Dip test - QC2d-1 - Revision 01

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):

1	AA
2	BI
81	FF
85	FM
86	FX
87	FX_1
88	FX_6
89	FX_12
90	FG_1
91	FG_6
92	FG_12
93	FX_X
94	FG_X
104	RA
105	RR_01
113	SS_1
123	RT_1
172	PH
174	POM
175	PON
176	POX
177	PP
197	QE
198	QL
199	QLX
200	QO
201	QOX
211	TA
212	TAM
213	TAN
215	TAX
221	TG
222	TGM
223	TGN
225	TGX
227	TJM
262	UU
264	UN
265	UX

Dip test flags

Flag value	Definition	useinfo(2) consequence
fs=4	Kontrollert. Mistanke om feil detektert i QC1-3. Ingen tilsvarende feil i QC2d-1. Ingen korreksjon.	Friskmeldt.
fs=5	Kontrollert. Ingen mistanke om feil detektert i QC1-3. Mistanke om feil detektert i QC2d-1.Ingen korreksjon.	Originalverdi noe mistenkelig.
fs=9	Kontrollert. Observert endring høyere enn testverdi. Korrigert automatisk.	Originalverdi sikkert feilaktig.

Previous met.no dip tests

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.