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Water Vapor Issues (05_L2)

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 in the Introduction sublink (the top link along the LHS of this page).   Note that a checkmark (✔) in the tables below means Data Issue or Quality Statement applies.  A blank means it's been fixed or does not apply.




Water Vapor Data Issues: Table of Contents & Anchor Links  (Note: Anchor Links point to a specific place within this page.)

Collection/Platform where Issues Apply
Issue Impact C6.1/Terra C6.1/Aqua C6.0/Terra C6.0/Aqua Anchor Link
#1. Bad Terra IR WV Profiles (Band 27)

H

 

 

 ✔

 

Link

#2. Bad Near IR WV

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Link

#3. Suspect Nighttime IR WV

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Link




Issue #1: Incorrect Terra IR Water Vapor Profiles (in MOD07 and copied to MOD05) from Band 27 Crosstalk

Description: In the month of April 2016, this update was received from the PGE03 (Atm Profile / Cloud Mask) developers: A band 27 cross-talk problem (in Terra only) that started around the year 2010 and became more pronounced over time, produced incorrect IR Water Vapor profiles with artificially low moisture content in the middle atmospheric layer and excessively high values in the upper troposphere. The MODIS Calibration Support Team (MCST) is still investigating possible fixes for this problem. The IR Water Vapor profile data is in an SDS called "Water_Vapor_Infrared" in the 05_L2 (Water Vapor Product) file. Note that this is a duplicate of the same SDS in the 07_L2 (Atm Profiles Product). Finally, note that the alternate Water Vapor parameter based on NIR bands: "Water_Vapor_Near_Infrared", which is only in the 05_L2 (Water Vapor Product) file, is not affected by this problem.

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
C6.0 PGE03 (All Versions) ≥ 2010 001 (01/01/2010) Corrected in C6.1 Corrected in C6.1

Data Dates Affected: ≥ January 2010

Affected Platform: Terra Only

Collections Affected: Collection 6.0 (Fixed in Collection 6.1)

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Issue #2: Bad Near-Infrared (NIR) Water Vapor Data

Description: There was a problem in the Near IR (NIR) Water Vapor Product in Collection 006 related to the use of re-aggregated L1B as input. The solution was to use the original non-aggregated L1B and reprocess the entire Aqua data record.

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
C6.0 ≤ PGE04 v6.0.37 ≤ 2014 191 (07/10/2014) C6.0 ≥ PGE04 v6.0.38 ≥ 2014 195 (07/14/2014)

Data Dates Affected: July 2002 to July 2014

Affected Platform: Aqua Only

Collections Affected: Collection 6.0

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Issue #3: Suspect Infrared (IR) Water Vapor Data at Night

Description: It should noted that the Infrared (IR) Water Vapor Data is copied from 07_L2 into 05_L2. There was a problem in the Collection 6 (C6) Atmosphere Profile Product (07_L2) for nighttime data only. In the nighttime (07_L2) granules, an error occurred in selecting the proper GDAS (NCEP 1-Degree Global Data Assimilation Model) re-analyses ancillary data file. Instead of selecting the file closest in time with a less than 3 hour time differences between the GDAS time and the granule time, the algorithm selected the wrong GDAS file time resulting in as much as a 6 hour time difference. The 07_L2 algorithm uses the surface pressure variable of the GDAS reanalyses to determine the lowest level of the atmospheric temperature, moisture, and ozone profiles. To set the lowest level as accurate as possible is very important for integrating the water vapor content of the column and the layer mean of water vapor close to the surface. The error affected the 07 L2 SDS's "Water_Vapor" and "Water_Vapor_Low". The values were just "marginally off" but affected all granules globally. Since the Infrared (IR) Water Vapor Data data is copied from 07_L2 into 05_L2 HDF files, both the 05_L2 and 07_L2 HDF data products were affected.

PGE Versions & Production Dates of Problematic & Corrected Data:

Problematic Data Corrected Data
PGE Versions Production Dates PGE Versions Production Dates
C6.0 ≤ PGE04 v6.0.37 ≤ 2014 191 (07/10/2014) C6.0 ≥ PGE04 v6.0.38 ≥ 2014 195 (07/14/2014)

Data Dates Affected: July 2002 to July 2014 (Nighttime Granules only)

Affected Platform: Aqua Only

Collections Affected: Collection 6.0

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