Discovery Multimet Data Quality Control Report
 
 
 

Jesse Enloe and Shawn R. Smith
 
 
 
 
 
 

World Ocean Circulation Experiment
 
 
 
 
 
 

Surface Meteorological Data Assembly Center

Center for Ocean Atmospheric Prediction Studies

Florida State University
 

June 4, 2001
 

Report WOCEMET 99-15

Version 2.0


 



 

Addendum:

Members of the WOCE Hydrographic Project Office (WHPO) and WOCEMET met at the 13th Data Products Committee (DPC) meeting in College Station, TX to discuss reconciliation of the WOCE cruise line designators. This was done in anticipation of the future release of version 3 of the WOCE global data set, and resulted in changes to several WOCE cruise line designations.

On June 4, 2001 WOCEMET deleted the line designations I__08A/00 and S__04I/03. These lines will now be referenced as ISS01_/03. The quality control information for these data sets has been left in the report for the user, but please note that the lines previously known as I__08A/00 and S__04I/03 are now referenced under the designator ISS01_/03.

WOCEMET removed the WOCE designation for the cruise known as "unknown" (08/01/94-08/22/94). The quality control information for this data has been left in the report for the user, but please note that the line previously known as "unknown" (08/01/94-08/22/94) is NOT a WOCE cruise line.

WOCEMET updated the data provider for the cruise "unknown" (08/01/94-08/22/94) to Herring.

WOCEMET updated the designation for the cruise known as "unknown" (02/25/95-03/08/95) to be referenced as ISS01_/10. The quality control information for this data has been left in the report for the user, but please note that the cruise previously known as "unknown" (02/25/95-03/08/95) is now referenced under the designator ISS01_/10.

WOCEMET updated the data provider for the cruise ISS01_/10 to Bryden.


 



 

Introduction:

This report summarizes the quality of surface meteorological data collected by the research vessel Discovery (identifier: GLNE) Multilmet automated data collection system during seven WOCE cruises beginning 6 February 1993 and ending 18 November 1996. The pre-quality controlled data were provided to the Florida State University Data Assembly Center (DAC) in electronic format by D. Martin Gould of the British Oceanographic Data Center (BODC) and were converted to standard DAC netCDF format. The data are then processed using an automated screening program, which adds quality control flags to the data, highlighting potential problems. Finally, the Data Quality Evaluator (DQE) reviews the data and current flags, whereby flags are added, removed, or modified according to the judgement of the DQE and other DAC personnel. Details of the WOCE quality control procedures can be found in Smith et al. (1996). The data quality control report summarizes the flags for the Discovery Multilmet data, including those added by the BODC, the preprocessor, and the DQE.


 



 

Statistical Information:

The Discovery Multilmet data are expected to include observations taken every minute for the following variables on all WOCE cruises:
 

Time

(TIME)
Latitude (LAT)
Longitude (LON)
Earth Relative Wind Direction (DIR)
Earth Relative Wind Speed (SPD)
Sea Temperature (TS)
Atmospheric Pressure (P)
Air Temperature (T)
Wet Bulb Temperature (TW)
Downwelling Longwave Radiation (RAD)
Downwelling Shortwave Radiation (RAD2)
Photosynthetically Available Radiation (RAD3)

 

Details of the cruises are listed in Table 1 and include cruise dates, number of records, number of values, number of flags, and total percentage of data flagged. A total of 4,172,772 values are evaluated with 134,509 flags added by the BODC, the preprocessor, and the DQE resulting in a total of 3.22% of the values being flagged.
 

Table 1: Statistical Cruise Information
 
CTC
Dates
Number of Records
Number of Values
Number of Flags
Number Flagged

I__08A/00;
ISS01_03;
S__04I/03

ISS01_/04

ISS01_/07

UNKNOWN

ISS01_/08

UNKNOWN

AR_12_/07

02/06/93 - 03/18/93
 
 

03/23/93 - 05/02/93

02/19/94 - 03/30/94

08/01/94 - 08/22/94

01/07/95 - 02/21/95

02/25/95 - 03/08/95

09/28/96 - 11/18/96

57,183
 
 

56,189

56,160

25,140

64,050

15,420

72,960

686,196
 
 

681,816

673,920

301,680

768,600

185,040

875,520

8,630
 
 

5,124

39,389

1,597

28,140

6,908

44,721

1.26
 
 

0.75

5.84

0.53

3.66

3.73

5.11


 



 

Summary:

The Multimet data from the Discovery proves to be of excellent quality. No major problems were found in the data. The distribution of flags for each variable is detailed in Table 2. The BODC Q-flag was assessed by the BODC to any data that was thought to be questionable by the BODC.
 

Table 2: Number of Flags and Percentage Flagged for Each Variable

Variable

B

D

G

H

J

K

L

Q

R

S

Total Number of Flags

Percentage of Variable Flagged

TIME

LAT

LON

DIR

SPD

TS

P

T

TW

RAD

RAD2

RAD3

 

 

 

 

4,632

719

 

 

 

 

1,555

95,296

 

 

 

 

 

 

 

7,320

7,320

 

 

 

 

 

 

 

720

1,671

 

812

 

 

 

 

 

 

 

 

 

 

28

2

 

 

 

 

 

 

 

 

 

 

 

 

 

24

 

 

 

 

 

163

191

231

597

2,190

1,841

 

 

 

 

61

61

 

 

 

 

 

 

 

 

 

 

 

 

5,186

512

225

127

10

 

101

 

1,597

 

543

543

 

 

 

 

 

 

 

 

 

 

 

 

89

60

4

2

37

2

37

 

 

0

604

604

5,438

6,115

2,850

754

10,371

9,163

162

1,555

96,893

0.00

0.17

0.17

1.56

1.76

0.82

0.22

2.98

2.64

0.05

0.45

27.86

Total Number of Flags

102,202

14,640

3,203

30

24

5,213

122

7,758

1,086

231

134,509

 

Percentage of All Variables Flagged

2.45

0.35

0.08

0.00*

0.00*

0.12

0.00*

0.19

0.03

0.01

3.22

*Percentage < 0.01


 



 

The Q Flag:

The Discovery Multimet data came to the DAC already quality controlled by the BODC. The BODC suspect data flag was converted to a Q-flag (questionable) under our flagging system. The Q-flag was assessed to data the BODC found to be suspect.

