1. Remote Sensing for Geologic Mapping and Analysis
Using spatial and spectral information to characterize geologic features

2. Textbook for geologists (2002)
Can study remote sensing from a geologic perspective in a UW Geology Dept. course

4. Brandberg Massif, Namibia
Granitic intrusion in desert

5. Geologic map of the Sheep Mt. Anticline, Wyoming, based on air photos.
From Banjeree and Mitra AAPG Bulletin 88(9):

6. Learning Objectives
What are the primary applications of remote sensing for geologists?
Be able to define lithology, structure, and landform, and recognize common examples in air photos.
How do drainage patterns help us interpret geology?
Why are spectral data especially important to geologists?
How can aerial photography contribute to soil mapping?
What do we mean by 1st through 5th order soil maps?
What are absorption features, and why are they important?
What is gossan?
How can we use spectral features to find hydrocarbons?

7. Application of images to…
Lithology
Structure
Landforms
Drainage
Soils
What do each of these mean??
Lithology—rock types. Structure—folding, faulting, deformation. Landforms—terrain features formed by natural processes that appear similar wherever found (erosional or depositional). Drainage patterns—aggregate of flow channels whether or not with water in them. Soils—soil types expressed on the surface.

8. Devil’s Tower – Lithology? Structure? Surrounding rock??
(Air Photo Courtesy Louis Maher, Jr.)

9. Types of Lithology
Igneous
Sedimentary
Metamorphic
What are each of these, and what are some examples??
Igneous: rock formed directly from molten mass: intrusive (granite) or extrusive (basalt) are common examples.
Sedimentary: sediment deposited and lithified (turned to rock) after being transported by water, wind and/or gravity: sandstone, siltstone, shale, limestone are common examples
Metamorphic: formed by action of heat or pressure on previously existing rock: gneiss, schist, slate, and quartzite are common examples

10. What kind of rock is this? What clues are you using?
Igneous Rocks (basalt flows) at Craters of the Moon, ID
(Air Photo Courtesy Louis Maher, Jr.)

11. Sedimentary Rocks (badlands) in South Dakota
What kind of rock?
Sedimentary Rocks (badlands) in South Dakota
(Air Photo Courtesy Louis Maher, Jr.)

12. What’s the scale of this photo?
What kind of rock?
What’s the scale of this photo?
Metamorphic Rock from Grand Canyon (not an air photo!)
(Courtesy American Geological Institute)

13. Mapping lithology using imagery.
Interpretation requires knowledge of relationships between the lithology and:
Climate
Topography
Drainage pattern
Jointing and faulting
Texture
Vegetation
Spectral properties of minerals that comprise rock types
Photointerpretation clues: tone, size, context, shape, etc.
Interpreters should be trained to understand these relationships on images and in the field

14. Climate Affects the way rocks weather.
Affects the associations of vegetation with particular rock types
Affects soil formation from rock parent material
Affects erosional patterns
All of these influence the appearance of different rocks in images.

15. Drainage patterns Drainage patterns are easy to see on images
Offer clues to many geologic characteristics of an area (e.g., topography, bedrock, surface texture and hardness, jointing, etc.)
Obvious importance for hydrologic mapping, modeling, and management
Often influence human land use

16. Drainage patterns
A. Dendritic
B. Parallel
Dendritic: horizontal sediment or uniformly (homogeneous) resistant bedrock; gentle slope
Parallel: moderate to steep slopes fine textured deposits or fractured bedrock or in areas of parallel elongate landforms
Trellis: dipping or folded bedrock
Rectangular: jointed or faulted bedrock
Radial: volcanoes, domes, basins
Annular: domes or basins
Multibasinal - flat-lying glacial terrain; karst (limestone) terrain
Contorted: metamorphic rocks
disc.gsfc.nasa.gov/.../ geo_images_4/Fig4.1.gif Originally from Howard, 1967

17. What kind of drainage is this?
What causes it?
Rectangular drainage on Volga River (caused by faulting)
(Satellite image)

18. Dendritic drainage pattern
Type of drainage?
Dendritic drainage pattern
(Photo courtesy Michael Collier)

19. Igneous rocks on air photos: Basalt flow example
Topography: flat to hilly
Drainage: parallel or internal
Photo tone: dark or sometimes spotted
Gully type: none (not erosive)
Igneous Rocks (basalt flows) at Craters of the Moon, ID
(Air Photo Courtesy Louis Maher, Jr.)

