STUDY OF AQUATIC VEGETATION IN TUCURUÍ RESERVOIR (BRAZIL) USING AIRBORNE SAR-C 
MULTIPOLARIZATION DATA. 
Mauricio Almeida Noernberg 
Oceanographer 
National Institute of Space Research - INPE 
Brazil 
Commission VII, Working Group 5 
KEY WORDS: Aquatic Vegetation, Multipolarimetric SAR-C, SAREX 92, Biophysical Indices. 
ABSTRACT: 
Aquatic vegetation communities are among the most productive in the world. In recent years the use of radar data have increased 
significantly, and have been used to estimate biomass trough empirical models. In this study the discrimination capability of two 
important aquatic vegetation genera (Eichhornia sp. and Scirpus sp.) was studied. These genera are present in Tucuruí reservoir, 
Brazil. Airborne SAR C multipolarization data was used. Three biophysical indices were calculated in order to study the type of 
interaction between microwave radiation and canopy. 
1. INTRODUCTION 
Aquatic vegetation communities are among the most productive 
in the world. However, their rapid and uncontrolled growth can 
result in a number of undesirable problems such as: obstruction 
of water flow, changes in water quality, decrease in oxygen 
levels, and increase in human health hazards (Junk and 
Howard-Williams, 1984; Barrow, 1987). Aquatic vegetation 
communities also play an important role in the carbon cycle, 
sequestering CO, from the atmosphere through photosynthesis 
and releasing it through respiration. They are also an important 
source of methane (CH,) to the atmosphere (Wetzel and Grace, 
1983; Morrissey et al., 1994). 
The use of remote sensing data in ecological models has 
increased during the last years. A series of empirical models 
were developed to estimate biomass from remote sensing radar 
images (Le Toan et al., 1992). Most of these models are based 
on the relationship between radar backscatter and biomass, it is 
though important to ensure that the radar backscatter 
information is reliable. 
The objective of the experiment was to investigate the effect of 
polarization on the discrimination of different aquatic 
vegetation genera using airborne multipolarization C band SAR 
data. 
2. STUDY AREA 
The test site for this study is the Tucuruí reservoir, located 300 
Km south from Belém, Pará State, Brazil limited by the 
coordinates of 3?43'S; 49?12"W and 5?15'S; 50?00"W. It is the 
largest reservoir in operation in the Amazon region. The water 
reservoir surface is estimated to be around 2700 km?. The area 
covered by aquatic vegetation during the dry season represents 
2096 of the reservoir's surface (Abdon and Meyer, 1990). The 
specific test site is the Pucuruí inlet (Figure 1). 
U H E TUCURUI 
PARÁ 
sram f 
e: 
BRAZIL 
  
Figure 1. Study area. 
Five major genera of aquatic vegetation are usually found in the 
Tucuruí reservoir. Eichhornia sp., Salvinia sp. and Pistia sp. 
(free-floating); Typha sp. (emergent); and Scirpus sp. (floating 
leafed). For this study only Eichhornia sp. and Scirpus sp. will 
be aimed (Figure 2). The Eichhornia sp. has fine roots, 
produces stolons and viable seeds. Its leaves are 10 to 15 cm 
long, upright and bright green. The Scirpus sp. is the most 
widespread aquatic plant in the Tucuruí reservoir, with stands 
that are not homogeneous. Plants grow to a height of 1 to 2 
meters and its roots are attached to the dead trees. 
The reservoir is surrounded by tropical dense forest. Since the 
reservoir was filled without removing the forest, large areas are 
always occupied by dead tree trunks that emerge off the water 
surface. 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996