Jesse Enloe and Shawn R. Smith
World Ocean Circulation Experiment
Surface Meteorological Data Assembly Center
Center for Ocean Atmospheric Prediction Studies
Florida State University
August 20, 2001
Report WOCEMET 99-09
Version 3.0
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 December 21, 2000, WOCEMET removed the WOCE designation for the cruise AR_12_/08. The quality control information for this data has been left in this report for the user, but please note that the line previously known as AR_12_/08, is NOT a WOCE cruise line.
On August 20, 2001 WOCEMET updated the designator for the line previously known as AR_27_/01 to be listed as AR_05_/03 with cross references to lines AR_07W/11 and AR_12_/08. The quality control information for this data has been left in this report for the user but please note that the line previously known as AR_27_/01 is now listed as AR_05_/03.
Introduction:
This report summarizes the quality of surface meteorological data collected by the Meteor (identifier: DBBH) DVS system during five WOCE cruises beginning 28 December 1996 and ending 14 September 1997. The data were provided to the Florida State University Data Assembly Center (DAC) on CD-ROM by K. Motamedi at the Bundesamt für Seeschiffahrt und Hydrographie, Germany. They were then converted to standard DAC net CDF format and then processed using an automated screening program, which adds quality control flags to the data, highlighting potential problems. Finally, the Data Quality Evaluator (DQE) reviewed the data and current flags, whereby flags were 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 Meteor DVS surface meteorological data, including those added by both the preprocessor and the DQE.
Statistical Information:
The Meteor DVS data are expected to include observations taken every minute on all five WOCE cruises. Values for the following variables were collected:
| Time | TIME |
| Latitude | LAT |
| Longitude | LON |
| Platform Heading (gyrocompass) | PL_HD |
| Platform Course (Ins) | PL_CRS |
| Platform Speed (Ins) | PL_SPD |
| Platform Speed (EDD Log) | PL_SPD2 |
| Port Platform Relative Wind Direction | PL_WDIR |
| Port Platform Relative Wind Speed | PL_WSPD |
| Starboard Platform Relative Wind Direction | PL_WDIR2 |
| Starboard Platform Relative Wind Speed | PL_WSPD2 |
| Port Earth Relative Wind Direction | DIR |
| Port Earth Relative Wind Speed | SPD |
| Starboard Earth Relative Wind Direction | DIR2 |
| Starboard Earth Relative Wind Speed | SPD2 |
| Port Sea Temperature | TS |
| Starboard Sea Temperature | TS2 |
| Atmospheric Pressure | P |
| Port Air Temperature | T |
| Starboard Air Temperature | T2 |
| Port Dewpoint Temperature | TD |
| Starboard Dewpoint Temperature | TD2 |
| Port Relative Humidity | RH |
| Starboard Relative Humidity | RH2 |
| Atmospheric Radiation | RAD |
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 4,243,177 values were evaluated with 215,530 flags added by the preprocessor and the DQE for a total of 5.08% of the values being flagged. Note that the EDD Log platform speed data on three of the cruises were found to be of poor quality and are not included in the statistical results. These values will not be released (discussion below).
Table 1: Statistical Cruise Information
|
CTC |
Dates |
Number of Records |
Number of Values |
Number of Flags |
Percentage Flagged |
|
AR_26_/01 AR_12_/08 A__02_/04 AR_27_/01 AR_07E/07 |
12/28/96 – 01/22/97 05/15/97 – 06/01/97 06/11/97 – 07/02/97 07/06/97 – 08/12/97 08/16/97 – 09/14/97 |
26,822 24,163 30,275 52,181 40,979 |
670,550 579,912 756,875 1,252,344 983,496 |
23,906 15,265 51,913 57,373 67,073 |
3.57 2.63* 6.86 4.58* 6.82* |
| *PL_SPD2 removed due to poor quality |
Summary:
The overall quality of the data collected by the Meteor is fair, with 5.08% of the reported values being flagged for potential problems. However, the overall quality of the meteorological data varies greatly from variable to variable. The placement of the instruments for T, T2, TD, TD2, RH, and RH2 on the superstructure in the proximity of the exhaust stack caused a major problem, resulting in extensive flagging of these variables. Moreover, the EDD Log platform speed (PL_SPD2) on the three cruises AR_12_/08, AR_27_/01, and AR_07E/07 were found to be of extremely poor quality and were not included in the public release. Table 2 details the distribution of flags among the remaining variables.