20. Sedimentary rocks on air photos: Example – sandstone in arid climate
Topography: flat or table like (mesas, etc.) but can be highly eroded
Drainage: dendritic
Photo tone: light and banded (can vary considerably)
Gully type: none to deep depending on steepness
Where is this? Can you name these features?
Sedimentary rocks (sandstone) at Castle Valley, UT
(Air Photo Courtesy Louis Maher, Jr.)

21. Geologic Structure
Geologic structures are any features caused by deformation of rock (folding, faulting, etc.)
Structure is important for trapping hydrocarbons, controlling water flow, understanding stratigraphy, etc.
Includes:
Strike and dip
Folds (e.g., anticlines, synclines, domes, basins, etc.)
Faults (e.g., normal, reverse, horst and graben, etc.)
Joints
Unconformities

24. Can you name this Wyoming feature?
Sheep Mountain anticline in Bighorn Basin of Wyoming
(Air Photo Courtesy Louis Maher, Jr.)

25. What are the linear features?
Type of rock?
What are the linear features?
Sandstone jointing in Arches National Park
(Air Photo Courtesy Louis Maher, Jr.)

26. Mapping and analyzing geologic structure with images
Interpreter looks for changes in tone and texture that represent boundaries between geologic units
Works best where vegetation cover is minimal
But…can sometimes see changes in underlying strata related to changes in overlying vegetation
Can sometimes enhance edges with digital filters
Can use stereo techniques to measure elevation changes for calculating dip angles

27. Geologic map of Wyoming’s Casper Arch
(Image Courtesy NASA.)

28. Landsat 8 image

29. Landforms and Geomorphology
Definition of landforms varies with discipline
Geologist may have different view than soil scientist or hydrologist
Creating a landform key is important aspect of image interpretation
Landforms are strongly influenced by underlying geology and climate

30. Broad categories of landforms
Coastal and oceanic (e.g., fjord, ismuth, beach, etc.)
Erosional landforms (e.g., canyon, cuesta, gully, etc.)
Fluvial (river related) landforms (e.g., braided channel)
Mountain and glacial landforms (e.g., cirque, peak, etc.)
Slope landforms (e.g., terrace, cuesta, plain)
Volcanic landforms (e.g., cinder cone, lava flow)
Depositional landforms (e.g., alluvial fans)
Etc. (there are many ways to think about landforms)

31. Glacial moraine near Pinedale, Wyoming What kind of landform? Where?
(Air Photo Courtesy Louis Maher, Jr.)
What kind of landform? Where?

32. Great Sand Dunes, Colorado
(Air Photo Courtesy Louis Maher, Jr.)

33. Mapping and analyzing landforms with high spatial resolution images
Identifying landforms on images requires using many clues
Topography
Drainage pattern
Drainage texture
Photo tone and texture
Vegetation patterns
Land use patterns
Scale of landform determines scale of imagery necessary to map. Landforms occur across scales.

