Dip test - QC2d-1 - Revision 01

The above cartoon is just to illustrate the order of t0,t1 and t2. Note in email exchanges the same time labels have been described as t-2, t-1 and t. (Please let me know if there is a specific convention that you prefer to be adopted and this page will be updated ….ed).

The flag fs=2 is detected on the observation A(t2), the previous value A(t1) is also flagged fs=2, and the next previous value A(t0) is flagged fs=1.

 If  
    | A(t2) - A(t0) | < | A(t1) - A(t0) | 
 and 
    | A(t2) - A(t1) | > DELTA

where DELTA is dependent on the parameter

    
   set fs=9 on A(t1) 
   set fs=4 on A(t2)

A(t1) receives a corrected value by interpolation. The interpolation method can be linear or by Akima algorithm.

Relevant parameters are all those subject to the step check (QC1-3a):

The report 24/93 KLIMA “Theoretical analysis of the dip-test in quality control of geophysical observations” by Petter Øgland describes a diptest run independent from a previous step test.

http://klima.dnmi.no/rapporter/Klimarapporter/1993/24_93.pdf

Comparison between Øgland's parameter δ and the current Kvalobs step criterium shows:

 δ(UU) = 30%  versus the Kvalobs step(UU) = 30%
 δ(FF) = 30 m/s versus the Kvalobs step(FF) = 10 or 12.5 m/s
 δ(TA) = 10.5 °C versus the Kvalobs step(TA) = 7,5 °C

For wind and temperature the Kvalobs dip test will flag more often than by Øgland's formula. For humidity will Øgland's formula gives error flags without corresponding flag from the Kvalobs dip test. This occurs in a “skew” dip when the step test criterion is met in one of the two cases.