PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM SPACECRAFT_NAME = "CASSINI ORBITER" INSTRUMENT_NAME = "COMPOSITE INFRARED SPECTROMETER" OBJECT = TEXT INTERCHANGE_FORMAT = ASCII PUBLICATION_DATE = 2018-04-01 NOTE = "N/A" END_OBJECT = TEXT END Cassini Composite Infrared Spectrometer Time Sequential Data Record Archive ERRATA.TXT 23 May 2005 C.A. Nixon University of Maryland Updated: October 11, 2005 ERROR 1 Updated: March 30, 2006 ERROR 2 Updated: March 29, 2010 UPDATE 1 Updated: July 1, 2011 UPDATE 2 Updated: July 1, 2012 UPDATE 3 Updated: September 25, 2014 UPDATE 4 4 Dec 2014 M. Kaelberer Removed section on interferences as AAREADME, DATASET.CAT, and DATASIS.PDF all still contain references to interference-related documents. 5 Feb 2018 M. Kaelberer Update 5 ============================================================================== INTRODUCTION ============================================================================== This file contains a listing of errors, anomalies, and other notes regarding the data archive from the Cassini orbiter CIRS instrument. Although considerable care has gone into making this volume, errors are both possible and likely. Users of the data are advised to exercise the same caution as they would when dealing with any other unknown data set. Reports of errors or difficulties would be appreciated. Please contact one of the persons listed herein. ============================================================================== DISCLAIMER ============================================================================== Although considerable care has gone into making this volume, errors are both possible and likely. Users of the data are advised to exercise the same caution as they would when dealing with any other unknown data set. Reports of errors or difficulties would be appreciated. Please contact one of the persons listed herein. ============================================================================== KNOWN CALIBRATION ERRORS AND RESOLUTIONS ============================================================================== ERROR 1: (October 11, 2005). The initial PDS delivery of October-December 2004 data, dated October 1st 2005, was found to have a calibration error. The problem was that December 2004 reference interferograms of space and shutter were not correctly linked into the directory tree when the calibration pipeline code was run, and so were overlooked. The calibration algorithm at the present time searches +/- 50 days from a given date to find reference IFMs, and so data from October 11th through end of December were potentially affected. The biggest effect was a 20% difference in radiance noticed for the Titan TB spectra (12/13/04), which prompted the problem to be diagnosed. RESOLUTION 1: The directory tree linkage was repaired and the calibration re-run. Corrected spectra will be archived to the PDS, replacing the existing volumes COCIRS_0410, COCIRS_0411 and COCIRS_0412. The version number will remain at v1.0 as the algorithm was unchanged; the problem was operator error. ---------------------------------------------------------------------------- ERROR 2: (March 30, 2006) An error in the Fast Fourier Transform (FFT) methodology used to transform asymmetric-length interferograms (IFMs), most CIRS IFMs, has recently been identified. CIRS IFMs scan for a short time prior to zero-path difference (ZPD, or 'white light point') and usually for a greater time after ZPD, in order for the highest spectral resolution to be obtained in the shortest possible time. However, when weighting the IFMs, 'unique' spatial frequency data points, i.e. those occurring only on the 'long side' of the IFM at positive path difference, must be weighted by x2.0 relative to those spatial frequencies which occur on both sides of the IFM. In practice, this was applied using a step function which multiplied some samples x1.0 and others by x2.0. The problem was that ringing was occurring due to the sharp transition of the step function, both in the middle when the weighting sharply changed from 1.0 to 2.0, but also at either end where the weighting dropped from 1.0 to 0.0. The 'ringing' was visible as a ripple near the beginning and end of spectra from each focal plane. RESOLUTION 2: A cosine-shape ramp was applied both to the ends and the middle of the step function, instead of a sharp transition. This has now virtually eradicated the ripple. The new algorithm came into effect in late January 2006 for all new CIRS products created after that time. Hence, PDS data delivered for April 1, 2006, which includes the April-June 2005 data period and all subsequent deliveries is unaffected by the ripple, whereas all previous data (through end of March 2005) is affected at the present time. There are currently plans to re-deliver earlier data processed with the new algorithm, but after further updates and improvements to the algorithm have been completed. ---------------------------------------------------------------------------- UPDATE 1: (March 29, 2010) The entire CIRS dataset has been re-delivered as Version 2.0, which brings all previous volumes up to the same calibration level as currently used by the CIRS team. See file: DATA/APODSPEC/RELNOTES.TXT for CIRS release info. PDS version 2.0 is equivalent to CIRS version 2.4. All previous PDS data (version 1.0) corresponds to CIRS versions 2.3 and earlier, depending on delivery date. ---------------------------------------------------------------------------- UPDATE 2: (July 1, 2011) The entire CIRS dataset has been re-delivered as Version 3.1. Release notes for the re-delivery can be found in CATALOG/DATASET.CAT under the heading 'PDS VERSION 3.1'. Content previously found in DATA/APODSPEC/RELNOTES.TXT and DATA/UNCALIBR/RELNOTES.TXT is now in CATALOG/DATASET.CAT. ---------------------------------------------------------------------------- UPDATE 3: (July 1st, 2012) From 01/01/11 onwards, release v3.1 is actually using data from a minor revision, known internal to the team as v3.1.1. However this appears in the PDS files as v3.1 as second decimals are not permitted. v3.1.1 fixes a minor bug in the navigation geometry that affected Q-points 6-9. This may affect both the NAV_DATA, and calibrated data based on it in APODSPEC. This fix will be propagated into the forthcoming v3.2 expected 10/01/12, and at that time all earlier volumes will be redelivered to incorporate the fix. ---------------------------------------------------------------------------- UPDATE 4: (September 25, 2014) The entire CIRS dataset has been re-delivered as Version 3.2. Release notes for the re-delivery can be found in CATALOG/DATASET.CAT under the heading 'PDS VERSION 3.2'. ---------------------------------------------------------------------------- UPDATE 5: (February 5, 2018) The entire CIRS dataset has been re-delivered as Version 4.0. Release notes for the re-delivery can be found in CATALOG/DATASET.CAT under the heading 'PDS VERSION 4.0'.