Field notes

The facilities delivered on this page are derived from tools in an out-of-date version of the online introductory geophysics course at the Colorado School of Mines. The current version of that course is at http://galitzin.mines.edu/INTROGP/index.jsp.

Introduction

Because of the complexity of seismic surveying, extensive field notes, known as OB (Observer) sheets, are routinely recorded while conducting seismic investigations. The quality and accuracy of these field notes can vary greatly and can directly affect the interpretability of the survey because the interpreter and field crew may never see each other. If field notes are incorrect or incomplete, it may be impossible to process or interpret the observations, or the final interpretation may be biased.

Field notes

One of the field notes sheets from the survey is given below. In writing these field notes the following nomenclature has been used;

• Record Length - The total time duration after the initiation of the source that ground motion is recorded.
• Sample Rate - Ground motion is not recorded continuously. Rather, every so often, the ground motion that the seismometer senses is sampled by the recording instrument and stored onto tape. This process is called digitizing. Sample rate specifies the time interval, in milliseconds, at which measurements are made.
• Group Interval - In the context of this particular set of OB sheets, this number specifies the distance between geophones.
• Src Cnt - Simply an incremental counter of the number of sources initiated.
• Reel # - The tape number on which the data referred to is stored.
• First File - The Field File Identification Number by which the data stored on the tape is referred.
• Src Loc - The location of the source in station numbers.
• Comments - This simply contains comments about the particular recording. It may contain information on the source, information on noise, or other information the recorder felt was relevant.

Field notes are in four sections:
  - Recording Parameters,
  - Source Parameters,
  - Receiver Parameters, plus
  - a table listing the records kept and some comments about each record.
Note, a "record" is a set of seismograms from all geophones, generated using one shot or source. Please examine field notes , and answer the questions in the lab exercise instructions page.

Field notes page: To print this separately, right click the notes page image and
- if using Internet Explorer select "Print picture ..." or
- if using FireFox select "View Image" then print the page .