represented the most advanced geothermal project in Chile and it had been studied 
since more than ten years ago. In this way, it would be easier to compare remote 
sensing data with existing information. This pilot experience was developed with 
the valuable cooperation of Aerphotogrammetric Service (SAF), Geothermal Committee 
of CORFO and the partial sponsoring of Service for Scientific Development, Univer 
sity of Chile, = 
A S.A.F. Twin Otter airplane was used to fly with one multiband camera 
and one thermal infrared scanner. Besides, a field portable photographic labora- 
tory was carried to be set up at Calama Airport (about 80 km East from El Tatio), 
the operation center during one week (January 1980). In this was it was possible 
to develop multiband photographies and thermal images in near real time, to iden- 
tify the gaps in photographic coverage, the specially interesting zones to be 
flown at lower altitudes, and to better plan the field verification activities. 
This field operation methodology was very good because all the main necessary in- 
formation was obtained before returning to Santiago. This operation form will be 
used in future detailed studies. Besides, the two remote sensors employed were 
very useful and accurate (in spite of being analogic sensors, with direct recor- 
ding in B/W film). : 
The spectral bands of multiband camera were: AMB-1 or blue (0.4-0.5 um), 
AMB-2 or green (0.5-0.6 um), AMB-3 or red (0.6-0.7 um) and AMB-4 or near infrared 
(0.7-0.9 um). These spectral bands are similar to Landsat MSS-4,5,6. Mosaics (B/W) 
were made with bands AMB-2,3,4. Besides these three mosaics, color composites ( 
Diazo techniques) were made for specially interesting areas, to enhance certain 
features such as vegetation, water, different types of salty soils and rocks. Pho- 
to 1 shows a partial example of multiband photographies. Because multiband photo- 
graphies did not have spatial distortion, it were very useful to be compared with 
the "stretched" thermal images. These photos were obtained at an original scale 
1: 7.000 (approx.) and more than 600 multiband photographies were taken. 
Thermal images were obtained in the spectral band 8-14 um, with a therm 
al resolution of 0,25? C. The original scale was 1: 10.000 (flight direction or T 
longitudinal) and 1: 25.000 (transversal or cross flight direction),approximately. 
In spite of this stretching effect, it was not problem to identify all the thermal 
and geologic features because the undistorted multiband photographies were used 
as an easy and accurate reference. A global mosaic was also made with thermal in 
mages and photographic enlargements and enhancements (including colored density 
slicing) were made for specially interesting zones. Thermal images represented 
a key element to study geothermal fields. Different rocks units were easily iden- 
tified trough its different thermic properties (conductivity and inertia); this 
units would not be easily identified because usually there is not good stratigra- 
phic control to be recognized in the field. The alignment of hot water springs 
allowed to identify geologic faults and linements . The thermal contrast among 
different matterials also was very useful to identify geologic structural features 
(faults, linements, foldings, others). Photo 2 shows an example of the excellent 
quality of these thermal images. Because the thermal images were obtained very 
early in the morning (about 4:30 A.M., before sunrise) the thermal contrast was 
really good: El Tatio is about 4.500 meters over sea level and at this hour, the 
environmental temperature is some degrees Celsius below zero and so, only the mat- 
terials having internal energy should appear in white tones in these images. For 
this reason, thermal images obtained at early hours are very adequate to study 
geothermal activity over the high altitude geothermal fields in Los Andes Range. 
Multiband photographies were obtained at conventional aerophotogrammetric hours. 
As à conclussion, it can besaid that the use of aereal remote sensors, 
specially thermal IR scanner, is very useful to study geothermal fields (explora- 
tion stage) in Los Andes Range. Thermal images are key element to identify the 
main geologic structural features that characterize a geothermal field. Photo 3 
and Figure 2 show the results obtained for El Tatio. This information must be ve- 
576 
hm 
L^ 
Ee EP REA 
ME De UN A ERES, LLENO 
72° 
189% 
OCEAN 
PACIFIC 
ANTOFA 
241 
  
FIG. la. I 
geothermal 
  
FIG. Ib, 
at El Tai 
hours (ge 
  
PHOTO 2. 
at El Tat 
with higl 
us — —