4. Results
4.1. Colour aerial image
The colour orthorectified mosaic (Fig. 3) has a pixel size of
1.8 cm. Due to choosing the right time of the day for flying; no
shadows in the imagery were detected, maintaining the integrity of
the geothermal area. The mosaic displays the boundary of the
geothermal surface manifestations clearly as bare ground with
patches of white, grey and pink contours caused by the geothermal
heat and the chemical discharge. The mosaic also shows the runoff
channel caused during the last heavy rainfall. The vegetation surrounding
the surface manifestations exhibit colours ranging from
healthy green to brown and grey dead plants. The main purpose of
the colour imagery was to provide the GCPs for georeferencing the
TIR imagery. Without any issue the GCPs were identified and its
coordinates (Table 3) were extracted.
4.2. Thermal infrared aerial image
The orthomosaic of the thermal infrared imagery is shown in
Fig. 4. The orthorectified mosaic has a pixel size of 0.5 cm, signifi-
cantly better resolution than in the colour mosaic. The colour scale
is non-linear. It stretches subtle differences near inferred ambient
temperatures and compresses inferred temperature differences at
higher temperatures. A warm to hot thermal anomaly range was
computed by normalizing the values of the orthorectified mosaic.
Numerous warm to hot thermal anomalies exist in the study
area, and appear as hot bare ground. These features are associated
with steam heated ground rather than discharging geothermal
springs or streams. The inferred TIR image shows that inferred high
temperatures (red colour, temperatures >90 C) occur and dominate
west side of the surface manifestation, whereas the warm
areas (green to blue colours, temperatures < 50 C) can be seen
toward the southeast end. Emphasis was given to collecting images
with a high overlap, the quality report from Pix4Dmapper