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(meteorobs) A view of Perception Coefficients from 3 years ago...
Cleaning up some VERY old emails in my archives today, I happened on the
following very clear and informative message from Rainer Arlt of IMO. He sent
this in reply to a query about individual Perception Coefficients I posted on
'meteorobs' way back in Summer of 1998... So my question now is: What is the
current state of Perception Coefficient studies, either in the Americas or
across the Water, and has the prevailing knowledge and opinion about these
individual correction factors changed in any significant way since 1998?
***
Note for newer members of the list: individual Perception Coefficient, or 'cP',
is one of several factors, including Limiting Magnitude (LM) and Percentage
Obstruction correction factor (F), which can be applied to an individual's
observed meteor rates, to derive a so-called Corrected Hourly Rate (HR). This
HR is in turn corrected for a given meteor shower's radiant altitude during
the time of the observation, to derive a so-called "Zenithal Hourly Rate" or
ZHR, which (in theory) can be compared across the entire globe, over many
nights and many, many observers under widely varying conditions.
In the particular case of 'cP', this correction is intended to account for all
the differences in meteor perception attributable to one particular individual,
regardless of that observer's recorded LM or F factors at any given time. In
effect, 'cP' is a "fudge factor" meant to be constant for the observer, across
multiple nights and conditions. However, note that Rainer is in fact saying
that cP for a given individual is NOT a constant number, but rather a function
dependent on some characteristics of the particular shower being observed.
Clear skies,
Lew Gramer
------- Forwarded Message
Date: Sat, 5 Sep 1998 17:19:52 -0400
From: Rainer Arlt <100114.1361@compuserve.com>
Subject: Old query regarding 'Cp', from Adam Marsh...
To: Lew Gramer <dedalus@latrade.com>
Cc: Adam Marsh <riker@net2000.com.au>
Lew, Adam,
The main scheme for the derivation of perception coefficients is taking an
average ZHR and look for the ZHR average of a single observer. The factor
by which they differ is the perception coefficient. Statistically this is
not easy. Such a cP should bderived from a number of averaged ZHRs, and the
ZHR should not change much over this period, since ZHR average and the
observer's average may not represent exactly the same period of time.
Moreover, we have to be sure that the average ZHR is very close to the true
ZHR, and this will only be given from a huge sample of individual ZHRs.
Hence, it is extremely difficult to derive the cP from a group only. Of
course, one can diminish the scatter in the values by this, but the
uncertainties about cP as being an observers' characteristic value are
large.
In principle cP =3D ZHR_ind / ZHR_avg. Better is a time of constant ZHR and
cP=3D1/n_ind * sum(ZHR_ind)/ZHR_avg. The cP depends on the population index.
It can be more suitably expressed by a shift in limiting magnitude (which
is the actual characteristics of the observer): delta_lm=3Dlog(cP) / log(r),
with r being the population index of the shower at the time at which the cP
(i.e. the ZHR_avg) was determined.
Best wishes,
Rainer
------- End of Forwarded Message
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