International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
350000
35,5000
360900
Figure 6b: Results of classifications by Maximum Likelihood
method (southern part) of the September 1989 image.
For some soils units such; as the regosols, lithosols,
colluvial and complex units; the multispectral
Classification give conformal results with the
pedological map. Otherwise, these units are well
classified. But then, for the alluvial soils, hydromorphic,
calcimagnesic and isohumic the classification present
some anomalies.
The alluvial soils staking out the hydrographic system
are well discriminated. In revenge, they are distinctly
overvalued with regard to the map and they confound
with isohumic soils and zones of shades. The similarity of
their respective spectral signatures in the visible is an
explanation (see graph of the spectral signatures) insofar
as the humidity rate of these soils is in the origin. The
zones to the shade - on the time of taking images [i.e] 09h
45 GMT- constitutes an other problem that the resulted
soils signature, obeys to the same phenomenon that the
one of humid soils super weak reflectance in the visible.
It is in the P.L.R that the distinctions appear. If they are
always imposed, then we can really assign it to a
problem of standard deviation in the PIR bigger than the
one of visible.
The soils hydromorphic are absent from the
classification as homogeneous class, but present under
the form of pixels .scattered in the image. This is
attributed to the methods of classification «by pixels»
utilized, or to a real reduced spatial extension with regard
to the spatial resolution of TM images.
A confusion also appears between the soils isohumic and
calcimagnesic. In the plains, the calcimagnesic soils are
amalgamated with the isohumic soils, because of their
content in elevated humidity, this confers to them near
radiometric values of those isohumic soils. However, on
the piedmonts and the glacier, the calcimagnesic soils
102
confound with the regosols to reason- presumably- of the
moisture erosion which provokes a scouring of the
superficial horizon, giving it a lucid hue near the one thus
regosols. It is that the named unit «complex» appears in
the plain on the classified image. This is considered quite
normal since the unit in question is also constituted
partially by regosols, localized exactly in the plain.
4. CONCLUSIONS
The so-called approach of classification of
remote sensing data in the cartography showed that:
= Globally, the results are powerful if we utilize the
methods of classifications type Maximum Likelihood
However, for the detail and of the precision of the
classes limits, it is impossible to have a « blind»
confidence on the results. This actually is explained by
the heterogeneous and the complex character of the tests
parcels, since that the soils are only rarely naked and
monospecific.
=» The spectral properties of the surfaces are generally
those of the vegetation and therefore decrease the
interest of the classifications in pedology, except in
the regions where the plant cover is absent or little
abundant. A phenological study of the vegetation of
the survey region imposes for the choice of the
periods of the satellite images acquisition.
l. An anomaly which is expressed either by an
overestimate or an under estimation, like it is the
case of the alluvial soils which is overestimated,
whereas the soils isohumics or calcimagnesic are
rather under estimated.
2. Another anomaly which is expressed by absence
of the hydromorphic soils, despite the sampling
settled.
REFERENCES
Bildgen P., Lafage H. Et Kersabiec A. M. 1988.
Télédétection: étude de la réponse spectrale et
classification des sols agricoles du département des
BOUCHES-DU- RHONE. 113ème Congrès national
des sociétés savantes, STRASBOURG, 1988. Pp 45-
59,
Cassirame P. 1977. Méthodes de classification des
données multidimensionnelles en télédétection.
Application à la cartographie d’une région agricole
(Camargue). Thèse doctorat en physique Spatiale à
l’université PAUL SABATIER, TOULOUSE, 89 p.
DUBUCQ 1989. Reconnaissance des sols par
télédétection et leur comportement par rapport a
l'érosion dans le LAURAGAIS. Thése 36 cycle,
université de Paul sabatier de Toulouse. 273p.
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Estimatit
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pp 1-11.
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