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.

Water hyacinth (WH) is one of the dreadful noxious invasive species whose origin is traced to South America. Compared to in-situ measurements, remote sensing offers a less expensive way of monitoring WH. In this research, the Optimization of Power Difference (OPDiff) change detection technique was used in mapping WH. Sentinel-1 IW SLC data from 2017 to 2022 were analyzed to get polarimetric covariance matrices using the VV, VH and VV*VH. Pre-processing, co-registration and detection steps were carried out using the GPT processor of ESA SNAP graph builder. The OPDiff applied in the study areas enabled the detection and extraction of spatial extent of WH in single image and in time series by identifying the changes occurring on the minimum eigenvalues. When evaluated against Sentinel-2 data, the algorithm recorded on average 92.6% & 89.9% precision and accuracy respectively. Heatmaps were generated for the study area and demonstrated variability of WH in time and space. This research demonstrates the capability of using polarimetric radar data to detect and monitor WH.

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.

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.

The main objective of this paper to show the potential of multitemporal Sentinel-1 (S-1) and Sentinel-2 (S-2) for detection of water hyacinth in Indian wetlands. Water hyacinth (Pontederia crassipes, also called Eichhornia crassipes) is one of the most destructive invasive weed species in many lakes and river systems worldwide, causing significant adverse economic and ecological impacts. We use the expectation maximization (EM) as a benchmark machine learning algorithm and compare its results with three supervised machine learning classifiers, Support Vector Machine (SVM), Random Forest (RF), and k-Nearest Neighbour (kNN), using both synthetic aperture radar (SAR) and optical data to distinguish between clean and infested waters.

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.