Directly remote sensing plastic pollution within the open ocean has proven to be challenging. Therefore, other methods of detecting marine plastics through a proxy should be explored. Radar satellites are sensitive to surface roughness and can therefore detect dampening of wind-driven capillary waves on the sea surface. Plastics within the ocean have been found to be colonized by microbes, which can produce surfactants, substances which can dampen the short capillary waves on the ocean. This research investigates whether a ground radar instrument is capable of detecting plastisphere-based surfactant dampening within a semi-natural environment setting. We find that we can observe reduced backscatter from dampening effects that are occurring within our experiment setting. We also find that the backscattering from experiments involving plastisphere-based surfactants are significantly different from control experiments where microbial production is stopped.

The remote sensing of marine plastics is a relatively new field and research into radars capabilities for monitoring / detection is mostly limited. Here, we utilize the use of a C- and X-band ground radar to understand the capabilities for monitoring marine plastic pollution. Results show that backscattering differences can be found between reference acquisitions of clean water and test water filled with plastics, in both C- and X-band frequencies. With X-band detecting significant differences in backscattering in 48/68 test cases, and C-band detecting differences in 20/67 test cases.

The Soil Moisture and Ocean Salinity (SMOS) mission of the European Space Agency (ESA), together with NASA's Soil Moisture Active Passive (SMAP) mission, is providing a wealth of information to the user community for a wide range of applications. Although both missions are still operational, they have significantly exceeded their design life time. For this reason, ESA is looking at future mission concepts, which would adequately address the requirements of the passive L-band community beyond SMOS and SMAP. This article proposes one mission concept, TriHex, which has been found capable of achieving high spatial resolution, radiometric resolution, and accuracy, approaching the user needs. This is possible by the combination of aperture synthesis, formation flying, the use of general circular orbits, and alias-free imaging.

Plastics in the riverine environment are of major concern due to their potential pathways into the wildlife and more generally the ocean. Dams are capable of trapping marine plastics within the riverine environment. This entrapment changes the surface roughness of the area with the marine debris. Radar satellites are sensitive to surface roughness and can therefore detect these changes. This research investigates areas in Serbia and Boznia & Herzegovina using ESA Sentinel-1 polarimetric SAR data. This study shows the feasibility of detecting large accumulations of plastic near dams, with detectors capable of achieving 75-85% positive detection ratings with a 0.1% false alarm rate. Additionally, we find the use of single VV polarization is inadequate for this task and PolSAR data are needed.

This This paper reviews the choice of polarisation axes in aperture synthesis arrays for remote sensing of the Earth, in particular when using dual polarisation receivers. In this case, as it is shown, there is the freedom of adopting rotated polarisation axes across the array without signal loss. This is not possible in systems having dual polarised antennas connected to single channel receivers, as then, polarisation time multiplexing requires the same antenna polarisation at any time in all elements of the array if signal loss is to be avoided. The flexibility allowed by the first type of instrument leads to a simpler antenna design and system architecture, providing a clear advantage over other polarisation schemes. The review of the choice of the polarisation axes is performed in the frame of the development of an advanced antenna for a future L-band aperture synthesis radiometer, but the analysis is general and applicable to any instrument of this kind. This is a study undertaken by the European Space Agency aiming at a possible future high-resolution follow-on mission to the currently flying Soil Moisture and Ocean Salinity (SMOS) mission.

Plastics within the ocean have been found to be colonised by microorganisms that, as a by-product of their metabolism, produce surfactants. Short capillary waves on the sea surface can get dampened due to the increased surface elasticity of these surfactants. Radar satellites are sensitive to surface roughness and can therefore detect the dampening of these waves. This research investigates areas inside the Atlantic, Pacific and Indian Ocean gyres using ESA Sentinel-1 and DLR TerraSAR-X data. We found out that we can observe several surfactant instances in the gyres and these are not correlated to medium or high level of chlorophyll. We can exclude that they have origin in biogenic slicks. Among other possible unknown origins, we hypothesise that these surfactants are produced from plastic concentrations within the ocean.