This file chronicles data processing changes/improvements to the ACE level 2
data accessible from the ACE Science Center. Routine updates of new data
are NOT reported here. This file only records changes in data processing
which result in changed data, i.e. new versions of the data.

February, 2021	SWEPAM Level 2 data from 2013 to the present have been reprocessed to account
		for changes in CEM detector gains over time.  While for many years gain
		changes were observed in only 2 of the detectors, in recent years additional
		detectors have begun to show gain changes.  This reprocessing accounts for
		changes in these additional detectors with time, and significantly improves
		the density values calculated from SWEPAM data. 
		Spacecraft pointing continues to have a significant effect on SWEPAM moments
		quality, but this new data set extends the range of pointing angles at
		which valid moments can be calculated.

March, 2017 	For SWICS, An issue has been corrected in which, for proton speeds lower than
		300 km/s, the calculation of proton densities was sometimes off by an
		aspect-angle dependent scaling factor.
		Please see the Release notes for more details:
                http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ssprotons/swics_protons_release_notes.txt

Aug 08, 2016	Complete reprocess of SWEPAM/SWICS merged solar wind data set,
		from beginning of mission, using SWICS Level 2
		Version 1.1 Proton Data, now available as an independent data set from
		http://www.srl.caltech.edu/ACE/ASC/level2/lvl2DATA_SWICS_PROTONS.html

Jul 13, 2016 	New release of SWICS Solar Wind  proton data, completely reprocessed,
		from 1998-2015. This is therefore a new version (v1.1) and has some
		corrections and bug fixes applied that were sufficient to warrant a
		re-processing of the data set.
		Please see the Release notes for more details:
                http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ssprotons/swics_protons_release_notes.txt

Feb 2016	New release of SWICS 2.0 Level 2 data from Jan 1 2015
		onwards. Fixes a problem where some data were incorrect by a few %.

Sept 30, 2015	Release of EPAM 12-second fluxes. Same data items as in the 5-minute
		and hourly EPAM data.

June 2015	New release of SWICS 1.1 Level 2 data.
		SWICS 1.1 Version 4.09 contains a few incremental improvements
		that optimize the ion identification model and reveal more
		counts of low-density species. The process for removing
		accidental coincidence events has been improved, leading to a
		small increase in identification of rare ions such as Fe6+,
		Fe7+, and C4+. In addition, the forward model for ion
		identification now uses all charge states of all 11 elements,
		making the ion count assignment as accurate as possible.
		Statistical improvements were also made in the model so that
		ion thermal speeds are calculated with a higher degree of
		accuracy, particularly in the slow wind.
		Please see the Release notes for more details:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ssv4/swics_lv2_v4_release_notes.txt

May 2015	Release of SWICS Solar Wind Proton Data at 12-minute time-resolution.
		Please see the Release notes for more details:
                http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ssprotons/swics_protons_release_notes.txt

April 2015	The 5-minute and hourly EPAM spin-averaged flux data sets provided by the ASC
		have been reprocessed, using updated energy-bands and geometry factors.
		Statistical uncertainties are now handled in a consistent manner for both the
		hourly and the 5-minute averages. All fluxes are now calculated by the ASC
		from rates data provided directly by the EPAM team.

March 2015	A major new release of the SWICS Level 2 data, using completely redesigned analysis
		methods. 
		Please see the Release notes for more details:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ssv4/swics_lv2_v4_release_notes.txt
		and
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ss2/swics_lv2_V2_release_notes.txt

July 22, 2014	The SIS team has released a new version of the SIS Level 2
		data. The new analysis includes a better calculation of the
		time-dependent geometry factor and a data cut to eliminate
		chance-coincidence events resulting from disabled strips.  <a
		href="/ACE/ASC/DATA/level2/sis/sis_release_notes">Release
		Notes</a> for details.

