Evaluation of aquatic coverage on ponds of Nhecolândia subregion in the Pantanal through Landsat and SPOT data

Abstract

The objective of this work was to evaluate areas covered by aquatic plants in ponds and temporary drainage channels through optical sensors. The area of study is part of the Nhecolândia subregion of the Brazilian Pantanal wetland and is characterized by ponds of fresh and salt-lakes waters, temporarily covered by aquatic macrophytes and algae. TM (Thematic Mapper)-Landsat digital image, from Aug. 26, 1993, and HRV-SPOT digital image, from June 12, 1987, were used. An overflight was made in the study area to obtain 35 mm photographs of some ponds, and field work was carried out to survey the spatial distribution and floristic composition of the aquatic plantas in the ponds. Algorithms of slicing and maximum likelihood classification were applied on selected ponds. Areas with predominance of Salvinia auriculata and Scirpus cubensis were well discriminated. Presence of aquatic plants was easily observed on Landsat bands 4 and 5. However the difficulty to distinguish areas occupied by different aquatic plants, through the use of data with spatial resolution of 20 to 30 meters, suggests that studies based on aerial photographs and radiometers may produce more detailed results.