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THE NERC MST RADAR FACILITY AT ABERYSTWYTH
FILE FORMAT FOR VERSION-1 MST RADAR RADIAL DATA
WARNING: Version-1 MST radar data products are DEPRECATED
Users are encouraged to make use of Version-2 radial files.
Click here to find out more about the different versions of the signal processing.

File contents
These files contain radial (i.e. along-beam) profiles of the radar return parameters (noise power, signal power, Doppler shift and spectral width) for different beam pointing directions. Data are recorded at 150 m intervals in range and cover the approximate range 2 - 20 (for the ST mode) or 58 - 96 km (for the M mode). For most purposes the Cartesian data will suffice and it should only be necessary to examine the radial data for specialist studies.
Click here to find out about the contents of other files.

File naming convention:
radar-mst_capel-dewi_YYYYMMDD_AARRRr.na

YYYY is a 4-digit year [1990 - ]
MM is a 2-digit month [01 - 12]
DD is a 2-digit day [01 - 31]
AA is the altitude mode ['st': approximately 2 - 20 km | 'm': approximately 58 - 96 km]
RRR is the range resolution (m) [150 | 300 | 600 | 1200 | 2400 | 4800]
i.e. radar-mst_capel-dewi_20030601_st300r.na contains 300 m resolution radial data over the ST altitude range for 1st June 2003.
Click here for the background to the file naming convention.

File location: /badc/mst/data/mst-products-v1/radial/
Click here for the location of other files.

Archiving convention: YYYY/MM
Click here for a further explanation.

File availability
Version-1 products are primarily available for the period 1st June 2003 - 31st Decemeber 2004.

File format
NASA-Ames files, with a File Format Index of 2110, are used. i.e. the same as for Version-2 data products. However, there are some small differences in the file contents.

Only those aspects of the file format which are essential for reading the data will be described. For a full description of the NASA-Ames formats, consult the Gaines and Hipskind [1998] document.

The Cartesian file for 1st June 2003 will be used as an example. Text in green represents actual file contents. Text in red is for explanatory purposes only.
Header Lines
Line 1: 80 2110
Integer 1 corresponds to the total number of header lines, nr_header_lines
Integer 2 corresponds to the File Format Index

Line 7: 2003 06 01 2003 06 12
Integers 1 - 3 correspond to the year, month and day on which the observations were made.
Integers 4 - 6 correspond to the year, month and day on which the file was created.

Line 13: 999.99 999.99 999.999 99.999 999 9
These are the numbers which represent missing data values for the 'primary variables' (see below)

Line 44: 3605 1
Integer 1 corresponds to the total number of dwells in the file, nr_dwells_total
Integer 2 corresponds to the number of cycle formats used, nr_cycle_fmts - typically 1, but occaissionally more.

Line 47: 7
Line 48: 515
These lines contain nr_cycle_fmts integers each. Each integer corresponds to a successive cycle format number, cycle_fmt_nr.
The line 47 integers correspond to the number of dwells per cycle for each succesive cycle format number, nr_dwells_per_cycle(cycle_fmt_nr).
The line 48 integers correspond to the number of cycles which use each succesive cycle format number, nr_cycles_per_fmt(cycle_fmt_nr).
These numbers are not required in order to read in the data, but explain how the total number of dwells are distributed. The sum of nr_cycles_per_fmt(cycle_fmt_nr) * nr_cycles_per_fmt(cycle_fmt_nr) (over all nr_cycle_fmts) is equal to nr_dwells_total.
Data reading loop
After reading the above mentioned lines, wind forward to line (nr_header_lines + 1) where the data begin. Associated with each cycle of observation there is a single line of auxiliary variables followed by nr_gates lines of primary variables. Owing to an oversight, the value of nr_gates is not recorded in the header. However, it can be read from the first line of auxilliary variables and is the same for every dwell thereafter. The data can therefore be read with a simple loop structure of the form (shown here in Fortran syntax):
do total_dwell_nr = 1,nr_dwells_total
  read_auxiliary_variables
  do gate_nr = 1,nr_gates
    read_primary_variables
  end do
end do

Reading auxiliary variables
The auxiliary variables line contains 17 values (a mixture of floating point numbers, F, and integers, I), shown here for the first dwell of the first cycle: 105 130 1 1 1 11 27.7 6.0 8 2 2 320 18 147 512 128 1
Value 1: Cycle time (s) I
Technically speaking this is the second independent variable rather than an auxiliary variable. The time is given in seconds since 00:00:00 UTC for the day in question.

