Remote Sensing, Rocks and Soils
Prospecting and Exploration
• What we’re looking for is subtle
• Most rocks, even the most favorable, do
not have extractable resources
• 1% of mineral occurrences are worth
detailed study
• 1% of those are worth drilling
• 1% of those are worth mining
Geologic
Map of
Wisconsin
Gravity
Map of
Wisconsin
Gravity
Mean value about 9.8 m/sec2 = 1 g
About 0.5% smaller at equator than poles
Map unit = gal (for Galileo) = 1 cm/sec2
Mean gravity = 980 gal
Maps contour in mgal = 10-6 g
Modern gravimeters can detect .001 mgal
variations (= 1 ppb)
• A gravimeter is essentially a spring balance.
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Gravimeter
Gravity Maps
• Gravity varies by latitude due to earth’s
equatorial bulge and centrifugal force
• Need altitude correction = 0.3 mgal/m = 3 x 10-7
g/m
• Altitude only correction = Free-Air Anomaly Map
• Correct for mass between you and sea level =
Bouguer Anomaly Map
• Correct for variations in thickness of crust =
Isostatic Anomaly Map
Colorado Bouguer Map
Colorado Isostatic Map
Chicxulub
Impact Basin
Gravity Map
Gravity Mapping
• Simple corrections for
latitude and altitude
• Density = Lithology
• Can sense deep into
crust
• Gravimeters are
basically sensitive
spring balances
• Fragile
• Prone to drift
• Discrete data points
• Labor intensive, low
detail
Magnetic
Map of
Wisconsin
Geomagnetism
• Magnetic field of Earth = 40 microtesla =
40,000 nt
• Varies from 25 to 70 mt
• Non-axial
• Not centered on the earth
• Varies over a human lifetime
Overall Magnetic Field of Earth
MAGSAT Map of Earth
Magnetic Mapping
• Corrections are
complex and time
variable
• No simple correlation
with lithology
• Can’t sense deep into
crust because heat
destroys magnetism
• Magnetism is
electromagnetic
phenomenon
• Instruments can be
purely electronic
• Can record
continuously
• Can be extremely
detailed
Gravity and Magnetic Mapping
• Greater sensing depth
• Complex corrections
• Greater detail possible
Gravity and Magnetic Mapping
Gravity maps
Magnetic Maps
Mechanical Instrument
Instruments are purely electronic
Discrete readings
Continuous readings
Less detail
Great detail
Can sense to great depths
Can sense only a few kilometers
deep
Simple corrections for latitude and
elevation
Complex corrections in time and
space
Density correlates with rock type
No simple correlation with rock
type
Satellite
Image of
Wisconsin
Grand
Canyon
Lake
Vostok,
Antarctica
Copper
Mines, Iran
Saline Valley,
California
The Moon
Mercury
Mars
False
Color
View
Remote
and Not
So Remote
Sensing
Telling Minerals Apart
Martian Minerals?
Absorption
Bands
Radar
Interferometry:
L’Aquila, Italy,
2009
Haiti,
2010
Haiti, 2010
Damage, Port au prince
Chile, 2010
Chile 2010
Chile, 2010, GPS
Ice Flow, Antarctica
Kilauea,
Hawaii
Venus
Topography of Venus
Radar
Map of
Venus
Radar
Map of
Venus
Venus Gravity Maps
Gravity Map of Mars
Titan
Radar Image, Titan
Lakes on
Titan
Sun Glint
Laser Rangefinder
Laser Reflector
LAGEOS
Herstmonceaux
Castle (London)
• Latitude increasing
(moving N)
• Longitude increasing
(Moving E)
Lamont Earth
Observatory
(Near New York)
• Latitude increasing
(moving N)
• Longitude decreasing
(Moving W)
Trans-Atlantic Plate Motion
• New York moving west at 15.4 mm/yr
• London moving east at 16.6 mm/yr
• Relative motion = 32 mm/yr
Churchill,
Manitoba
• Latitude decreasing
(moving S)
• Longitude decreasing
(Moving W)
• Rising rapidly
Real-Time Plate Motions
Sturgeon Bay,
Wisconsin