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Geoscience Data Repository
Glossary
Magnetism
- Aeromagnetic data
- Measured variations in the Earth's magnetic field, collected from an airplane, typically flown at low altitude (300 m or less). Aeromagnetic surveys usually consists of a large number of parallel flight lines to provide continues data coverage.
- Geomagnetism
- The study of the Earth's magnetic field
- Inclination
- The angle that the Earth's magnetic field vector makes with the surface of the Earth
- Magnetic anomalies
- Small deviations in the observed magnetic field strength relative to values predicted by a global or national reference model
- Magnetic declination
- Angle between the magnetic north and true geographic north
- Remanence
- Property of, particularly volcanic, rocks to be permanently magnetized in the direction of the Earth's magnetic field that existed at the time that the rock cooled below a certain temperature, which we call the Curie temperature (~-400-500 o). The direction of magnetization of these rocks does not change when they are transported to another location on earth.
- Susceptibility
- Property of certain rocks to be magnetized in a direction parallel to the magnetic field they are in. The direction of magnetization of these rocks changes if they are moved to another location on earth
- Units
-
- nT
- Unit of magnetic field strength (nano Tesla)
Gravity
- Bouguer gravity anomalies
- Variations in the Earth's gravitational acceleration, corrected for the height above sealevel, of the observation and for the total mass of rock between the observation point and sea level
- Density
- Physical rock property defined as total mass divided by volume (kg/m3 )
- Free-air gravity anomaly
- Deviation of the observed gravity field at sealevel from the value predicted by a global model
- Gravimeter
- High precision instrument to measure minute variations in the Earth's gravitational attraction that exist as a result of density variations in the underlying rock formations
- Gravity anomalies
- Deviations from the predicted gravity field
- Isostasy
- Process of vertical adjustments of anomalous mass to balance the upward floating and the gravitational downward force. A good example is an iceberg, floating in water.
- Newton's law of gravity
- Two masses attract each other with a force that is proportional to both masses and inversely proportional to the squared distance between them. This force is called the gravitational attraction.
- Units
-
- mGal
- Unit of gravitational acceleration, equivalent to 0.00001 m/s2
Radioactivity
- AGRS
- Airborne Gamma-Ray Spectrometry
- NaI
- Each of the 14 NaI detectors used in the GSC's Airborne Gamma-Ray Spectrometry system is a single cylindrical crystal of Sodium Iodide (NaI), having a volume of approximately 3.5 L.
- K
- potassium, i.e. K40 (units: %)
- eU
- equivalent uranium concentration by weight (the spectrometer directly measures Bi214, that is an indirect measure of uranium) (units: ppm)
- eTh
- equivalent thorium concentration by weight (the spectrometer directly measures Tl208, that is an indirect measure of thorium) (units: ppm)
- Total Count
- all counts from 400 to 3000 keV (units: cps or uR/h)
- Natural Exposure
- computed from K (%), eU (ppm), eTh (ppm) concentrations:
Exposure = 1.505 K + 0.625 eU + 0.31 eTh (uR/h)
'Exposure' is different from the traditional 'Total Count', in that it excludes radiation from man-made contaminants. - Natural Air Absorbed Dose Rate
- computed from K (%), eU (ppm), eTh (ppm) concentrations:
Absorbed Dose Rate = 13.08 K + 5.43 eU + 2.69 eTh (nGy/h) 'Natural Air Absorbed Dose Rate' is different from the traditional 'Total Count', in that it excludes radiation from man-made contaminants. - eU/eTh, eU/K, eTh/K
- ratios of K, eU, eTh that are useful for interpretation
- Units
-
- ppm
- unit of concentration by weight (part per million), used for eU (uranium) and eTh (thorium)
- %
- for potassium (K40): unit of concentration by weight
for VLF: unit of signal strength - Ur
- unit of radioelement concentration by weight
(1 Ur is defined as the total count rate from 1 ppm uranium in equilibrium) - µR/h
- unit of Exposure (micro Roentgen/hour)
- nGy/h
- unit of Natural Air Absorbed Dose Rate (nano Gray/hour)
