Fix time variables in netcdf creation

base_time is epoch seconds
time_offset is seconds from base_time
time is hours from midnight

aosstower/level_b1/nc.py

@@ -75,7 +75,7 @@ def write_dimensions(nc_file):
 
 def create_variables(nc_file, first_stamp, database, chunk_sizes=None, zlib=False):
     # base_time long name
-    btln = 'base time as unix timestamp'
+    btln = 'Base time in Epoch'
 
     # base time units
     btu = 'seconds since 1970-01-01 00:00:00'
@@ -83,21 +83,25 @@ def create_variables(nc_file, first_stamp, database, chunk_sizes=None, zlib=Fals
     # base time string
     bts = first_stamp.strftime('%Y-%m-%d 00:00:00Z')
 
-    # time long name
-    tln = 'Time offset from base_time'
+    # time offset long name
+    to_ln = 'Time offset from base_time'
 
-    # time units
-    tu = 'seconds since ' + first_stamp.strftime('%Y-%m-%d 00:00:00Z')
+    # time offset units
+    to_u = 'seconds since ' + first_stamp.strftime('%Y-%m-%d 00:00:00Z')
+    # 'time' units
+    t_u = 'hours since ' + first_stamp.strftime('%Y-%m-%d 00:00:00Z')
 
     coordinates = {
         # fields: type, dimension, fill, valid_min, std_name, longname, units, valid_max, cf_role, axis
-        'time': [np.float64, ('time',), -999., None, None, "Time offset from epoch",
-                 "seconds since 1970-01-01 00:00:00Z", None, None, None],
+        'time': [np.float64, ('time',), -999., None, None, "Hour offset from midnight",
+                 t_u, None, None, None],
         'lon': [np.float32, tuple(), -999., -180., 'longitude', None, 'degrees_east', 180., None],
         'lat': [np.float32, tuple(), -999., -90., 'latitude', None, 'degrees_north', 90., None],
         'alt': [np.float32, tuple(), -999., None, 'height', 'vertical distance', 'm', None, None],
+        # int64 for base_time would be best, but NetCDF4 Classic does not support it
+        # NetCDF4 Classic mode was chosen so users can use MFDatasets (multi-file datasets)
         'base_time': [np.int32, tuple(), -999., None, 'time', btln, btu, None, None],
-        'time_offset': [np.float64, ('time',), -999., None, 'time', tln, tu, None, None],
+        'time_offset': [np.float64, ('time',), -999., None, 'time', to_ln, to_u, None, None],
         'station_name': ['c', ('max_len_station_name',), '\0', None, None, 'station name', None, None, 'timeseries_id'],
     }
 
@@ -184,12 +188,8 @@ def calculate_wind_gust(wind_speed_5s, wind_speed_2m):
 
         http://www.nws.noaa.gov/asos/pdfs/aum-toc.pdf
 
-    Criteria Summary
-    ----------------
-
-    Wind Gust:
-
-        1. 2 minute average
+    Note: This operates on wind data in meters per second even though the
+    ASOS User's Guide operates on knots.
 
     Arguments:
         wind_speed_5s (Series): 5-second average of instantaneous wind speed magnitudes in m/s
@@ -289,15 +289,17 @@ def write_vars(nc_file, frame, database):
     base_epoch = frame.index[0].replace(hour=0, minute=0, second=0, microsecond=0).value // 10**9
 
     fileVar = nc_file.variables
+    # base_time is midnight of the current day
     fileVar['base_time'].assignValue(base_epoch)
     fileVar['time_offset'][:] = time_epoch - base_epoch
-    fileVar['time'][:] = time_epoch
+    # hours since midnight
+    fileVar['time'][:] = (time_epoch - base_epoch) / (60 * 60)
 
     # write coordinate var values to file
     # alt might not be right, need to verify
     fileVar['lon'].assignValue(station.LONGITUDE)
     fileVar['lat'].assignValue(station.LATITUDE)
-    fileVar['alt'].assignValue(328)
+    fileVar['alt'].assignValue(station.ELEVATION)
 
     # write station name to file
     fileVar['station_name'][:len(STATION_NAME)] = STATION_NAME
@@ -370,6 +372,8 @@ def create_giant_netcdf(input_files, output_fn, zlib, chunk_size,
         chunk_sizes = [frame.shape[0]]
 
     first_stamp = dt.strptime(str(frame.index[0]), '%Y-%m-%d %H:%M:%S')
+    # NETCDF4_CLASSIC was chosen so that MFDataset reading would work. See:
+    # http://unidata.github.io/netcdf4-python/#netCDF4.MFDataset
     nc_file = Dataset(output_fn, 'w', format='NETCDF4_CLASSIC')
     write_dimensions(nc_file)
     create_variables(nc_file, first_stamp, database, chunk_sizes, zlib)

aosstower/station.py

@@ -5,8 +5,9 @@ from datetime import timedelta
 # Time between data samples in seconds
 DATA_INTERVAL = timedelta(seconds=5)
 
-# station elevation in meters above the surface in feet
-ELEVATION = 325
+# these heights are for the top of the penthouse roof
+ELEVATION = 329.522  # meters above mean sea level
+HEIGHT = 294.8338  # height in meters above ground level
 
 # Id of station from v1 records
 ID = 1