RadxClutter

RadxClutter identifies persistent clutter in radar data, flags it, and writes out the statistics.

Generally the reflectivity (DBZ) field will be used for the clutter identification. You are asked to select a reflectivity threshold that will be consistently exceeded by the presence of clutter. Reading data from a time period of a number of hours (at least) we compute the fraction of time that the reflectivity at each gate, in each ray, exceeds that threshold. Since non-AP clutter is a persistent phenomenon, the presence of clutter will yield a high time fraction for clutter gates. The identification step is the 'first pass' of this procedure. This will save out the clutter statistics as a CfRadial file to the output directory.

In the optional 'second pass', you can read the clutter statistics, and then use those to censor clutter from any series of CfRadial files that have a matching scan strategy. The rule for censoring is as follows: If a gate is flagged as having clutter in the statistics volume, the reflectivity in the measured volume will be compared to the statistics. If the measured reflectivity exceeds the mean reflectivity, plus a specified multiple of the standard deviation, weather is likely to be present at that gate and it will not be censored. If the reflectivity does not pass this test it will be censored - i.e. it will be set to a specified low value. The use of X times the standard deviation above the mean allows us to account for variability in the clutter reflectivity from one time to the next. 'X' is the parameter 'n_sdev_for_clut_threshold'.

Scientific Background

RadxClutter is partially based on the following paper.

Lakshmanan V., J. Zhang, K. Hondl and C. Langston: A Statistical Approach to Mitigating Persistent Clutter in Radar Reflectivity Data. IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Vol. 5, No. 2, April 2012. DOI: 10.1109/JSTARS.2011.2181828.

Prerequesites

The following items are required:

Radar data (any Radx supported format, e.g., cfradial) over a period of at least 6 hours where there is no significant weather and the ray geometry is consistent

Parameter file

RadxClutter uses one parameter file that includes the basic parameters related to data location and field names, which is similar to the parameter files for the other Radx applications.

Ensure file is up to date

To obtain the default parameter file, use the following command:

/path/to/lrose/install/bin/RadxClutter -print_params > param_file_name

If you already have a parameter file and simply want to check for (and add) updated parameters while retaining current parameters, use the following command:

/path/to/lrose/install/bin/RadxClutter -params orig_param_file_name -print_params > new_param_file_name

Important parameters

Data Input

input_dir: directory containing radar data (if not specified on the command line and if mode = REALTIME)
mode: determines if the program waits for new files (REALTIME), moves through start and end times specified on the command line (ARCHIVE), or moves through list of files specified on the command line (FILELIST)

Action

action: tell RadxClutter whether to analyze clutter statistics or filter reflectivity power for gates that are not overridden by weather (i.e., ANALYZE_CLUTTER or FILTER_CLUTTER)

Scan Details

scan_mode: scan type (i.e., PPI or RHI)
sweep_fixed_angles: list of fixed angles for desired sweeps (e.g., elevations or azimuths)
first_ray_angle, last_ray_angle: set limits of scan angles
ray_angle_resolution: angle difference between rays
az_tolerance_deg, elev_tolerance_deg: tolerance for differences between angles to match expected geometry
max_range_km: specified maximum range (km), gates beyond this range are removed

Algorithm Details

dbz_field_name: reflectivity field name
clutter_dbz_threshold: if data is persistently above this value then the gate is a clutter location
use_vel_field: option to use velocity field to confirm clutter (TRUE or FALSE)
vel_field_name: velocity field name
max_abs_vel: maximum absolute radial velocity
specify_clutter_frequency_threshold: option to specify clutter frequency threshold (see parameter file for more details)
clutter_frequency_threshold: clutter frequency threshold

Clutter Statistics Output

clutter_stats_output_dir: path to clutter statistics output
dbz_mean_field_name: field name for mean dBZ
dbz_sdev_field_name: field name for standard deviation of dBZ
clut_freq_field_name: field name for clutter frequency
clut_flag_field_name: field name for clutter flag

Filtered Output

dbz_filt_field_name: field name for filtered dBZ
clutter_stats_path: path to output volume containing clutter statistics
n_sdev_for_clut_threshold: number of standard deviations above the mean for the clutter threshold
filt_output_dir: path to filtered output volumes

Running RadxClutter

To check all command line options for RadxClutter, including debugging options and file paths, type the following command into a terminal.

/path/to/lrose/install/bin/RadxClutter -h

Once your parameter file is complete, use a command similar to the following to run the application:

/path/to/lrose/install/bin/RadxClutter -params param_file_name

The user can also specify the location of cfradial files in the following manner:

/path/to/lrose/install/bin/RadxClutter -f /path/to/cfradial/files/ -params param_file_name