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Level 1B
Instrument Performance History
Non-uniform digital count (DN) bin-fill factors (bin-width)
Description | L1B Impact | L2 Impact | Cause | Mitigation | Schedule | History
DESCRIPTION:
On-orbit analyses show that the DN (digital number, or count) bin-width fill-factors frequently vary by factors of two and greater from one DN value to the adjacent DN value. These characteristics are most prominent for Bands 31 - 36, but may be present in all bands. These patterns are channel-dependent for Bands 31 – 36.
IMPACT TO L1B DATA SET:
The non-uniformity is apparent in DN patterns of 2's, 4's, 8's, 16's and sometimes 32's. Pre-launch DN quantitative uncertainty was assessed by the instrument builder as up to +2.7/-1.0.
ESTIMATED IMPACT TO L2 SCIENCE PRODUCTS:
Analyses of sea surface temperature have indicated that this uncertainty due to non-uniform bin-fill is likely to be the limiting source of error in the SST retrieval.
CAUSE OF EFFECT:
The effect is related to the presence of system noise "at the moment" an analog signal is converted to its digital equivalent. The presence of a noise equivalent to one bit or less will appear as different DN patterns depending on the noise that is present in the moment for which a bit is being determined.
MITIGATION APPROACH/ADDED TESTING TO CHARACTERIZE EFFECT:
Pre-launch sensor thermal vacuum testing of the Terra MODIS showed that this characteristic was less of a problem for the B-side electronics than the A-side electronics. Therefore, the decision was made to switch from the A-side (primary) electronics to the B-side (backup) electronics. The Terra MODIS configuration was switched to the B-side on October 30, 2000 and analyses show a reduction in ADC noise as a result. The so-called "bin-filling" effects appears to have been reduced by a factor of 2 for the LWIR bands used in the Pathfinder SST product.
ESTIMATED SCHEDULE TO COMPLETE:
Reassess in new side-A era, summer 2001.
HISTORY OF CHARACTERISTIC:
| Epoch Number |
Time Span | Version Number at start of epoch |
General Characteristics | Improvements | Documentation |
|---|---|---|---|---|---|
| 1 | Feb. 24, 2000 - Oct. 30, 2000 2000055.1550 - 2000304.1400 |
2.3.2.0 | Ubiquitous, but most prominent in LWIR PC bands. | Not applicable. | |
| 2 | Oct. 30, 2000 - June 15, 2001 2000304.1600 - 2001. |
2.4.4.0 | Corrected bug in emissive bands PC_XT pre-processing. PC LUTs updated based on 2000084 moon observation. | Not prominent on side-B. | |
| 3 | July 2, 2001 - present 2001183.2100 - present |
3.0.0.6 | Ubiquitous, but most prominent in LWIR PC bands. | Not applicable. | MsWG histograms, July 25, 2001 |
Description | L1B Impact | L2 Impact | Cause | Mitigation | Schedule | History
Please contact Jack Xiong with any technical questions concerning these pages.
Responsible Civil Servant:
Dr. Jack Xiong <Xiaoxiong.Xiong.1@gsfc.nasa.gov>
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Last Update: July 1, 2008