Arch GeoPhysics Flashcards
What is Geophysics:
The earth science concerned with the physical process and physical properties of the earth and its surrounding space environment, and the use of technology and quantitative methods.
True or False. GeoPhysical Surveyors typically find out the results of the ground truthing of their surveyor.
False
True or false. Most geophysical surveyors are archaeologists
F
What are some reasons Arch GeoPhys is NOT used in CRM
- Costs too much
- Doesn’t work i.e. unrealistic expectations, poor surveyor, wrong survey method
- Anomalies present but unsure where to dig
- It’ll replace traditional archaeology
Where did many of misconceptions surrounding GeoPhysical study in Archaeology come from?
In the 1980s when the discipline was first gaining traction in the archeological industry it was over sold as a miracle method.
Why should it be used
- Guides and targets future archaeological survey
- Non-Invasive/ Non-Destructive
- Allows for site management
- Increased spatial extent of subsurface knowledge without excavation
- Less cost; if part of research plan
What GeoPhysical technique was introduced in the 40s?
Resistivity
What GeoPhysical technique was introduced in the 50s?
Magnetic testing strategies
What GeoPhysical technique was introduced in the 80s?
high res seismic, ground and space radar, infrared imagery and self potential methods
What have been the primary advances in Geophysical Techniques since the 80s?
Software improvements, imagining, display and GPR
When preforming testing what should your line spacing be?
Depends on what you want to find, but .25 m is typically best
What is the magic number when identifying a pattern?
3
Why is know what your are looking for important in a geophysical test?
Historics show up easer with large, regular anomalies whereas precontract data will be more challenging to tease out. Knowing what you are looking for tells you what sort of anomalies to look for in the data.
How does GPR work?
- Detects abrupt changes in materials below the ground.
- Two antenna one transmits reflects off of subsurface variations (boundaries between contrasting materials)
- One line collects Y and Z data but taking consecutive parallel transects creates 3D data that can be spliced together with programs like RADAN.
What is an anomaly?
A different reflective value compared to the rest of the soils
When reviewing GeoPhysical data, what is important to remember about anomalies?
NOT ALL ANOMALIES ARE ARCHAEOLOGICAL
How does a magnetometer/gradiometer work?
-When natural sediment patterns are disturbed which in turn interrupts the natural magnetic pattern in the soil
Why would you use/ not use a magnetometer/gradiometer?
- For finding magnetic artifacts
- Data lacks vertical expression
- can be used in variable environments
How does resistivity/ conductivity work?
- Disruption of natural sediments also disturbs grain size patterns
- Causes a variation in electric conductivity
Why is gridded regular testing in one direction best for geophysical surveys?
Data is easy to read and translate to the field environment for ground truthing.
– “zigzag” muddles the data, may distort anomalies
Why use more than one geophysical system?
The data from the utilized systems confirm presence of anomalies, will help rule out false positives, and one system might find data another missed.
Why ground truth?
- -Geophysical anomalies are typically something
- -Not all archaeological features result in geophysical anomalies
- -Geophysics cannot conclusively –ID the true source of anomaly
- -Excavation of anomalies must follow geophysical survey to determine the true source of anomalies in the data
Data Dictionary
Creating a list of features and their associated attributes to be collected in the field.
Why use a data dictionary
Using preset attribute descriptions forces users to standardize the way data is collected and attributed
Archaeological Geophysics
Technologies and methods of geophysics applied to archaeological sites in order to answer archaeological questions
Why are geophysical surveys that are conducted “in house” at CRM firms more successful?
More likely the archaeologists are in collaboration with GEOPHYS testers and/or the tester are archaeologist/have training.
What qualities are ideal for potential geophys survey sites?
- Large areas
- You want a non-destructive methods
- when its likely a historic site
- when you ID arch features in Phase I /II
- when you have potential features that are too deep to access with traditional excavation.
Is the landscape appropriate? Dramatic Slope
No
Is the landscape appropriate? Very saturated soils
No
Is the landscape appropriate? Farm field
Yes
Is the landscape appropriate? Clearing with some trees
Yes but the trees will need mapping in
Is the landscape appropriate? Parking lot/ Urban development
Yes
Is the landscape appropriate? Dense forest
No
Is the landscape appropriate? Trash and undergrowth
No, but maybe if it were cleaned up
What soils are the most idea for accurate sensing?
Sandy loam, urban
What is the “staged approach” to ground truthing?
- Review the results
- probe the anomoly soils to see if they are different
- STP or unit to
- Strip landscape
When collecting GPR what signals are recorded? Which one records arch anomalies?
- Air wave
- Ground Wave
- Critically refracted Wave
- Refracted Wave
- Reflected wave
dielectric constant
the ability of a substance to store electrical energy in an electric field
Attenuation
gradual loss in intensity of the
electromagnetic wave through a medium (soil and sediment)
common-offset profiling
vary the distances of the two antenna from a fixed mid-point to
obtain multi-fold common mid-point (CMP) coverage
How do you deal with topography when running GPR?
You either need to digitally correct for topography
or take topography into consideration when conducting the interpretations.
