Re: IOTA global OWC event tagging criteria
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Hi Steve,
A couple of comments.
When I said that tagging will not be linked to regions I meant only for the automated global tagging which will be the extension of IOTA Occultations. People can still tag events with local tags if they pick a sub-selection of the global events for a regional feed/tag. Because one event can be tagged with multiple tags, this is not going to be an issue. In those instances the local tag can be used as a first level of filtering criteria i.e. someone interested in handpicked events in their region. OW will still apply further filtering on the top of that.
> For OWC, I would add star altitude, twilight conditions (combination of sun altitude and
the distance from the sun), and time since nautical twilight (for multi-station deployments)
Unfortunately these are all location related parameters and cannot be applied at OWC level for tagging. Along the path of the same event observers will have different star altitudes and twilight. So again OW will be doing the filtering for this.
In regards to SNR. This will not be available during the actual filtering process in OWC and cannot be used directly for filtering/tagging. What I was refering to is that the important parameters (whch you listed as: star mag, mag drop, and event duration) can be derived from a pre-agreed SNR for a high quality events. Then the three magnitude, drop and duration parameters can be derived from the fixed SNR and for one of the more sentive and low noise cameras available to amateurs. While this will not be a perfect crieteria, there is no intention for it to be perfect. I see it as using a more systematic approach to filter out events for which satisfactory SNR could not be achieved even with the better integrating cameras available to amateurs. In the end OW will still filter our some or even many of those events based on the observer's OW filter choices for magnitude, duration etc.
So I think that agreeing on a meaningful SNR for a successful occultation is an important step forward that we need to take. In classical photometry sense I think that SNR of 3 is considered an rough minimum for an acceptable quality photometric measurement. May be we can try starting at SNR of 3 and try to find evidence in both ways to see if this value should be lowered or increased.
Hopefully this explains better what I mean by SNR being part of our theoretical approach to global event tagging in OWC.
Cheers.
Hristo
On Tuesday, July 13, 2021, 9:09:17 AM GMT+10, Steve Preston via groups.io <stevepr@...> wrote:
Hristo said:
¡°Because OWC has all events on a global scale and because OW does filtering based on a distance, the distance from a location or the geographical region will not be part
of the tagging criteria/filter.¡±
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Everyone should note what Hristo has said here.? When tagging events, you cannot filter the events by location (either distance from a location or by a region).? This limitation represents a major change for many of the current feeds.?
Many of the current feeds are based on a region (e.g. NALowMag for North American low mag drop events).? I¡¯m not saying this limitation is problem, but it is different from the approach with Occult.? With OWC, ¡°feed generators¡± will only tag events for the
entire world, not their region.? Afterward, observers will use distance filtering to see the tagged events near them.
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Filtering Criteria:
Many years ago David Dunham and I worked out a set of criteria for prioritizing (and filtering events). ?The key elements were the path uncertainty, star mag, mag drop, and event duration. ?One could easily divide this into two factors:
path certainty and ¡°observability¡±.? The star mag, mag drop, and event duration are all key factors in determining the difficulty in observing an event (observability).? For OWC, I would add star altitude, twilight conditions (combination of sun altitude and
the distance from the sun), and time since nautical twilight (for multi-station deployments).
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SNR/Viability:
I strongly recommend that we avoid trying to use SNR as a filtering criteria.? The SNR of recording is based on too many factors which are hard to predict or will be changing over time.? Atmospheric conditions (e.g. humidity, clouds, seeing
conditions) vary considerably over regions and time (and have a large impact on SNR).? Cameras and recording systems have a huge impact.? ?Star magnitudes are variable and not precisely matched to the instrumental response curves of our cameras ¨C which leads
to concerns over precision.? Observers already use a variety of camera/recording configurations and more will appear in the near future.? Although OWC can deal with this complexity, it will require a LOT of work to maintain an accurate set of guidelines for
OWC which covers all of these combinations.? And, finally, I suspect the question of ¡°min SNR¡± is not an easy question to determine.
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Given all the complexities of trying to use SNR, I recommend that we only use broad guidelines based on aperture and a nominal set of equipment ¨C this sounds like Hristo¡¯s ¡°Accessibility¡± category.?
Steve
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