README.KnownIssues.TXT
Purpose: List caveats with the Aquarius data set.

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Aquarius data accuracy and errors have been carefully documented as part of project Calibration/Evaluation efforts.  The mission
requirement is that the global rms salinity error not exceed 0.2 psu on average globally at 150x150 km and monthly time scales. The latest version
of the Aquarius data, the V5.0 "end of mission" Aquarius dataset, fully meets this standard as indeed did V4.0 before it.  Users are, 
however, still urged to carefully read the latest Aquarius data validation analysis documentation available in the Aquarius /docs directory 
(AQ-014-PS-0016_AquariusSalinityDataValidationAnalysis_DatasetVersion5.0.pdf) to understand the accuracy, 
limits and warnings about when and where residual errors could be misinterpreted as oceanographic signals, particularly in certain regions 
and on certain time scales due to factors such as galactic reflection, radio frequency interference (RFI) and other outstanding sources.   
Aquarius salinity data are generally known to have issues near the coast as well as at high latitudes. Version 2.0 of the dataset isolated 
and corrected for The "quasi-monthly" calibration errors. Enhancements with version 3.0 of the dataset included corrections for ascending/descending
orbit biases, and improvements in the salinity retrieval roughness correction (by use of both V and H polarizations), modifications to the radiometer
drift correction, Antenna temperature polarization coefficients (TND), and flagging protocols.  Further improvements with version 4.0 included: 
improvement of the salinity retrieval geophysical model for SST bias, empirical correction for observed coupling of 3rd into 1st Stokes 
parameter, significant wave height correction, estimation of SSS uncertainties (both systematic and random components) at L2 and inclusion of a new density
variable.  Enhancements to the end-of-mission version 5.0 data include: improvement of the salinity retrieval geophysical model for SST bias, 
estimates of SSS uncertainties (systematic and random components) at L3 (monthly product), and inclusion of new spiciness and rain-flagged SSS L2 variables and L3 products.
Full details of algoritm changes are available in the associated ATBD documentation.


For information on specific events impacting the Aquarius/SAC-D observatory that may have implications for Aquarius data,
users should consult the Aquarius Event Logs (see README.EventLog.txt for details).  Also, when using the Aquarius L2 product,
user should be cognizant of relevant data quality attributes and apply quality flags judiciously when undertaking analyses.
These are fully described in the Aquarius Data Users Guide also available in the /Aquarius/DOCS directory of the PO.DAAC site.


*** Please note that for the v2.0 Aquarius L3 Sea Surface Salinity (SSS) products (daily, 7-day, monthly, 3-month), some SSS pixel values 
were observed to in the negative range and different from the designated NoFill (Null) value of -32767 or ValidMin, ValidMax values.  This was
due to a localized land flagging issue in the V2.0 L3 data, and has now been fixed in V3.0.
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