Table 2: Number of Flags and Percentage Flagged for Each Variable
Variable
B
D
E
F
G
H
J
K
S
Total Number of Flags
Percentage of Variable Flagged
TIME
LAT
LON
PL_HD
PL_CRS
PL_SPD
PL_SPD2
PL_WDIR
PL_WSPD
PL_WDIR2
PL_WSPD2
DIR
SPD
DIR2
SPD2
TS
TS2
P
T
T2
TD
TD2
RH
RH2
RAD
1
2
12,544
18,122
14,455
16,355
14,414
403
1
284
1
33
33
18
64
37
59
16
16
6,938
6,704
1,533
2,324
1,468
2,030
2,246
2,157
13,354
11,587
15,854
22,727
21,716
25,786
656
1
1
1
44
1
1
101
177
84
169
1
6
345
122
159
129
55
123
64
8
0
34
35
0
0
1
6,750
1
1
0
0
2,037
2,520
1,836
2,264
2,263
2,179
345
31,598
26,238
32,338
37,196
21,898
25,850
20,146
0.00
0.02
0.02
0.00
0.00
0.00*
3.87
0.00*
0.00*
0.00
0.00
1.17
1.44
1.05
1.30
1.30
1.25
0.20
18.12
15.04
18.54
21.33
12.55
14.82
11.55
Total Number of Flags
12,547
63,346
689
66
178
32
6,938
130,142
1,592
215,530
Percentage of All Values Flagged
0.30
1.49
0.02
0.00*
0.00*
0.00*
0.16
3.07
0.04
5.08
*Percentage < 0.01
Deleted Data:
Platform Speed (EDD Log):
The Meteor measured two platform speeds: a speed over the ground (PL_SPD) from the Inertial Navigation System (Ins) and a speed with respect to the water (PL_SPD2). On the AR_26_/01 cruise, PL_SPD2 proved to be accurate, having speeds similar to that of PL_SPD. Beginning with the AR_12__/08 cruise, PL_SPD2 began recording highly variable and very noisy data that were dissimilar to PL_SPD, and continued throughout the entire cruise. On the A__02_/04 cruise, PL_SPD2 data started off as the AR_12_/08 cruise had ended. However, on the morning of 17 June, it appears that the problem with the instrument corrected and the EDD log subsequently recorded accurate data for the remainder of the cruise. From the first day of the AR_27_/01 cruise to the last day of the AR_07E/07 cruise, PL_SPD2 showed problems similar to the AR_12_/08 cruise. In the cruises where PL_SPD2 recorded highly questionable data throughout the entire cruise, it was determined that the variable should be removed completely, and not be included in the public release. In the case where the problem was apparently corrected during the cruise, the variable remained, with the suspect data appropriately assessed the K flag by the DQE.
Major Problems:
Exhaust:
As stated previously, the placement of the instruments used to measure air temperature, relative humidity, and dewpoint temperature with respect to the exhaust stack caused major problems. These instruments are located on a tower just in front of and at a height just above the top of the exhaust stack. In due course, whenever there is a ship relative wind in proximity of 180 degrees (from stern to bow), the rising exhaust is carried directly to the instruments. The exhaust, being warm and moist, increases the measured air and dewpoint temperatures from one to five ºC, or more, and relative humidity as much as 10-15% and higher. After a change in ship-relative wind direction, the exhaust clears from the instruments and variables return to normal. The data are affected anywhere from a few minutes to several hours. The response to this trend is not uniform for any of these variables. The DQE attempted to flag all such events as suspect (K). But the user may want to employ a filter based on the ship relative wind direction.
Flow Distortion and Ventilation:
The ship's winds experienced flow distortion with a related ventilation problem. When there was a ship relative wind direction in the proximity of 90 degrees (from the starboard side) the ship's port-side instruments, being now partially blocked from the wind by the tower on which they are mounted, sometimes recorded highly variable wind direction and wind speed, noticeably anomalous to the trend. During such occurrences, the temperature and relative humidity instruments, inadequately ventilated, demonstrated an increase in temperature, and, consequently, a decrease in relative humidity. The problem also occurred on the starboard side instruments when the ship relative wind direction was in the proximity of 270 degrees (from the port side). In the earth relative wind, the problem was more notable in the wind speed than in the wind direction. Sometimes, only the wind speed was affected. The temperature and relative humidity aberrations were not consistent with the wind changes, and at times, occurred when the earth relative wind was not affected and didn't occur when the earth relative wind was affected.
This problem was flagged by the DQE as suspect (K) where possible, and spikes (S) where only a few values needed to be flagged. The flow distortion problem was not as easily identifiable and not always able to be flagged. The user may want to consider a smoother for the wind data when the ship relative wind is in the proximity of 90 and 270 degrees.
Dewpoint Temperature:
Both the port and starboard dewpoint temperature sensors experienced anomalously high readings sporadically throughout all five cruises. This caused the preprocessor to flag the temperature and dewpoint with the D flag, indicating the dewpoint temperature as greater than the air temperature. When such an incident transpired, the dewpoint was flagged as suspect (K) and the D flag was subsequently removed from the corresponding temperature values. The relative humidity was sometimes affected as well. Where the DQE determined the relative humidity readings as suspect, it too received the K flag.
Other Problems:
Sea Temperature:
In the final cruise, both the port and starboard sea temperature sensors experienced abrupt changes of one to two degrees C. These episodes were flagged at the beginning and end of each discontinuity with the discontinuity flag (H).
Radiation:
The radiation data were plagued by the preprocessor-assessed bounds flag (B) throughout the entire first cruise during non-daylight hours. The problem is likely due to a calibration error. During the fourth cruise, in the early morning hours of 8 July, the data demonstrated an oscillation before sunrise. The oscillation, between about zero and 20 W·m-2, was flagged as suspect and thought to be an instrument malfunction. On the final cruise, on 9 September, 9:33 a.m., the instrument suffered a severe malfunction, recording values of -200 W·m-2. The instrument never recovers from this, recording bad data for the remainder of the cruise and was assessed the J flag (indicating data of poor quality, and are not to be used) by the DQE.
Spikes:
Isolated spikes occurred in most of the variables throughout the data. Spikes are relatively common occurrences in automated data, caused by such factors as electrical interference and ship accelerations. These individual points were assigned the S flag.
Final Comments:
The DQE recommends that the user employ a filter on the air and dewpoint temperatures, as well as the relative humidity sensor when the ship relative wind is anywhere in proximity of 180º (± ~30º) due to the problem of exhaust.
A smoother may also be needed for the earth relative wind when the port relative wind direction is in propinquity of 270º (± ~30º) and/or the starboard relative wind direction in propinquity of 90º (± ~30º) due to the flow distortion/ventilation problem.
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