Podcast
Questions and Answers
What is the primary purpose of a Brunton compass?
What is the primary purpose of a Brunton compass?
- To calculate the rotation of the Earth
- To obtain clinometer readings and measure azimuth angles (correct)
- To measure ground distances accurately
- To determine magnetic declination
What does a Brunton compass provide a resolution of in terms of vertical angles?
What does a Brunton compass provide a resolution of in terms of vertical angles?
- 15 arcminutes
- 30 arcminutes (correct)
- 45 arcminutes
- 1 degree
What does magnetic declination represent?
What does magnetic declination represent?
- The deviation of the Earth's axis from its original position
- The difference between true north and magnetic north (correct)
- The rotation angle of the Earth
- The angle between the Brunton compass needle and the true north
In what year did D.W. Brunton receive a patent for his compass design?
In what year did D.W. Brunton receive a patent for his compass design?
Which feature of the Brunton compass makes it convenient for field geologists?
Which feature of the Brunton compass makes it convenient for field geologists?
What aspect of measurements is a Brunton compass accurate to within azimuth?
What aspect of measurements is a Brunton compass accurate to within azimuth?
What is the back bearing when the compass bearing to a destination is 90 degrees?
What is the back bearing when the compass bearing to a destination is 90 degrees?
If the azimuth notation mentions N25oE, what would be the equivalent in quadrant notation?
If the azimuth notation mentions N25oE, what would be the equivalent in quadrant notation?
When measuring a ground distance, what is the importance of distinguishing between horizontal distance and slope distance?
When measuring a ground distance, what is the importance of distinguishing between horizontal distance and slope distance?
What is the azimuth notation for a compass bearing of 300 degrees?
What is the azimuth notation for a compass bearing of 300 degrees?
In map notation, what does the term 'strike' refer to?
In map notation, what does the term 'strike' refer to?
If a dip is measured as 45 degrees SE, in which quadrant does this angle fall?
If a dip is measured as 45 degrees SE, in which quadrant does this angle fall?
How can you calculate the height of an object using a clinometer?
How can you calculate the height of an object using a clinometer?
What is the purpose of a Brunton compass in geology?
What is the purpose of a Brunton compass in geology?
What is the correct formula to calculate height from a distance and angle?
What is the correct formula to calculate height from a distance and angle?
In azimuth bearing, which direction does 0° refer to?
In azimuth bearing, which direction does 0° refer to?
What is the key function of an orienteering compass used by geologists?
What is the key function of an orienteering compass used by geologists?
When measuring vertical angles with a clinometer, what should be done to ensure accurate readings?
When measuring vertical angles with a clinometer, what should be done to ensure accurate readings?
Study Notes
Brunton Compass
- The Brunton compass was designed by Colorado mining engineer D.W. Brunton in 1894 and became widely used throughout the world.
- It combines the principles of a surveyor's compass, prismatic compass, clinometer, hand level, and plumb.
- It is accurate to 1/2 degree (30 minutes) in azimuth and has a 10 arcminute resolution for vertical angles.
Parts of a Brunton Compass
- Short sight with peephole
- Compass box with vertical line
- Long sighting arm
- Magnetic declination adjustment screw
- Parts of a compass face front peephole
Magnetic Declination
- Magnetic declination is the difference between true north and magnetic north.
- Example: a bearing of 42° would be northeast and a bearing of 200° would be southwest.
Back-Bearing or Back-Azimuth
- A back-bearing or back-azimuth is a projection of the azimuth or bearing from the origin to the opposite side of the azimuth circle.
- To calculate the back bearing, add 180 degrees to the compass bearing to your destination if the bearing is less than 180 degrees.
Measuring Ground Distances
- Horizontal distance vs. slope distance
Map Directions
- Azimuth notation: 0°
- Quadrant notation: N72°E
- Example: N40°W
- 180°
- Azimuth notation: 072°
- Quadrant notation: N40°W
Map Notation of Planar Structures
- Strike: 040°
- Dip: 30° SE or 120° 30°
Navigation
- Navigation involves the determination of position and direction.
Clinometer Scale
- A clinometer is an instrument used to measure an angle of inclination or elevation.
- The clinometer of the compass gives the capability of measuring vertical angles both below and above your line of sight.
- Formula: Height = x tan q, where "x" is equal to the distance and "q" is the angle in relation to the ground and the top of the object.
Getting the Inclination Angle
- Using the compass clinometer, inclination values can be positive (+) or negative (-) relative to horizontal.
Orienting Compass
- Another field compass used by geologists is called an orienteering compass.
Bearing
- A bearing is a measurement of direction between two points, measured in degrees, from the reference line of North.
- Bearings are generally given in one of two formats, an azimuth bearing or a quadrant bearing.
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Description
Test your knowledge on Earth's magnetic field generation and the use of a clinometer in measuring vertical angles. Learn about convection in the outer core and how it leads to the creation of a magnetic field, as well as the practical application of a clinometer in surveying.
