Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Fix negative channel 3A slope calibration coefficient in AVHRR reader #2123

Merged
merged 3 commits into from Jul 29, 2022
Merged

Fix negative channel 3A slope calibration coefficient in AVHRR reader #2123

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
9554805
Also the slope of channel 3A can be negative
Jun 10, 2022
ea9b102
Channel 3a is in index 2
Jun 10, 2022
4d88d41
Handle negative slope2 the same way for all visible channels
Jun 13, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
17 changes: 8 additions & 9 deletions satpy/readers/aapp_l1b.py
View file
Open in desktop
Expand Up @@ -593,15 +593,14 @@ def _vis_calibrate(data,
intercept2 = da.from_array(data["calvis"][:, chn, coeff_idx, 3],
chunks=line_chunks) * 1e-7

if chn == 1:
# In the level 1b file, the visible coefficients are stored as 4-byte integers. Scaling factors then convert
# them to real numbers which are applied to the measured counts. The coefficient is different depending on
# whether the counts are less than or greater than the high-gain/low-gain transition value (nominally 500).
# The slope for visible channels should always be positive (reflectance increases with count). With the
# pre-launch coefficients the channel 2 slope is always positive but with the operational coefs the stored
# number in the high-reflectance regime overflows the maximum 2147483647, i.e. it is negative when
# interpreted as a signed integer. So you have to modify it.
slope2 = da.where(slope2 < 0, slope2 + 0.4294967296, slope2)
# In the level 1b file, the visible coefficients are stored as 4-byte integers. Scaling factors then convert
# them to real numbers which are applied to the measured counts. The coefficient is different depending on
# whether the counts are less than or greater than the high-gain/low-gain transition value (nominally 500).
# The slope for visible channels should always be positive (reflectance increases with count). With the
# pre-launch coefficients the channel 2, 3a slope is always positive but with the operational coefs the stored
# number in the high-reflectance regime overflows the maximum 2147483647, i.e. it is negative when
# interpreted as a signed integer. So you have to modify it. Also chanel 1 is treated the same way in AAPP.
slope2 = da.where(slope2 < 0, slope2 + 0.4294967296, slope2)

channel = da.where(channel <= intersection[:, None],
channel * slope1[:, None] + intercept1[:, None],
Expand Down