RESUME
Le pouvoir réfléchissant de l'eau mesure en
laboratoire est toujours fonction de sa turbidite. Cette
turbidite est due aux particlules solides en suspension dans
l'eau et pour un type donne^ de solide il y a une bonne
correlation entre sa concentration et la turbidite. Mal
heureusement cette correlation varie pour different^ matériaux,
puand less particules en suspension sont de la matière végétale
comme on en trouve dans un lac eutrophie, on peut detecter des
changements de pouvoir réfléchissant a distance. Deux experi
ences sur des lacs indiquent qu / il y a une bonne correlation
entre la luminosité^ d'images ERTS et 1' eutrophication du lac.
INTRODUCTION
Lake eutrophication, or a lake's state of enrichment,
is rapidly becoming a very important aspect relating to the
control and use of lakes and watersheds. Agencies responsible
for managing the quality of fresh water lakes are becoming more
and more interested in lake eutrophication and practical methods
for establishing eutrophic classification of lakes. While many
methods of such classification have been tried or proposed, no
one method as yet has been universally agreed upon. Field
methods such as in-situ sampling over an extended period of time
are presently used by some agencies. But with such methods the
number of lakes which can be sampled, analyzed, and evaluated
in a years time is rather small unless a gigantic field effort
is put forth of a size beyond normal operational limits of that
agency. What is needed is a system which will provide a quick
yet accurate indication of the eutrophic level of lakes over a
large geographical region, and at the same time require a minimum
of field samples.
The authors feel that they are developing just such
a system based on the correlation between water reflectance
values obtained from Earth Resources Technology Satellite (ERTS)
imagery and the water quality parameter of turbidity caused by
living organic matter. Just a few judiciously chosen water
samples are required simultaneous with the ERTS overpass in order
to "calibrate” that satellite image for this task. The ERTS
imagery then if properly analyzed can be used to classify many
of the lakes in the frame as to algae-caused turbidity which is
associated with the state of eutrophication.
