|CTC||Dates Checked||Number of Records||Number of Values||Number of Flags||Percent Flagged|
|P__21E/00||03/27/94 - 04/08/94||18604||390684||113855||29.14|
|P__21E/00||04/27/94 - 05/14/94||24808||520968||148290||28.46|
|P__21W/00||05/19/94 - 05/29/94||15782||331422||88901||26.82|
|P__21W/00||05/31/94 - 06/20/94||26890||564690||227202||40.23|
However, the Melville IMET data did not contain the needed parameters to compute a true wind. In fact, 100% of the platform heading data and 100% of the wind compass data were 0.0 degrees. This is unrealistic for a ship on a 3 month cruise.
Table 1: Number and Percentage of Flags Used per Variable
|Variable||B||F||G||J||K||L||S||Total Number of Flags||Percentage of Data Flagged|
|Percentage of data flagged||3.46||0.05||0.74||6.57||0.14||0.00||0.20||11.72|
For some research applications, the DAC created a course corrected true wind (substituting the course for the heading in the calculation). These approximate true wind values would be acccurate for some applications, however they have a quantity of high frequency noise and are likely less reliable at low ship speeds. The course corrected winds can be obtained upon request.
The remaining data are in good shape, despite the high percentage of flags. PRECIP had observations that were so noisy that they were incomprehensible. These, such as the PRECIP data on 03/27/94, were as "J". Pressure was also flagged with "J" flags because the system would report the same pressure for several days in a row, one example being 05/07/94-05/09/94 when 1019.1mb was recorded as pressure for that entire period. T, T2, and RH were also all flagged with "J" for similar reasons.
The only other major problem with the data set was that the Epply precision spectral pyranometer used with the IMET system seemed to have a calibration problem. The atmospheric radiation should be near, but above, 0.0 W/m2 during nightfall. However, the pyranometer would return a reading below 0.0 W/m2. This resulted in 45,462 "B" flags being assigned by the prescreener. These flags were left as an indication of the problem.
The prescreener also assigned 9,753 "G" flags to P. This was due to the Melville being located close to the Antarctic coastline and encountering very low atmospheric pressures. The analyst left these flags for descriptive purposes. A relatively large number(271) of spikes were also found in the P data. Almost all of these were single values, within a day's normal observations, close to 0.0.
In addition to the "J" flags described above, PRECIP also had 2 other problems. One is that the data contains 2,287 spikes. The analyst allowed that water can slosh around within the rain guage, resulting in a large amount of noise within the data. The "S" flags were for values that did not fall within the normal range of noise (which the analyst determined to be 1-2mm). The other problem was that the PRECIP data on 06/06/94 did not seem to be accurate. Specifically, the observations were at exactly the same value for half of the day, then the data became very noisy, fluctuating between 0mm and 20mm for the rest of the day. All of this day's values (950) were flagged with "K".
One other problem worth noting exists. On 06/05/94, the records for TS, T2, T, RH, and RAD all have observations for the first 3 hours, then there is no data for 21 hours. When observations reappear, they are all at 0.0 for the remainder of the day. The values at 0.0 were flagged with "J", and the values during the first 3 hours, 170 observations, were flagged with "K".
All the flags described are indicative of major problems in the data set. There are an assortment of other flags that don't represent any major problems, but rather are expected when such a large data set is quality controlled. For purposes of brevity, these flags will not be discussed.