Part 4 : Types of Error – Systematic Errors

1. Systematic errors exist from instrument calibration, observational procedures and the data pre-processing for atmospheric and other effects.
   
2. Physical sources of systematic errors are
   
   1. Temperature,
      
   2. Humidity,
      
   3. Pressure changes.
      
3. All physical sources will affect :-
   
   1. angle measurement, distance measurement either by tapes or EDM
      
   2. will cause the bending of photogrammetry light rays due to atmospheric refraction,
      
   3. lack of adequate adjustment of equipment
      
4. Can be eliminated by :-
   
   1. Adjusting the instruments
      
   2. Using certain procedure during measurement, example: levelling survey collimation errors can be minimized by taking measurement at equal distance from the level.
      

Mikhail, (1974) said " systematic effect take on different forms depending on the value and sign of each of the effects. If the value and sign remain the same all through the measuring process, we would have the so-called constant error. An example of this is making distance measurement with a tape that is either too short (or too long) by a constant value. All length measured by that tape will undergo the same systematic effect due to the tape alone. If the sign of the systematic effect changes, perhaps due to personal bias of an observer, the resulting systematic errors are often called counteracting. For example, on a aerial photograph earth curvature and atmospheric refraction cause opposite displacement of image points. Thus the systematic effect due to the first counteracts that due to the second."

Mikhail, E. M. (1974). Observation and Least Square, A Dun-Donnelley Publisher, New York