The data from different interferometers is then cross-correlated over similar times to determine any time delays and the implied height of turbulent regions estimated. The nrao interferometer has been collecting data on the Chajnantor site in Chile since May 1995, while the lsa interferometer on that site has data from June 1998. So, for instance, no data appears on the web for the lsa interferometer from May to September 1999 inclusive. The output is two sets of matching time and phase series, each 1000 seconds long. So, on this occassion, the sampler clock has 'run fast' collecting all the necessary data in 56 rather than in 60 seconds.
Subsequent integrations show that the clock then slowed down.
So far, I have only found one day of data exhibiting this feature. The greater the lag-time, the higher the turbulence. The wind directions are measured clockwise from North and indicate the direction FROM which the wind is blowing. Subsequent plots for that date indicate that the wind direction and speed are changing. These plots are less well-defined and a definite lag time is harder to obtain.