[Heig] [UCDList_1-7_RFM] discussion on new terms for UCDs in the high energy domain
Baptiste Cecconi
ceccobapts at yahoo.fr
Fri Apr 17 14:58:32 CEST 2026
Hi Ian,
I understand the semantics-related concerns of your community, and I had the same when I arrived: I do planetary sciences and heliophysics, and we manage in-situ measurements (like local magnetic field or particle distribution functions of local plasma, or even rock sampled with a drill by a rover on Mars…), so yes, there are many many diverse ways to measure and acquire astrophysical data.
What I'm trying to say is that UCDs are not meant to model detailed concepts specific to a sub-field of astronomy, but to allow interoperability between the data services (across domains). I also admit that the current UCDs list contains historical terms that are very specific, but they are not really used, so we tend to focus on semantically transverse terms.
To me, what you are willing to implement is a data model or an ontology / vocabulary of terms for HEA, which is different from the UCDs. I would very welcome this vocabulary in Semantics, as a separate vocabulary, which could be linked to the parameters of your dataset using the "utype" parameter.
Furthermore, I insist that the UCD term definitions are really loose (on purpose). The definition of "src.var.pulse" is "Pulse", not "Pulse of a source" (which may not mean anything…). For instance, my data products are tagged with "phot.flux.density", although I don't observe photons, but rather electric field, but the definition of the concept fits my need, despite the parent stating "photometry".
Cheers
Baptiste
> Le 14 avr. 2026 à 17:01, Dr. Ian N. Evans <ievans at cfa.harvard.edu> a écrit :
>
> Hi Baptiste,
>
> As we argue in our note, "src.var.amplitude;src.var.pulse;stat.uncalib” (or variations thereof) is not a meaningful replacement, because it combines terms that are not relevant to PHA (or even relevant to a potential majority of events from a HEA detector).
>
> “src.var.amplitude” (and indeed “src.var.pulse”) are subterms of “src” which is described in the UCD document as “Observed source viewed on the sky”. Events recorded by a HEA detector often have nothing to do with an “observed source viewed on the sky”. Depending on the detector, a (possibly very) significant fraction of the observed events arise from background (either cosmic or instrumental) and have nothing to do with an “observed source viewed on the sky”. These events still have a measured pulse height/PHA.
>
> “stat.uncalib” is a subterm of “stat” which is described in the UCD document as “statistical parameters”. However, each single event has a single measured pulse height PHA and is not a “statistical parameter”.
>
> So these combinations would describe PHA in terms that are simply not applicable/correct.
>
> The UCD REC states “The major goal of UCD is to ensure interoperability between heterogeneous datasets. The use of a controlled vocabulary will hopefully allow an homogeneous, non-ambiguous description of concepts that will be shared between people and computers in the IVO.” Your proposed replacement is general (but misleading for the reasons identified above), but I think it would actually inhibit the goal of interoperability between different HEA datasets from various missions because it is too general. In other words, one could not use your proposed replacement to meaningfully identify columns of data from different HEA missions to cross-compare.
>
> An important take-away here is the HEA data are different! There is no real equivalent to PHA for lower energies (physically because the incoming photons/particles are sufficiently low energy that they are not ionizing), so interoperability with lower energy data is not relevant for PHA (specifically).
>
> We will also propose new or updated UCDs/UCD definitions for electromagnetic spectrum (specifically, gamma-ray energies), particle types, and photometry quantities (where current UCDs are too vague to allow meaningful interoperability with the HEA regime). However, the HEIG is still discussing these proposal internally and is not yet ready to submit specific proposals for these areas.
>
> The UCD proposals are not really relevant to the HEA ObsCore Extension (i.e, data discovery). They are specifically intended to help VO tools identify comparable HEA data columns sufficiently well that “interoperability between heterogeneous datasets” (between HEA and other wavebands where this makes sense, and between datasets from the many different HEA facilities where comparison with other wavebands just doesn’t make sense - as is the case for PHA) is actually possible with reasonable unambiguity.
>
> Thanks,
> —Ian
>
>> On Apr 14, 2026, at 08:26, Baptiste Cecconi <ceccobapts at yahoo.fr> wrote:
>>
>> Hi Ian,
>>
>> Thanks for the detailed explanation. I understand the preference for a more straightforward term that can be easily understood by your community.
>>
>> The scope of the UCDs is to cover the whole astronomy community. We regularly receive requests for rather specific terms from astronomy communities (solar physics, planetary sciences, radio astronomy, etc).
>>
>> Our role is to evaluate the proposed new terms and see how it fits to the scope of the UCD list. We also try to see how a term could be reused in other contexts. The UCDs should remain generic enough so that the whole IVOA community shall be able to reuse the terms. In addition, the role of UCDs is not to identify a specific concept, but to help VO tools identify comparable columns or parameters in data services.
