Ship Track Cloud Analysis for the North Pacific Area
Abstract
Anomalous cloud lines produced by stack exhaust from ships in the North Pacific Ocean basin are analyzed. These cloud lines or 'ship tracks' are observed most clearly in the channel 3 near-infrared satellite imagery obtained from the NOAA-9 AVHRR sensor. The ship tracks are produced as hot exhaust gases are expelled into the atmosphere creating an aerosol concentration higher than background areas. These aerosols serve as cloud condensation nuclei (CCN) and cause a shift in the cloud droplet distribution to a higher concentration of smaller droplets. Channel 3 AVHRR data are sensitive to cloud droplet size and show these ship tracks as an increase in radiance. An existing ship track detection algorithm is examined and improvements are developed and evaluated. The existing algorithm works well in areas with uniform cloud cover which contain well defined ship track cloud lines. However, it begins to break down in areas with no ship tracks, cloud free areas and regions of transition from one cloud regime to another. An improved algorithm is developed which is able to improve the analysis in these problem areas. Comparison of this algorithm with the original algorithm shows a twofold increase in the percentage of valid ship tracks detected. Neither algorithm is capable of fully representing all the ship track pixels in given image but the feasibility of this type of analysis is clearly shown. The detection algorithm is also adapted to evaluate large scale areas of data as a precursor to the development of a ship track cloud climatology for the North Pacific Ocean. While computer processing time becomes a limitation, some ability is shown for the analysis of large scale areas.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1988
- Accession Number
- ADA201992
Entities
People
- Steven E. Morehead
Organizations
- Naval Postgraduate School