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RE: (meteorobs) ZHR discrepancies?
Mike,
The reality is that observations by one person at one location do not have
a valid statistical basis (due to lack of numbers, and individual FOV and
conditions) for creating "real" ZHR's. That is the purpose of the IMO, to
accumulate individual observations, using standardized methods, to allow
"normalization" of the data to standard conditions. In our case at the
NJAA, we have had 2 experienced observers through much of the peak, so we
can perhaps SUGGEST rates at our location. However, whether that is valid
for a particular time remains to be seen (statistics are unforgiving) when
high quality observations are combined. That's why all each individual
observer can do is to record what he/she sees at a
time/location/conditions. I will be posting combined NJAA obs of the peak
shortly, but they are only based on 2 observers, looking at a similar point
in the sky. I only create EZHR's for the fun (and possible use in defining
peak times) NOT to suggest that the EZHR's created are accurate within a
factor of 2 or 3. I would also suggest that many newer observers were
overwhelmed in trying to record data for peak times; i.e. over 10 per
minute. I know in my case it required extreme concentration to be able to
record counts and magnitude data throughout the peak. Had the rates been
doubled, it would have been MUCH more difficult. Had I not had hundreds of
hours of experience, they also would have been suspect. the best one can
say about my individual obs is that they are consistent, and valid within
my level of experience and conditions.
Wayne from joisey
----------
From: mlinnolt@alum.mitdot edu[SMTP:mlinnolt@alum.mitdot edu]
Sent: Wednesday, November 21, 2001 3:45 PM
To: meteorobs@atmob.org
Subject: (meteorobs) ZHR discrepancies?
I was reading various reports and noticed significant inter-observer
variation in ZHR during specific time slots being reported. I presume
everyone is using a similar formula to calculate ZHR, where the radiant
elevation factor is given by 1/sin(elevation) and limiting magnitude
correction by r^(LM-6.5).
So how can we be seeing ZHR's varying by a factor of 5 at the same times
for different observers? Is it possible the microstructure of the stream
varies so much over different locations? The time spans of the observations
seem too long for that. It could just be individual perception rates of the
observers, of course, especially at the fainter end. But a factor of 5 is
hard to explain even this way.
Any thoughts?
Mike Linnolt
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