MEMORANDUM

From     :	H.Clarke	Document Ref     :	aep.mem.092
To          :	AATSR Contacts List	Date                    : Issue                   : File ID                 :	06 December 2005 1 AEP_MEM_092

SUBJECT      : Third AATSR Users Bulletin

Visible Channel Long Term Drift

The long term drift rates of the AATSR visible channels for the period from October 2002 to December 2004 have been analysed by Dave Smith at RAL. The results are detailed in Visible Channel Long Term Drift Analysis Using Desert Targets (PO-TN-RAL-AT-0542) D. Smith, Issue 1.0, 16 May 2005, distributed with this bulletin.

At the end of this technical note, the application of a systematic drift correction to AATSR L1b data is recommended. In response to this report, the AATSR Quality Working Group recommended that the visible channel calibration auxiliary file (ATS_VC1_AX), issued daily to the Envisat PDS, should include a correction for this effect.

As a result, please note that all AATSR data acquired from 30 November 2005 onwards will contain this systematic correction for visible channel drift.

The first VC1 file to contain this correction was:

ATS_VC1_AXVIEC20051129_182740_20051127_190440_20051204_190440

generated on 29 November 2005. All VC1 files generated after this date will include the correction. The filenames of the auxiliary file applied to L1b data can be found in the Data Set Descriptors included in the Specific Product Header of each product.

Data acquired prior to 30 November 2005 does not yet contain this correction. This should be addressed during the second reprocessing of the AATSR data set, planned for Spring 2006. In the meantime, users can correct their historical data themselves using the formula given in Section 4 of the above technical note.

Any questions on this issue should be directed to aatsr@dpqc.org in the first instance.

Revised SST Retrieval Coeffcients

A new set of AATSR SST retrieval coefficients were disseminated to the Envisat PDS on 05 December 2005, at 10:24.⁽¹⁾  They are contained in:

ATS_SST_AXVIEC20051205_102103_20020101_000000_20200101_000000

Once again, details of the auxiliary files applied to L2 data can be found in the Data Set Descriptors included in the Specific Product Header of each product.

The retrieval coefficients previously in use were based on the same atmospheric spectroscopy as was used for ATSR-1 and ATSR-2, which pre-dated the more recent releases of the HITRAN molecular spectroscopy database. This new set of retrieval coefficients are based on the HITRAN 2000 database.

Only data processed after 05 December 2005 will contain SSTs retrieved with these new coefficients. The systematic processing of all historical data with the new coefficients will be another objective of the second AATSR reprocessing, planned for Spring 2006.

A copy of the binary file containing the new AATSR SST coefficients is available from  http://www.envisat.esa.int/services/auxiliary_data/aatsr/.

As before, any questions on this issue should be directed to aatsr@dpqc.org in the first instance.