Evaluation of various satellite sensors for waterline extraction in a coral reef environment: Majuro Atoll, Marshall Islands Hiroya Yamano a,b, ⁎ , Hiroto Shimazaki a , Tsuneo Matsunaga a , Albon Ishoda c , Caleb McClennen d , Hiromune Yokoki e , Kazuhiko Fujita f , Yoko Osawa g , Hajime Kayanne g a Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan b UR 128 CoRéUs, Institut de Recherche pour le Développement, BP A5 98848 Nouméa cedex, New Caledonia c Marshall Islands Marine Resources Authority, Majuro, MH 96960, Marshall Islands d Environmental Protection Authority, Majuro, MH 96960, Marshall Islands e Center for Water Environment Studies, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan f Department of Physics and Earth Sciences, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan g Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan Received 27 February 2006; received in revised form 2 June 2006; accepted 2 June 2006 Available online 28 July 2006 Abstract The ability of five satellite sensor bands (IKONOS band 4, Terra ASTER bands 3 and 4, and Landsat ETM+ bands 4 and 5) was examined to extract the waterline at coral reef coasts (Majuro Atoll, Marshall Islands) using different wavelength regions (near infrared [NIR] and shortwave infrared [SWIR]) and different spatial resolutions (4, 15, and 30 m). After performing georeferencing and normalization of the images, density slicing was used to extract the waterline. Comparisons of extracted waterline positions with ground-level data for eight transects and global positioning system (GPS) tracks of the island shorelines showed that NIR bands were superior to SWIR bands because of the characteristics of the coral reef coasts, including a lack of foam and suspended sediments (which can affect the NIR wavelength region, if present) and the presence of remnant water on reef flats during low tide (which can affect the SWIR wavelength region). A linear relationship was found between the estimation errors of waterline positions and the spatial resolutions of the NIR sensors. Analysis on estimation errors and image costs showed that Terra ASTER band 3 was the most cost-effective sensor for extracting waterlines with reasonable accuracy. The results serve as general guidelines for using satellite-derived data to estimate intertidal topography and detect and monitor shorelines in coral reef environments. © 2006 Elsevier B.V. All rights reserved. Keywords: Coral reef; Shoreline; Remote sensing; IKONOS; Terra ASTER; Landsat ETM+ 1. Introduction Topographic measurements of beach and intertidal zones have various uses, including coastal defense, coast- al environment management, economic exploitation of Geomorphology 82 (2006) 398 – 411 www.elsevier.com/locate/geomorph ⁎ Corresponding author. Fax: +81 29 850 2572. E-mail address: hyamano@nies.go.jp (H. Yamano). 0169-555X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.geomorph.2006.06.003