Reading NetCDF#

This reader utilizes netCDF4-python.

In this example, we read NetCDF files from different sources using a generic reader from \(\omega radlib's\) io module.

[1]:

import wradlib as wrl
from wradlib.io import read_generic_netcdf
from wradlib.util import get_wradlib_data_file
import os

NetCDF Format#

The NetCDF format also claims to be self-describing. However, as for all such formats, the developers of netCDF also admit that “[…] the mere use of netCDF is not sufficient to make data self-describing and meaningful to both humans and machines […]” (see here). Different radar operators or data distributors will use different naming conventions and data hierarchies (i.e. “data models”) that the reading program might need to know about.

\(\omega radlib\) provides two solutions to address this challenge. The first one ignores the concept of data models and just pulls all data and metadata from a NetCDF file (wradlib.io.read_generic_netcdf(). The second is designed for a specific data model used by the EDGE software (wradlib.io.read_edge_netcdf()).

Note

For radar data in CfRadial1 or CfRadial2 format the openradar community published xradar where xarray-based readers/writers are implemented. That particular code was ported from \(\omega radlib\) to xradar. Please refer to xradar for enhancements for polar radar.

From \(\omega radlib\) version 1.19 CfRadial reading code is imported from xradar-package whenever and wherever necessary.

Please read the more indepth notebooks cfradial1_backend and cfradial2_backend.

Generic NetCDF reader (includes CfRadial)#

\(\omega radlib\) provides a function that will virtually read any NetCDF file irrespective of the data model: wradlib.io.read_generic_netcdf(). It is built upon Python’s netcdf4 library. wradlib.io.read_generic_netcdf() will return only one object, a dictionary, that contains all the contents of the NetCDF file corresponding to the original file structure. This includes all the metadata, as well as the so called “dimensions” (describing the dimensions of the actual data arrays) and the “variables” which will contains the actual data. Users can use this dictionary at will in order to query data and metadata; however, they should make sure to consider the documentation of the corresponding data model. wradlib.io.read_generic_netcdf() has been shown to work with a lot of different data models, most notably CfRadial (see here for details). A typical call to wradlib.io.read_generic_netcdf() would look like:

[2]:

fpath = "netcdf/example_cfradial_ppi.nc"
f = wrl.util.get_wradlib_data_file(fpath)
outdict = wrl.io.read_generic_netcdf(f)
for key in outdict.keys():
    print(key)

Downloading file 'netcdf/example_cfradial_ppi.nc' from 'https://github.com/wradlib/wradlib-data/raw/pooch/data/netcdf/example_cfradial_ppi.nc' to '/home/runner/work/wradlib/wradlib/wradlib-data'.

comment
title
Conventions
source
version
references
instrument_name
institution
field_names
history
dimensions
variables

EDGE NetCDF#

EDGE is a commercial software for radar control and data analysis provided by the Enterprise Electronics Corporation. It allows for netCDF data export. The resulting files can be read by wradlib.io.read_generic_netcdf(), but \(\omega radlib\) also provides a specific function, wradlib.io.read_edge_netcdf() to return metadata and data as seperate objects:

[3]:

fpath = "netcdf/edge_netcdf.nc"
f = wrl.util.get_wradlib_data_file(fpath)
data, metadata = wrl.io.read_edge_netcdf(f)
print(data.shape)
print(metadata.keys())

Downloading file 'netcdf/edge_netcdf.nc' from 'https://github.com/wradlib/wradlib-data/raw/pooch/data/netcdf/edge_netcdf.nc' to '/home/runner/work/wradlib/wradlib/wradlib-data'.

(360, 240)
dict_keys(['TypeName', 'DataType', 'Latitude', 'Longitude', 'Height', 'FractionalTime', 'attributes', 'NyquistVelocity-unit', 'NyquistVelocity-value', 'vcp-unit', 'vcp-value', 'radarName-unit', 'radarName-value', 'ColorMap-unit', 'ColorMap-value', 'Elevation', 'ElevationUnits', 'MissingData', 'RangeFolded', 'RadarParameters', 'PRF-unit', 'PRF-value', 'PulseWidth-unit', 'PulseWidth-value', 'MaximumRange-unit', 'MaximumRange-value', 'ConversionPlugin', 'az', 'r', 'site', 'time', 'max_range'])

[4]:

# A little helper function for repeated tasks
def read_and_overview(filename):
    """Read NetCDF using read_generic_netcdf and print upper level dictionary keys"""
    test = read_generic_netcdf(filename)
    print("\nPrint keys for file %s" % os.path.basename(filename))
    for key in test.keys():
        print("\t%s" % key)

CfRadial example from S-Pol research radar TIMREX campaign#

[5]:

filename = "netcdf/cfrad.20080604_002217_000_SPOL_v36_SUR.nc"
filename = get_wradlib_data_file(filename)
read_and_overview(filename)


Print keys for file cfrad.20080604_002217_000_SPOL_v36_SUR.nc
        Conventions
        version
        title
        institution
        references
        source
        history
        comment
        instrument_name
        site_name
        scan_name
        scan_id
        platform_is_mobile
        n_gates_vary
        dimensions
        variables

Example PPI from Py-ART repository#

Example RHI from Py-ART repository#

Example EDGE NetCDF export format#

[8]:

filename = "netcdf/edge_netcdf.nc"
filename = get_wradlib_data_file(filename)
read_and_overview(filename)


Print keys for file edge_netcdf.nc
        TypeName
        DataType
        Latitude
        Longitude
        Height
        Time
        FractionalTime
        attributes
        NyquistVelocity-unit
        NyquistVelocity-value
        vcp-unit
        vcp-value
        radarName-unit
        radarName-value
        ColorMap-unit
        ColorMap-value
        Elevation
        ElevationUnits
        MissingData
        RangeFolded
        RadarParameters
        PRF-unit
        PRF-value
        PulseWidth-unit
        PulseWidth-value
        MaximumRange-unit
        MaximumRange-value
        ConversionPlugin
        dimensions
        variables