Jun 17, 2014:	MAG data from 2013/151 onwards have been re-released with new calibrations.
		Less than 0.2nT changes...see the release notes for details:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/mag/mag_release_notes

Jun 13, 2013:	Re-release of SWICS Level2 2hr for the whole mission. Corrected bug
		that caused rates to be too low.
		Please see the Release notes for more details:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ssv3/swics_lv2_v3_release_notes.txt

Jan 23, 2013:	The CRIS Level 2 data product has been re-evaluated following changes made to
		the data cuts and the calculation of the geometry factors and SOFT hodoscope
		efficiencies.  Bugs in the positioning and thicknesses of the silicon detector
		stacks and the calculation of the depth of incident particles have been
		corrected.
		Please review the Release notes:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/cris/cris_release_notes
		
Apr 30, 2012:	Re-release of SWICS Level2 2hr and daily averages for the
		whole mission. Corrected issue which caused Fe-containing data products to differ
		substantially between 2h and 1d resolution, evident mainly in long (~30
		day) averages.  Fe/O ratio changed by up to 50% in portions of both 2h
		and 1d datasets (unchanged in other portions).
		Please see the Release notes for more details:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/ssv3/swics_lv2_v3_release_notes.txt
		
Nov 10, 2010:   Re-release of the SIS Level 2 data for the whole mission.
		We identified and eliminated contamination from penetrating
		particles evident in the range 7 intensities.  The effect is
		most evident when examining long time integrations of quiet
		time periods.
		Please see the Release notes for more details:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/sis/sis_release_notes

Apr 2, 2010:    Re-release of the CRIS Level 2 data for the whole mission.
		The CRIS Team has re-evaluated the production of CRIS Level 2 data,
		implementing several changes that were incorporated in the analysis
		presented in George et al., ApJ 698, 1666 (2009).  These include
		revisions to the hodoscope grammage, interaction probabilities, and
		data cuts and geometry factors for events stopping deep in the
		instrument.  In addition, a bug in the maps of the SOFT hodoscope has
		been repaired, slightly changing the calculation of trajectories, and
		the parsing of the data telemetry stream has been made more robust,
		which results in the recovery of a small number (~0.1%) of additional
		events.  The overall effect of these changes is typically to reduce the
		absolute intensities by a small amount, by up to a few percent.  Together
		these changes have some effect on the width and centers of the CRIS
		energy bins; PLEASE USE THE NEW ENERGY VALUES (available at
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/cris/cris_energy_bands.txt)
		WITH THESE NEW DATA!
		Also, please review the Release notes:
		http://www.srl.caltech.edu/ACE/ASC/DATA/level2/cris/cris_release_notes
		
Mar 31, 2010:  	Re-release of the SIS Level 2 data for the whole mission.
		We added a small correction for spallation within the
		instrument to the calculated intensities.  These corrections
		are greatest for deep range and heavier ions; they range from
		0.9993 for range 0 He to 0.9227 for range 7 Ni (note: these
		are division factors; i.e., the intensities are divided by
		these numbers).  All the data from mission start to date were
		reprocessed to incorporate these corrections.
		Release notes are accessable from the SIS Level
		2 data documentation web page:
		http://www.srl.caltech.edu/ACE/ASC/level2/sis_l2desc.html.

Mar  3, 2010:   Unintended CRIS Data Change

		The CRIS Team has re-evaluated the production of CRIS Level 2 data,
		implementing several changes that were incorporated in the analysis
		presented in George et al., ApJ 698, 1666 (2009).  These include
		revisions to the hodoscope grammage, interaction probabilities, and
		data cuts and geometry factors for events stopping deep in the
		instrument.  In addition, a bug in the maps of the SOFT hodoscope has
		been repaired, slightly changing the calculation of trajectories, and
		the parsing of the data telemetry stream has been made more robust,
		which results in the recovery of a small number (~0.1%) of additional
		events.  The overall effect of these changes is typically to reduce the
		absolute intensities by a small amount, by up to a few percent.  At
		present we are evaluating the effects of these changes on our energy
		bins (which are expected to be at the few percent level), and once
		this is completed in a few weeks we will release the new data.

		Unfortunately, test files using this new analysis were inadvertently
		placed on the CRIS level 2 site on Feb 24, 2010, 2:40pm PST, replacing
		the older files there; also data from Bartels Rotations 2407 and 2408
		were generated using the new analysis.  CRIS DATA FILES DOWNLOADED
		BETWEEN FEB 24 and MAR 3 2010, OR ANYTHING FROM BR 2407 DOWNLOADED
		PRIOR TO MAR 3, SHOULD NOT BE USED WITHOUT THE APPROPRIATE CHANGES TO
		THE ENERGY BINS, WHICH WE ARE STILL WORKING ON.  For the time being, we
		are restoring the old files to the site until we have finished
		evaluating the new ones.

