holland, the Netherlands. Marine and Petroleum Geology, 77, 1338–1354. https://doi.org/10.1016/j.marpetgeo.2016.08.014).

As the ocean is a non-static mass of water, the fate of oil on the sea surface depends on: the quantity, the physical properties of the hydrocarbon and the environmental conditions. The different physical-chemical-oceanographic processes in the spilled oil have a long time scale and impact the perceptibility in SAR images (Chaturvedi et al., 2020bChaturvedi, S. K., Banerjee, S., & Lele, S. (2020). An assessment of oil spill detection using Sentinel 1 SAR-C images. Journal of Ocean Engineering and Science, 5(2), 116–135. https://doi.org/10.1016/j.joes.2019.09.004).

The Sentinel-1, TerraSAR X and COSMOSkyMed satellites operate in the X band, this being the best band for remote sensing of oil slicks with regard to Bragg scattering. Each of these SAR satellites has polarimetric imaging modes that may have application for remote sensing of oil spills(Lohberger et al., 2018Lohberger, S., Stängel, M., Atwood, E. C., & Siegert, F. (2018). Spatial evaluation of Indonesia’s 2015 fire‐affected area and estimated carbon emissions using Sentinel‐1. Global Change Biology, 24(2), 644–654. https://doi.org/10.1111/gcb.13841).

2.3 The COSMO-SkyMED satellite constellation

The COSMO-SkyMed (CSK) program, developed by the Italian Space Agency (ASI), is a constellation of four (currently three satellites are fully operational and one was deorbited and substituted by two satellites of new generation) medium-sized satellites in low Earth sun-synchronous polar orbit, located in the same orbital plane and each equipped with a high-resolution multimode SAR that operates in X-band. The four satellites have been arranged in a one-day interferometric configuration between both the second and third satellites, while the first and fourth satellites are positioned with a 90 degree offset to optimize the temporal performance of the overall constellation. The CSK constellation can operate in different mission configurations with specific orbital geometry that directly characterizes the system's capabilities and performance (Battagliere et al., 2012Battagliere, M. L., Covello, F., & Coletta, A. (2012). COSMO-SkyMed Background Mission: Overview, objectives and results.; Daraio et al., 2016Daraio, M. G., Battagliere, M. L., & Coletta, A. (2016). COSMO-SkyMed results after 5 years of full constellation exploitation. In IGARSS 2016—2016 IEEE International Geoscience and Remote Sensing Symposium (pp. 2050–2053). IEEE. https://doi.org/10.1109/IGARSS.2016.7729529).

The constellation is capable of acquiring images of the entire world in all atmospheric conditions, day and night, without latitude limitations. The SAR payload has been designed to acquire data in different modes depending on the image area and the resolution that can be obtained. The following table describes the main characteristics of the different sensor modes available (Battagliere et al., 2019Battagliere, M. L., Virelli, M., Lenti, F., Lauretta, D., & Coletta, A. (2019). A Review of the Exploitation of the Operational Mission COSMO-SkyMed: Global Trends (2014-2017). Space Policy, 48, 60–67. https://doi.org/10.1016/j.spacepol.2019.01.003).

In this way, the e-GEOS ftp site e-GEOSwas enabled to download from Cuba the SAR images of the CSK constellation of the ScanSAR Huge mode, comprising an area per image of 200 x 200 km with 100 m spatial resolution, covering 350,000,00 km² of the area of interest in 48 hours, and reaching 80% coverage. This results in 15 coverages of each area per month.

2.4 Availability of Sentinel 1 SAR Satellite

Sentinel-1 operations are based on a series of closely coordinated activities involving satellites and the ground segment. The satellites are routinely monitored and controlled by the Flight Operations Segment (FOS) managed by ESA-ESOC. The FOS ensures the overall security of the satellite; Routine tasks include executing all platform activities and commanding payload programs (Potin et al., 2019Potin, P., Rosich, B., Miranda, N., Grimont, P., Shurmer, I., O’Connell, A., Krassenburg, M., & Gratadour, J.-B. (2019). Copernicus Sentinel-1 Constellation Mission Operations Status. In IGARSS 2019—2019 IEEE International Geoscience and Remote Sensing Symposium (pp. 5385–5388). IEEE. https://doi.org/10.1109/IGARSS.2019.8898949).

Strict orbit maintenance control for the Sentinel-1 satellite results in small baselines for SAR interferometry and is of primary importance for most InSAR applications. The Terrain Progressive Scan (TOPS) technique has been implemented in the main default SAR imaging mode over land, the interferometric wide swath (IW) mode (as well as in the extra wide swath, EW, mode used mainly at sea for sea ice monitoring and maritime surveillance) (Potin et al., 2017Potin, P., Rosich, B., Miranda, N., Grimont, P., Bargellini, P., Monjoux, E., Martin, J., Desnos, Y.-L., Roeder, J., Shurmer, I., O’Connell, A., Torres, R., Krassenburg, M., & Gratadour, J.-B. (2017). Sentinel-1 mission status. In 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (pp. 5525–5528). IEEE. https://doi.org/10.1109/IGARSS.2017.8128255).

