Data acquisition and reduction Flashcards
What does a station, a traverse and a grid/array mean?
A station is one place where measurements have been taken.
Multiple stations along a line form a traverse.
If traverses are close to each other they form a grid/an array.
What does the causative target mean?
The subsurface structure that is gonna be detected by the geophysical survey.
What does data reduction mean?
Converting data into a more useful form
What is an anomaly?
A part of a profile/contour map that is above or below the surrounding average. The presence of a target if often revealed by the anomaly - the target is often referred to as the anomalous body.
What is signal and noise?
The signal is the wanted part of the measurements while noise is the unwanted variations. Which is which depends on the purpose of the survey.
How can the signal-to-noise ratio be improved?
By repeating and averaging the measurements. The signal parts will add up - called stacking. The noise which is mostly random tends to cancel out
What is the inversion problem?
Finding the form of the causative body from the anomaly, for more than one body could produce the results. Related to non-uniqueness.
What is a model?
A structure defined by its physical properties that could account for the measured data. A simplified version of reality
Why is resolution a problem when modelling?
The resolution of the grid of stations is often not sufficient to reveal all details. There are theoretical and practical limits on resolution.
Configuration of grid of stations important, having too much spacing between stations impacts resolution for example.
What is inverse modelling (data inversion)?
Deduction of the form or properties of a target from measured data or anomaly.
Calculations of model responses are done and then
a comparison with the measured data.
Models are found by using various computer algorithms.
What is forward modelling (trial and errror method)?
The model is guessed and the model response calculated.
The model response is then compared with the measured data and the model is adjusted until they match each other sufficiently well.
An iterative method.
What is important when doing a geological interpretation?
It is done to translate the model into geological terms and therefore it’s important to consider all available information. For example geological context, outcrop information, boreholes, geophysical surveys
What is a contour plot?
A 2D plot that shows contours, for examply topography on maps. It is used to visualise spatial data
What is false illumination?
It is a method used to enhance contouring, shadows and colours for example.
What does time-lapse modelling mean?
It is 3D surveying repeated at different times to monitor for example oil extraction.
