### From Lrose Wiki

RadxKdp ingests polarimetric radar data and calculates $\displaystyle{ K_{DP} }$ from $\displaystyle{ \phi_{DP} }$.

### Overview

RadxKdp uses a couple different methods to calculate $\displaystyle{ K_{DP} }$ from $\displaystyle{ \phi_{DP} }$. In general, $\displaystyle{ K_{DP} }$ is calculated from the $\displaystyle{ \phi_{DP} }$ slope between range gates (after smoothing and unfolding the $\displaystyle{ \phi_{DP} }$ data). Filtering smears out $\displaystyle{ K_{DP} }$ in range, so an additional field (KDP_SC) is constrained by $\displaystyle{ K_{DP} }$ estimated theoretically from $\displaystyle{ Z_H }$ and $\displaystyle{ Z_{DR} }$.

### Scientific Background

A detailed explanation of the procedure used to estimate $\displaystyle{ K_{DP} }$ can be found here.

Information about how attenuation is estimated from $\displaystyle{ K_{DP} }$ can be found here.

### Prerequesites

The following items are required:

• Two parameter files to run RadxKdp and to calculate $\displaystyle{ K_{DP} }$.

### Parameter files

RadxKdp uses two separate parameter files. The first includes the basic parameters related to data location and field names, which is similar to the parameter files for the other Radx applications. The second includes the parameters that set the filtering length, method, and relevant coefficients necessary to calculate $\displaystyle{ K_{DP} }$ and estimate attenuation.

#### 1) Main parameter file

##### Ensure file is up to date

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

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

##### Important parameters

Input params

• 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)

Input field information

• SNR_available: determines if SNR data is in the file or needs to be calculated from $\displaystyle{ Z_H }$
• VARIABLE_field_name: tells RadxKdp the polarimetric variable names in the ingested cfradial files

Computing KDP

• KDP_params_file_path: path to the $\displaystyle{ K_{DP} }$-specific parameter file

Output fields

• output_fields: specify the fields to be written to the output file (including attenuation-corrected fields)

Output format

• output_format: select the preferred file type (usually CFRADIAL)

Output directory

• output_dir: files will be written to this directory

#### 2) KDP-specific parameter file

##### Ensure file is up to date

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

/path/to/lrose/install/bin/RadxKdp -print_params_kdp > 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/RadxKdp -params_kdp orig_param_file_name -print_params_kdp > new_param_file_name

##### Important parameters

Unfolding and filtering

• KDP_fir_filter_len: Filter length applied to $\displaystyle{ \phi_{DP} }$

Handling phase shift on backscatter (PSOB)

• KDP_psob_method: Method to handle PSOB

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