When you convert Vector data to ASCII, time is output in the .SEN files (which record data at 1 Hz), but not in the .DAT files (which record “rapid” sensors, including velocity). Here’s how to figure out the velocity time.
1) When the Vector starts a burst of data, it requires one second to wake up. As it wakes up, it collects data from the first second without transmitting sound. This result is output in the .VHD file, and you can use it to find the Vector’s acoustic noise level.
2) The first sample in the .SEN file corresponds to the second second of the burst. During the second second, no velocity data is collected.
3) The first velocity data corresponds to the beginning of the second .SEN sample.
Here is an example to illustrate: If you tell the Vector to start at 12:00:00, the first velocity sample begins at 12:00:02.0. So, if you are sampling at 16 Hz, the first velocity sample is complete at 12:00:02.0625. If you are sampling at 2 Hz, then the first velocity sample is complete at 12:00:02.50. Since the Vector is pinging continuously during each sample, the best time for the sample would be the midpoint of the measurement. So the time for the first 2 Hz sample would be 12:00:02.25, and the time for the first 16 Hz sample would be 12:00.02.0312.
The same works for continuous sampling, where you treat the entire measurement as consisting of only one burst.