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Cloud Data Issues

Tracking of known problems and subsequent fixes is an important issue for MODIS data users. This page will act as a repository of all known MODIS Atmosphere Data Product problems, as well as how to determine the problematic version (and the fixed version) of the HDF data -- therefore data users should check this page for updates regularly. Data Users unfamiliar with how to properly track problems and fixes by determining the version of their downloaded HDF files should refer to the documentation at the bottom of this page.

Discontinuity in Collection 6 Aqua Data July 2016 and later

Description: 

A step function discontinuity (of about 1 to 2%) has been noted in the Collection 6 (006 or C6) Level-1B (L1B) input calibrated radiance data for MODIS Aqua data starting in July 2016 (moving forward), which impacts the downstream C6 MODIS Atmosphere Level-2 (L2) and Level-3 (L3) MODIS Aqua data.  This discontinuity should be noted by data users -- and will be fixed when the Aqua data dates from launch (July 2002) through June 2016 are reprocessed to Collection 6.1.  This Collection 6.1 (061 or C61) reprocessing will remove this few percent step function discontinuity.  Data users of MODIS Aqua Data for all Level-2 (L2) and Level-3 (L3) Daily atmosphere products should be aware of this step function discontinuity and replace their Collection 006 data with the new Collection 061 Aqua data when that becomes available in late 2017.

Guidance to Users: Users should note there is step function discontinuity of a percent or two starting in July 2016 for all MODIS Atmosphere Aqua data products.  This step function discontinuity will be fixed with the Collection 6.1 (061) Aqua reprocessing slated to begin in the Fall of 2017. Users should replace all C6 Aqua data with C61 Aqua data when it becomes available in late 2017.

Data Dates Affected: 1 July 2016 (Day 183) and forward -- a data discontinuity of a few percent will be noted.

Affected Platform: 
Aqua Only
Products Affected: 
Collections Affected: 

Missing Terra Data between 5 Aug 2017 and 6 Aug 2017

Description: 

Following the Terra Deep Space Calibration on August 5th, 2017 (2017 217) there were some faulty C6 Terra MODIS Atmosphere data as the focal plane temperatures did not return to nominal values until the day after - August 6th, 2017 (2017 218) 1420 UTC. So the granules for the time period between 2017 217 23:00 UTC and 2017 218 14:15 UTC were removed before the downstream Atmosphere processing. Data users will notice missing MODIS Atmosphere Data during this period for all Level-2 (L2) and Level-3 (L3) Daily atmosphere products.

Data Dates Affected: Note there will be Missing Terra Data between 2017 217 (5 Aug 2017) at 23:00 UTC and 2017 218 (6 Aug 2017) at 14:15 UTC for all MODIS Atmosphere L2 and L3 Daily products.

Affected Platform: 
Terra Only
Products Affected: 
Collections Affected: 

NISE (Snow and Ice Cover) Ancillary Input Anomaly

Description: 

NISE Snow and Ice Cover Ancillary Data is used by both Cloud Top Properties (CTP) and Cloud Optical Properties (COP), which are both part of the Cloud Product (06_L2).

NISE is a 5-day running average snow and sea ice cover (yes/no for snow and a percentage cover for sea ice) from the SSM/I-SSMIS instrument provided by the NSIDC (National Snow and Ice Data Center). The product is output on a polar grid at 20km resolution. If the granule time is before 12:00 UTC, the NISE product from the previous day is used, otherwise the product from the granule's day is used. The data in this product is used in conjunction with the gap-filled surface albedo product and the 1/10 degree broadband surface emissivity product in order to establish the final value of surface albedo or surface emissivity depending on the spectral channel.

A problem was previously identified in NISE where it was under-reporting snow cover over North America, and a bit less so over Northern Europe and Asia. This anomaly in ancillary input cascades through the Cloud Retrieval algorithm and produces anomalous results in a number of Cloud Product parameters.  The L2 Cloud Algorithm team has determined that the solution to this issue is to switch this snow and ice ancillary input from NISE to GEOS-5. However, that will not be done "mid-stream" -- so this fix is being held back until a reprocess of the data record is undertaken (Collection 061) sometime during 2017.

March 2017 update on this issue:

The MODIS cloud optical and microphysical properties product (MOD06) uses the NISE ground snow cover extent to determine which channel should be used as the non-absorbing band during retrieval of cloud optical thickness and cloud effective radius. In order to perform a good quality retrieval, we would like the surface to be as dark as possible. When there is snow on the ground, the standard 0.65 micron channel we use over land becomes very bright. However, the 1.2 micron channel remains dark for snow-covered surfaces. For bare ground 0.65 micron channel is better than 1.2 micron. In order to make the choice between 0.65 and 1.2 micron we need to know whether or not there is snow on the ground. The NISE product is used by the operational MOD06 product to make this determination.

