NEXRAD Level 2#
[1]:
import cmweather # noqa
import xarray as xr
from open_radar_data import DATASETS
import xradar as xd
Download#
Fetching NEXRAD Level2 radar data file from open-radar-data repository.
[2]:
filename = DATASETS.fetch("KATX20130717_195021_V06")
Downloading file 'KATX20130717_195021_V06' from 'https://github.com/openradar/open-radar-data/raw/main/data/KATX20130717_195021_V06' to '/home/docs/.cache/open-radar-data'.
xr.open_dataset#
Making use of the xarray nexradlevel2
backend. We also need to provide the group. Note, that we are using CfRadial2 group access pattern.
[3]:
ds = xr.open_dataset(filename, group="sweep_0", engine="nexradlevel2")
display(ds)
<xarray.Dataset> Size: 42MB Dimensions: (azimuth: 720, range: 1832) Coordinates: elevation (azimuth) float64 6kB ... time (azimuth) datetime64[ns] 6kB ... * range (range) float32 7kB 2.125e+03 2.375e+03 ... 4.599e+05 longitude float64 8B ... latitude float64 8B ... altitude int64 8B ... * azimuth (azimuth) float64 6kB 0.2582 0.7526 1.272 ... 359.3 359.8 Data variables: DBZH (azimuth, range) float64 11MB ... ZDR (azimuth, range) float64 11MB ... PHIDP (azimuth, range) float64 11MB ... RHOHV (azimuth, range) float64 11MB ... sweep_mode <U20 80B ... sweep_number int64 8B ... prt_mode <U7 28B ... follow_mode <U7 28B ... sweep_fixed_angle float64 8B ... Attributes: instrument_name: KATX scan_name: VCP-11
[4]:
ds
[4]:
<xarray.Dataset> Size: 42MB Dimensions: (azimuth: 720, range: 1832) Coordinates: elevation (azimuth) float64 6kB ... time (azimuth) datetime64[ns] 6kB ... * range (range) float32 7kB 2.125e+03 2.375e+03 ... 4.599e+05 longitude float64 8B ... latitude float64 8B ... altitude int64 8B ... * azimuth (azimuth) float64 6kB 0.2582 0.7526 1.272 ... 359.3 359.8 Data variables: DBZH (azimuth, range) float64 11MB ... ZDR (azimuth, range) float64 11MB ... PHIDP (azimuth, range) float64 11MB ... RHOHV (azimuth, range) float64 11MB ... sweep_mode <U20 80B ... sweep_number int64 8B ... prt_mode <U7 28B ... follow_mode <U7 28B ... sweep_fixed_angle float64 8B ... Attributes: instrument_name: KATX scan_name: VCP-11
[5]:
import numpy as np
np.testing.assert_almost_equal(ds.sweep_fixed_angle.values, 0.4833984)
Plot Time vs. Azimuth#
[6]:
ds.azimuth.plot()
[6]:
[<matplotlib.lines.Line2D at 0x7f8a64007110>]

Plot Range vs. Time#
We need to sort by time and specify the y-coordinate.
[7]:
ds.DBZH.sortby("time").plot(y="time", cmap="HomeyerRainbow")
[7]:
<matplotlib.collections.QuadMesh at 0x7f8a63e85220>

Plot Range vs. Azimuth#
[8]:
ds.DBZH.plot(cmap="HomeyerRainbow")
[8]:
<matplotlib.collections.QuadMesh at 0x7f8a6414bec0>

