Add meta_data dictionary to reader class.

pygac/__init__.py

@@ -22,6 +22,7 @@
 
 import logging
 import os
+import numpy as np
 
 from pygac.version import __version__  # noqa
 
@@ -52,3 +53,10 @@ def centered_modulus(array, divisor):
     arr = array % divisor
     arr[arr > divisor / 2] -= divisor
     return arr
+
+
+def calculate_sun_earth_distance_correction(jday):
+    """Calculate the sun earth distance correction."""
+    # Earth-Sun distance correction factor
+    corr = 1.0 - 0.0334 * np.cos(2.0 * np.pi * (jday - 2) / 365.25)
+    return corr

pygac/gac_io.py

@@ -83,7 +83,11 @@ def save_gac(satellite_name,
              bt3, bt4, bt5,
              sun_zen, sat_zen, sun_azi, sat_azi, rel_azi,
              qual_flags, start_line, end_line,
-             gac_file, midnight_scanline, miss_lines):
+             gac_file, meta_data):
+
+    midnight_scanline = meta_data['midnight_scanline']
+    miss_lines = meta_data['missing_scanlines']
+    corr = meta_data['sun_earth_distance_correction_factor']
 
     last_scan_line_number = qual_flags[-1, 0]
 
@@ -199,10 +203,6 @@ def save_gac(satellite_name,
     starttime = start.strftime("%H%M%S%f")[:-5]
     enddate = end.strftime("%Y%m%d")
     endtime = end.strftime("%H%M%S%f")[:-5]
-    jday = int(start.strftime("%j"))
-
-    # Earth-Sun distance correction factor
-    corr = 1.0 - 0.0334 * np.cos(2.0 * np.pi * (jday - 2) / 365.25)
 
     # Apply scaling & offset
     bt3 -= 273.15

pygac/gac_klm.py

@@ -624,8 +624,7 @@ def main(filename, start_line, end_line):
                     sun_zen, sat_zen, sun_azi, sat_azi, rel_azi,
                     qual_flags, start_line, end_line,
                     reader.filename,
-                    reader.get_midnight_scanline(),
-                    reader.get_miss_lines())
+                    reader.meta_data)
     LOG.info("pygac took: %s", str(datetime.datetime.now() - tic))
 
 

pygac/gac_pod.py

@@ -430,8 +430,7 @@ def main(filename, start_line, end_line):
                     sun_zen, sat_zen, sun_azi, sat_azi, rel_azi,
                     qual_flags, start_line, end_line,
                     reader.filename,
-                    reader.get_midnight_scanline(),
-                    reader.get_miss_lines())
+                    reader.meta_data)
     LOG.info("pygac took: %s", str(datetime.datetime.now() - tic))
 
 

pygac/gac_reader.py

@@ -31,6 +31,7 @@
 import types
 
 from pygac import (CONFIG_FILE, centered_modulus,
+                   calculate_sun_earth_distance_correction,
                    get_absolute_azimuth_angle_diff)
 try:
     import ConfigParser
@@ -64,6 +65,7 @@ def __init__(self, interpolate_coords=True, adjust_clock_drift=True,
             tle_thresh: Maximum number of days between observation and nearest
                 TLE
         """
+        self.meta_data = {}
         self.interpolate_coords = interpolate_coords
         self.adjust_clock_drift = adjust_clock_drift
         self.tle_dir = tle_dir
@@ -255,15 +257,35 @@ def compute_lonlat(self, width, utcs=None, clock_drift_adjust=True):
 
         return lons.reshape(-1, width), lats.reshape(-1, width)
 
+    def get_sun_earth_distance_correction(self):
+        """Get the julian day and the sun-earth distance correction."""
+        self.get_times()
+        year = self.times[0].year
+        delta = self.times[0].date() - datetime.date(year, 1, 1)
+        jday = delta.days + 1
+        return calculate_sun_earth_distance_correction(jday)
+
+    def update_meta_data(self):
+        """Add some metd data to the meta_data dicitonary."""
+        if 'sun_earth_distance_correction_factor' not in self.meta_data.keys():
+            self.meta_data['sun_earth_distance_correction_factor'] = (
+                self.get_sun_earth_distance_correction())
+        if 'midnight_scanline' not in self.meta_data.keys():
+            self.meta_data['midnight_scanline'] = self.get_midnight_scanline()
+        if 'missing_scanlines' not in self.meta_data.keys():
+            self.meta_data['missing_scanlines'] = (
+                self.get_miss_lines()).astype(int)
+
     def get_calibrated_channels(self):
+        """Calibrate the solar channels."""
         channels = self.get_counts()
         self.get_times()
+        self.update_meta_data()
         year = self.times[0].year
         delta = self.times[0].date() - datetime.date(year, 1, 1)
         jday = delta.days + 1
 
-        # Earth-Sun distance correction factor
-        corr = 1.0 - 0.0334 * np.cos(2.0 * np.pi * (jday - 2) / 365.25)
+        corr = self.meta_data['sun_earth_distance_correction_factor']
 
         # how many reflective channels are there ?
         tot_ref = channels.shape[2] - 3

pygac/tests/test_io.py

@@ -212,8 +212,7 @@ def test_save_gac(self, check_user_scanlines, slice_channel, avhrr_gac_io,
             rel_azi=mm,
             qual_flags=mm,
             gac_file=mm,
-            midnight_scanline=mm,
-            miss_lines=mm
+            meta_data=mm
         )
         slice_channel.return_value = mm, 'miss', 'midnight'
         strip_invalid_lat.return_value = 0, 0

pygac/tests/test_reader.py

@@ -341,6 +341,15 @@ def test_correct_times_thresh(self, get_header_timestamp):
         self.reader.correct_times_thresh()
         numpy.testing.assert_array_equal(self.reader.utcs, utcs_expected)
 
+    def test_calculate_sun_earth_distance_correction(self):
+        """Test the calculate sun earth distance correction method."""
+        self.reader.utcs = np.array([315748035469, 315748359969,
+                                     315751135469, 315754371969,
+                                     315754371969]).astype('datetime64[ms]')
+        self.reader.times = self.reader.to_datetime(self.reader.utcs)
+        corr = self.reader.get_sun_earth_distance_correction()
+        numpy.testing.assert_almost_equal(corr, 0.96660494, decimal=7)
+
 
 def suite():
     """Test suite for test_reader."""