Date: Thu, 25 Mar 2004 12:46:01 -0800 (PST) From: Shawn Brooks Reply-To: sbrooks@dcs04.jpl.nasa.gov To: Mitch Gordon cc: Mark Showalter Subject: Voyager UVS Archive Peer Review X-Junkmail-Status: score=6/60, host=arc-relay1.arc.nasa.gov Howdy, OK, gentlemen, here is what I have; please find my discussion of the UVS data archive below. Sorry that I've taken so much longer than I said I would. Now that I look over the whole archive again, it strikes me how little of it I was able to really peruse. Therefore, I fear that my comments on this data set will be of limited use. In general, I felt that, as usual, the archiving of this data was very well done and warrants few changes. However, there were a couple (see the one about the MEAN_SIGNAL field in the .LBL files!) that I think should be addressed. If you have any questions or would like me to re-visit portions of the archive to write a more extensive analysis, please let me know. I'd be more than happy to do it. It's very important to me that I fulfill the obligation for which I signed up. --- Shawn PS - At least I caught some typos! ************************************************************************** The Voyager UVS ring occultation data set is a rather extensive one, seeing as how it contains occultation data from three planetary encounters. Furthermore, the differing characteristics of the three ring systems also complicates the archiving of these data into one volume. Thus, it is a testament to the cleverness of the architecture of the PDS archiving system that these data can be archived into one consistent, sensible (albeit complex) volume. The data contained within are well documented. They appear at different stages from raw data to a fully-polished, edited data set. The documentation that appears with the data look to be rather complete. For example, the detail provided in the documentation of the derivation of the Saturn occultation calibration profile is very useful. The determination of these background counts is clearly not a trivial matter and the description included in file /DOCUMENT/SPROFILE/SPROFILE.PDF yields insight into the preparation of the data. Generally speaking, the data are carefully presented in a fashion that make them easy to examine once the background information to the volume has been fully digested by the user (and there is a lot of this!). More specifc comments follow. They are generally organized by the archive directory to which the comments are pertinent. They are preceded by some more general comments and followed by typographical errors I catalogued as I read through the documentation files. General comments The naming conventions strike me as somewhat awkward. Is it necessary, for example, to begin each file in this archive with a 'U' for UVS? Is this some PDS restriction? Otherwise, this one extra character could be used to further specify the data files, seeing as how all of the data on this archive are UVS data and every file begins with a 'U'. In a similar vein, I found the way in which the particular occultations are named to be a little awkward as well. Seems that there should be a more descriptive way to differentiate occultations by two different stars other than something such as 'U1' versus 'U2', but I admittedly cannot think of one that also conforms to PDS restrictions. This is perhaps a personal preference, however, and I do not strongly advocate any changes. I would naively think that all of the programs that were used to manipulate the raw data should be located under the SOFTWARE directory. I think they should be. Could the program files located under the DOCUMENTS directory not be moved to the SOFTWARE directory? It seems that there was some motivation to separate the supported software from the unsupported software, but I think that this distinction could be maintained with a specific subdirectory titled something like UNSUPPORTED within the SOFTWARE directory. This is probably a minor point, but it was initially unclear to me that ring opacity is used interchangeably with optical depth. For example, in the calibration description file CALIB/CALINFO.TXT, it is stated that "With these parameters, it is possible to convert from UVS counts to optical depth tau by inverting this equation: counts = STELLAR_SIGNAL * exp(-tau/MU) + BACKGROUND_SIGNAL Here MU is the cosine of the incidence angle, which can be found in the label of the corresponding geometry file." All of the data file labels refer to MEDIAN_NORMAL_OPACITY. This would probably not confuse anyone more familiar with ring occultation data, but it may be useful for a beginner to know. An additional statement after the quote above to the effect of tau represents optical depth or ring opacity would have cleared this up for me. Or, some mention of this in the .LBL files. (I see some mention in the DOCUMENT/TUTORIAL.TXT beneath a discussion of the calibration files now, but an extra mention or two couldn't hurt, given the large number of files in this volume.) DOCUMENT This issue of descattering seems to be an important one. Can anything be said about the extent to which this would affect the UVS spectra (i.e. the data that have not been co-added)? Likewise, the limit-cycle motion effects mentioned in the TUTOIRAL.TXT file seem important. I could not find mention of it anywhere but in this file. Should this information not be repeated? A quick reference in the information files in the EDITDATA or NOISDATA directories, for instance, might be appropriate. EASYDATA The .LBL files all say that MEAN_SIGNAL field in the .TAB files is formatted F7.3. However, they all appear to formatted F8.3!!! All of the other fields are formatted in a fashion consistent with what appears in the .LBL files. IMAGES I've always found that dealing with images in VICAR format can be difficult. I have an IDL routine (it originated