		We thank the users who called this issue to our attention, and we
		apologize for any inconvenience this may have caused.

Sep 30, 2009: Re-release of the SWICS Level 2 data for the whole mission.
              Data have been reprocessed to remove/greatly-reduce a 6-month
	      periodicity in the elemental abundances.
	      Releae notes are available at
	      http://www.srl.caltech.edu/ACE/ASC/level2/ssv3_l2desc.html

Aug 21, 2008: Release of new version of ULEIS Level 2 data for whole mission,
              generated with udf_lister program including all efficiency updates.
              List of instrument saturations updated;  several additional periods added.

Jun 23, 2008: Re-release of the SIS Level 2 data for the whole mission.
              Addition of intensities for Na, Al, Ar, Ca, and Ni, plus a few
	      other minor changes in teh analysis code.
              Release notes are accessable from the SIS Level
	      2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/sis_l2desc.html.
	      
Jan 24, 2008: Re-release of the SWEPAM Level 2 data for Bartels rotations
              2366 - 2372 (12/07/2006 thru 06/13/2007).
	      Data have been reprocessed to incorporate updated instrument
	      calibrations which account for changing CEM gains over time.
	      Changes were based on weekly on-board calibrations.
	      
Apr 28, 2007: First release of MAG Level 2 data at 1-second resolution.
              The MAG team will release data in stages, working backwards
	      in time from the present to the beginning of the mission.
	      
Apr 26, 2007: Re-release of the SIS Level 2 data for the whole mission.
              Release notes are accessable from the SIS Level
	      2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/sis_l2desc.html.
	      
Apr  4, 2007: Re-release of the SWEPAM Level 2 data for Bartels rotations
              2342 - 2361 (02/27/2005 thru 08/20/2006). Data have been reprocessed 
              to incorporate updated instrument calibrations.  Based on increased 
              time at CEM voltage Level 2, the instrument geometric factors have 
              been better defined, particularly for the off-axis CEMs.  We also 
              better account for changing CEM gains over time, based on weekly 
              on-board calibrations.
	      
Jan 19, 2007: The EPAM team identified a timing drift in the EPAM data. This timing
              drift was ~ 1 minute/year. The team has identified the source of this
	      drift and fixed the problem. The entire entire EPAM hourly-averaged
	      dataset has been regenerated. The 5-minute averages have not yet been
	      regenerated.

Feb 14, 2006: Re-release of the SWEPAM Level 2 data for Bartels rotations
              2342 - 2348 (02/27/2005 thru 09/03/2005). Incorporates the new geometric
	      factors for operation at CEM voltage level 2.
	      
Oct  1, 2005: an entirely new version of the SWICS-SWIMS level 2 data has been
              released. Release notes are accessable from the SWICS/SWIMS Level
	      2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/ssv2_l2desc.html.

Mar 31, 2005: Re-release of the SWEPAM Level 2 data for Bartels rotations
              2331 - 2335, and rotation 2324.
	      This change was required to update the instrument calibrations.
              See the SWEPAM Release Notes for details. Release notes
              are accessable from the SWEPAM Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/swepam_l2desc.html.

Mar 28, 2005: New version of MAG level 2 data for 2003-087 onwards.
              An incorrect calibration had been applied, affecting
	      only periods with |B| < 4 nt. Error was < 1 nT, in the
	      direction of the spacecraft spin-axis.
              See the MAG Release Notes for details. Release notes
              are accessable from the MAG Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/mag_l2desc.html.
	      
Dec 31, 2003: noise on EPAM P1, P2, P3, P4, P5, P6 channels from 2003-302
              onwards - the data for these channels is replaced with fill-data.

Nov 30, 2003: New release of ULEIS level 2 data, from start of mission
              to date. Updated instrument calibration efficiency.
	      
May 28, 2003: New version of SWEPAM data for entire mission. Updated
              instrument calibrations. Included velocities even at
	      times when all other moments are unreliable. Reprocessed data
	      during most solar particle events to account for the high
	      background levels.
              See the SWEPAM Release Notes for details. Release notes
              are accessable from the SWEPAM Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/swepam_l2desc.html.
	      
Dec 13, 2002: New version of SWEPAM level 2 data for Bartels rotations 2295
              and 2297. This change adds some data points during several high
	      background intervals.
              See the SWEPAM Release Notes for details. Release notes
              are accessable from the SWEPAM Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/swepam_l2desc.html.

