This document shows a suggested approach to generate geological maps from satellite images, which represent a powerful tool to characterize an area prior fieldwork, saving energy and money during the process and using the free sources from NASA and the USGS. This exercise mapped a Colombian area called Media Luna Syncline

1. Geological mapping using
satelital Images
Geographic Information Systems and Remote Sensing Project
Diego Alexander Bedoya Gonzalez
Master in Hydrogeology and Environmental geosciences
Georg-August University of Göttingen

2.  OBJECTIVE. Apply all the tools learned in the GIS and remote sensing courses in
order to produce 1 complete detailed geological map through the analysis of
satelital image sources and Arcgis as processing tool.
http://www.wvgs.wvnet.edu/www/m
aps/Geologic_Map_of_WV.png

3. Study area
 The study area has an extension of 1800 km2 and is located in the department of
Tolima, Colombia, South America, between the geographical coordinates 74°38‘ -
75°0' west longitude and 3°42‘ - 4°5‘ north latitude.

4.  Geologically, the study area corresponds
to the Prado syncline, which is one of the
mega geological structures of Colombia,
created by the compressive tectonic
deformation of the triple point among
Nazca, South America and Caribbean
plates.
• The area is located in the eastern branch of the Colombian Andes, which is
constituted by a thick sequence of sedimentary rocks that crop out by the
tectonic reverse process generated in the Late Miocene (10 M.y.), going
from an extensive basin to a compressive one.

5. Sources of Information
 The ‘USGS Earth Explorer’ search engine was used to obtain satellite
Images, prioritizing the Landsat 7 ETM+ and Landsat 8 products, due
to their better characteristics and new instruments that allow the
acquisition of new bands images.
 Likewise, this server was used for downloading ASTER Global DEM
images (GDEM) for the generation of surface contours and 3D
processing.
 Finally, complement information that could complement and
corroborate the elaborated model was sought in the Colombian
Geological Survey.

6. Work procedure
Steps for geological mapping

7. 1. Good Image Selection
 Main Problem: Cloud cover due to orographic rains and Intertropical Convergence Zone
(ITCZ)
https://www.atmos.washington.edu/1998Q4/211/gr3_1.gif https://farm8.staticflickr.com/7477/15953993008_8db649c1f2_b.jpg

8. Selected Image
(Landsat 8 image, 2015)
Image with clouds and gaps*.
(Landsat 7 Image, 2016)
*After 2003, the Scan Line Corrector (SLC) of Landsat-7 data failed, resulting in data gaps across the
scene. Source: USGS Earth Explorer

9. 2. Georeferencing and Storage
 Once the satelital image package was downloaded, one new Arcgis data frame was set
in order to georefernce all the work in the same coordinate system - For this Study: UTM -
Datum: wgs84, Zone: 18N
 New Geodatabase was created in order to get better structural design, performance
and data management experience in relation with shape file collections.
Colin Childs, ESRI Education Services

10. 3. Geoprocessing – True Color Image 30 m.
 New composite image from bands 1 to 7 was created in order to generate true and false
images of the stdudy area.
1. True color Image (band 2 (red) , band 3 (green) and band 4 (blue)
2. Water mask ( band 4 (blue) / band 2 (red)
Band 1: detects deep blues and violets. is useful
for tracking fine particles like dust and smoke in
shallow water and air.
Band 9: detects anything that appears clearly in
it must be reflecting very brightly and/or be
above most of the atmosphere. Main Use: detect
cirrus clouds
Band 10 and 11: detect the thermal infrared, or
TIR and they are used to see heat in air.
http://2.bp.blogspot.com/-
NUNWcSBi3qk/UgU6CbPKHrI/AAAAAAAAA28/3Fyw2XM1x4s/s1600/Bandpasse
sL7vL8_Jul20131-1024x611.jpg

11. Composite True color image. Resolution:
30 m
Composite Water mask image.
Resolution: 30 m. Division of band 4 by
band 2, highlights in black wáter bodies.

12. 4. Geoprocessing – True Color Image 15 m.
 The combination of 30m resolution true image with the Pancromatic band 8 image,
resulted in a new true color image with 15m of resolution
30 meters
resolution
15 meters
resolution

13.  ASTER images were used to create
contours of the study area
(countours each 50m) and TIN
Surface.
 ‘’Triangular irregular networks (TIN)
are digital means to represent
surface morphology. TINs are a
form of vector-based digital
geographic data and are
constructed by triangulating a set
of vertices (points)’’.
4. Geoprocessing – ASTER Images
ASTER image without processing.
Source: USGS Earth Explorer. "ASTER GDEM is a product of
METI and NASA."

