rified in terrain (partially) but it is enough reliable to conclude that this me-
thodology should be employed in the preliminar exploration steps of a geothermal
field, because many efforts and time could be saved due to its great value to allow
the planing of geologic field activities, As a main result, this experience show-
ed many structural features (geologic faults and linements) that could not be iden
tified through conventional means. In the other hand, the main geologic units that
had been formerly identified through conventional means, are also contained in this
remote sensing data. For more details in this experience, please see Refs. 1,2,3.
PROSPECTION STAGE: IDENTIFICATION OF GEOTHERMAL ZONES BY USING
MULTISPECTRAL AND MULTITEMPORAL LANDSAT IMAGES,DEL MAULE LAGOON
A successful pilot experience was developed (1981) over Del Maule La-
goon zone (Fig. 3), Central Zone of Chile. Because airborne remote sensors are
adequate for detailed studies of previously identified geothermal fields, it was
necessary to develop a methodology to identify new areas of geothermal activity
(prospection stage). Because no thermal satellite images were available from Land-
sat, an interesting methodology was determined to be used over snowed areas in Los
Andes Range. This methodology is based in the indirect identification of thermal
activity through the observation of the abnormal snowmelting conditions near vol-
canic structures.
Four Landsat multispectral and multitemporal images were used over this
pilot zone (Sep. 6, 1977; Dec. 9,1978; Apr. 19, 1978; Feb. 1, 1979). These images
were acquired to Instituto de Pesquisas Espaciais (INPE), Brasil, in traditional
false color composites, scale 1: 250.000. These colored images allowed to enhance
certain features, such as snow, vegetation and water bodies, near volcanic struc-
tures, This methodology is based on the corelation of permanent features(geologic
faults and linements, volcanic structures, hydrothermal alteration zones, identi-
fied geothermal sources, topography, hydrologic net) and variable features (snow
distribution near volcanic areas, vegetation and water bodies variations in snowed
areas). Three steps must be followed to obtain results: 1) Compilation of geologic
antecedents, through the use of existing information and Landsat images (specially
useful to identify volcanic structures, enhanced by snow distribution,and also geo
logic faults and linements); these permanent features can be summarized on a trans-
parent map. 2) Analysis of variable features (through the use of multispectral/
tio geo - | multitemporal Landsat images); specially interesting areas are those zones where
sociated liquid water or vegetation spots remain abnormally uniced during cold season due
sion). to the proximity of volcanic structures. 3) Integral analysis of the information
obtained in steps l and 2. A new map of forecasted potential areas of geothermal
activity is here produced and these areas must be confirmed or discarded by using
. existing information or by doing field verification activities.
T In this pilot experience, all the existing or known geothermal sources
350 were included in the forecasted areas and field activities allowed to confirm other
s- forecasted areas (Photo 4 , Fig. 4). This pilot experience was very successful.
T However, new areas must be studied along Chile to obtain a general methodology,
z valid for the whole country (because snow distribution varies too much from North
à J to South along Chile). This methodology does not assure 100% reliability : it
aut mainly identifies water springs and due to the proximity of these springs to vol-
Vn. canic centers, it can be forecasted as potential sources of thermal water. Anyway,
NO this methodology allows to reduce the prospected regional zone to some specific
369. areas and, depending on the potential importance of these geothermal areas for the
$ region, more detailed studies can be accomplished by using airborne remote sensors
and field geologic activities.
«t
M NATIONAL AND CONTINENTAL STUDIES ON GEOTHERMAL ACTIVITY
Based on the former positive results and the feasibility to monitor
Le and volcanic activity through the observation of abnormal snowmelting near volcanic
Centra
581
um RE F pu
C , du ER am cá T
WE NR e D LTD IQ AD MD Uo ae —— —(—X te et M
