This sequence of screenshots shows a situation encountered in one case using AIS data where it transpired that the shipboard GPS receiver appeared to be affected by reflections of the GPS signals from parts of the ship’s structure.

Picture 1 – this was how the anomaly appeared when the GPS positional data from the AIS dataset was plotted.

 

 

 

Picture 2 – the source data file was examined in detail and, having decided that the problem appeared to be related to the latitude data, all latitude values for the time when the anomaly was present were plotted against their corresponding time stamp. It can be seen that there were two latitude values for each time stamp.

 

 

 

Picture 3 – the erroneous latitude data was identified and removed to leave the true values.

 

 

Picture 4 – when the animation was re-run, the anomalous data had disappeared.