14. Contours and TIN Surface allow identify hard rocks units (high slopes) from soft
rocks units (soft slopes)

15. Combination of
TIN and contour
map

16. 5. Identify rock layers in satelital images
 Rocks layers were identified through the 15 m resolution
satelital image.
 The process took into acount layers edges that are
continous and can be folllow sideways. (Original Lateral
Continuity – Steno’s Principle)
 V rock pattron could be observed

17. A B
Identification of rock layers and its lateral continuty in 1 single part of the area.

18. Continous rock layers identified on the whole study area

19. 6. Identify topografical Rule of V´s
(dip direction)
 In order to identify dip direction of the rocks layers, it was necessary applying the
rule of V´s to the previous step. (This process required the contours of the study
area )
Relation between Intersection of
rock layers and Topography

20. The V formed by the contours of the terrain (black lines) and the v formed by the layers of the
rock (red lines) are open in the opposite direction, indicating rocks in that area dip in the
direction of the slope at a greater angle (red arrows show the dip direction of the rocks)

21. 7. Identify Strike and dip angle
 By definition, the strike of 1 rock layer is the line that joins 2 points of the
same height on the same Surface of 1 rock layer. This angle is given in
azimuthal notation refering with the north.
 Dip angle of a rock is the angle between horizontal and the slope of the
rock. This has to be measured perpendicular to the strike line.
https://s3.amazonaws.com/gs-waymarking-images/0043483f-
e9a9-4c09-8df3-3f3281c570fd.jpg
https://fractalplanet.files.wordpress.com/2014/03/strikedip3.jpg

22. Purple lines joint 2 points of the
same height, on the same rock
layer (strike).
Dip angle can be calculated as
follows:
Dip angle = tan-1 (delta h / delta x)
Delta y= differnce of height
between 2 strike lines (contours
difference = 50 meters)
Delta x= horizontal distance
between the 2 strike lines

23. Strike lines (purple)
found in all the
study area

24. 8. Create slope map and slope contacts
Slope map is a very useful tool in the geological
mapping process due to topography changes are the
result of changes in rocks units, folds and faults. One
big approach in geology classification was obtained
with this map and its interpretation

25. High reolution satelite image (15m) and its corresponding slope map. Reddish colors represent the highest slopes whilst Greenish
colors represent the smallests ones.

26. Slope map of the area.
Reddish colors represent the
highest slopes whilst
Greenish colors represent
the smallests ones.
Blue lines are inflicted limits
of slopes values as a result
of changes in geological
units

27. 10. Define packages of geological
units (adjust contact among units)
The final delimitation of geological units in the study
area was made overlaping slope contacts map with
the high resolution satelital image. The continuity of
rocks in the image generated a better stroke of each
rock package and its relation with the topography
(rule of V´s).

28. Blue lines: inflicted limits of slopes values. Red lines: Inflicted limits of geological units,
modified from slope lines.

29. 11. Identify general geological structures
(folds and faults) and units order
 General geological structures were identified joining all recollected data in
previous steps (strike, dip, dip direction, hardenss of rock units, drainage
patron), giving as a result 1 regional syncline structure with its associated
anticline. Furthermore, 3 big thrust faults was found affecting and moving
the 2 main folds.
 Stratigraphic sequence was identified from geological structures. (Anticline
has the oldest rocks in the center of the fold while syncline has the youngest
ones in the center of the fold).

30. Units order in Anticline and
syncline folds. 1 is the oldest
rock while 8 is the newest one).
http://www.physci.mc.maricopa.edu/Geology/Leighty/Online%20Classes
/GLG103online/GLG103_Lab09_StructuralGeology/GLG103online_Lab09_
AnticlineSyncline01_640x433.jpg
Structural and geological map of the area. Red lines
represent contacts among rock units and black lines
represent geological structures (folds and faults)

31. 13. Generate the final geological map
(Layout)
 At the end, the following map features were create in Arcgis in order to generate the
final output in PDF format:
• Title
• Legend
• Measured and graticule gird
• Regional location
• Graphic Scale
• Reference system
• Author
• Source of information

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510000
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410000
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440000
450000
450000
74°40'W
74°40'W
74°50'W
74°50'W
4°0'N 4°0'N
3°50'N 3°50'N
Geological map, Prado Synclinel
±
0 5 102.5
Km
65°0'0"W
65°0'0"W
70°0'0"W
70°0'0"W
75°0'0"W
75°0'0"W
80°0'0"W
80°0'0"W
10°0'0"N 10°0'0"N
5°0'0"N 5°0'0"N
0°0'0" 0°0'0"
Structural_geology
Type_of _structure
F Anticlinal
M Synclinal
(( Reverse Fault
(( Thrust fault
o Structural_Data
Geological_contacts
Main_rivers
Prado dam
Town
Contour_lines
Geological_units
Unit
A
B
C
D
E
F
G
H
I
J
K
L
Coordinate System: WGS 1984 UTM zone 18N
Projection: Transverse Mercator
Datum: WGS 1984
false easting: 500,000.0000
false northing: 0.0000
central meridian: -75.0000
scale factor: 0.9996
latitude of origin: 0.0000
Units: Meter
Author: Diego Bedoya Gonzalez
Drawn from: Landsat 8 and ASTER Global DEM (GDEM),
"ASTER GDEM is a product of METI and NASA."
0 500 1,000250
Km
±

33. Thank you very much for your attention.
Vielen dank für ihre Aufmerksamkeit.