ENH: read_mmcr method to read ARM MMCR b1-level data files (#1704)

* ENH: `read_mmcr` method to read ARM MMCR b1-level data files

* STY: pep8

* STY: linting

* STY: linting

* STY: linting

* FIX: add options to read dual-pol channel data; PRT from file instead of hardwired handbook values

Author: isilber

pyart/aux_io/__init__.py

@@ -14,6 +14,7 @@
 """
 
 from .arm_vpt import read_kazr  # noqa
+from .arm_vpt import read_mmcr  # noqa
 from .d3r_gcpex_nc import read_d3r_gcpex_nc  # noqa
 from .edge_netcdf import read_edge_netcdf  # noqa
 from .gamic_hdf5 import read_gamic  # noqa

pyart/aux_io/arm_vpt.py

@@ -218,3 +218,267 @@ def read_kazr(
         elevation,
         instrument_parameters=instrument_parameters,
     )
+
+
+def read_mmcr(
+    filename,
+    field_names=None,
+    additional_metadata=None,
+    file_field_names=False,
+    exclude_fields=None,
+    include_fields=None,
+    mode_names=None,
+    mode_to_extract=None,
+):
+    """
+    Read millimeter wavelength cloud radar (MMCR) b1 NetCDF ingest data.
+
+    Parameters
+    ----------
+    filename : str
+        Name of NetCDF file to read data from.
+    field_names : dict, optional
+        Dictionary mapping field names in the file names to radar field names.
+        Unlike other read functions, fields not in this dictionary or having a
+        value of None are still included in the radar.fields dictionary, to
+        exclude them use the `exclude_fields` parameter. Fields which are
+        mapped by this dictionary will be renamed from key to value.
+    additional_metadata : dict of dicts, optional
+        This parameter is not used, it is included for uniformity.
+    file_field_names : bool, optional
+        True to force the use of the field names from the file in which
+        case the `field_names` parameter is ignored. False will use to
+        `field_names` parameter to rename fields.
+    exclude_fields : list or None, optional
+        List of fields to exclude from the radar object. This is applied
+        after the `file_field_names` and `field_names` parameters. Set
+        to None to include all fields specified by include_fields.
+    include_fields : list or None, optional
+        List of fields to include from the radar object. This is applied
+        after the `file_field_names` and `field_names` parameters. Set
+        to None to include all fields not specified by exclude_fields.
+    mode_names: dict
+        Keys are mode dimension indices. Values are the corresponding mode
+        abbreviations and prt. Using default values if None.
+    mode_to_extract: str or None
+        Abbreviation of mode to extract.
+        Extracting all data for all modes if None.
+
+    Returns
+    -------
+    radar_out : Radar or dict of Radar objects
+        If `mode_to_extract` is None, returns a dict with keys representing operated modes and
+        values the corresponding `Radar` object.
+        If `mode_to_extract` is specified returning the `Radar` object corresponding to the that
+        mode.
+
+    """
+
+    if mode_names is None:
+        mode_names = {
+            1: "bl",
+            2: "ci",
+            3: "ge",
+            4: "pr",
+            5: "dualpol_ch0",  # Dual-pol receiver 0
+            6: "dualpol_ch1",  # Dual-pol receiver 1
+        }
+
+    # create metadata retrieval object
+    filemetadata = FileMetadata(
+        "cfradial",
+        field_names,
+        additional_metadata,
+        file_field_names,
+        exclude_fields,
+        include_fields,
+    )
+
+    # read the data
+    ncobj = netCDF4.Dataset(filename)
+    ncvars = ncobj.variables
+
+    # 4.1 Global attribute -> move to metadata dictionary
+    metadata = {k: getattr(ncobj, k) for k in ncobj.ncattrs()}
+    metadata["n_gates_vary"] = "false"
+
+    # 4.2 Dimensions (do nothing)
+
+    # 4.3 Global variable -> move to metadata dictionary
+    if "volume_number" in ncvars:
+        metadata["volume_number"] = int(ncvars["volume_number"][:])
+    else:
+        metadata["volume_number"] = 0
+
+    global_vars = {
+        "platform_type": "fixed",
+        "instrument_type": "radar",
+        "primary_axis": "axis_z",
+    }
+    # ignore time_* global variables, these are calculated from the time
+    # variable when the file is written.
+    for var, default_value in global_vars.items():
+        if var in ncvars:
+            metadata[var] = str(netCDF4.chartostring(ncvars[var][:]))
+        else:
+            metadata[var] = default_value
+
+    # 4.4 coordinate variables -> create attribute dictionaries (`_range` is generated in loop below)
+
+    # 4.5 Ray dimension variables
+
+    # 4.6 Location variables -> create attribute dictionaries
+    # the only difference in this section to cfradial.read_cfradial is the
+    # minor variable name differences:
+    # latitude -> lat
+    # longitude -> lon
+    # altitdue -> alt
+    latitude = cfradial._ncvar_to_dict(ncvars["lat"])
+    longitude = cfradial._ncvar_to_dict(ncvars["lon"])
+    altitude = cfradial._ncvar_to_dict(ncvars["alt"])
+
+    # 4.7 Sweep variables -> create atrribute dictionaries
+    # this is the section that needed the most work since the initial NetCDF
+    # file did not contain any sweep information
+    sweep_number = filemetadata("sweep_number")
+    sweep_number["data"] = np.array([0], dtype=np.int32)
