Changes between Initial Version and Version 1 of FAQ/aplmask

Timestamp:

Oct 18, 2011, 10:18:39 AM (14 years ago)

Author:

benj

Comment:

--

FAQ/aplmask

@@ +1 @@
+=== Q: What do the values in the mask file delivered with my data represent? ===
+
+'''A:'''[[BR]]
+There is a description of this data at the bottom of the accompanying
+.hdr file for the mask files. The values are:
+
+|| Value || Description ||
+|| 0     || Good data   ||
+|| 1     || Underflows  ||
+|| 2     || Overflows   ||
+|| 4     || Bad pixels in the CCD detector ||
+|| 8     || Pixel affected by uncorrected smear ||
+|| 16    || Dropped scans ||
+
+If there is more than one issue with a pixel it will have a value equal
+to the sum of the corresponding values. For example, a bad pixel which
+has also overflowed would have DN=6 (2+4).
+
+The bad pixels in the CCD detector (i.e. the pixels marked 4 in the mask
+file and in the separate ASCII file) come from a list supplied
+by the manufacturers resulting from the Hawk instrument calibration.
+These pixels are supposedly not recording accurately and are not to be
+trusted. We know this list to contain certain inaccuracies and hope to
+generate a more representative list in the future.
+
+The masks have been generated as a by product of applying the
+calibration to the raw data. So if during calibration the value of a
+pixel has underflowed (gone below 0) then we give it a value of
+1 in the mask file.  Similarly, if the data has overflowed (> sensor
+maximum) we will apply a value of 2 to the mask.
+
+In the level 1 data, underflowing pixels are set to 0 (the minimum
+possible for an unsigned integer).  An overflowed level 0 pixel may
+result in a valid but wrong level 1 value, which is kept if it is less
+than 65535 (the maximum allowed level 1 data value) or otherwise forced
+to 65535.  We retain the computed value mostly in order to allow people
+to quickview the image more easily without scaling problems, but it
+should be masked when actually used.
+
+[wiki:FAQ Back to FAQ]