34. Soils Soils can be mapped at a wide range of scales and precision
1st order surveys are most detailed and 5th order are least
Lower (1st, etc.) order surveys require detail found in air photos
Almost all soil mapping requires a combination of field survey and remote sensing
Typical project uses manually interpreted aerial photography followed by field work to label the interpreted units

35. Examples of soil map order
Small plot level 1st order 1:8,000 scale Detailed soil map 2nd order 1:20,000 scale Soil association map 4th order 1:250,000 scale Statewide soil map 5th order 1:1,000,000 scale

36. Soil survey on air photo
(From Wikipedia)

37. Spectral applications
Minerals have distinct reflectance signatures with spectrally narrow features
Lithologic mapping depends largely on discrimination of minerals
Broad-scale structural mapping can also benefit from satellite RS
Mineral and petroleum exploration is more efficient with imagery

38. Spectral Absorption Features

39. Spectral matching: Software looks for best match of unknown spectra (from image) to known spectra (from libraries)
Is this a good match??

40. Or image classification…
Choose appropriate bands for the minerals of interest
Use image classification to group image pixels into classes based on those bands
Combine or split classes as needed to make a map of mineralogy/lithology.
Iron oxide on moon.
Map NOT based on fieldwork!

41. Mineral and petroleum exploration
Spectral data allow geologists to narrow search areas and eliminate unproductive ground work
Can map large structures, diagnostic mineralogy and lithology, and outcrop locations quickly
Mineral clues can point to areas associated with gold, silver, copper, and other metal-bearing minerals
Petroleum is usually more deeply buried and requires structural analysis, but often there are surface clues

42. Case Study: SW Utah ore prospecting
Oxidized iron ore called “gossan” by prospectors can indicate mineralization associated with valuable minerals
Gossan has a distinctive look (left). Often gossan occurs with other minerals like copper (below) or gold
(Modified from the NASA RS Tutorial)

43. Landsat-based prospecting in Utah
Part of a Landsat image covering SW Utah (near Zion NP)
White Mountain
Classic gossan staining
Basin deposits
Wah Wah Mts. (block fault)
Prospectors look for telltale gossan and enhance imagery to make it stand out

44. Band ratios – enhancement of spectral features
This image shows the ratio of two spectral bands to highlight gossan, which appears as yellow/brown area
Ratio of TM bands 7/5 (Mid-IR bands) is often good for enhancing mineralogy

45. Advantage of spectral prospecting for gossan
Landsat imagery free
Spectral information in Landsat sufficient to create believable map of gossan
Significantly narrows the search area to constrain ground-based prospecting
Potentially increases profitability

46. Other examples: Copper prospecting in Nevada with ASTER imagery

47. Hyperspectral mapping of a mining district in Utah

48. Case study 2: Petroleum prospecting
Petroleum requires source of hydrocarbons and a trapping formation
(Modified from the NASA RS Tutorial)

49. Contribution of multispectral satellite imagery?
Focus is on identifying trapping structures
Satellite imagery allows rapid survey of large areas at low cost
Lithology mapping allows identification of key formations
Mapping of fracture patterns useful for understanding traps – fractures let hydrocarbons migrate through rock
Satellite surveys must be followed up by surface exploration and usually drilling to understand buried structures

50. Landsat MSS image with “hazy” tones linked to know hydrocarbons
Anadarko Basin in Oklahoma
Source

51. Ratio image (composite of three band ratios) of area A from previous slide. Oil-bearing formation looks reddish.
Turns out that hydro-carbons leaking through surface rocks were altering them spectrally
Rocks associated with key formations are spectrally different
Source

52. Similar leak of hydrocarbon gas in Wind River Basin, Wyoming caused the alteration of rocks in tan oval area in center of this image.

53. Vegetation effects
Geologists and remote sensing scientists in Michigan have found stressed vegetation in vicinity of hydrocarbon gas leaks
Shows up in the “red edge” of the vegetation spectral curve
Even without leaks, vegetation can be associated with particular formations or it can follow structural features and fractures

54. Summary
High spatial or spectral resolution imagery is widely used for various aspects of geology
Choice of images depends on scale, spectral requirements, etc.
Image interpretation for geology usually requires a coupled field component
Interpreters must have comprehensive knowledge of a broad set of indicators that give clues to underlying geology