Overall the impact of the change appears to be rather minimal. Some places have more snow -- some places have less. The exact map changes day to day and it does not appear that there will be any noticeable impact on mean monthly statistics of retrieved cloud optical thickness or cloud effective radius.

See the PDF document and Movie file linked below for a bit more detail (information and imagery).

NISE Issue Document (PDF)

  NISE Issue Movie (MP4)

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
≤ PGE06 v6.0.92 ≤ 2016 334 (11/30/2016) ≥ PGE06 v6.0.93 ≥ 2016 335 (12/1/2016)

Data Dates Affected: 1 December 2016 (Day 335) and forward

Affected Platform: 
Aqua and Terra
Products Affected: 
Collections Affected: 

GDAS Change Impacts

Description: 

New GDAS data is causing problems in the 1km Cloud Top Properties Algorithm causing bad (Level-2) 1km Cloud Top Properties data, as well as bad (Level-2) 1km Cloud Optical Properties data, to make it into distributed public HDF files starting for data dates in May 2016. For Level-3, the impact is mostly in the Cloud Optical Property SDS's since mostly the 1km COP data is propagated from L2 to L3, however there is one 1km CTP Joint Histogram that is computed in L3, which will be affected. Most of the other CTP SDS's in L3 are not impacted, since most of those are computed from the 5km L2 CTP data. A potential fix for this bad data is still being investigated as of May/June 2016. A fix should eventually be implemented, at which time affected data (data Dates of May 11, 2016 and later) will be rerun (corrected) and made available.

See the (draft) PDF document linked below for a bit more detail (information and imagery).

For more information, view this PDF document: 

GDAS Issue Document (PDF)

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
≤ v6.0.85 (Aqua) & 6.0.91 (Terra) ≤ 2016 132 (05/11/2016) Not Corrected Not Corrected

Data Dates Affected: 11 May 2016 (Day 132) and forward

Affected Platform: 
Aqua and Terra
Products Affected: 
Collections Affected: 

MOD06 (Aqua 5km Cloud Top Properties) Occasional chunks of missing CT data around Southern Africa in a 3 hour time window only (occuring only intermittantly).

Description: 

In early 2015, it was noticed that very occasionally there were areas of missing Cloud Top Properties (derived from 5km CT L2 ) data in L3 in the area of Southern Africa. This was traced back to the Level-2 5km Cloud Top Properties source data (06_L2). And later was diagnosed as a black body warm-up/cool-down issue that only occurs between 0900 and 1230 UTC. This actually was found to occasionally affect the 5km CT data since Aqua launch in July 2002, however it's been slowly getting worse over time.

Since this only impacts 5km Cloud Top Properties data and not 1km Cloud Top Properties data, the 1km Cloud Optical Properties data is not affected!

Here is a sample L3 image of Cloud Fraction (from Cloud Mask) for Daytime for 13Nov2014, which shows the missing data issue fairly clearly.

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
All ≥ July 2002 (Since Aqua launch) Not Corrected Not Corrected

Data Dates Affected: July 2002 to Current (Since Aqua launch)

Affected Platform: 
Aqua Only
Products Affected: 
Collections Affected: 

MOD35 (Terra Cloud Mask) False Clouds over Ocean (Impact of the MODIS Terra Band 29 (8.6 µm) radiometric calibration drift on cloud products)

Description: 

In early 2015, it was noticed that recent Terra Collection 6 (C6) cloud top pressure products (MOD06) contained ocean regions with an anonymously high incidence of low clouds. This was traced to false clouds being reported by the cloud mask (MOD35). In turn, this was found to be the result of errors in the b29-b31 brightness temperature difference (BTD) high (ice phase) cloud test. As a result, a substantial number of clear pixels were being flagged as cloudy by this test. The text that follows is a summary of the impact of the MODIS Terra Band 29 (8.6 µm) radiometric calibration drift on cloud products. MOD35 includes a spectral test using the brightness temperature difference (BTD) between band 29 (8.6 µm) and band 31 (11 µm), referred to here as the b29-b31 BTD test. This test is used only over water surfaces. The root problem is a gradual warming in the Terra MODIS b29 channel over the years, that is not being captured by the on-board calibration systems and apparently related to crosstalk issues. Monthly time series trend analysis of Terra MODIS cloud products indicates that the significance of the impact may extend back to 2010. In lieu of a successful fix to the L1B algorithm for b29, an adjustment to the 8.6-11 µm MOD35 test threshold was delivered to the production test system to quantify the impact. Testing of this potential fix in the data is ongoing as of September 2015. A fix should eventually be implemented, at which time affected data will be rerun (corrected) and made available. See the PDF document linked below for for detailed information and imagery.