>>
>> This is why we have proposed an other term, combining existing UCDs. Our proposed replacement is "src.var.amplitude;src.var.pulse;stat.uncalib" which conveys the idea of the "Amplitude of a Pulse in Uncalibrated units". As an outsider, this UCD fits rather well your description.
>>
>> For the HEA obscore extension, it is important to accurately define the columns of the extension. The definition of a "PHA" or "Pulse Height" column shall be done in the extension, not in the UCD list. UCDs should be seen as hints, not fully qualified concepts.
>>
>> Cheers
>> Baptiste
>>
>>> Le 13 avr. 2026 à 22:51, Dr. Ian N. Evans via semantics <semantics at ivoa.net> a écrit :
>>>
>>> Hi Mireille,
>>>
>>> For HEA, I prefer “pulseHeight” or “pha” rather than “pulse.amplitude”.
>>>
>>> Historically in X-ray and space-based gamma-ray astronomy, the instrument-derived measure of photon energy is termed PHA, which was derived from “Pulse Height Analyzer” (the description of the electronic circuit that measures the quantity). More recently PHA tends to be listed as “Pulse Height Amplitude”, but this is not the origin of the term. PHA is more informally termed “Pulse Height”.
>>>
>>> However, the precise quantity that defines the PHA value varies somewhat depending on the how the instrument works.
>>>
>>> For some types of detectors (especially those used in earlier high energy instrumentation) the peak amplitude of the voltage pulse produced when a high energy photon was detected, digitized by an A/D converter, and normalized to some range (e.g., 0-255, 0-1023 etc.), was used to define the PHA value because for those detectors the signal peak scales approximately with input photon event energy.
>>>
>>> For other kinds of detectors, the integrated area under the curve of the pulse is used to define PHA value; this definition is typically used if the detector records charge per event (e.g., a CCD detector), since the integrated charge scales approximately with input photon event energy for these kind of detectors.
>>>
>>> In both cases the typical high-energy astrophysicist would term the measured value PHA (or pulse height) because the details of how the detector works are less important than knowing that the value is the measured proxy for energy (prior to folding through the responses).
>>>
>>> Scientists who are responsible for actually developing calibrations or response functions may in some cases need to know the peak pulse amplitude, integrated pulse area, pulse rise and fall times, and pulse width (especially for instruments with very fast response times). However the astrophysicist who is using the data to do science very likely doesn’t care about such nuances.
>>>
>>> Thanks,
>>> —Ian
>>>
>>>> On Apr 13, 2026, at 12:26, Mireille Louys via heig <heig at ivoa.net> wrote:
>>>>
>>>> Hi Heig & semantics members ,
>>>>
>>>> I have summarized the UCD changes requests on this page : https://wiki.ivoa.net/twiki/bin/view/IVOA/UCDList_1-7_RFM <https://www.google.com/url?q=https://www.google.com/url?q%3Dhttps://wiki.ivoa.net/twiki/bin/view/IVOA/UCDList_1-7_RFM%26source%3Dgmail-imap%26ust%3D1776702390000000%26usg%3DAOvVaw0NsQesG9V4sKVxZ8_NuWjd&source=gmail-imap&ust=1776774386000000&usg=AOvVaw0HlII_7UcHmpTJgvLldk_3>
>>>> These are the current terms to be discussed for improving the UCD vocabulary and exercise UCDs in the High energy domain as well.
>>>>
>>>> Your comments are welcome , via email on both lists .
>>>>
>>>> Many thanks, Mireille
>>>>
>>>> --
>>>> --
>>>> Mireille Louys, MCF (Assistant Professor)
>>>> Centre de données Astronomiques (CDS) Equipe Images, ICube
>>>> Observatoire de Strasbourg Telecom Physique Strasbourg
>>>> 11, rue de l' Université 300, Bd Sebastien Brandt CS 10413
>>>> F-67000 Strasbourg F-67412 Illkirch Cedex
>>>> --
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>>>
>>> —
>>>
>>> Dr. Ian Evans
>>> Astrophysicist
>>> Chandra X-ray Center
>>> Center for Astrophysics | Harvard & Smithsonian
>>>
>>> Office: (617) 496 7846 | Cell: (617) 699 5152
>>> 60 Garden Street | MS 81 | Cambridge, MA 02138
>>>
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>>
>
> —
>
> Dr. Ian Evans
> Astrophysicist
> Chandra X-ray Center
> Center for Astrophysics | Harvard & Smithsonian
>
> Office: (617) 496 7846 | Cell: (617) 699 5152
> 60 Garden Street | MS 81 | Cambridge, MA 02138
>
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