modis2airs_collect: add use of MISSING flag

flags.py

@@ -3,3 +3,4 @@
 INVALID = 1
 LOW = 2
 HIGH = 4
+MISSING = 8

modis2airs_collect.py

 import numpy
 import sys
 
+from flags import *
 from modis_bright import modis_bright
 from pyhdf.SD import SD, SDC
 from util import HdfWriter
@@ -47,12 +48,13 @@ bt_mean[:] = modis_bright(rad_mean)
 std_bt[:] = modis_bright(rad_mean + rad_std) - bt_mean
 
 # for any pixel where N is zero, use fill values for the other
-# variables
+# variables and set the MISSING flag
 missing_idxs = (n == 0)
 rad_mean[missing_idxs] = -9999.0
 rad_std[missing_idxs] = -9999.0
 bt_mean[missing_idxs] = -9999.0
 std_bt[missing_idxs] = -9999.0
+flags[missing_idxs] = MISSING
 
 # output to HDF
 writer = HdfWriter(output_file)