File format for v1 Cartesian data

Users are encouraged to make use of Version-2 Cartesian files.
Click here to find out more about the different versions of the signal processing.

File contents
The files contain altitude profiles (from approximately 2 - 20 km for the ST mode, and from approximately 58 - 96 km for the M mode, both at 150 m intervals) of the eastward, northward and upward components of the wind velocity and the following radar return parameters: vertical beam signal power, aspect sensitivity, spectral width and beam-broadening corrected spectral width. The time separation between the profiles is typically a few minutes. A radar-derived tropopause altitude and sharpness is given for each set of profiles.
Click here to find out about the contents of other files.

File naming convention:

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. contains 300 m resolution Cartesian 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/cartesian/
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: 93 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: 9999.99 9999.99 9 99 999.999 9 999.99 9 999.99 9 99.999 9 99.999 9
These are the numbers which represent missing data values for the 'primary variables' (see below)

Line 40: 130 515
Integer 1 corresponds to the number of altitude gates per cycle, nr_gates
Integer 2 corresponds to the number of cycles in the file, nr_cycles
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. The data can therefore be read with a simple loop structure of the form (shown here in Fortran syntax):
do cycle_nr = 1,nr_cycles
  do gate_nr = 1,nr_gates
  end do
end do

Reading auxiliary variables
The auxiliary variables line contains 5 integers, shown here for the first cycle in the file: 105 130 1 10936 3
Integer 1: Cycle time (s)
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.

Integer 2: Number of range gates
This is the same as nr_gates given in line 40 of the header and so can be ignored.

Integer 3: Cycle number
This is the same as cycle_nr used in the data reading loop and so can be ignored.

Integer 4: Tropopause altitude (m)
This is the altitude of the (static stability) tropopause, in metres above mean sea level, determined from the altitude profile of the vertical beam signal strength.

Integer 5: Tropopause sharpness factor
0 corresponds to an indefinite tropopause
1 corresponds to lower-intermediate sharpness
2 corresponds to upper-intermediate sharpness
3 corresponds to a definite tropopause
Note that when the tropopause is indefinite, i.e. when the sharpness factor is 0 or 1, the tropopause altitude might have little meaning.
Reading primary variables
Each primary variable line contains 15 values (a mixture of floating point numbers, F, and integers, I), shown here for the first line of the first cycle:
1686.0 1.81 7.98 3 0 0.015 3 66.26 3 11.56 3 0.204 3 0.158 3
Value 1: Altitude (m) F
Technically speaking this is the first independent variable rather than a primary variable. The same altitude grid is used for all cycles and so only needs to be saved once. The altitude is given in metres above mean sea level.

Value 2: Eastward wind (m s-1) F
or zonal velocity

Value 3: Northward wind (m s-1) F
or meridional velocity

Value 4: Horizontal wind reliability flag I
This applies to both the eastward and northward components of the wind. The same convention is used for the reliability flags associated with all parameters - see below

Value 5: Complementary beam horizontal velocity variability factor (m s-1) I
This is an experimental horizontal wind reliability factor and can be ignored. In the standard-mode, the MST radar makes observations in the Vertical, NE6, SE6, SW6 and NW6 beam directions. The NE component of the horizontal wind can therefore be derived from the Vertical/NE6 or Vertical/SW6 beam pair combinations. Similarly the SE component can be derived from the Vertical/SE6 or Vertical/NW6 combinations. The variability factor is defined as the root of the sum of the squares of the differences between the estimates in the NE and SE azimuths. A small value - less than 5 m/s - indicates that that the different wind estimates are consistent. Larger values indicate that they are not and suggest that the associted velocity components are probably unreliable.

Value 6: Upward air velocity (m s-1) F
Note that this value can be biased for a number of reasons and should be interpreted as being representative rather than necessarily as quantitatively accurate. In particular, little significance should be attached to values of less than approximately 0.1 m/s. Absolute values of the order of 1 m/s give a reliable indication of the presence of mountain wave or convective activity.

Value 7: Upward air velocity reliability flag I
See below

Value 8: Radar return signal power (dB) F
Corresponds to obervations made with a vertically directed beam.
P(dB) = 10 × log10[P(linear)]

Value 9: Radar return signal power reliability flag I
See below

Value 10: Radar return aspect sensitivity (dB) F
The ratio of radar return signal power for a vertically directed beam to that for a beam directed 6° off-vertical.

Value 11: Radar return aspect sensitivity reliability flag I
See below

Value 12: Radar return spectral width (m s-1) F
This is for observations made by a vertically directed beam and corresponds to to an e-1/2 half-width for a Gaussian shaped signal. Note these values need to corrected for the effects of beam-broadening before they can be interpreted in terms of turbulent activity.

Value 13: Radar return spectral width reliability flag I
See below

Value 14: Beam-broadening corrected spectral width (m s-1) F
This is the highest order radar data product and is sensitive to errors and uncertainties in several lower order products. Care should therefore be taken with its interpretation. In principal it gives the standard deviation of turbulent velocities about the mean vertical velocity.

Value 15: Beam-broadening corrected spectral width reliability flag I
See below

Data Reliability flags
The same convention is used for all reliability flags:
0: poor signal strength, poor temporal continuity
1: good signal strength, poor temporal continuity
2: poor signal strength, good temporal continuity
3: good signal strength, good temporal continuity
For most purposes, the temporal continuity is much more significant than the signal strength in terms of reliability. It is therefore best to reject all data points with flag values of 0 or 1 and accept those with values of 2 or 3. However, the temporal continuity algorithm is not perfect. Under conditions of a sharp (temporal) increase in wind speed, or the presence of large amplitude mountain wave activity, high signal strength data points can be flagged as having poor temporal continuity, i.e. with a reliability flag value of 1, even when they are apparently reliable. If you are having difficulties with a particular dataset, please contact the NERC MST Radar Facility Project Scientist.

The values of the radar return aspect sensitivity, radar return spectral width and beam-broadening corrected spectral width are a little more sensitive to the signal strength. Care should therefore be taken with the interpretation of values which have a reliability flag value of 2.

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]