Transcript imagery_tagup_cliang_2012-12-04-NCCStatus.ppt

NCC Status
December 04, 2012
Calvin Liang
Stephanie Weiss
NGAS A&DP
Path Forward to Investigate NCC EDR Issues
• Proposed steps to investigate NCC issue:
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•Completed
•In Work
•Planned
1.
Collect SVDNB, GDNBO, and IVOBC granules from August 16-17th, 2012 – Around new
moon
2.
Construct stray light correction lookup table (LUT) from new moon data
3.
Apply stray light correction LUT to new moon granules using NGAS stray light correction
algorithm
4.
Determine best functional fit to corrected radiances and account for night glow. (In work right
now)
5.
Produce a new GVVSSE/GVVSLE LUT based on the new functional fits.
6.
Remove stray light in problematic granules
7.
Run the latest version of the NCC EDR algorithm in ADL on stray light corrected granules
(results are shown using ADL 3.1)
8.
Inspect output to determine whether some of the problems identified in the granules go away
with stray light correction
9.
If it is found that fixing stray light does not completely solve the problems, then we will delve
into the NCC EDR algorithm logic (Wrote offline NCC code for testing)
Radiance vs Solar Zenith After Stray Light
Correction
New Lunar
table to
account for
night glow
Straylight
removed
Noise floor 7e-11
Some overcorrection but
very little
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Current SZA cutoff = 105
C. Liang, NGAS
Issues with NCC Algorithm:
• Currently the solar and lunar tables are identical. If there were no night glow,
this would not be an issue.
– Dynamic range between the solar radiances (~10-2) and night glow (~10-9 to ~10-11) span 7-9
orders of magnitude vs. the dynamic range between the lunar radiances (10-7) is only about 2-4
orders of magnitude. This causes many of the NCC albedos to fall out of range because
assuming the lunar and solar tables to be identical creates too large a gain difference between
maximum lunar radiances and the night glow.
– Possible solutions:
• Either we need to subtract out night glow in the GVVSSE and GVVSLE LUT and add a night
glow term into the NCC algorithm
• Rescale the lunar table such that the night glow starts at an earlier lunar angle such that
when the night glow portion of the curve is rescaled by the lunar irradiance, the night glow is
at the proper level (method used for the subsequent results).
• Given the NCC albedo range of [0,5] auroras get cut out (too bright)
• Algorithm truncates negative radiances (darkest of scenes)
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VNCCO-npp-d20120612-t0006266-e0007556b03229-c20121128164800490932-ng-sw.png
Aurora overwhelms albedo because aurora radiances are
~10-7 , roughly what you expect from a bright full moon
image with lunar zenith angles near 0.
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VNCCO-npp-d20120612-t0010428-e0012136b03229-c20121128164836145891-ng-sw.png
Lunar
Solar
Lunar
Solar
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If aurora is in the scene where both the solar and lunar
zenith angles are around 105, the albedos on the lunar side
will overwhelm the solar side.
VNCCO-npp-d20120612-t0014555-e0016351b03229-c20121128164838068159-ng-sw.png
NCC works well when solar
conditions dominate. Data
that spans ~4-6 orders of
magnitude now only span 1.
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Aurora Imagery (NCC)
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Aurora Imagery (SDR)
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Summary
• For lunar conditions, the albedo range limit of [0,5] cuts out
– Negative radiances which leads to removal of real features that are observable in the DNB SDRs
– Auroras because they are too bright
• Conditions for which the sun’s illumination dominates, the NCC product
produces good results. Results in the terminator are satisfactory
• Question: How do the end users want to use the NCC product?
– The DNB SDR radiances, though they are not projected onto their respective geolocation,
produce very nice imagery for day and night conditions. Auroras are particularly nice using the
SDR imagery (can easily be geolocated)
– NCC really serves to reduce the dynamic range of atmospheric/ground features in the terminator
where the SDR imagery span ~4-6 orders of magnitude.
– Aurora conditions will be problematic for NCC.
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