Geoscience Reference
In-Depth Information
Task
Correction algorithm
Quality factor
QC
QI
Evaluation of technical
radar parameters
Set of technical radar
parameters
-
x
Assessment of effects
related to distance to
radar site
Horizontal and vertical
beam broadening
-
x
Using Doppler filter or
3-D clutter map
Presence of ground
clutter
Ground clutter removal
x*
x
Analysis of 3-D
reflectivity structure.
Using dual-polarization
parameters
Removal of non-
meteorological echoes
Presence of the non-
meteorological echoes
x
x
Presence of beam
blockage
Beam blockage correction
Using topography map
x
x
Based on attenuation
coefficient. Using dual-
polarization parameters
Correction for
attenuation in rain
Attenuation in rain along
the beam path
x
x
Spatial variability
evaluation
Analysis of 3-D
reflectivity structure
Spatial variability of
reflectivity field
x
* commonly the correction is made by built-in radar software.
Table 1. Groups of quality control algorithms (correction QC and characterization QI) for
3-D reflectivity (
Z
) data.
4.1 Technical radar parameters
This algorithm aims to deliver data quality metric only. A set of technical radar
parameters that impact on data quality can be selected as quality factors. The parameters
are for instance: operating frequency, beam width, pointing accuracy in elevation and
azimuth, minimal detectable signal at 1000 m, antenna speed, date of last electronic
calibration, etc. (Holleman et al., 2006). All the factors are static within the whole radar
range and characterize quality of each particular radar so different radars can be
compared in terms of their quality. The threshold values for which the quality index
becomes lower than one should be set for all parameters according to the common
standards.
4.2 Horizontal and vertical broadening of a radar beam
Radar measurements are performed along each beam at successive gates (measurement
points in 3-D data space), which represent certain surrounding areas determined by the
beam width and pulse length. Since the radar beam broadens with the distance to the radar
site, the measurement comes from a larger volume and related errors increase as well. There
is no possibility to correct this effect, however it can be quantitatively determined and taken
into account in the total quality index.
The horizontal and vertical broadening of radar beam for each gate can be geometrically
computed knowing its polar coordinates: elevation, azimuth, and radial distance to radar site,
