Transcript Aerial Photography for Geologic Mapping and Analysis

Using spatial and spectral information to characterize geologic features
Textbook for geologists (2002)
Can study remote sensing from a
geologic perspective in a UW
Geology Dept. course
Brandberg Massif,
Namibia
Granitic intrusion in
desert
Geologic map of the
Sheep Mt. Anticline,
Wyoming, based on
air photos.
From Banjeree and Mitra.
2004. AAPG Bulletin
88(9):1227-1237.
 What are the primary applications of remote sensing for
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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?
 Lithology
 Structure
 Landforms
 Drainage
 Soils
What do each of these mean??
Devil’s Tower – Lithology?
Structure? Surrounding rock??
(Air Photo Courtesy Louis Maher, Jr.)
Types of Lithology
• Igneous
• Sedimentary
• Metamorphic
What are each of these, and what are some
examples??
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.)
What kind of rock?
Sedimentary Rocks (badlands) in
South Dakota
(Air Photo Courtesy Louis Maher, Jr.)
What kind of rock?
What’s the scale of this photo?
Metamorphic Rock from Grand
Canyon (not an air photo!)
(Courtesy American Geological Institute)
 Interpretation requires knowledge of relationships
between the lithology and:
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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
 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.
 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
A. Dendritic
Drainage patterns
• 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
B. Parallel
What kind of drainage is
this?
What causes it?
Rectangular drainage on Volga
River (caused by faulting)
(Satellite image)
Type of drainage?
Dendritic drainage pattern
(Photo courtesy Michael Collier)
 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.)
 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.)
 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:
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Strike and dip
Folds (e.g., anticlines, synclines, domes, basins, etc.)
Faults (e.g., normal, reverse, horst and graben, etc.)
Joints
Unconformities
Can you name this Wyoming
feature?
Sheep Mountain anticline in
Bighorn Basin of Wyoming
(Air Photo Courtesy Louis Maher, Jr.)
Type of rock?
What are the linear
features?
Sandstone jointing in Arches
National Park
(Air Photo Courtesy Louis Maher, Jr.)
 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
Geologic map of Wyoming’s
Casper Arch
(Image Courtesy NASA.)
Landsat 8 image
 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
 Coastal and oceanic (e.g., fjord, ismuth, beach, etc.)
 Erosional landforms (e.g., canyon, cuesta, gully, etc.)
 Fluvial (river related) landforms (e.g., braided
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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)
What kind of landform? Where?
Glacial moraine near Pinedale,
Wyoming
(Air Photo Courtesy Louis Maher, Jr.)
Great Sand Dunes, Colorado
(Air Photo Courtesy Louis Maher, Jr.)
 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.
 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
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
Soil survey on air photo
(From Wikipedia)
 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
Spectral Absorption Features
Spectral matching: Software looks for best match of unknown
spectra (from image) to known spectra (from libraries)
Is this a good match??
 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!
http://www.psrd.hawaii.edu/July0
4/newMineral.html
 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
 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)
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
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
 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
Hyperspectral mapping of a mining district in Utah
 Petroleum requires source of hydrocarbons and a
trapping formation
(Modified from the NASA RS
Tutorial)
 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
Landsat MSS image
with “hazy” tones linked
to know hydrocarbons
Anadarko Basin in
Oklahoma
Source
Ratio image (composite of
three band ratios) of area
A from previous slide.
Oil-bearing formation
looks reddish.
Turns out that hydrocarbons leaking through
surface rocks were altering
them spectrally
Rocks associated with key
formations are spectrally
different
Source
Similar leak of
hydrocarbon gas in
Wind River Basin,
Wyoming caused the
alteration of rocks in
tan oval area in
center of this image.
 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
 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