THE NERC MST RADAR FACILITY AT ABERYSTWYTH
The reliability flag variable
A flag value of 0 implies that the associated data products are NOT reliable.
A flag value of 1 implies that the associated data products ARE reliable.
The reliability flag has the same dimensions (click here for an explanation of netCDF nomenclature) as the data product(s) it represents. For the radial files, there is only one reliability flag (signal_component_is_reliable) which covers the variables signal_power, radial_velocity, spectral_width, first_velocity_bin_number, final_velocity_bin_number, and peak_smooth_psd_to_noise. The netCDF attributes are as follows:
- signal_component_is_reliable
(time, range, signal_component_number) BYTE
- long_name = "Signal component reliability flag"
- units = "1"
- flag_values = 0b, 1b
- flag_meanings = "signal_component_is_not_reliable signal_component_is_reliable"
- coordinates = "latitude longitude"
- units = "1"
- ****_data_are_reliable
(altitude, time) BYTE
- long_name = "**** reliability flag"
- units = "1"
- flag_values = 0b, 1b
- flag_meanings = "data_are_not_reliable data_are_reliable"
- coordinates = "latitude longitude"
- units = "1"
The reliability flag values are determined from the results of a number of tests which are coded bitwise into a 16-bit signed integer. Typically these individual tests can be ignored. However, under extreme atmospheric conditions, e.g. associated with convective activity, data products may fail individual tests causing them to be flagged as being unreliable overall. The availability of results from the individual tests can be used to consider data points which would otherwise be ignored. Not all data products use all tests.
Treating the reliability details value as a 14-bit unsigned integer (it only ever contains positive values, including zero), bit 00 is the least significant bit. Consequently the result (either a 0 or a 1) of a particular test can be determined from an operation of the form:
The contents of individual bits are as follows:
 |
Bit number | |
Information |
| 00 | 1 if a datum is available. | ||
| 01 | 1 if the peak smoothed power spectral density (PSD) is greater than a set threshold | ||
| 02 | 1 if the signal component belongs to a radial chain | ||
| 03 | 1 if the signal component fits overall radial continuity | ||
| 04 | 1 if a secondary signal component belongs to a radial chain | ||
| 05 | 1 if the signal component is consistent with uni-directional time continuity | ||
| 06 | 1 if the signal component is consistent with bi-directional time continuity | ||
| 07 | 1 if a complementary beam exists | ||
| 08 | 1 if the complementary horizontal wind components have both passed lower order reliability checks | ||
| 09 | 1 if the complementary horizontal wind components have both passed lower order reliability checks for the orthogonal azimuth | ||
| 10 | 1 if the complementary horizontal wind components differ by a set amount | ||
| 11 | 1 if the complementary horizontal wind components differ by a set amount | ||
| 12 | 1 if theta_s correction has been applied to the horizontal winds | ||
| 13 | 1 if the beam-broadening correction of spectral width results in a usable value |