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THE NERC MST RADAR FACILITY AT ABERYSTWYTH
MST RADAR VERSION-3 RELIABILITY DETAILS
MST radar radial and Cartesian data products produced from version-3 processing typically have an associated reliability flag variable and a reliability details variable.

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"
For the Cartesian files there are a number of reliability flags, each one representing a separate group of data products. The template below shows the netCDF attributes for reliability flag covering data product (group) ****:
****_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"
The reliability details variable
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:

reliability_details_value & 2**(bit_number) == 2**(bit_number)

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


Internal Links:
Return to the top of the page
Explanation of netCDF terminology
File format for v3 radial data
File format for v3 Cartesian data
Page maintained by David Hooper
Last updated 8th November 2006