THE NERC MST RADAR FACILITY AT ABERYSTWYTH
The principal data products from the 915 MHz Met Office boundary-layer wind-profiler are the wind speed and (meteorological convention) direction, as functions of time and altitude; radial velocities and signal-to-noise ratios (S/Ns) for individual beam directions are also given. Observations are made in both a "low" mode, covering the approximate altitude range 0.1 - 2.0 km at 0.1 km intervals, and a "high" mode, covering the approximate altitude range 0.2 - 8.0 km at 0.2 km intervals; the useful coverage varies with atmospheric conditions.
Each file begins with a blank line and is then followed by a sequence of 96 records; 48 for the low mode and 48 for the high mode. NOTE that the order of low and high mode records is not necessarily the same for each 30 minute period; it is therefore necessary to determine the mode from the inter-pulse-period, IPP, in header line 7 described below. The first 15 lines of the first record in la010903 are shown as follows exactly as they appear in the file:
Aberystwyth LAP3000 WINDS rev 4.1 52.40 -4.00 50 01 09 03 00 00 18 0 29 3 20 08:11 (2.5) 08:10 (2.5) 08:10 (2.5) 204 204 73 73 700 700 23 23 17.5 17.5 1 2000 2000 20 20 700 700 295 90.0 115 66.4 205 66.4 HT SPD DIR Radials... 0.158 9999 999 3.0 -1.0 -0.4 7 7 6 36 13 12 0.254 9999 999 3.6 -0.5 -0.0 7 7 8 26 30 24 0.351 9999 999 4.1 -0.3 -0.2 6 5 8 25 18 23 0.447 9999 999 4.0 -2.0 0.1 6 6 7 24 15 13 0.543 4.1 302 4.1 -1.6 -0.2 6 9 8 23 12 11
For most purposes the only header information that is actually required consists of the date and time of observation from line 4, the number of altitude gates, NAG, from line 5 (each record consists of NAG+11 lines), and the pulse length from line 7. In the explanations of the line contents below, some of the horizontal spacings have been altered for the sake of clarity. The text shown in red is for descriptive purposes only and does not appear in the files.
Lines 1 - 3 give the station name, the file format and station position, respectively; they are the same in all records.
Aberystwyth LAP3000
WINDS rev 4.1
52.40 -4.00 50
LAT LONG ELEV
- LAT - Latitude North (°)
- LONG - Longitude East (°)
- ELEV - Elevation above mean sea level (m)
- LONG - Longitude East (°)
Line 4 gives the date and time at the start of the consensus period.
01 09 03 00 00 18 0 YY MM DD hh mm ss UTOFF
- YY - Year (00 - 99)
- MM - Month (01 - 12)
- DD - Day (01 - 31)
- hh - Hour (00 - 23)
- mm - Minute (00 - 59)
- ss - Second (00 - 59)
- UTOFF - Offset required to convert to UT (mins)
- MM - Month (01 - 12)
Line 5 gives observational format details.
29 3 20 CAP NBD NAG
- CAP - Consensus averaging period (mins)
- NBD - Number of beam directions used to derive the wind information
- NAG - Number of altitude gates, i.e. number of data lines in each record
- NBD - Number of beam directions used to derive the wind information
Line 6 gives consensus details for each beam direction used; the beam directions are given in line 9.
08:11 (2.5) 08:10 (2.5) 08:10 (2.5) NCRC:NCT CWS NCRC:NCT CWS NCRC:NCT CWS
- NCRC - Number of cycles required to make
consensus
- NCT - Number of cycles in total (for each consensus period)
- CWS - Consensus window size (m s-1)
- NCT - Number of cycles in total (for each consensus period)
Line 7 gives observation format details. Two values are given for each parameter; the first relates to the off-vertical beam observations and the second to vertical beam observations.
204 204 73 73 700 700 23 23 NCC NCC NSP NSP PLEN PLEN IPP IPP
- NCC - Number of coded cells
- NSP - Number of spectra
- PLEN - Pulse length (ns)
- IPP - Inter-pulse period (us); IPP < 40 corresponds to low mode observations and IPP > 40 to high mode observations
- NSP - Number of spectra
Line 8 gives more observation format details; again the first of each value corresponds to off-vertical beam observations and the second to vertical beam observations.
17.5 17.5 1 2000 2000 20 20 700 700 MDV MDV VC TDFG TDFG NRG NRG RGI RGI
- MDV - Maximum Doppler velocity, i.e.
that corresponding to the Nyquist frequency of the spectra
- VC - Vertical correction applied to oblque beams? (0 = no, 1 = yes)
- TDFG - Time delay to first range gate (ns)
- NRG - Number of range gates
- RGI - Range gate interval (ns)
- VC - Vertical correction applied to oblque beams? (0 = no, 1 = yes)
Line 9 gives the beam pointing directions.
295 90.0 115 66.4 205 66.4 AZIA ELEA AZIA ELEA AZIA ELEA
- AZIA - Azimuth angle, from North = 0°
- ELEA - Elevation angle, from horizontal = 0°
Line 10 gives labels for the columns that follow
HT SPD DIR Radials...
Lines 11 to (10 + NAG), of which only the first 5 are shown, give the actual data. Radial data (columns 4 to 12) are given in the beam order defined in line 9.
0.158 9999 999 3.0 -1.0 -0.4 7 7 6 36 13 12
0.254 9999 999 3.6 -0.5 -0.0 7 7 8 26 30 24
0.351 9999 999 4.1 -0.3 -0.2 6 5 8 25 18 23
0.447 9999 999 4.0 -2.0 0.1 6 6 7 24 15 13
0.543 4.1 302 4.1 -1.6 -0.2 6 9 8 23 12 11
Z SPD DIR VRAD VRAD VRAD NCMC NCMC NCMC S/N S/N S/N
- Z - Altitude above ground (km)
- SPD - Horizontal wind speed (m s-1); a value of 9999 indicates that no consensus was reached
- DIR - Meteorological convention horizontal wind direction, i.e. FROM which the wind is blowing (°); a value of 999 indicates that no consensus was reached.
- VRAD - Radial component of wind velocity, +ve indicating towards the radar (m s-1)
- NCMC - Number of cycles making consensus
- S/N - Average signal-to-noise ratio of cycles in consensus
- SPD - Horizontal wind speed (m s-1); a value of 9999 indicates that no consensus was reached
Line (11 + NAG) contains a single $ character.