 

The R Flag:

The R-flag represents values that were interpolated by the BODC and are considered to be of good quality by the DAC.

 

D-Flags:

A total of 14,640 D-flags were assessed to T and TW for failing the T>TW test. The wet bulb and air temperatures for these periods were recording very close to the same temperatures, which would indicate that the reservoir for the psychrometer had run dry.

 

B-Flags:

The vessel traversed into the extremely cold waters of the Antarctic Circle. Due to the high salinity of the ocean in that region due to brine rejection, it is possible for the sea temperature to actually fall a few degrees below freezing without solidifying. These negative sea temperature values, though realistic at only a degree or so below freezing received the B-flag.

Earth relative wind speed was assessed a total of 4,632 B-flags. These flagged data values were recorded wind speeds in excess of 200 m/s, even up to 1000 m/s.

There were numerous B-flags assessed to RAD2 and RAD3 by the preprocessor throughout five of the seven cruises, representing radiation values less than 0 W/m. These physically unrealistic negative radiation values are likely the result of the instrument not being tuned to low radiation values.

 

G-Flags:

The G-Flags assessed to the data by the preprocessor highlight values that are greater than four standard deviations from the climatological mean (da Silva et al. 1994). The G-flag is only found on earth relative wind speed, sea temperature, and air temperature in this data set. However, the majority of the G-flagging for these variables occurred on the second cruise (ISS01_/04). On this cruise, the vessel traversed the south pacific seas, south of the 40 south latitude line. In this region of the globe, little is known of the climatology, as the data is sparse. Consequently, the G-flagged values may be realistic, though extreme observations.

 

H-Flags:

The H-flag is used at times of abnormally large changes in values in a relatively short amount of time, causing a discontinuity in the data. For example, on 24 March 1993, air temperature dropped ~4C in one minute. Pressure, on 29 October 1996 has a normal variability of ~0.1 mb/minute. However it demonstrated an abrupt change of ~0.5 mb in one minute. An H-flag was placed at the beginning and end of these discontinuities.

 

J-Flags:

There were 24 J-flags assessed by the DQE to RAD on 1 March 1995. The J-flags were assessed to values of downwelling longwave radiation in excess of 500 W/m, up to 2000 W/m.

 

K-Flag:

Earth relative wind speed and direction both demonstrated stair stepping - a feature sometimes found in calculated earth relative winds that echo ship movement, often due to errors in true wind calculation and/or flow distortion. Since platform speed, course, and heading were not provided with the data, determination of these problems are inconclusive. However, the data thought to have problems were flagged as suspect with the K-flag.

The sea temperature while the ship was still in port at the beginning of the ISS01_/08 cruise was flagged with the K-flag as it was about 4-5C higher than the sea temperature once it left port.

There was a suspected ventilation problem associated with the air temperature and wet bulb temperature. Again, there was not enough supporting meteorological data to confirm this assumption and therefore the suspect data was flagged with the K-flag. A filter may also be needed for air temperature on a number of cruises.

There were 108 K flags and 2 S flags assessed to the temperature by the DQE. The temperature data that were flagged demonstrated characteristics resembling those associated with a ventilation problem. There was not enough supporting meteorological data to identify this as a definite problem. Therefore, the user should note that other temperature data demonstrating these characteristics that were left unflagged could be experiencing a ventilation problem. Verification from the BODC of a potential problem will be investigated.


 



 

Spikes:

Isolated spikes occurred in most of the variables throughout the data. Spikes are a relatively common occurrence with automated data, caused by various factors (i.e. electrical interference). These individual points were assigned the S-flag.


 



 

Other Flags and Missing Data:

Not only was there a lack of meteorological variables, but several of them were plagued with sporadic gaps in the data. This made flagging difficult for the DQE, as there were not enough meteorological supporting data to flag potential problems. Flagging by the DQE was sparse, also because the data had already been quality controlled by those that provided it and have the most knowledge of the data's limitations.

On the fourth cruise, the majority of the data was missing. Also, the last day of each cruise (except the first and fourth one) all the data were missing except for the position data. In the case where all data were missing other than the position data, the file was removed and will not be released publicly (2 May 1993, 30 March 1994, 1 August 1994, 2 August 1994, 3 August 1994, 4 August 1994, 21 February 1995, 8 March 1995, 18 November 1996).


 



 

Final Comments:

The DQE cautions that some wind data and temperature data may be in need of a smoother, as they become noisy at some parts in the data set.


 



 

References:

Smith, S.R., C. Harvey, and D.M. Legler, 1996: Handbook of Quality Control Procedures
     and Methods for Surface Meteorology Data
.WOCE Report No. 141/96,Report WOCEMET
     96-1, Center for Ocean-Atmospheric Prediction Studies Florida State University,
     Tallahassee FL 32306-2840

da Silva, A.M., C.C. Young and S. Levitus, 1994: Atlas of Surface Marine Data 1994, Volume 1:
      Algorithms and Procedures.
NOAA Atlas Series.