backend_kwargs#
Beside first_dim
there are several additional backend_kwargs for the nexradlevel2 backend, which handle different aspects of angle alignment. This comes into play, when azimuth and/or elevation arrays are not evenly spacend and other issues.
[9]:
help(xd.io.NexradLevel2BackendEntrypoint)
Help on class NexradLevel2BackendEntrypoint in module xradar.io.backends.nexrad_level2:
class NexradLevel2BackendEntrypoint(xarray.backends.common.BackendEntrypoint)
| Xarray BackendEntrypoint for NEXRAD Level2 Data
|
| Method resolution order:
| NexradLevel2BackendEntrypoint
| xarray.backends.common.BackendEntrypoint
| builtins.object
|
| Methods defined here:
|
| open_dataset(self, filename_or_obj, *, mask_and_scale=True, decode_times=True, concat_characters=True, decode_coords=True, drop_variables=None, use_cftime=None, decode_timedelta=None, group=None, lock=None, first_dim='auto', reindex_angle=False, fix_second_angle=False, site_coords=True, optional=True)
| Backend open_dataset method used by Xarray in :py:func:`~xarray.open_dataset`.
|
| ----------------------------------------------------------------------
| Data and other attributes defined here:
|
| __annotations__ = {}
|
| description = 'Open NEXRAD Level2 files in Xarray'
|
| open_dataset_parameters = ('filename_or_obj', 'mask_and_scale', 'decod...
|
| url = 'tbd'
|
| ----------------------------------------------------------------------
| Methods inherited from xarray.backends.common.BackendEntrypoint:
|
| __repr__(self) -> 'str'
| Return repr(self).
|
| guess_can_open(self, filename_or_obj: 'str | os.PathLike[Any] | ReadBuffer | AbstractDataStore') -> 'bool'
| Backend open_dataset method used by Xarray in :py:func:`~xarray.open_dataset`.
|
| open_datatree(self, filename_or_obj: 'str | os.PathLike[Any] | ReadBuffer | AbstractDataStore', *, drop_variables: 'str | Iterable[str] | None' = None) -> 'DataTree'
| Backend open_datatree method used by Xarray in :py:func:`~xarray.open_datatree`.
|
| open_groups_as_dict(self, filename_or_obj: 'str | os.PathLike[Any] | ReadBuffer | AbstractDataStore', *, drop_variables: 'str | Iterable[str] | None' = None) -> 'dict[str, Dataset]'
| Opens a dictionary mapping from group names to Datasets.
|
| Called by :py:func:`~xarray.open_groups`.
| This function exists to provide a universal way to open all groups in a file,
| before applying any additional consistency checks or requirements necessary
| to create a `DataTree` object (typically done using :py:meth:`~xarray.DataTree.from_dict`).
|
| ----------------------------------------------------------------------
| Data descriptors inherited from xarray.backends.common.BackendEntrypoint:
|
| __dict__
| dictionary for instance variables
|
| __weakref__
| list of weak references to the object
[10]:
ds = xr.open_dataset(filename, group="sweep_0", engine="nexradlevel2", first_dim="time")
display(ds)
<xarray.Dataset> Size: 42MB Dimensions: (time: 720, range: 1832) Coordinates: elevation (time) float64 6kB ... * time (time) datetime64[ns] 6kB 2013-07-17T19:50:21.652000 .... * range (range) float32 7kB 2.125e+03 2.375e+03 ... 4.599e+05 longitude float64 8B ... latitude float64 8B ... altitude int64 8B ... azimuth (time) float64 6kB ... Data variables: DBZH (time, range) float64 11MB ... ZDR (time, range) float64 11MB ... PHIDP (time, range) float64 11MB ... RHOHV (time, range) float64 11MB ... sweep_mode <U20 80B ... sweep_number int64 8B ... prt_mode <U7 28B ... follow_mode <U7 28B ... sweep_fixed_angle float64 8B ... Attributes: instrument_name: KATX scan_name: VCP-11
open_nexradlevel2_datatree#
The same works analoguous with the datatree loader. But additionally we can provide a sweep string, number or list.
[11]:
help(xd.io.open_nexradlevel2_datatree)
Help on function open_nexradlevel2_datatree in module xradar.io.backends.nexrad_level2:
open_nexradlevel2_datatree(filename_or_obj, mask_and_scale=True, decode_times=True, concat_characters=True, decode_coords=True, drop_variables=None, use_cftime=None, decode_timedelta=None, sweep=None, first_dim='auto', reindex_angle=False, fix_second_angle=False, site_coords=True, optional=True, lock=None, **kwargs)
Open a NEXRAD Level2 dataset as an `xarray.DataTree`.
This function loads NEXRAD Level2 radar data into a DataTree structure, which
organizes radar sweeps as separate nodes. Provides options for decoding time
and applying various transformations to the data.
Parameters
----------
filename_or_obj : str, Path, file-like, or DataStore
The path or file-like object representing the radar file.
Path-like objects are interpreted as local or remote paths.
mask_and_scale : bool, optional
If True, replaces values in the dataset that match `_FillValue` with NaN
and applies scale and offset adjustments. Default is True.
decode_times : bool, optional
If True, decodes time variables according to CF conventions. Default is True.
concat_characters : bool, optional
If True, concatenates character arrays along the last dimension, forming
string arrays. Default is True.
decode_coords : bool, optional
If True, decodes the "coordinates" attribute to identify coordinates in the
resulting dataset. Default is True.
drop_variables : str or list of str, optional
Specifies variables to exclude from the dataset. Useful for removing problematic
or inconsistent variables. Default is None.
use_cftime : bool, optional
If True, uses cftime objects to represent time variables; if False, uses
`np.datetime64` objects. If None, chooses the best format automatically.
Default is None.
decode_timedelta : bool, optional
If True, decodes variables with units of time (e.g., seconds, minutes) into
timedelta objects. If False, leaves them as numeric values. Default is None.
sweep : int or list of int, optional
Sweep numbers to extract from the dataset. If None, extracts all sweeps into
a list. Default is the first sweep.
first_dim : {"time", "auto"}, optional
Defines the first dimension for each sweep. If "time," uses time as the
first dimension. If "auto," determines the first dimension based on the sweep
type (azimuth or elevation). Default is "auto."
reindex_angle : bool or dict, optional
Controls angle reindexing. If True or a dictionary, applies reindexing with
specified settings (if given). Only used if `decode_coords=True`. Default is False.
fix_second_angle : bool, optional
If True, corrects errors in the second angle data, such as misaligned
elevation or azimuth values. Default is False.
site_coords : bool, optional
Attaches radar site coordinates to the dataset if True. Default is True.
optional : bool, optional
If True, suppresses errors for optional dataset attributes, making them
optional instead of required. Default is True.
kwargs : dict
Additional keyword arguments passed to `xarray.open_dataset`.
Returns
-------
dtree : xarray.DataTree
An `xarray.DataTree` representing the radar data organized by sweeps.
[12]:
dtree = xd.io.open_nexradlevel2_datatree(filename, sweep=4)
display(dtree)
<xarray.DatasetView> Size: 232B Dimensions: () Data variables: volume_number int64 8B 0 platform_type <U5 20B 'fixed' instrument_type <U5 20B 'radar' time_coverage_start <U20 80B '2013-07-17T19:51:38Z' time_coverage_end <U20 80B '2013-07-17T19:52:00Z' longitude float64 8B -122.5 altitude int64 8B 195 latitude float64 8B 48.19 Attributes: Conventions: None instrument_name: KATX version: None title: None institution: None references: None source: None history: None comment: im/exported using xradar scan_name: VCP-11
Plot Sweep Range vs. Time#
[13]:
dtree["sweep_4"].ds.DBZH.sortby("time").plot(y="time", cmap="HomeyerRainbow")
[13]:
<matplotlib.collections.QuadMesh at 0x7f8a5aca7cb0>

