ediment 
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e of the 
(RGB), 
In order to quantify the brightness temperature 
gradients observed in the images, the algorithm 
developed by Bartolucci & Lozano-Garcia (1985, apud 
Baban, 1993) was applied: 
T(k) = 260,454218 + 0,294398DN - 0,000249DN? 
Where: T(K) = brightness temperature, in Kelvin; and 
DN = digital number. The highest and lowest digital 
numbers of each image were used in the determination 
of their thermal gradients. 
3. RESULTS 
The images of 1984 and 1985 were acquired by the 
satellite in low-tide, while the 1986 one represented the 
beginning of flood tide. Tidal heights and amplitudes 
presented very close characteristics in the periods. The 
weather also exhibited similar conditions for all images, 
with the dominance of a continental hot and dry air 
mass in the Brazilian southeastern coast. This situation 
validates images' comparison. 
All images demonstrated the great influence of the 
inner waters into the adjacent coast. The estuarine 
fronts were clearly visible and presented a strong 
variability in shape, dimension and spectral response in 
the time series. The observed extensions of the front, 
perpendicular to the coastline, were 6,5 Km (1984), 4,8 
Km (1985) and 7,7 Km (1986). 
The enhanced image from April 1984 (Figure 1) 
presented a very strong signal in the visible bands for 
the region of the estuarine front (mainly on TM-3). 
The lowest digital numbers, in relation to de adjacent 
waters, were verified in the September 1986 image 
(Figure 2), which indicated a strong absorption in the 
area of the front for all visible bands, remarkably on 
TM-1. The image of May 1985 seemed to represent 
intermediary conditions between the two extremes, and 
was not reproduced in this paper. 
The external boundaries of the inner fluxes were clearly 
identified in the visible bands, always associated to 
higher digital numbers. The best band to individualize 
the front's body was TM-3 in the image of 1984, and 
TM-1 in the image of 1986. Very consistent results 
were also presented by the densitometric transects, 
which clearly delineated the estuarine front. Digital 
numbers for TM-3 were sensibly higher in 1984 image. 
4. DISCUSSION 
A satellite image from the ocean, in the visible bands, 
has its characteristics determined by the properties of 
79 
the light interaction with water and with it's suspended 
and dissolved constituents. 
The best spectral interval for the measurement of 
suspended sediments is located between 0.55 um and 
0,65 um (Johnson & Munday Jr., 1983). This roughly 
corresponds to bands TM-2 and TM-3. The presence of 
high digital numbers on these bands strongly indicates 
an effective suspended solid's concentration at surface, 
as it was verified on 1984 image. 
Yellow substances are well known for promoting an 
intense change in the color of coastal waters. The 
introduction of these organic acids increases the 
absorption coefficient of the water, specially in the 
lowest wavelengths (Witte et al., 1982). Consequently, 
a high absorption (low digital numbers) on TM-1 may 
be interpreted as an indicator of dissolved organic 
matter, as it can be seen on the image of 1986. 
Therefore, the strong differences detected in the time 
series seem to indicate a variability in the composition 
of the water flux through the tidal inlet, with an 
alternation in the predominance of suspended 
inorganic particulate or dissolved organic compounds. 
These differences are possibly related to seasonal 
controlling, since in winter the pluviometric totals are 
very weak in the region and suspended solids 
exportation decreases. The 1986 image, besides the 
absence of inorganics and the strong presence of yellow 
substance, also suggests a consequent higher 
exportation of organic matter to the adjacent coast. 
Another possibility of interpretation is to consider the 
existence of similar yellow substance concentrations in 
both images, which could be masked by the huge 
presence of inorganic matter in the image of 1984. 
Digital numbers' readings on TM-1 corroborate with 
this idea. 
Local resuspension of bottom sediments was also 
verified in all dates, mainly on band TM-3, and 
confirmed by field investigations. A strong signal was 
always associated to the position of a submerged 
sedimentary terminal lobe, which is part of the ebb 
tidal delta, indicating a secondary source of inorganic 
material. 
Offshore to the inlet, satellite data and in situ current 
measurements confirmed the influence of longshore 
currents in the redistribution of inner waters. 
Suspended sediment patterns suggest that the estuarine 
flux acts as a hydraulic jetty and induces a 
northeastward transport . 
The highest brightness temperature gradient in the 
scene was obtained for the image of 1986 (with a 
variation from 20,8 °C to 24,0 °C). This was the only 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996