MODIS Terra Band 29 (8.6 micron) impact of calibration drift on cloud products (PDF)

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
All ≥ 2010 001 (1/1/2010) Not Corrected Not Corrected

Data Dates Affected: January 2010 to present (but worse 2014 and beyond)

Affected Platform: 
Terra Only
Products Affected: 
Collections Affected: 

Data Quality Statement for the Level-2 5-km and 1-km Cloud Top Property Products

Description: 

For C6 a number of updates and improvements were made to the cloud top property products (cloud top pressure, height, temperature and cloud effective emissivity) and are documented extensively in Menzel et al. [2008, J. Appl. Meteor. Climatol., 47, 1175-1198]. In C5 and earlier versions, these parameters were available only at 5-km spatial resolution. In C6, these parameters are now available for the first time at the same 1-km resolution as the cloud optical and microphysical properties. The figure below provides an example Aqua MODIS granule from 28 August 2006 at 1630 UTC. A false color image is shown in (a), the 5-km cloud top heights in (b) and 1-km cloud top heights in (c). The 1-km product more accurately captures the broken low cloud field seen near the center of the image. Also note the linear structure in the comma-shaped cloud feature of a mid-latitude storm (lower right) that is easily seen in both products but is not obvious in the false color image. This striping, seen in the highest cloud top retrievals, is caused by mismatches between observed radiances and the 1-degree resolution NWP model profiles of temperature, moisture, and ozone that are necessary inputs to the CO2-slicing algorithm. Additional information, including comparisons of C6 cloud top heights to those derived from the CALIOP lidar, are available in Baum et al. [2012, J. Appl. Meteor. Climatol., 51, 1145-1163].

Guidance for Users: The updated 5-km and new 1-km cloud top property products underwent extensive testing and evaluation, and are expected to be of better quality than the C5 products. Users should choose between the 1-km and 5-km products based on individual needs. For example, the 1-km product is best if finer spatial resolution is a paramount concern, and the 5-km version is suggested for comparisons with heritage data such as HIRS. The 5-km product generally exhibits higher signal to noise characteristics, i.e., more spatially consistent retrievals when clear-sky minus cloudy-sky radiance differences are very small. Users should be aware that the aggregated cloud top property parameters (and associated histograms) in the 08_D3/E3/M3 daily/eight-day/monthly global gridded Level-3 products are currently based on the 5-km Level-2 products.

Data Dates Affected: All Data Dates

Affected Platform: 
Aqua and Terra
Products Affected: 
Collections Affected: 

Data Quality Statement for the Level-2 1-km and 5-km Infrared (IR) Cloud Phase

Description: 

For C6 a number of updates and improvements were made to the IR cloud phase that are documented extensively in Baum et al. [2012, J. Appl. Meteor. Climatol., 51, 1145-1163]. In C5 and earlier versions, this parameter was available only at 5-km spatial resolution; in C6, it is now available for the first time at the same 1-km resolution as the cloud optical and microphysical properties. However, instead of replacing the existing 5-km IR phase product with the new 1-km version, the algorithm development team decided to maintain in C6 a version of the 5-km product for continuity with C5. Users should be aware that the processing framework changed significantly for the 1-km IR phase retrieval. Because the older framework for the 5-km phase retrieval could not be easily modified without a complete rewrite, among other constraints, algorithm development and evaluation focused instead on the 1-km products. Differences between the 1-km and 5-km products should be expected. The cloud phase figure provides an example Aqua MODIS granule (28 August 2006, 1630 UTC; false color image in upper left panel) for which the 1-km and 5-km IR cloud phase products significantly diverge; the discrimination of optically thin cirrus as being of ice phase is improved significantly in the 1-km retrievals over that in the 5-km retrievals.

Guidance for Users: The new 1-km IR cloud phase underwent extensive testing and evaluation through comparison with CALIPSO/CALIOP products, and is expected to be of better quality than the heritage 5-km products. Furthermore, it is likely that the 1-km and 5-km products will continue to diverge as further improvements to the 1-km products are made over time. Users are thus advised to use the 1-km IR phase product both now and in the future. Users should also be aware that the aggregated IR cloud phase (and associated histograms) in the 08_D3/E3/M3 daily/eight-day/monthly global gridded Level-3 products are currently based on the 5-km Level-2 products.

