wiki:cookbook/RADVOL-QC_NMET
Last modified 4 years ago Last modified on 12/18/13 11:37:48

1. Algorithm name

Removal of non-meteorological echoes and quality characterization (as a part of RADVOL-QC package) – RADVOL-QC: NMET

2. Basic description

a) Physical basis of the algorithm

Investigation of echo location and intensity.

b) Amount of validation performed so far

Works operationally in IMGW since 2013 to correct data before using for Meteo Flight system (for air traffic control).

c) References (names and contact information of all developers during the evolutionary history, scientific papers)

  • Operational work: IMGW, Department of Ground Based Remote Sensing.

3. ODIM metadata requirements for I/O

  • Top-level “where”: height.
  • Dataset-specific “what”: gain, offset, nodata, undetect.
  • Dataset-specific “where”: elangle, nbins, nrays, rscale.

4. Input data

a) What kind of radar data (including the list of previous algorithms and quality flags applied)

object=PVOL or SCAN; quantity=DBZH, otherwise TH.

b) Other data (optional and mandatory, applying “universally” agreed formats, geometry)

None

5. Logical steps, using any of: text, flow charts, graphics, equations (or references to equations), conditional branches in “all possible cases”.

In the detector two stages of non-meteorological echo removal are introduced: for “low” (subalgorithm A), and “high” (subalgorithm B) types of the echoes.

Set of the algorithm parameters

Description Denotation Default value
QINMET value for non-meteorological echoes NMET_QI 0.75
QINMET value for uncorrected non-meteorological echoes NMET_QIUn 0.3
Minimum value of reflectivity in NMET echo detector (algorithm A) (dBZ) NMET_AReflMin -15.0
Maximum value of reflectivity in NMET echo detector (algorithm A) (dBZ) NMET_AReflMax 5.0
Minimum value of height in NMET echo detector (algorithm A) (km) NMET_AAltMin 1.0
Maximum value of height in NMET echo detector (algorithm A) (km) NMET_AAltMax 3.0
Threshold for NMET echo detection (algorithm A) NMET_ADet 0.2
Threshold for meteorological echo altitude (algorithm B) (km) NMET_BAlt 20.0

At first the XML file is checked whether there exists group for a considered radar (based on the radar name read from "what"/source(NOD)), which contains the algorithm parameters. If "yes", then parameters are read from that XML group, but if it is impossible for a particular parameter, then default value from source code is taken. If the group does not exist, parameters are read from <default> group in XML file in analogous way.

If the algorithm is run by means of BALTRAD toolbox then all the algorirthm parameters for each specific radar should be placed in relevant XML file by the BALTRAD system admin. Default parameters are placed in the file by admin as well. Moreover, the algorithm default parameters are also included in software.

“Low” non-meteorological echo removal

For “low” non-meteorological echo removal a detection scheme is employed, in which the two parameters are investigated: radar reflectivity Z and height of echo above radar level H. Detection function D(Z) for parameter Z is linear in range defined by its minimum and maximum values NMET_AReflMin and NMET_AReflMax:

$ D(Z) = \begin{cases}
1    & \textrm{for\ } Z <= \text{NMET}\_\text{AReflMin} \\
\frac{\text{NMET}\_\text{AReflMax} \ - \ Z}{\text{NMET}\_\text{AReflMax} \ - \ \text{NMET}\_\text{AReflMin}}    & \textrm{for\ } \text{NMET}\_\text{AReflMin} < Z < \text{NMET}\_\text{AReflMax}  \\
0    & \textrm{for\ } Z >= \text{NMET}\_\text{AReflMax}   
\end{cases}   $

and analogically for D(H) with minimum and maximum values NMET_AAltMin and NMET_AAltMax.

The detector threshold is compared with product of the two functions, and if:

$ D(Z) \cdot D(H)  > \text{NMET}\_\text{ADet}   $

and there is no echo at neighbouring higher elevation then the echo is removed as non-meteorological one.

“High” non-meteorological echo removal

In the second subalgorithm “high” spurious echoes are all echoes detected at altitudes higher than NMET_BAlt (km) where any meteorological echo is not possible to exist. All the “high” echoes are removed.

Quality index

Quality index QINMET due to non-meteorological echoes is defined as follows:

$ QI_{NMET} = \begin{cases}
\text{NMET}\_\text{QI}  & \textrm{for gate with non-meteorological echo\ } \\
1                        & \textrm{for gate without non-meteorological echo \ } 
\end{cases} $

6. Output

a) Data type using ODIM notation where possible, e.g. DBZH

Corrected DBZH, with "pl.imgw.radvolqc.nmet" added to data-specific "how"/task, and the algorithm parameters added to "how"/task_args.

b) Quality index (QI) field

Quality index (QI = 0 for bad data, QI = 1 for excellent data) with "pl.imgw.radvolqc.nmet" in quality-specific "how"/task, and the algorithm parameters in "how"/task_args.

7. Outline of a test concept exemplifying the algorithm, as a suggestion for checking that an implementation has been successful.