DATA UPGRADE: RE-CALIBRATION OF SOHO/MDI DOPPLER DATA PRIOR TO FINAL ARCHIVE SUBMISSIONTHE MICHELSON DOPPLER IMAGER ON THE SOLAR AND HELIOSPHERIC OBSERVATORY (SOHO/MDI) OBSERVED THE SUN FROM FEBRUARY 1996 THROUGH APRIL 2011 PROVIDING A NEARLY UNINTERRUPTED 15 YEAR SERIES OF DOPPLER DATA FOR HELIOSEISMIC STUDIES. TOGETHER WITH THE CONTINUING OBSERVATIONS OF THE HELIOSEISMIC AND MAGNETIC IMAGER ON THE SOLAR DYNAMICS OBSERVATORY (SDO/HMI) BEGINNING IN MAY 2010 THIS REPRESENTS A HELIOSEISMIC DATA SERIES WITH WHICH SOLAR PHYSICISTS MAY INVESTIGATE THE SUN'S INTERIOR DYNAMICS AND STRUCTURES AS THEY EVOLVE OVER NEARLY TWO SOLAR CYCLES. THE SOHO INSTRUMENTS WERE DESIGNED TO OPERATE WITH THE SPACECRAFT AXIS ALIGNED IN ONE DIRECTION WITH THAT OF THE SUN'S ROTATION AXIS AND FOR THE FIRST SEVEN YEARS OF THE MISSION IT DID SO. DUE TO A MALFUNCTION OF THE SOHO ANTENNA IN JUNE 2003 IT BECAME NECESSARY TO REORIENT THE SPACECRAFT ONCE EVERY THREE MONTHS SO THAT ITS AXIS ALTERNATELY POINTED IN THE DIRECTION OF THE SOLAR NORTH AND SOUTH POLES. SUCH REALIGNMENTS POSED NO PROBLEM FOR THE MAGNETIC IMAGERY AND WERE NOT THOUGHT TO SERIOUSLY AFFECT THE DOPPLER CALIBRATION EITHER. LOCAL HELIOSEISMOLOGY DEPENDENT ON THE ANALYSIS OF PHASE DIFFERENCES OF THE OSCILLATION SIGNALS AT DIFFERENT LOCATIONS ON THE SOLAR DISC HOWEVER IS VERY SENSITIVE TO TINY ERRORS IN THE CALIBRATION OF THE DOPPLER SIGNAL. IT HAS BEEN DISCOVERED THAT THE FLOWS AND STRUCTURES INFERRED FROM HELIOSEISMOLOGY ARE SIGNIFICANTLY DIFFERENT BETWEEN THE TIMES WHEN THE SPACECRAFT WAS IN OPPOSITE ORIENTATIONS. CONSEQUENTLY ABOUT HALF OF THE MDI DATA ACQUIRED DURING THE PERIOD OF 2003 TO 2011 ARE NOT COMPARABLE WITH THE REST OF THE MISSION DATA. ANALYSIS OF DATA FROM SDO/HMI WHICH USES A VERY SIMILAR OBSERVING TECHNIQUE TO MDI REQUIRING SIMILAR CALIBRATION DURING A RECENT PERIOD WHEN THE SPACECRAFT WAS ANTI-ALIGNED FROM ITS NORMAL DIRECTION HAS LED TO NEW INSIGHTS AND IMPROVEMENTS IN THE DOPPLER CALIBRATION FOR THAT INSTRUMENT. CALIBRATION DATA TAKEN OVER THE COURSE OF THE MDI MISSION WILL ALLOW US TO APPLY THESE IMPROVEMENTS TO THE MDI CALIBRATION PROCEDURE AS WELL. WE PROPOSE TO IMPLEMENT THESE IMPROVEMENTS IN THE MDI DOPPLER CALIBRATION PROCEDURE AND TO RECALIBRATE THE DOPPLER DATA DURING SELECTED INTERVALS WHEN SOHO WAS REGULARLY FLIPPING ORIENTATION. HELIOSEISMIC ANALYSIS FOR THOSE PERIODS WILL ESTABLISH THE EXTENT TO WHICH THE RECALIBRATION CORRECTS THE DEFICIENCIES OF THE ORIGINAL CALIBRATION. IF THERE IS SIGNIFICANT IMPROVEMENT AS EXPECTED THEN WE WILL RECALIBRATE THE DOPPLER DATA FOR THE ENTIRE MISSION INCORPORATING THE NEW DATA IN THE MDI RESIDENT ARCHIVE WHERE THEY WILL BE AVAILABLE FOR BOTH REVISITED AND NEW ANALYSIS BY THE COMMUNITY PRIOR TO FINAL ARCHIVE SUBMISSION. DATA OF IMPROVED AND MORE CONSISTENT QUALITY OVER A LONG TIME SPAN WILL HELP US TO BETTER UNDERSTAND THE SUN AND ITS ACTIVITY CYCLES.