Data Dates Affected: All data dates

Affected Platform: 
Aqua and Terra
Products Affected: 
Collections Affected: 

Four Minor Corrections including updated Surface Albedo and Alternate Solution Logic (ASL)

Description: 

The following changes entered Aqua forward processing starting on the production date given below. Aqua data generated before the corrected Production Date (noted below) was not reprocessed. Terra was not impacted as Terra processing had not yet begun when the problem was found and fixed.

Surface Spectral Albedo Dataset updated through 2013: The MOD06 ancillary land/snow albedo dataset is an 8-day cadence (16-day average) gap-filled dataset derived from the Collection 5 MOD43 product. With a recent update of the ancillary dataset through 2013, MODAPS is reprocessing all 2013 MOD06 cloud optical property datasets for C6 Aqua. In addition, forward processing (2014 and onward) will use the albedo dataset from the corresponding 2013 time period. This was found to have minor impact on cloud optical retrievals for a monthly aggregation from a test version of the MODIS Atmosphere Level-3 product. (Data Impact from this item was of minor consequence)

Alternate Solution Logic (ASL) algorithm: Instances occur when the retrieved cloud optical thickness is > 150 and the shortwave infrared (SWIR) or mid-wave infrared (MWIR) channel reflectance is within the valid look-up table (LUT) solution space for cloud effective radii (CER) retrievals. For such pixels, the previous ASL CER solution interpolation routine occasionally defaulted to the closest LUT grid point CER integer value instead of interpolating between the two adjacent LUT grid points. This update now provides interpolated CER. This minor issue generally only occurs at high latitudes and large solar zenith angles. (Data Impact from this item was of minor consequence)

Cloud Optical Thickness (1.6 and 3.7 micron retrievals) capped at 150: A bug fix was implemented to fix a few Cloud Optical Thickness 16 & 37 Retrievals that were beyond the 150 maximum. This was happening for a small number of very bright clouds (typically at low sun angles. In this new version, all valid COT retrievals fall in the 0 to 150 range. (Data Impact from this item was of minor consequence)

New Scattering Parameter SDS attribute: To improve documentation for Cloud Product (06_L2) data users, local attributes have been added to the 2-dimensional Scattering Property SDSs to provide the MODIS channels and cloud effective radii corresponding to the rows and columns of the datasets. The modified SDSs and their dimensions follow.

  • Liquid Water Cloud LUT Scattering Parameter SDSs (7 channels x 18 effective radii):

            1.) Asymmetry_Parameter_Liq, 2.) Single_Scatter_Albedo_ Liq, 3.) Extinction_Efficiency_Liq

  • Ice Cloud LUT Scattering Parameter SDSs (7 channels x 12 effective radii):

            1.) Asymmetry_Parameter_Ice, 2.) Single_Scatter_Albedo_Ice, 3.) Extinction_Efficiency_Ice

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
≤ PGE06 v6.0.79 ≤ 2014 258 (9/15/2014) ≥ PGE06 v6.0.80 ≥ 2014 259 (9/16/2014)

Data Dates Affected: January 2013 to April 2014

Affected Platform: 
Aqua Only
Products Affected: 
Collections Affected: 

Cloud Optical Thickness (1.6 and 3.7 micron retrieval) Overflow

Description: 

A few Cloud Optical Thickness 16 & 37 Retrievals are outside the expected valid range of 0 to 150. The intended maximum reported value for a successful Cloud Optical Thickness (COT) retrieval was increased from 100 in Collection 5 to 150 in Collection 6 (C6). However the new C6 COT datasets Cloud_Optical_Thickness_16 and Cloud_Optical_Thickness_37 were inadvertently not limited to 150. Therefore, for a small number of very bright clouds (typically at low sun angles), these two COT datasets can exceed 150 or become negative due to an integer overflow (beyond a COT value of 327.67, which corresponds to a packed short integer value of 32767 (the largest I*2 value that can be stored)). Users are advised that if they encounter a COT value in these datasets that is either greater than 150, or less than 0 but not a fill value, then the value should be set back to 150. This minor COT dataset issue has been remedied for Aqua forward processing starting on "Data Date" January 1, 2013 (with an HDF File "Production Date" of 2014 111 or later). Since the problem was found before C6 Terra processing began, no C6 Terra data was impacted.

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
≤ PGE06 v6.0.73 ≤ 2014 110 (4/20/2014) ≥ PGE06 v6.0.74 ≥ 2014 111 (4/21/2014)

Data Dates Affected: July 2002 to December 2012

Affected Platform: 
Aqua Only
Products Affected: 
Collections Affected: