DNB Cross Talk Review
1 July 2014
Steve Miller (CSU-CIRA)
Contributions from William Straka (UW-CIMSS), Curtis Seaman (CSU-CIRA), Lushalan
Liao (NGST), Stephanie Weiss (NGST), and Steve Mills (Renaissance Man Eng.)
Overview
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Raytheon FP13 lab tests suggest cross talk may exist between certain detectors &
aggregation modes in the High Gain Stage.
Out of specification by up to factor of 3, depending on certain pixel/aggregation
mode combinations.
Would manifest as possible spurious signal in detectors 1 and 16 (i.e., first and last
scan lines of a 16 scan line bundle).
In the product paradigm, the cross talk is from detector 9 into 16, and from 8 into
1 (this is flipped from Raytheon charts which are shown in ‘sensor order’.)
Options to correct non-compliance:
– Accept waiver for use-as-is.
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No cost impact, no delivery schedule impact
– Change require to encompass existing performance as measured for F1 VIIRS NPP and JPSS J1
(requires a corresponding verification documentaion change to TPs, RVP, RVSS, etc.)
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“Very low” cost impact for req. and verif. document changes, no delivery schedule impact
– Redesign DNB Timing Card (FPGA timing)
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“Low” cost impact, no impact on instrument delivery schedule
3rd
option (timing card) ostensibly benign, but “low cost” is relative and there may
be other risks and unanticipated impacts to a redesign
Need to establish that the issue is significant enough to warrant Option 3
This document does not constitute an official guidance/recommendation on the
waiver request—simply supporting information
FP-13 Testing
• Cross talk into HGB side in response to HGA side illumination
• Recipient detectors 1 and 16 (off-diagonal) are the main offenders, although some
adjacent detector cross talk is prevalent in HGB (broadening of the diagonal)
• No cross talk of note in the mid and low gain stages—this is a HG issue
EFR3461 Investigation
DNB Module Level using J1 FPA at operating temperature (simulating operation conditions)
• Note that the cross talk into detectors 1 and 16 are most prominent at Agg Mode 1
(nadir) and nearly negligible at Agg Mode 32 (edge of scan).
• Timing must be more precise at lower aggregation modes, when more sub-detectors
are being combined.
• Note the significant performance differences between HGA and HGB…nominally the
two should be identical
• HGA and HGB are typically averaged to produce HGS in operations
November 2012
HGSdn = 0.5(HGA+HGB)
Possible sign of spurious
cross talk in detectors 1, 16
(Note: instantaneous
values may be much higher)
Courtesy, L. Liao (NGST)
• Statistics suggest that the effects of the cross talk do exist in the data
• Difficult to find (uncommon) but may be significant when they do appear.
7 May 2014 2129 UTC Persian Gulf Gas Flares
Possible
Cross Talk
• Occasional spurious signals in the presence of strong gas flares.
• Adjacent darkening in adjacent lines of same scan angle—sign of possible cross talk.
• Not seen in cities. Sometimes seen in fires…
Provisional Summary
• Operational data show indications of the cross talk
problem.
• Difficult to identify in DNB imagery. Extreme cases of
isolated gas flares may provide examples of worst-case
scenarios.
• Effects not discerned over most anthropogenic light sources
(cities, ships, etc.)
• We continue to search for examples, including possible
HGA and HGB exclusive imagery collected during VROP 702
(pending).
• An Option 3 fix to the DNB timing card may introduce
unanticipated risks.
• There exist other issues (stray light leakage) which may
present more pressing issues in terms of DNB performance.