International Journal of Applied Earth Observation and Geoinformation 4 (2002) 147–160 Azimuth cut-off model for significant wave height investigation along coastal water of Kuala Terengganu, Malaysia Maged Marghany a,∗ , Zelina Ibrahim b , Johan Van Genderen c a Institute of Oceanography (INOS), University College Science and Technology Malaysia (KUSTEM), 21030 Mengabang Telipot, Kuala Terengganu, Malaysia b Head Division of Water Quality and Environment, National Hydraulic Research Institute of Malaysia, Block A JPS Complex, Km 7 Jalan Ampang, 68000 Ampang, Malaysia c Head Division of Applied Geomorphological Survey, International Institute for Aerospace Survey and Earth Sciences (ITC), P.O. Box 6, 350 Boulevard 1945, 7500 AA Enschede, The Netherlands Accepted 18 February 2002 Abstract The present work is used to operationalize the azimuth cut-off concept in the study of significant wave height. Three ERS-1 images have been used along the coastal waters of Terengganu, Malaysia. The quasi-linear transform was applied to map the SAR wave spectra into real ocean wave spectra. The azimuth cut-off was then used to model the significant wave height. The results show that azimuth cut-off varied with the different period of the ERS-1 images. This is because of the fact that the azimuth cut-off is a function of wind speed and significant wave height. It is of interest to find that the significant wave height modeled from azimuth cut-off is in good relation with ground wave conditions. It can be concluded that ERS-1 can be used as a monitoring tool in detecting the significant wave height variation. The azimuth cut-off can be used to model the significant wave height. This means that the quasi-linear transform could be a good application to significant wave height variation during different seasons. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Azimuth cut-off; ERS-1; Wave spectra; South China Sea 1. Introduction The azimuth cut-off is the degree to which the SAR image spectrum is constrained in the azimuth direc- tion. The azimuth cut-off is affected by the wind and wave conditions in a quasi-linear forward-mapping model (Vachon et al., 1997). The quasi-linear model ∗ Corresponding author. Tel.:+609-6683294; fax: +609-6692187/6697418. E-mail addresses: mmm@kustem.edu.my, magedupm@hotmail.com (M. Marghany), iphk06@pop.moa.my (Z. Ibrahim), gendern@itc.nl (J. Van Genderen). should use the information of wind speed and signif- icant wave height for modeling ERS-1 wave spectra with the real ocean waves. There are several stud- ies have been carried by Hasselamann et al., 1985; Hasselmann and Hasselmann, 1991; Vachon and Dobson, 1996; Vachon et al., 1997) to develop wave spectra simulation model based on the azimuth cut-off information. This is because of the fact that in SAR images, waves propagating are in the azimuth direction. Hasselamann et al. (1985), Raney and Vachon (1991), Dobson and Vachon (1994), Vachon et al. (1994), Vachon et al. (1997) concluded that azimuthally-traveling wave components contribute an 0303-2434/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0303-2434(02)00012-0