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Remote sensing for resources development and environmental management
Damen, M. C. J.

Thematic Mapper digital data with path row annotation
223/76 were acquired on Jan. 19, 1985. Within this
area, a segment, of 512x512 pixels, which locates
on the margin of the Ivai river and about 50 km
south-west of Maringá, Paraná State, was selected
for investigation. This segment was chosen not only
due to its representativeness for the crops in the
region, but also the cooperation provided by an
agrobusiness company, where ground information
such as crop type and variety, planting/harvesting
dates, crop conditions, field practice, yield etc
were available. On the date of imaging, predominant
cover types in this subscene were soybeans,
sugarcane, com and gallery forest. Pasture and a
small amount of reforestation and bare soil (i.e.
plowed fields) were also presented. Soybeans were
at the flowering stage, com plantations were
entering senescence, while sugarcane fields of
various varieties were at different phenological
stages and percentages of ground cover depending
whether the field under consideration was planting
or ratoon crop. Information contents of this segment
was extracted from CCTs and stored on disk file
for subsequent analyses. Based on the field
information, 25 samples varying from 36 to 200
pixels,were chosen for the above cited cover types,
and located on the image monitor of an interactive
image analysis system in INPE. These sampled areas
were used for band combination study and served later
as training areas for supervised digital analysis.
2.1 Triplet band selection for color image
For color composition, a subset of 3 bands should
be selected from the available TM bands and for
this purpose we used the criterion of entropy. The
technique of principle component analysis was not
included because the color image resulted from the
first three eigenvectors is
scene dependent and the unknown color-surface
relationships make the understanding of the
physical meaning difficult. Any three TM bands form
a three-dimensional feature space and the
associated variance-covariance matrix defined an
ellipsoid within the space. According to the
entropy criterion, the triplet with the ellipsoid
of the maximum volume should be chosen (Young and
Calvert, 1984). The advantage of this criterion
over other feature selection methods, based on the
maximum total variance, is discouraging the
inclusion of highly correlated bands in the
selection. Theoretically, the maximum ellipsoid
volume represents the maximum variation in tonality,
thus it should be a proper criterion in band
combination selection for color image production.
In this study the entropy with and without a priori
of normal distribution were both tested. Once the
band triplet was chosen, the color assignment was
nade as suggested in Sheffield's study (1985) :
green, which is most sensitive to hunam eyes, is
assigned to the band with the highest variance, red
to the band of the second largest variance, and
blue to the band of the smallest variance. The
program implemented in our image analysis system
gives the first six-band triplets, the prime colors
were then assigned, slides were taken from the
image monitor and visual evaluations were made on
these slides for their interpretabilities.
2.2 Band selection for digital analysis
The best TM band combination for digital analysis
should take into account the accuracy of the
classification results and the computer time
consumed. The discrimination function, "Jeffereys-
Matusita distance" or the J-M distance, was used as
the criterion for band combination. In multiclass
classification problem we can chose the band
combination, which maximizes the mean J-M distance
between two classes or that maximizes the minimum
J-M distance. In this study both criteria were
applied to select the best hand combination if 2,3,
4 or 5 TM bands were used for digital analysis.
Plotting the separabilities of the best 2,3,4 and 5
bands the optimal band combination was chosen. For
classification, training statistics of the 25 samples
were used to charecterize the spectral responses of
the cover types considered. These training statistics
were then utilized to classify the whole area using a
maximum likelihood decision rule of the image
analysis system. Comparisons were made on: (1)
alphanumeric print-outs (2) the classification
matrix, (3) the computer time consumed, and (4)
the upper bound of the probability of error by the
J-M criterion. After these comparisons the best
band combination for crop discrimination was
3.1 TM color image composite
Table 1 shows the basic statistics and coefficients
of correlation for the six TM bands investigated.
As expected, intercorrelations were found among
visible bands, between bands 4 and 5 and between
5 and 7 for this highly vegetated area. The NIR
band 4 has the highest variance and a wider spread
of grey level indicating more information content
than the other bands. Decreasing variances are
observed from NIR to middle IR and then to the
visible bands. The ranked first six band triplets
by the entropy criterion, with and without the
Jaussian priori, are listed in table 2. Independent to
whether the priori was used or not, band 4 was the most
important TM band for color compositing. The second
band included in the triplet was band 5 and the
last was a visible band or band 7. Once the band
triplet was decided color coding was assigned
according to the amplitudes of their variances; in
our case green to the NIR band, red to middle-IR
band and blue to the visible band. If both middle-
IR bands were included in the combination, then red
was assicmed to band 5 and blue to band 7. Visual
comparisons of slides taken from the image monitor
for the selected color capos ites showed that when
bands 4 and 5 were included in the band triplet
together with any one of the visible bands or band
7, color appearances of vegetations were similar.
Thus, we could not claim preference over any one
of the combinations. Coparing the conventional
false color caposite (FCC) ; assigning blue to band
2, green to band 3 and red to band 4, to any of the
ranked combinations no significant improvement in
visual crop discrimination was noted. Under this
condition the conventional FCC is favoured over the
entropy selections because no additional training
of photointerpreter on the color-surface relations
is required. This conclusion, drawn from the 512x
512 pixels subscene, may be too local-specific.
Acquisition of FCCs for the quadrant using
conventional and the first ranked band combination
will be requested for a further investigation.
3.2 Band selection for digital analysis
The ranked first six band combination, when 2,3,4
or 5 bands were used in digital analysis, are
shown in table 3. Plotting the separabilities of
the best combinations (Fig.l) we note that the
statistical structure for crop discrimination had
three or four dimensionalities. These results are
in agreement with that obtained in previous studies
by Townshend (1984) and Anuta et al. (1984). No
matter whether the criterion of Max. J-M niean. or
Max. J-M min was used, the best three-and four-
band combinations, which should be included in digital
analysis, were the same; they were bands 2-4-5 and
Table 1 -
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