File ID :
06 December 2005
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:
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 firstname.lastname@example.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:
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 email@example.com in the first