The input of fresh water is very limited, since no strong 
river reaches the system. Tides, which present a 
maximum amplitude of 1,20 m, are the main agents for 
estuarine circulation and for the mixture between 
chemical-physical properties. By the time of this 
experiment, a very small drainage basin, with an area 
of 1.339 Km?, was responsible for most of the fresh 
water input. Tidal creeks also represent an important 
source for fresh water (collected basically from rain), 
and may present up to 8 Km of extension and 
maximum depths of 7,0 m. 
These small water bodies were developed over 
Pleistocenic terraces, which are covered by tropical rain 
forests. Expressive mangroves have established in their 
margins, contributing for the high productivity of the 
area. The decomposition of leaves from these types of 
vegetation regularly promotes the "brownishment" of 
the water color, mainly after huge storm rains, which is 
related to the introduction of humic and fulvic acids in 
the system. These dissolved organic compounds are 
optically referred as "yellow substances". 
The particulate inorganic sediments in the water 
column predominantly come from Pleistocenic sandy 
terrace's erosion and from bottom  sediment's 
resuspension, since river input is inexpressive. The 
highest concentrations occur near to the bottom, 
associated to maximum current speeds, both on ebb 
and flood tides. Bottom currents always present 
threshold velocities high enough to erode and 
transport fine and very fine sands, which predominate 
in the bottom (Bonetti Filho et al., 1995). The water 
transparency in the area is rarely higher than 2,0 m 
and total suspended solids present an average 
concentration between 30 mg/l and 40 mg/l. 
2. METHODOLOGY 
Although ideal conditions for water quality monitoring 
from orbital platforms occur when simultaneous in situ 
data are available, many authors agree that a previous 
knowledge of the study site's oceanography may lead to 
a good qualitative approach (Robinson, 1984). 
During this experiment, the extensive cloud coverage 
of the area did not permit the acquisition of real time 
data, and demanded the use of previously acquired 
LANDSAT-5/TM images for the investigation. 
Despite this, oceanographic data were collected aboard 
research vessels during two field trips, on August 1993 
and February 1994. 
In these occasions a series of water quality parameters 
was collected, following transects along the estuarine 
front and in 25 hour anchor stations inside the system, 
to help in the interpretation of the front's 
78 
oceanographic characteristics. Suspended sediment 
concentration (fractionated on its organic and 
inorganic compounds), currents (speed and direction), 
salinity, temperature and pH were sampled and gave a 
very good support to the interpretation of orbital data. 
The time series was composed by three continued years 
of images, generated in the following dates: April 17, 
1984; May 22, 1985; and September 14, 1986. Their 
WRS reference was 220.77. For the three images, 
meteorological and tidal information were analyzed in 
detail. LANDSAT-5 bands TM-1, TM-2 and TM-3 
were used for the study of water surface compounds, 
band TM-4 for water/land separation and band TM-6 
for brightness temperature determination. 
The images were co-registered and processed in full 
resolution (pixels with 30 x 30 m for reflected bands 
and 120 x 120 m for thermal band) and the working 
scale, in the system's monitor, was 1:85.333. The 
Brazilian SITIM-340 image processing system was used 
for digital treatment, which was composed by a number 
of steps previously described by Bonetti Filho et al. 
(1994). Basically, they were: 
a) Histogram's Analysis: conducted to characterize 
digital numbers distribution and to determine the 
values for atmospheric correction; 
b) Atmospheric Correction: applied to minimize the 
atmospheric contribution to the scene, following the 
method of the darkest pixel subtraction (Chavez, 1975); 
c) Digital Numbers Surveying and Densitometric 
Transects: determined by direct digital reading along 
the estuarine front, perpendicular to the coastline, to 
help in the quantification of the differences detected in 
the time series; 
d) Water/Land Separation: applied from the 
generation of a mask, derived from water classification 
on TM-4, used to maximize the performance of the 
posterior contrast enhancement; 
e) Linear Contrast Enhancement: the function was 
determined from histogram's analysis, individually for 
each TM band, in order to increase visual 
discrimination; 
f) Pseudo-Color: generated by the equalization of each 
band into 14 classes (5 classes for TM-6, due to its 
lower spectral dynamics) and the latter application of a 
mnemonic color palette; 
g Color Composition: obtained from the use of the 
enhanced bands TM-3, TM-2 and TM-1 (RGB), 
without land information. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996 
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