Symposium on Remote Sensing for Resources Development and Environmental Management / Enschede / August 1986
Present state, changes and quality of Sologne and Brenne, two
French large wetlands, studied with the MSS and TM Landsat data
Michel Lenco
Ministry of Environment, Quality of Life Delegation, Neuilly s/Seine, France
Jean-Pierre Dedieu
Company SFERES-Teledetection, Montrouge, France
ABSTRACT : This work was undertaken to give original informations to local administrative and scientific autho
rities as an assistance to decision. At first, from Landsat TM and MSS data, the study yields cartographical
(at 1/50.000 scale) and numerical informations in 23 classes on the present state and the late 1975/84 changes
of the watershed land cover of two french large wetlands. Secondly, Landsat TM data processing in supervised
classification have afforded mapped informations about depth, aquatic vegetation, turbidity and outer tempera
ture of the ponds in ascertaining thresholds in channels 5, 1, 2, 3 and 6.
RESUME : Ce travail a été entrepris pour fournir des informations originales aux autorités administratives et
scientifiques locales en tant qu'aide à la décision. En premier lieu, à partir des données Landsat TM et MSS,
l'étude donne les informations cartographiques (à l'échelle de 1/50.000) et numériques en 23 classes sur l'état
actuel et les changements récents 1975/84 de l'occupation biophysique du sol du bassin versant de deux grandes
zones humides françaises. En second lieu, des traitements des données Landsat TM en classification supervisée
ont apporté des informations cartographiques sur la profondeur, la végétation aquatique, la turbidité et la
température de surface des étangs en procédant à des seuillages dans les bandes spectrales 5, 1, 2, 3 et 6.
1. INTRODUCTION
The aims of the study carried out in 1985 was to know
the present state and the late changes of ecozones
and land cover of the watershed and the water areas
of Sologne and Brenne, which are two large wetlands
of 130,000 and 145,000 ha extent respectively, situa
ted in the center of France below the Loire river.
There are several schemas both to bring out and pro
tect these two natural media where the changes were
important during the last ten years owing to hunting
and fishing or maize cultivation development,
and cattle breeding withdrawal. The remote sensing
seemed a good tool to give cartographical, quanti
tative and qualitative data on these humid areas as
an aid to the decision. The study was managed in col
laboration with local administrative and scientific
authorities.
2. METHOD
Two Landsat data recordings were used, a 7/27/1975 MSS
tape and 6/17/1984 TM tape. An improved and restored
false color image was elaborated for each date at
1/50.000 scale. After restoration, the ground resolu
tion (pixel) was 50 x 50m in the first case, and 30
30m in the second one. The three wavelenghts choosen
to establish the two restored images were 4, 5.and 7
for Landsat MSS, and 2, 4 and 5 for Landsat TM.
The second image was interpretated to study the
land cover of the two watersheds with the support of
topographical, geological and potential vegetation
maps and a sampling of photographies drawn out of the
last national coverage at 1/30.000 scale. It was pos
sible to obtain a classification with 23 items (see
hereafter results). Landsat TM data appeared interes
ting to detect easily meadows, cereals, conifers, wa
ter surfaces and wetlands with the level of the soil
humidity in the classes. Some difficult points needed
a control on the ground, during the mapping proces
sing : classification of wet vegetation on humid
areas near water surfaces.
The changes since 1975 were distinguished by compa
rison of interpretated TM data with corresponding MSS
data called on a screen in a processing station.
Between the two dates a perceptible increasing of
ponds in number and surface and a rise of the draina
ge to develop the maize cultivation were noticed. The
interpretated map was treated on computer to get sta
tistics in hectorage for each class and changes.
The channel 5 of 1984 Landsat TM data gives the possi
bility to draw out the water surfaces and the wave
lengths 1,2, 3 and 6 allow to study the characteris
tics of water surfaces (depth, nature of the bottom,
turbidity, aquatic,vegetation and temperature) in se
lecting thresholds" in supervised classification with
a discriminant analysis, because some ponds are regu
larly analyzed and watched by local scientists and
administrative authorities and were used as ground
data. It was possible also to observe on the ground
some ponds in june 1985 at the same period of the year
that the catch of TM data. In the middle infra red,
the channel 7 has brought nothing more than channel 5
to study the water surfaces.
* some ratios
3. RESULTS
3.1 Classifications for mapping at 1/50,000 scale
LAND COVER CLASSIFICATION
code category
1- Building areas
VI urban, dense
12 urban, mean and few dense
13 urban, diffuse
14 urban hold (industrial areas...)
15 bare soil, quarry, building yard
2- Agricultural areas
21 arable land
22 fields in copse (arable land and grassland)
23 wet meadows
24 reaped grassland and dry grassland
25 orchards, vineyards, nurseries
26 draining areas and areas in changing
3- Natural areas
31 hardwoods (oaks species,...)
32 softwoods (pines)
33 mixed forests
34 cuts
35 reafforestings (in conifers)
