Análise do potencial do sensoriamento remoto orbital na identificação de macroalgas marinhas bentônicas

Abstract

Benthic algal cover and trends in its changes are indicators of water state in coastal areas. Mapping benthic algal cover with conventional methods (scuba diving) provides great accuracy and high resolution yet is very expensive and time consuming. Due to the recent global changes, several parts of the Brazilian coast may be impacted jeopardizing benthic macroalgal ecosystems. Mapping that benthic macroalgal cover by remote sensing can significantly improve the decision making. However, it is required certain knowledge about the optical signatures of different bottom types. To use remote sensing properly, it is necessary to build a spectral library of the most common macroalgae found within the Brazilian coast. Thus, using a spectroradiometer in the field, in several Brazilian beaches, the reflectances were measured for red, green, and brown macroalgae, seagrass, sand, pebble, and wet and dry decaying mats of macroalgae and higher plants. That field data were organized toward the optical spectral bands found in the MERIS satellite and analyzed looking for the best index to represent each group (red, green and brown). The index 7/5 (similar to MERIS bands) separated the green algaes (Caulerpa racemosa = 0,76, ± 0,12; Ulva sp. = 0,42, ± 0,17), from red algaes (Hypnea musciformis = 1,29, ± 0,20; Acanthophora spicifera = 1,24, ± 0,21), but not from brown algaes (Padina gymnospora = 0,84, ± 0,28; Colpomenia sinuosa = 0,88, ± 0,32).