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Fliers are anomalous soundings that misrepresent depths. Their detection is based off on the threshold depth values that consider average depth recordings from adjacent data. In QAX, values that exceed the threshold are flagged as suspicious and require the operator to inspect their legitimacy.  


  1. Use QAX QA/QC tool to scan for fliers. Apply appropriate threshold values of the Laplacian and Gaussian operators that determine anomaly locations (see QAX SOP). In QAX, these are output as a series of raster files that can be imported to an active CARIS any geospatial applications project for overlay and confirmation.  Re-iterate scans after cleaning until fliers are satisfactorily eliminated 

  Pass Requirements  

  1. Fliers identified in the QAX scan have been identified and cleaned.  

  2. A scan of the data using QAX parameters as advised/calibrated by the operator results in a ‘Pass’ for flier identification. 





Test results   

  • Iteration 1 – fliers identified are cleaned 

  • Iteration 2 (maintain parameters) - fliers identified are cleaned 

  • Iteration 3 (maintain parameters) - fliers identified are cleaned 

  • Iteration 3 (maintain parameters) – flier check passes after four iterations (Figure 1) 




    This dataset is now considered free of fliers.