I noticed a problem with some of the M4 10 minute text files. The files from October 2011 to November 2012 have duplicate information.
For example, for “2011_December.txt”, the end of the file should be “31-12-2011 23:50:00”. Immediately following 23:50, data is repeated from “17-12-2011 01:40:00” and continues until “31-12-2011 23:50:00”.
To see this, go here: wind.nrel.gov/MetData/135mData/M4Twr/10min/mat/
And download Dec, 2011.
This pattern is similar for all of the files mentioned. After what should be the end of the file, data is repeated starting from some random place within the file. You can actually spot the problem files because they seem to be about twice the size of the other files.
Also, the text files are normally comma delimited. However, the repeated data has an extra space with the comma in each field. The repeated data is also 1 field short and does not have the final flag value.
This does not seem to affect the 10 minute MAT files and does not seem to affect the M5 tower. The M4 10 minute text data looks to still be usable, just have to trim the file when the end of month is reached.