DOC: Add example for dealiasing rhi data (#1775)

* DOC: Add example for dealiasing rhi data

* Update examples/correct/plot_dealias_rhi.py

Author: mgrover1

examples/correct/plot_dealias_rhi.py

@@ -0,0 +1,141 @@
+"""
+==========================================
+Dealias doppler velocities for an RHI file
+==========================================
+
+In this example doppler velocities from range height indicator (RHI) scans are dealiased,
+using custom parameters with the region-based dealiasing algorithm in Py-ART.
+"""
+
+print(__doc__)
+
+# Author: Max Grover (mgrover@anl.gov)
+
+import matplotlib.pyplot as plt
+from open_radar_data import DATASETS
+
+import pyart
+
+# Read data from the open-radar-data package
+file = DATASETS.fetch("cfrad.20211011_223602.712_to_20211011_223612.091_DOW8_RHI.nc")
+radar = pyart.io.read(file)
+
+#################################################
+# **Apply the default parameters for dealiasing**
+#
+# Now let's apply the default region-based technique
+
+# Retrieve the nyquist velocity from the first sweep
+nyq = radar.instrument_parameters["nyquist_velocity"]["data"][0]
+
+# Apply the dealiasing algorithm with default parameters
+velocity_dealiased = pyart.correct.dealias_region_based(
+    radar,
+    vel_field="VEL",
+    nyquist_vel=nyq,
+)
+
+# Add the field to the radar object
+radar.add_field("corrected_velocity", velocity_dealiased, replace_existing=True)
+
+# Visualize the output
+fig = plt.figure(figsize=(12, 4))
+ax1 = fig.add_subplot(121)
+display = pyart.graph.RadarDisplay(radar)
+display.plot(
+    "VEL",
+    ax=ax1,
+    vmin=-30,
+    vmax=30,
+    cmap="balance",
+    title="Uncorrected Radial Velocity",
+)
+cbar = display.cbs[0]
+# Modify the colorbar label and size
+cbar.set_label(label="Raw Radial Velocity ($V_{R}$) [m/s]", fontsize=12)
+plt.ylim(0, 10)
+plt.xlim(20, 60)
+
+ax2 = fig.add_subplot(122)
+display = pyart.graph.RadarDisplay(radar)
+display.plot(
+    "corrected_velocity",
+    ax=ax2,
+    vmin=-30,
+    vmax=30,
+    cmap="balance",
+    title="Corrected Radial Velocity",
+)
+cbar = display.cbs[0]
+# Modify the colorbar label and size
+cbar.set_label(label="Corrected Radial Velocity ($V_{R}$) [m/s]", fontsize=12)
+plt.ylim(0, 10)
+plt.xlim(20, 60)
+
+#################################################
+# **Refining the technique**
+#
+# If we use the default configuration, notice how extreme
+# the values are for the output. The algorithm keys on the
+# small variations in the clear air returns, and
+# results in much larger values than would be expected.
+# It is considered best practice to apply a base-level of
+# quality control here to improve the results. We can use velocity
+# texture as a base level, where the noisier data will be removed.
+
+# Calculate the velocity texture and add it to the radar object
+vel_texture = pyart.retrieve.calculate_velocity_texture(
+    radar,
+    vel_field="VEL",
+    nyq=nyq,
+)
+radar.add_field("velocity_texture", vel_texture, replace_existing=True)
+
+# Set up the gatefilter to be based on the velocity texture.
+gatefilter = pyart.filters.GateFilter(radar)
+gatefilter.exclude_above("velocity_texture", 6)
+
+# Dealias with the gatefilter and add the corrected field to the radar object
+velocity_dealiased = pyart.correct.dealias_region_based(
+    radar,
+    vel_field="VEL",
+    nyquist_vel=nyq,
+    gatefilter=gatefilter,
+)
+radar.add_field("corrected_velocity", velocity_dealiased, replace_existing=True)
+
+# Visualize the output
+fig = plt.figure(figsize=(12, 4))
+ax1 = fig.add_subplot(121)
+display = pyart.graph.RadarDisplay(radar)
+display.plot(
+    "VEL",
+    ax=ax1,
+    vmin=-30,
+    vmax=30,
+    cmap="balance",
+    title="Uncorrected Radial Velocity",
+)
+cbar = display.cbs[0]
+
+# Modify the colorbar label and size
+cbar.set_label(label="Raw Radial Velocity ($V_{R}$) [m/s]", fontsize=12)
+plt.ylim(0, 10)
+plt.xlim(20, 60)
+
+ax2 = fig.add_subplot(122)
+display = pyart.graph.RadarDisplay(radar)
+display.plot(
+    "corrected_velocity",
+    ax=ax2,
+    vmin=-30,
+    vmax=30,
+    cmap="balance",
+    title="Corrected Radial Velocity",
+)
+cbar = display.cbs[0]
+
+# Modify the colorbar label and size
+cbar.set_label(label="Corrected Radial Velocity ($V_{R}$) [m/s]", fontsize=12)
+plt.ylim(0, 10)
+plt.xlim(20, 60)