rafhirate −− converts NCAR Research Aviation Facility high sample rate data into plottable form
rafhirate tape_time
NCAR’s Research Aviation Facility stores data on their output tapes in logical records, with each logical record containing one second of data. For data rates greater than 1 Hz, successive samples within a one second period are grouped together. Rafread, which converts RAF data to common data format, maintains this organization, with one variable slice per logical record. Thus, plotting more than one second’s worth of data using cdfplot requires rearrangement of data into contiguous sequences. For 1 Hz data this is easily accomplished using the filter cdfcat, which concatenates data in fields from successive variable slices, resulting in a single variable slice. The resulting data are organized into one dimensional fields, which can be plotted against each other. In particular, they can be plotted against time, which is simply one of many fields on the RAF tapes.
For data rates greater than 1 Hz, cdfcat creates two dimensional fields, with data in a particular one second interval populating one axis, while successive one second groups occupy the other axis. Fortunately, the order is such that data are actually organized sequentially in time.
Rafhirate simply accepts cdfcat output and redefines the two dimensional variable fields to be one dimensional variable fields of the appropriate size. A special field, tape_time, the name of which the user must specify on the command line, is assumed to contain the time in seconds after midnight. This must be the same field that was converted to an index field by cdfcat. Additional index fields are generated by rafhirate, namely, etime, time5, time10, etc. Etime is simply the elapsed time (in seconds) after the start of the data segment, and is sampled at a 1 Hz rate. Time5 is elapsed time also, but is sampled at a 5 Hz rate, time10 is sampled at 10 Hz, etc. The purpose of these index fields is to provide fields against which data sampled at various rates can be plotted. Only those high rate time fields are produced that are required. Rafhirate accepts cdfcat output on the standard input and sends the modified common data format file to the standard output.
kestrel%cdfcat tptime 50000 51000 1001 < flt1 | rafhirate tptime > temp
kestrel%cdfplot etime,rm,1,p time10,theta,1,p < temp ; pg
In the first line, cdfcat concatenates data between times 50000 and 51000 seconds after midnight from the rafread−produced file flt1. Tptime is the name of the field containing the time. The result is sent to rafhirate, which puts the result into the file temp. The second line shows how to plot the fields rm and theta versus time. Rm is assumed to be sampled at 1 Hz, while theta is sampled at 10 Hz.