Detection of macroalgae blooms by complex SAR imagery.
Increased frequency and enhanced damage to the marine environment and to human society caused by green macroalgae blooms demand improved high-resolution early detection methods. Conventional satellite remote sensing methods via spectra radiometers do not work in cloud-covered areas, and therefore cannot meet these demands for operational applications. We present a methodology for green macroalgae bloom detection based on RADARSAT-2 synthetic aperture radar (SAR) images. Green macroalgae patches exhibit different polarimetric characteristics compared to the open ocean surface, in both the amplitude and phase domains of SAR-measured complex radar backscatter returns. In this study, new index factors are defined which have opposite signs in green macroalgae-covered areas, compared to the open water surface. These index factors enable unsupervised detection from SAR images, providing a high-resolution new tool for detection of green macroalgae blooms, which can potentially contribute to a better understanding of the mechanisms related to outbreaks of green macroalgae blooms in coastal areas throughout the world ocean.
Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China; Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth B2Y 4A2, Canada; Key Laboratory of Ocean Circulation and Waves, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China. Electronic address: shenhui@qdio.ac.cn.
Hui
H
Shen
Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth B2Y 4A2, Canada. Electronic address: william.perrie@dfo-mpo.gc.ca.
William
W
Perrie
North China Sea Branch of the State Oceanic Administration, 27 Yuanling Road, Qingdao 266061, China. Electronic address: liuqingrong@nmfc.gov.cn.
Qingrong
Q
Liu
Nanjing University of Information Science and Technology, 4 Longshanbei Road, Nanjing 210044, China. Electronic address: yjhe@nuist.edu.cn.
Yijun
Y
He
D004784:Environmental Monitoring / Q000379:methods*; D005068:Eutrophication; D011825:Radar; D058998:Remote Sensing Technology; D063809:Satellite Imagery; D012624:Seaweed / Q000254:growth & development*; D018531:Spacecraft
Green macroalgae blooms; High resolution early detection; Synthetic aperture radar (SAR); Unsupervised SAR index factor