DNB Cross Talk Review

1 July 2014Steve 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• 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. • 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.)• “Very low” cost impact for req. and verif. document changes, no delivery schedule impact

– Redesign DNB Timing Card (FPGA timing)• “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

Courtesy, L. Liao (NGST)

Possible sign of spurious cross talk in detectors 1, 16

(Note: instantaneous values may be much higher)

• 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.

November 2012HGSdn = 0.5(HGA+HGB)

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…

7 May 2014 2129 UTC Persian Gulf Gas Flares

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.