Mapping Sargassum beds off the coast of Chon Buri Province, Thailand, using ALOS AVNIR-2 satellite imagery

Abstract

Sargassum species grow on rocks and dead coral, forming dense seaweed beds in their growth seasons. Sargassum beds play a range of ecological roles in coastal waters, but their sustainability is threatened by pollution and reclamation within ASEAN countries with rapid economic growth. Before conservation initiatives can be implemented, it is necessary to establish their present distribution. These beds can be mapped using the noncommercial satellite, ALOS, which can provide multiband images using high spatial resolution optical sensors (sensitive to 10 m-2 plots), AVNIR-2. These images are of sufficient quality for examining coastal ecosystems and, in this study, for mapping the Sargassum beds in the waters off the coast of Sattahip, Chon Buri Province, Thailand. This coastal zone is a natural marine park reserve and protected from human activities such as fishery and reclamation. Biomass data were obtained in January, February, March, and December 2009 from quadrat sampling. The biomass of Sargassum aquifolium (Turner) C.Agardh at a bottom depth of 1 m and 1.5–2 m was determined to be 7.73 and 92.75 g dw m-2, while that of Sargassum oligocystum Montagne was found to be 44.05 and 87.97 g dw m-2, respectively. Ground truth data were obtained in February and October 2012 from serial images taken by manta tow. Supervised classification is a procedure for identifying spectrally similar areas on an image by identifying “training” sites of known targets and then extrapolating those spectral signatures to other areas of unknown targets. By applying this methodology, the Sargassum beds off Sattahip can be detected with an accuracy of about 70%. It is estimated that the error is caused by mixel effects of the bottom substrates in individual pixels, each of which covers an area of 10×10 m. Our results indicate that the images captured by ALOS AVNIR-2 are informative and useful for mapping the Sargassum beds in Southeast Asia.

Seasonal changes in water quality and Sargassum biomass in southwest Australia

“…However, the MTL of Sargassum in Point Peron is shorter than that found in previous studies in Rottnest Island, SWA (10-95cm) (Kendrick 1993) The present study was initially applied using WV-2 satellite remote sensing data to determine the spatial distribution of Sargassum and associated marine benthic habitats in the study area. This study can be considered as an original approach for the region when using more advantageous satellite remote sensing data, with higher spatial and spectral resolution, than the previous studies in Thailand with ALOS-AVNIR 2 images (10 m spatial resolution) (Noiraksar et al 2014), New Caledonia with Landsat (30 m) and Quickbird (2.4 m) images (Mattio et al 2008).…”

“…For example, lower resolution Landsat (30 m) and higher resolution Quickbird (2.4 m) satellite images have been used to estimate the spatial distribution of Sargassum beds in South West Lagoon, New Caledonia (Mattio et al 2008). Nevertheless, only a few studies have been carried out to assess of the spatial distribution of Sargassum and their temporal biomass variations in marine coastal areas using high-resolution satellite remote-sensing data (Noiraksar et al 2014).…”

Submerged Kelp Detection with Hyperspectral Data

“…Maximum likelihood classification (MLC) is a well-established supervised classification method and has often been applied for the mapping of brown algae e.g., [72,73]. MLC quantitatively evaluates the variance and covariance of the spectral pattern in each class to classify an unknown pixel.…”

Temporal changes in the biomass and distribution of Sargassum beds along the southeastern coast of the Baja California Peninsula

“…The genus Sargassum C Agardh (Phaeophyceae, Fucales, Sargassaceae) has a worldwide distribution, especially in tropical and subtropical regions (Noiraksar et al 2014), including the Gulf of California (Pacheco-Ruíz et al 1998). In this gulf, Sargassum species constitute the bulk of the fleshy macroalgal biomass, providing habitat for diverse communities of epiphytic algae and a surface canopy for understory algae, invertebrates, and fish (Norris 2010).…”

“…El género Sargassum C Agardh (Phaeophyceae, Fucales, Sargassaceae) presenta una amplia distribución, especialmente en regiones tropicales y subtropicales (Noiraksar et al 2014), incluyendo el golfo de California (Pacheco-Ruíz et al 1998). En el golfo, las especies de Sargassum constituyen la mayoría de la biomasa de macroalgas carnosas, y proporcionan hábitat para diversas comunidades de algas epifíticas y una cubierta para algas, invertebrados y peces del sotobosque (Norris 2010).…”