FIX: 8bit/16bit, big-endian/little-endian in nexrad reader (#231)

* fix 8bit/16bit, big-endian/little-endian in nexrad reader
* only apply mask for 2 byte data
* add history.md entry

docs/history.md

@@ -3,6 +3,8 @@
 ## 0.8.0 (2024-10-28)
 
 This is the first version which uses datatree directly from xarray. Thus, xarray is pinned to version >= 2024.10.0.
+
+* FIX: Correctly handle 8bit/16bit, big-endian/little-endian in nexrad reader (PHI and ZDR) ({issue}`230`) by [@syedhamidali](https://github.com/syedhamidali), ({pull}`231`) by [@kmuehlbauer](https://github.com/kmuehlbauer).
 * ENH: Refactoring all xradar backends to use `from_dict` datatree constructor. Test for `_get_required_root`, `_get_subgroup`, and `_get_radar_calibration` were also added ({pull}`221`) by [@aladinor](https://github.com/aladinor)
 * ENH: Added pytests to the missing functions in the `test_xradar` and `test_iris` in order to increase codecov in ({pull}`228`) by [@syedhamidali](https://github.com/syedhamidali).
 * ENH: Updated Readme ({pull}`226`) by [@syedhamidali](https://github.com/syedhamidali).

xradar/io/backends/nexrad_level2.py

@@ -600,16 +600,15 @@ def get_data(self, sweep_number, moment=None):
             ngates = moments[name]["ngates"]
             word_size = moments[name]["word_size"]
             data_offset = moments[name]["data_offset"]
-            ws = {8: 1, 16: 2}
-            width = ws[word_size]
+            width = {8: 1, 16: 2}[word_size]
             data = []
             self.rh.pos += data_offset
-            data.append(self._rh.read(ngates, width=width).view(f"uint{word_size}"))
+            data.append(self._rh.read(ngates, width=width).view(f">u{width}"))
             while self.init_next_record() and self.record_number <= stop:
                 if self.record_number in intermediate_records:
                     continue
                 self.rh.pos += data_offset
-                data.append(self._rh.read(ngates, width=width).view(f"uint{word_size}"))
+                data.append(self._rh.read(ngates, width=width).view(f">u{width}"))
             moments[name].update(data=data)
 
     def get_data_header(self):
@@ -1247,9 +1246,9 @@ def __init__(self, datastore, name, var):
             - len(datastore.ds["intermediate_records"])
         )
         nbins = max([v["ngates"] for k, v in datastore.ds["sweep_data"].items()])
-        self.dtype = np.dtype("uint8")
-        if name == "PHI":
-            self.dtype = np.dtype("uint16")
+        word_size = datastore.ds["sweep_data"][name]["word_size"]
+        width = {8: 1, 16: 2}[word_size]
+        self.dtype = np.dtype(f">u{width}")
         self.shape = (nrays, nbins)
 
     def _getitem(self, key):
@@ -1259,8 +1258,14 @@ def _getitem(self, key):
         except KeyError:
             self.datastore.root.get_data(self.group, self.name)
             data = self.datastore.ds["sweep_data"][self.name]["data"]
-        if self.name == "PHI":
+        # see 3.2.4.17.6 Table XVII-I Data Moment Characteristics and Conversion for Data Names
+        word_size = self.datastore.ds["sweep_data"][self.name]["word_size"]
+        if self.name == "PHI" and word_size == 16:
+            # 10 bit mask, but only for 2 byte data
             x = np.uint16(0x3FF)
+        elif self.name == "ZDR" and word_size == 16:
+            # 11 bit mask, but only for 2 byte data
+            x = np.uint16(0x7FF)
         else:
             x = np.uint8(0xFF)
         if len(data[0]) < self.shape[1]: