MODAPS PCR 12-001
| PCR Number | 12-001 |
|---|---|
| Date | 2012-01-27 |
| Initiator | Brian Wenny |
| Abstract | PGE02 v6.1.15 (LUT: v6.1.15_1) has been updated to remain consistent with change needed only for Terra products; to prohibit dropped granules due to both sides of PCLW electronics being on simultaneously; to develop new algorithms for estimating the uncertainties; to ensure the higher-order polynomial more accurately fits the available calibration data; and, to ensure the new algorithm accurately models the impacts due to the LWIR FPA temperature changes. |
| Problem Statement | 1. Detectors 29 and 30 of Terra band 2 suffer from cross-talk problems from another band, which affect only the first of the 4 sub-frames of data in each frame. The L1B code is currently written to treat as a fatal error the occurrence of any engineering data packet that indicates that PCLW (Photo Conductive Long Wave infrared) electronics side A and side B are on simultaneously. However the PC subsystem is one of only three on the MODIS instrument where it is in fact possible to have the side A and side B electronics on at the same time. This has never been done, and is unlikely to ever be done. However, corrupt data packets have been known to make it appear as if this was happening, usually for just a few scans.2. At the request of Science Team members, the calculation of the uncertainties was reviewed by MCST analysts. They concluded that the current calculations produce results that are not as accurate as they could be.3. The on-board calibrator may not be able to correctly track the gain change for a few RSB bands, and the RSB rvs derived from the Moon and SD calibrations may not be able to correctly reveal the rvs on-orbit change either.4. On-orbit changes in the LWIR FPA temperature have a noticeable impact to the default b1 for Aqua bands 33, 35 and 36 when the blackbody temperature is above a certain threshold. |
| Description of Change | 1. Provide new LUTs containing sub-frame bit flags for every detector in 250m and 500m bands indicating whether they are noisy or dead. Change the L1B code to mark pixels affected by dead sub-frames with a special fill value. Provide Metadata in the L1B product identifying which sub-frames are noisy and dead.2. Change the algorithm so that a granule will not be dropped due to both sides of PCLW electronics being on at the same time, unless this is true for all scans in the granule. For those scans where both sides of PCLW electronics are on at the same time, no calibration will be performed, and the pixels will be filled by a special value 65524 for the L1B Scaled Integer (SI) output.3. New algorithms have been developed for estimating the uncertainties, requiring corresponding changes in the LUTs.4. Change to model the RSB rvs with a 4th order polynomial instead of quadratic one, as a function of frame number. The dimension size of RSB rvs LUT has to be changed to accommodate the 4th polynomial coefficients.5. Change to calculate the temperature dependent default b1 usingb1 = default_b1_baseline*(1+c1*(Tlwir – Tlwir_baseline))where default_b1_baseline, c1 and Tlwir_baseline are provided by MCST through 3 new time-dependent LUTs, Tlwir is the real time LWIR FPA temperature. One old LUT named bb_t_sat_default_b1_aqua_table has been removed. |
| Products Affected | MYD021KM, MYD02HKM, MYD02QKM, MYD021QA1. A special fill value has been introduced for the pixels in L1B granule affected by in-operable sub-frames.2. A special fill value has been introduced to mark pixels filled because both sides of the PCLW electronics are turned on.3. The Uncertainty Indices SDSs in the L1B product4. The L1B product for RSB bands.5. The TEB bands (bands 33, 35 and 36) in L1B product during blackbody warm up/cool down events. |
| Software Affected | PGE02 v6.1.15, LUT: v6.1.15_1, Process: MOD_PR02AQUA, Recipe: PM1M_1(nrt)(m) v6.0.13 Input File: MYD02_Emissive_LUTs.hdf, MYD02_Reflective_LUTs.hdf , MYD02_QA_LUTs.hdf |
| Processing String to Receive the Change | Aqua Forward, Aqua Reprocessing |
| Downstream Product Effects | 1. As long as there are no Aqua detectors with sub-frame problems, there will be no change in the products due to the new sub-frame features.2. All downstream products will have entire granules of data available (that would otherwise not have been) if corrupt data packets make it appear that both sides of PCLW electronics were on for a few scans.3. Any downstream product using the L1B Uncertainty Indices will see somewhat more accurate values.4. Any downstream product using L1B reflectance and radiance product in RSB bands will see less spurious variation due to scan angle.5. Any downstream product using bands 33, 35 and 36 L1B data will see slightly more accurate vales, though the impact will only be significant during quarterly blackbody warm up/cool down events. |
| Data Granules to be Used for Science Testing | Granules between 2011233.0840 and 2011233.1315. |
| Justification | 1. Consistency with change needed currently only for Terra products..2. While calibration data are not reliable for the scans with both sides of electronics on, this should not cause the entire granule to be dropped. This is especially true since most such events are spurious, due to corrupt data packets.3. At the request of the users, a thorough re-analysis of the uncertainty indices was done, new algorithms were developed, and preliminary results were reported at the MsWG meeting, where they met the approval of the science teams.4. The higher-order polynomial more accurately fits the available calibration data, and preliminary feedback from the science teams has been positive.5. The new algorithm accurately models the impacts due to the LWIR FPA temperature changes. |
| Effective Date for Implementation of Change | 2012-01-31 |
| Status | Steve Platnick approved for Atmospheres, Sadashiva Devadiga approved for Land, Bryan Franz approved for Oceans and Michael King approved on 06/05/2012. |