Plot Sweep Range vs. Azimuth#
[14]:
dtree["sweep_4"].ds.DBZH.plot(cmap="HomeyerRainbow")
[14]:
<matplotlib.collections.QuadMesh at 0x7f8a47d81970>

[15]:
dtree = xd.io.open_nexradlevel2_datatree(filename, sweep="sweep_8")
display(dtree)
<xarray.DatasetView> Size: 232B Dimensions: () Data variables: volume_number int64 8B 0 platform_type <U5 20B 'fixed' instrument_type <U5 20B 'radar' time_coverage_start <U20 80B '2013-07-17T19:53:05Z' time_coverage_end <U20 80B '2013-07-17T19:53:25Z' longitude float64 8B -122.5 altitude int64 8B 195 latitude float64 8B 48.19 Attributes: Conventions: None instrument_name: KATX version: None title: None institution: None references: None source: None history: None comment: im/exported using xradar scan_name: VCP-11
[16]:
dtree = xd.io.open_nexradlevel2_datatree(filename, sweep=[0, 1, 8])
display(dtree)
<xarray.DatasetView> Size: 232B Dimensions: () Data variables: volume_number int64 8B 0 platform_type <U5 20B 'fixed' instrument_type <U5 20B 'radar' time_coverage_start <U20 80B '2013-07-17T19:50:21Z' time_coverage_end <U20 80B '2013-07-17T19:53:25Z' longitude float64 8B -122.5 altitude int64 8B 195 latitude float64 8B 48.19 Attributes: Conventions: None instrument_name: KATX version: None title: None institution: None references: None source: None history: None comment: im/exported using xradar scan_name: VCP-11
[17]:
dtree["sweep_0"]["sweep_fixed_angle"].values
[17]:
array(0.48339844)
[18]:
dtree["sweep_8"]["sweep_fixed_angle"].values
[18]:
array(6.19628906)
[19]:
dtree = xd.io.open_nexradlevel2_datatree(
filename,
)
display(dtree)
<xarray.DatasetView> Size: 232B Dimensions: () Data variables: volume_number int64 8B 0 platform_type <U5 20B 'fixed' instrument_type <U5 20B 'radar' time_coverage_start <U20 80B '2013-07-17T19:50:21Z' time_coverage_end <U20 80B '2013-07-17T19:55:11Z' longitude float64 8B -122.5 altitude int64 8B 195 latitude float64 8B 48.19 Attributes: Conventions: None instrument_name: KATX version: None title: None institution: None references: None source: None history: None comment: im/exported using xradar scan_name: VCP-11
[20]:
dtree["sweep_1"]
[20]:
<xarray.DatasetView> Size: 21MB Dimensions: (azimuth: 720, range: 1192) Coordinates: elevation (azimuth) float64 6kB ... time (azimuth) datetime64[ns] 6kB ... * range (range) float32 5kB 2.125e+03 2.375e+03 ... 2.999e+05 longitude float64 8B -122.5 latitude float64 8B 48.19 altitude int64 8B 195 * azimuth (azimuth) float64 6kB 0.2499 0.7938 1.252 ... 359.2 359.8 Data variables: DBZH (azimuth, range) float64 7MB ... VRADH (azimuth, range) float64 7MB ... WRADH (azimuth, range) float64 7MB ... sweep_mode <U20 80B 'azimuth_surveillance' sweep_number int64 8B ... prt_mode <U7 28B ... follow_mode <U7 28B ... sweep_fixed_angle float64 8B ...
[ ]: