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.

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 MappingGravity 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

SatelliteImage 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