Value 2: Number of range gates I
As mentioned above, this number nr_gates must be read from the first instance of an auxilliary variables line in order to determine the size of the inner data reading loop. The value remains the same for all dwells in the file.

Value 3: Cycle number I
which ranges between 1 and the sum of nr_cycles_per_fmt(cycle_fmt_nr) (over all nr_cycle_fmts).

Value 4: Cycle format number I, cycle_fmt_nr
which ranges between 1 and nr_cycle_fmts.

Value 5: Dwell number (within current cycle) I
which is different from total_dwell_nr (except for the first cycle). It ranges between 1 and nr_dwells_per_cycle(cycle_fmt_nr).

Value 6: Beam number I
which ranges between 1 and 17. The same information is contained within the next 2 auxilliary variables. Follow this link to see the relationship between beam number and beam pointing direction.

Value 7: Beam pointing azimuth (degrees) [clockwise from North] F
which can have values of 0.0° (for a vertically directed beam only), 27.5°, 72.5°, 117.5°, 162.5°, 207.5°, 252.5°, 297.5° or 342.5°.

Value 8: Beam pointing zenith angle (degrees) [from vertical] F
which can have values of 0.0°, 4.2°, 6.0°, 8.5° or 12.0°.

Value 9: Transmitter pulse length (μs) I
which can have values of 1, 2, 4, 8, 16 or 32 μs.

Value 10: Transmitter sub-pulse length (μs) I
which can have values of 1, 2, or 4 μs, for pulse lengths of 4 μs and longer for which pulse coding has been used. If the sub-pulse length is equal to the pulse length, then no pulse coding is used.

Value 11: Receiver bandwidth (μs) I
this is equal to the transmitter sub-pulse length, or to the pulse length if no pulse coding has been used, and determines the range resolution (values shown in brackets). Possible values are 1 μs (150 m), 2 μs (300 m), 4 μs (600 m), 8 μs (1200 m), 16 μs (2400 m) and 32 μs (4800 m). This value is the same for all dwells within a single file.

Value 12: Inter-pulse period (μs) I
This determines the maximum unambiguous range from which radar returns can be received (values in brackets). It can have values of 80 μs (12 km), 160 μs (24 km), 320 μs (48 km) and 640 μs (96 km).

Value 13: Bottom range gate number I
The bottom and top (next value) range gate numbers are given for reference only. The total number number of range gates was already given in value 2 and the range of each gate from the radar is shown in the first column of data for each dwell.

Value 14: Top range gate number I

Value 15: Number of coherent integrations I
This is the number of raw radar samples averaged.

Value 16: Discrete Fourier transform length I
This is the number of (averaged) samples from which a Doppler power spectrum is derived.

Value 17: Number of incoherent integrations I
This is the number of Doppler power spectra averaged together before the principal spectral parameters are evaluated.

Reading primary variables
Each primary variable line contains 7 values (a mixture of floating point numbers, F, and integers, I), shown here for the first range gate of the first dwell of the first cycle:
1645.0 35.39 52.52 0.798 0.267 34 1
Value 1: Range from the radar (m) F
Technically speaking this is the first independent variable rather than a primary variable. The same range gate grid is used for all dwells within the file and so only needs to be saved once. The range is given in metres away from the radar, which is at 50 m above mean sea level.

Value 2: Spectral noise power (dB) F
The noise power is included for reference and is not typically used as a parameter in its own right.

Value 3: Radar return signal power (dB) F

Value 4: Radial air velocity (m/s) F
Positive values imply motion AWAY from the radar.

Value 5: Radar return spectral width (m/s) F
This corresponds to an e-1/2 half-width. Follow this link for further information.

Value 6: Peak power spectral density (PSD) relative to the mean noise PSD (dB) I
This is used for reliability flagging. Signals with a value of greater than 10 dB are typically clearly distinguishable above the background noise. Signals with values of less than 10 dB might still be reliable but should be treated with caution.

Value 7: Reliability flag I
A value of 1 implies that the spectral parameters (values 3 - 5) are reliable and a value of 0 implies that they are not. The reliability flagging is based on the time continuity of the radial velocities.

Internal Links:
Return to the top of the page
Gaining access to the data
File naming convention
Data archiving convention
Data locations
The differences between signal processing versions
The contents of other data files
External Links:
Full description of the NASA-Ames formats: Gaines and Hipskind [1998]
Page maintained by David Hooper
Last updated 13th January 2005