Nov 26, 2002: New version of SWEPAM level 2 data for Bartels rotation 2295.
              This change adds some data points during the high background
              interval on days 267-270 (Sept 24-27, 2001).
              See the SWEPAM Release Notes for details. Release notes
              are accessable from the SWEPAM Level 2 data documentation web page:
              http://www.srl.caltech.edu/ACE/ASC/level2/swepam_l2desc.html.

Aug 19, 2002: New version of CRIS level 2 data, from the CRIS team.
              See the CRIS Release Notes for details. Release notes
              are accessable from the CRIS Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/cris_l2desc.html.

Jun 11, 2002: Release of new version of SWEPAM level 2 data for Bartels rotations
              2279-2295. New data incorporate the results of the weekly on-board
	      instrument calibrations. 
              See the SWEPAM Release Notes for details. Release notes
              are accessable from the SWEPAM Level 2 data documentation web page:
              http://www.srl.caltech.edu/ACE/ASC/level2/swepam_l2desc.html.

Apr 18, 2002: Improved handling of data gaps in SWEPAM 64-second averages,

Mar 29, 2002: New version of CRIS level 2 data, from the CRIS team.
              See the CRIS Release Notes for details. Release notes
              are accessable from the CRIS Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/cris_l2desc.html.

Feb 25, 2002: Improved handling of fill-data in EPAM daily and Bartels averages.

Nov 20, 2001: Improved accuracy of spacecraft position vector in GSM coordinate
              system (included in MAG and SWEPAM level 2 data).

Nov 20, 2001: Release of new version of EPAM level 2 data - improved LEMS30 ion
              data.
              See the EPAM Release Notes for details. Release notes
              are accessable from the EPAM Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/epam_l2desc.html.

Oct 30, 2001: Release of new version of SEPICA level 2 data - more species and
              more energy ranges.
              See the SEPICA Release Notes for details. Release notes
              are accessable from the SEPICA Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/sepica_l2desc.html.

Jun 19, 2001: MAG data processing improved:
              1. Improved filling of time-periods where no data exists from 
              the MAG instrument. 
              2. Fixed bug where first record of a day was skipped when there
	      were more than one maneuvers in the header of the MAG ascii data
	      file.  
              3. Modified code so that the MAG ascii data file for the day
	      before the beginning of a bartels rotations is scanned for
	      records that might fit into the rotation time-range.

Feb  6, 2001: SIS: require at least 25.5 days coverage for a valid Bartels average,
              to ensure that the average includes all solar events during the 
              period.

Feb  3, 2001: New version of CRIS level 2 data, from the CRIS team.
              See the CRIS Release Notes for details. Release notes
              are accessable from the CRIS Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/cris_l2desc.html.

Oct 25, 2000: Added release notes for EPAM data - these notes apply to
              EPAM data for July 14 - 16, 2000.: Release notes
              are accessable from the EPAM Level 2 data documentation
              web page:
              http://www.srl.caltech.edu/ACE/ASC/level2/epam_l2desc.html.
	      
Oct  3, 2000: SWEPAM level 2 data reprocessed to correct some problems
              with filling of data gaps and mapping record numbers to
	      time/date.

Sep 22, 2000: Documentation of EPAM level 2 composition data (from the
              CA60 telescope) was incorrect in some places, including
	      headers of downloaded data. Energy ranges and intensities
	      were quoted in units of MeV. The correct units are MeV/nucleon.
              
Sep 19, 2000: New version of SWEPAM level 2 data, from the SWEPAM team.
              See the SWEPAM Release Notes for details. Release notes
	      are accessable from the SWEPAM Level 2 data documentation
	      web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/swepam_l2desc.html.

Sep 18, 2000: Minor change to CRIS Bartels Rotation averages data processing:
              livetime for a valid Bartels rotation average was lowered from
	      30% to 3%. This means that 3 Bartels averages that previously
	      contained fill-data now contain valid data.

June 2000   : New version of CRIS level 2 data, from the CRIS team.
              See the CRIS Release Notes for details. Release notes
              are accessable from the CRIS Level 2 data documentation web page:
	      http://www.srl.caltech.edu/ACE/ASC/level2/cris_l2desc.html.