SCINTREX ENVI-MAG - Introduction; Sampling Intervals; Survey Planning

A
pplications
ENVI-MAG Manual B2-1
Chapter
Planning
2
Survey planning
Introduction
There are very specific criteria that need to be considered when carrying out a
magnetometer or gradiometer survey for environmental applications:
▲ the estimated depth at which the targets are and their nature (buried drums,
steel pipes or sheet metal),
▲ the precision and accuracy required of the surveys,
▲ the orientation of the target, i.e. is it elongated? This needs to be considered for
objects having a linear surface expression, such as pipes and sheets of metal.
Sampling intervals
Objects disposed of and/or buried by man are usually not at great depths;
within the first ten metres of the surface. The anomalies created by such buried
drums, pipelines or sheets of metal can produce relatively intense and narrow
anomaly profiles. However, as mentioned in the previous chapter (page B1-7),
the deeper the target, the broader the anomaly will be. Further, the anomaly will
become less intense when the magnetized body is at greater depths. Larger
targets will have broader anomalies and more intensely magnetized bodies
will have larger amplitudes.
These relationships of body size, depth and magnetization all have a direct
consequence on the station and line spacing, i.e. the density of the survey grid.
For instance, if an anomalous peak is only 2 metres in width or length and data
points are taken only every five metres in a square grid pattern, there is a very
good chance that the peak will be missed altogether!