GhostNet - Searching the Oceans for Dangerous Debris
by Jeremy Nicoll and Bill Pichel
Last summer a collaboration of Ghost-Net researchers from government, academia, and private industry conducted an aerial survey that reached from Astoria, OR, to Cold Bay, AK. The survey aircraft was instrumented with a collection of visible, IR and LIDAR sensors used to locate actual debris in the ocean.
GhostNet is a three-year, NASA funded research project designed to demonstrate the feasibility of identifying derelict fishing nets and other anthropogenic marine debris using data from satellite remote sensing, airborne and in situ buoy measurements.
The GhostNet project arose from a need to locate lost or abandoned fishing gear, especially high-seas drift nets, which pose a threat to all fish species inhabiting near-surface waters. Sea birds, sea turtles and marine mammals also risk entanglement in derelict nets.
When these nets drift into coral reef environments, they cause physical damage to the reefs and continue to entangle and kill animals inhabiting the reef’s ecosystem.
Collaborators designed the GhostNet project to locate derelict nets and other hazardous debris in the open ocean before they encounter reefs or wash ashore and do further damage. Regions of interest for GhostNet include the southeastern Bering Sea; the Gulf of Alaska; and the Subtropical Convergence Zone (STCZ) associated with the North Pacific subtropical high.
GhostNet researchers use a geographic information system to integrate a collection of satellite, aircraft, buoy, and static (i.e., bathymetry and coastline) data to identify potential sites where hazardous debris may be concentrated.
A combined suite of datasets used in the GhostNet project includes:
- SST images from NASA Moderate Resolution Imaging Spectro-Radiometer (MODIS), NOAA Coast-Watch Advanced Very High Resolution Radiometer (AVHRR), and NOAA Geostationary Operational Environmental Satellite (GOES),
- NASA MODIS chlorophyll imagery,
- Canadian Space Agency Radarsat-1 synthetic aperture radar (SAR) imagery and derived ship positions and high-resolution SAR wind images,
- NASA SeaWinds QuikSCAT scatterometer wind data and derived wind stress curl,
- NASA TOPEX/Poseidon altimeter data processed into sea surface height anomaly information,
- data from a MicroSas Optical Sensor – OCR-507,
- images from a green-laser (352 nm) LIDAR with a gated camera,
- video from a visible RGB camera,
- images from an infrared imager,
- sea surface temperatures from an infrared radiometer, and
- moored and drifting buoy reports every six hours from the National Centers for Environmental
Prediction and the NOAA Data Buoy Center. Staff at the Alaska Satellite Facility provide support through acquisition planning, image processing and consulting for SAR image interpretation.
Last summer’s GhostNet participants identified likely areas of debris accumulation by searching for convergent processes in the ocean using circulation models and analyses of scatterometer wind data.
Next they observed likely regions with multi-platform satellite imagery to pinpoint convergence zones.
Finally, the group made the aerial survey to verify the location of convergence zones and locate actual debris. The researchers discovered logs, fishing debris, and other foreign materials, which had become preferentially concentrated in the areas of convergence indicated by analysis of the data.