All Cloud Optical Thickness logarithmic statistics were mistakenly computed as natural log (base e) instead of common log (base 10). This was a software bug and has been resolved. All Collection 004 HDF files will have this error corrected. Collection 004 HDF files will become available in late October 2002 and can be identified by an ".004." version field in the HDF filename.

All Cloud Fraction Infrared statistics show values being too high due to a mistake in the MOD06_L2 input product where all clear pixels had a QA value of 0 (bad data) assigned. These clear pixels were not then included in the statistical computations. This problem will be fixed for Collection 004 data, which will commence on November 1st 2002. All the MODIS data collected thus far will be reprocessed with the Collection 004 algorithm during the following year. Collection 004 HDF files will be identified by an ".004." version field in the HDF filename.

Information provided by Paul Hubanks, NASA Goddard Space Flight Center


For data collected prior to 1 Nov 2001, the infrared water vapor products (SDS names of the form Atmospheric_Water_Vapor*) should be considered invalid for any retrieval location where the total precipitable water vapor (SDS Atmospheric_Water_Vapor_Mean) exceeds 7.0 centimeters (especially obvious at times over the African Sahara). Invalid data may be masked though in regions where a mix of valid and invalid data yield statistical results less than 7.0 centimeters. In addition, the total precipitable water vapor in these products has a wet bias on the order of 10-20%. The Level 2 infrared water vapor algorithms and products have not been corrected in order to maintain consistency in this first year of MODIS Collection 3 products. Spatial and temporal gradients are believed to be representative and useful. Corrections will be in place for data collected after 1 Nov 2001.

Information provided by Liam Gumley and Paul Menzel, University of Wisconsin