Systematic availability of Level 0 Products and GRD Level 1 products is also guaranteed for all data acquired in SM, IW and EW instrument modes (high speed modes) within 24 hours of detection and the 3 hours NRT from detection. It also includes the systematic availability of OCN Level-2 products for all data acquired in WV mode. As of November 2017, OCN level-2 products of systematic generation (IW, EW, SM), have been extended to all seas and oceans (Potin et al., 2017Potin, P., Rosich, B., Miranda, N., Grimont, P., Bargellini, P., Monjoux, E., Martin, J., Desnos, Y.-L., Roeder, J., Shurmer, I., O’Connell, A., Torres, R., Krassenburg, M., & Gratadour, J.-B. (2017). Sentinel-1 mission status. In 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (pp. 5525–5528). IEEE. https://doi.org/10.1109/IGARSS.2017.8128255).

Within the framework of Sentinel's free and open data policy, the opening of the data flow to all users took place on October 3, 2014 for Sentinel-1A. The open data access service is based on a high-capacity broadcast network that exceeds 20 Gbps. Statistics for the last 24 hours are available in real time on the Data Hub home page: https://scihub.copernicus.eu (Torres et al., 2012Torres, R., Snoeij, P., Geudtner, D., Bibby, D., Davidson, M., Attema, E., Potin, P., Rommen, B., Floury, N., Brown, M., Traver, I. N., Deghaye, P., Duesmann, B., Rosich, B., Miranda, N., Bruno, C., L’Abbate, M., Croci, R., Pietropaolo, A., … Rostan, F. (2012). GMES Sentinel-1 mission. Remote Sensing of Environment, 120, 9–24. https://doi.org/10.1016/j.rse.2011.05.028).

2.5 Computer tools received in technology transfer

Important tools for SAR image processing were installed at the Center for Marine Meteorology (CMM) of INSMET: SEonSE Platform (SEonSE Engine and SEonSE Portal), able to provide near real-time maritime situational awareness and operational maritime services 24 hours a day, 7 days (Oddone et al., 2021Oddone, A., Daffina, F., Quattrociocchi, D., Francioni, E., Gentile, V., Pieralice, F., Cesarano, L., Britti, F., Pietranera, L., Minati, F., Luzietti, L., Grandoni, D., Cardillo, P. F., Biscardi, M. A., & Bonetto, F. (2021). Satellite Sar Data Exploitation: Innovations and Potentialities for Earth Observation Advanced Monitoring and Servicing. In IGARSS 2021—2021 IEEE International Geoscience and Remote Sensing Symposium (pp. 1887–1890). IEEE. https://doi.org/10.1109/IGARSS47720.2021.9554026).

3.1 Digital processing of SAR images received from e-GEOS

The SAR images agreed upon in the international collaboration were downloaded by INSMET researchers in the period from October 1, 2022 to June 30, 2023. The SEonSE Engine application was used for digital processing, and the reports were displayed through the SEonSE Portal. Table 2 shows the number of acquisitions in the 9 months of SAR image downloads by INSMET from e-GEOS.

Each of these images was processed with digital processing tools to search for oil slicks and possible vessels violating hydrocarbon spills. Throughout this period, minor oil slicks were found in the area of interest, evidencing in some cases that vessels carrying out illegal practices at sea transit through the area. An example of this can be seen in figure 1.

All polygons of the detected spots were exported in different format files (.json, .tiff, .shape), which can be loaded with the different geographic information tools; and also, through program coded in different languages and applications such as the Lagrangian model of oil spills PETROMAR-3D that offer a forecast of the pollutant motion in the sea (Calzada et al., 2021Calzada, A. E., Delgado, I., Ramos, C., Pérez, F., Reyes, D., Carracedo, D., Rodríguez, A., Chang, D., Cabrales, J., & Lobaina, A. (2021). Lagrangian Model PETROMAR-3D to Describe Complex Processes in Marine Oil Spills. Open Journal of Marine Science, 11(01), 17–40. https://doi.org/10.4236/ojms.2021.111002).

3.2 SEonSE Portal Statistics

Once the digital processing of the images was carried out using the SEonSE Engine application, the outputs were assimilated by the SEonSE Portal. This web application showed the maps with the distribution of vessels and oil slicks in the EEZ of Cuba, as can be seen in figure 2, all the vessels that crossed the seas of Cuba between October 1, 2022 and on June 30, 2023. At first glance you can see the greater density of vessels towards the western portion of the Cuban archipelago, with a significant number of class A vessels (more than 100 m in length) mainly in the area of the Strait of Florida. Likewise, the oil slicks detected, which are represented as red or light green drops, depending on the case. They were most abundant in the western area, although they can also be seen in the central south and south east respectively.

Figure 3 shows a graphic report from the SEonSE Portal, referring to the types of vessels and oil slicks detected in the period indicated above. A total of 315 class A and 2 class B vessels (lengths between 50 and 100 m) can be seen, as well as a total of 66 oil slicks detected, 49 of them processed with high reliability.

In this way, there were 66 oil spills detected in the period between October 1, 2022 and June 30, 2023. Judging by the proximity to the coast of the oil slicks detected, the size, the duration hours and distance to the oil basins around Cuba; it could be suspected that a large part of the oil spills found could be discharged due to inappropriate behavior by the crew of some vessels, which violate international agreements to combat marine pollution. These assumptions would reinforce the need for constant monitoring of the waters surrounding the Cuban archipelago, especially when based on the surveillance and monitoring of these indisciplines with the technologies applied in this project, in many cases the offenders are also detected.

With the application of these technologies in Cuba through this collaboration, the efforts of the governments of Italy and Cuba materialize to comply with the Paris agreements and the Rio de Janeiro Agenda, referring to adaptation and mitigation to climate change, with a contribution to the care of the environment and coastal ecosystems, as well as the fight against pollution of the seas.