+
+    sweep_mode = filemetadata("sweep_mode")
+    sweep_mode["data"] = np.array(["vertical_pointing"], dtype=str)
+
+    fixed_angle = filemetadata("fixed_angle")
+    fixed_angle["data"] = np.array([90.0], dtype=np.float32)
+
+    sweep_start_ray_index = filemetadata("sweep_start_ray_index")
+    sweep_start_ray_index["data"] = np.array([0], dtype=np.int32)
+
+    # first sweep mode determines scan_type
+    # this module is specific to vertically-pointing data
+    scan_type = "vpt"
+
+    # 4.8 Sensor pointing variables -> create attribute dictionaries
+    # this section also required some changes since the initial NetCDF did not
+    # contain any sensor pointing variables
+
+    # 4.9 Moving platform geo-reference variables
+
+    # 4.10 Moments field data variables -> field attribute dictionary
+    # all variables with dimensions of 'time', 'heights' are fields
+    keys = [k for k, v in ncvars.items() if v.dimensions == ("time", "heights")]
+
+    # Determine if one or more modes are to be extracted and generate Radar object(s) output
+    if mode_to_extract is None:
+        modes = np.unique(ncvars["ModeNum"])
+        radar_out = {}
+    else:
+        modes = [key for key in mode_names.keys() if mode_names[key] == mode_to_extract]
+    for mode in modes:
+        mode_sample_indices = ncvars["ModeNum"] == np.array(mode)
+        active_range = ncvars["heights"][mode, :] > 0.0
+        range_arr = ncvars["heights"][mode, active_range] - altitude["data"]
+        time = cfradial._ncvar_to_dict(ncvars["time"])
+        time["data"] = ncvars["time"][mode_sample_indices]
+        _range = {
+            "long_name": "Range (center of radar sample volume)",
+            "units": "m AGL",
+            "missing_value": -9999.0,
+            "data": range_arr,
+        }
+
+        fields = {}
+        for key in keys:
+            field_name = filemetadata.get_field_name(key)
+            if field_name is None:
+                if exclude_fields is not None and key in exclude_fields:
+                    continue
+                if include_fields is not None and key not in include_fields:
+                    continue
+                field_name = key
+
+            d = {
+                k: getattr(ncvars[key], k)
+                for k in ncvars[key].ncattrs()
+                if k not in ["scale_factor", "add_offset"]
+            }
+            d["data"] = ncvars[key][mode_sample_indices, active_range]
+            fields[field_name] = d
+
+        # 4.5 instrument_parameters sub-convention -> instrument_parameters dict
+        # this section needed multiple changes and/or additions since the
+        # instrument parameters were primarily located in the global attributes
+        # this section is likely still incomplete
+
+        sweep_end_ray_index = filemetadata("sweep_end_ray_index")
+        sweep_end_ray_index["data"] = np.array([time["data"].size - 1], dtype=np.int32)
+
+        azimuth = filemetadata("azimuth")
+        azimuth["data"] = 0.0 * np.ones(time["data"].size, dtype=np.float32)
+
+        elevation = filemetadata("elevation")
+        elevation["data"] = 90.0 * np.ones(time["data"].size, dtype=np.float32)
+
+        omega = float(ncobj.radar_operating_frequency.split()[0])
+        frequency = filemetadata("frequency")
+        frequency["data"] = np.array([omega / 1e9], dtype=np.float32)
+
+        prt_mode = filemetadata("prt_mode")
+        prt_mode["data"] = np.array(["fixed"], dtype=str)
+
+        prt = filemetadata("prt")
+        prt["data"] = np.full(
+            time["data"].size, ncvars["InterPulsePeriod"][mode] * 1e-9, dtype=np.float32
+        )
+
+        nyquist_velocity = filemetadata("nyquist_velocity")
+        nyquist_velocity["data"] = np.full(
+            time["data"].size, ncvars["NyquistVelocity"][mode], dtype=np.float32
+        )
+
+        n_samples = filemetadata("n_samples")
+        n_samples["data"] = np.full(
+            time["data"].size, ncvars["NumSpectralAverages"][mode], dtype=np.float32
+        )
+
+        # 4.6 radar_parameters sub-convention -> instrument_parameters dict
+        # this section needed multiple changes and/or additions since the
+        # radar instrument parameters were primarily located in the global
+        # attributes
+        # this section is likely still incomplete
+        instrument_parameters = {
+            "frequency": frequency,
+            "prt_mode": prt_mode,
+            "prt": prt,
+            "nyquist_velocity": nyquist_velocity,
+            "n_samples": n_samples,
+        }
+
+        # 4.7 lidar_parameters sub-convention -> skip
+        # 4.8 radar_calibration sub-convention -> skip
+
+        Radar_tmp = Radar(
+            time,
+            _range,
+            fields,
+            metadata,
+            scan_type,
+            latitude,
+            longitude,
+            altitude,
+            sweep_number,
+            sweep_mode,
+            fixed_angle,
+            sweep_start_ray_index,
+            sweep_end_ray_index,
+            azimuth,
+            elevation,
+            instrument_parameters=instrument_parameters,
+        )
+        if mode_to_extract is None:
+            radar_out[mode_names[mode]] = Radar_tmp
+        else:
+            radar_out = Radar_tmp
+
+    # close NetCDF object
+    ncobj.close()
+
+    return radar_out