with Joel Plutchak at Brown University) that reads VICAR images into IDL format. Otherwise, I would be routinely frustrated by them. Would it not be possible to include the support images in some other format or include some software such as the routine that I described above? Getting the VICAR software can be very difficult and, I think, might be nearly impossible for foreign users of this data set. I suspect that reading images in VICAR format will be increasingly difficult decades from now. VECTORS Could not characters 7 and/or 8 be used to identify those VECTOR files that were generated under the assumption that the ring system is extended and equatorial? I think this would be useful for the user of these data. Mention is made of "small, systematic errors of order 0.01 degrees" introduced by the rotation algorithm of routine J2000_VR.FOR. It is not clear to me whether or not these errors are limited to this routine or whether or not such errors are manifest in the files generated by the routines J2000_VC.FOR and J2000_VE.FOR. Can this be made clear? TYPOGRAPHICAL ERRORS: DOCUMENT/TUTORIAL.TXT - "The instrument intrinsically recorded integers counts, where a single photon generated on average 2.5 counts. See DOCUMENT/NOISE/NOISE.PDF and NOISE.ASC for a the Rings Node's own estimate of UVS counts per photon." Should read "The instrument intrinsically recorded integer counts, where a single photon generated on average 2.5 counts. See DOCUMENT/NOISE/NOISE.PDF and NOISE.ASC for the Rings Node's own estimate of UVS counts per photon." -------------------------------------------------------------------------- "Because the signal in any give UVS spectrum is often rather small, it is conventional to coadd the spectral samples down into a single value per time step." Should read "Because the signal in any given UVS spectrum is often rather small, it is conventional to coadd the spectral samples down into a single value per time step." -------------------------------------------------------------------------- "As discussed in our Saturn Profile analysis, DOCUMENT/SPROFILE/SPROFILE.PDF and .ASC, the UVS team when to extraordinary efforts to model out these variations." Should read "As discussed in our Saturn Profile analysis, DOCUMENT/SPROFILE/SPROFILE.PDF and .ASC, the UVS team went to extraordinary efforts to model out these variations." -------------------------------------------------------------------------- "In addition, all invalid or missing samples have been flagged, meaning that they have been replaced a particular numeric value." Should read "In addition, all invalid or missing samples have been flagged, meaning that they have been replaced by a particular numeric value." -------------------------------------------------------------------------- "PN1G02 describes a hypothetical ring system using the pole inferred by Porco (1991) for the Adams Ring; this file is likely to more accurate for the Adams Ring and maybe for other rings as well." Should read "PN1G02 describes a hypothetical ring system using the pole inferred by Porco (1991) for the Adams Ring; this file is likely to be more accurate for the Adams Ring and maybe for other rings as well." -------------------------------------------------------------------------- EASYDATA/DATAINFO.TXT - "Note that, because the data from the beta Per occultation were dominated by the Uranian charged particle background, no ring profiles could be generated from the this occultation experiment." Should read "Note that, because the data from the beta Per occultation were dominated by the Uranian charged particle background, no ring profiles could be generated from this occultation experiment." -------------------------------------------------------------------------- GEOMETRY/GEOMINFO.TXT - "Describes a hypothetical ring system using the pole inferred by Porco (1991) for the Adams Ring. This file is likely to more accurate for the Adams Ring and maybe for other rings as well." Should read "Describes a hypothetical ring system using the pole inferred by Porco (1991) for the Adams Ring. This file is likely to be more accurate for the Adams Ring and maybe for other rings as well." -------------------------------------------------------------------------- VECTORS/DATAINFO.TXT "See DOCUMENT/POLES.TXT for a discussion of these rotation angle." Should read "See DOCUMENT/POLES.TXT for a discussion of these rotation angles." -------------------------------------------------------------------------- "Each vector file tabulates geometry parameters as a function of UVS spectrum index; this same index can be used to identify the corresponding data record or sample in one of the EDTIDATA files." Should read "Each vector file tabulates geometry parameters as a function of UVS spectrum index; this same index can be used to identify the corresponding data record or sample in one of the EDITDATA files." xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx SunJupiterSaturnNeptuneUranusEarthVenusMarsMercuryGanymedeTitanCallistoIo =========================================================================== "I don't think I'm alone when I say I'd like to see more and more planets fall under the ruthless domination of our solar system." Shawn M. Brooks - NRC Associate Jet Propulsion Laboratory 4800 Oak Grove Drive; M/S 230-205 Pasadena, California 91109 Phone: (818) 393-6380; FAX: (818) 393-4495 =========================================================================== LunaEuropaTritonPlutoTitaniaOberonRheaIapetusCharonArielUmbrielDioneTethys xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx *I think something is supposed to appear about my opinions expressed herein not representing those of the Jet Propulsion Laboratory, the California Institute of Technology or the National Aeronautics and Space Administration, which is most certainly the case.