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Re: (meteorobs) Are Sporadics Constant?

John,
      No doubt that our many experienced list elves have been sharpening
their intellectual knives readying for a response to your (important, I
feel) questions about sporadic activity.  I probably represent the worst
possible responder to your questions, but I have found that if I eat
enough shoe leather, the real answers will be forthcoming quite soon!

>>1.  If we are able to determine sporadic activity for a given hour
during the day, or month, are these data valid for the same hour >>of
other days, months, and years?
      The answer here is a clear no, that is, for a given observer in a
specific location.   We in the northern hemisphere are currently in the
period of lowest sporadic activity for the year, and this is due to the
inclination of the earth on its axis. As the northern hemisphere tilts
back up towards the autumnal equinox in September, sporadic rates will
reach their highest rates.  This, of course, also coincides with the
time of year when increased shower activity is occuring.  This would
make discernment of sporadic vs. shower members double difficult for
radio observers,I would guess.
      As for the change is sporadic meteor rates over the years, let me
quote a section from the AMS Web Page, concerning Dr. Charles P.
Olivier:
   "During the 1950's, the advent of more sophisticated techniques and a
shift in emphasis in the
                     professional community to photographic and radar
techniques led Dr. Olivier to shift the research
                     emphasis of the AMS to a long term statistical
study of the sporadic meteor flux. Containing many
                     years of previous observations, the AMS Visual
Database formed the basis for four catalogs giving the
                     average visual meteor rates seen for each hour of
the night during the year (Olivier, 1960, 1965, 1974a,
                     and 1974b). Three of these catalogs were for the
northern hemisphere and one for the southern
                     hemisphere. The northern hemisphere catalogs were
average rates over the years 1901-1958,
                     1959-1963, and 1964-1972. Dr. Olivier continued
this work throughout his retirement, and was
                     completing the manuscript for a fifth catalogue at
the time of his death in 1976."
     WhileI have seen only one of these very thorough catalogs (from the
'50's) it is clear that rates do change from year to year, thus the need
for some type of continuation of Dr. Olivier's work at the present time.

>>We know,  of course, that there is a cyclical pattern of radio meteor
activity over the 24 hour period due to the earth's rotation >>>and its
path around the sun.
     The 24 hour, or diurnal variation, would be strictly a result of
the earth's rotation, as sporadic rates reach their peak at or near 6:00
A.M. each day.  The  earth's apex point reaches culmination at this
time; at that time the observer is on the part of the earth that is
moving forward in it's solar orbit.

>>2.  How do we actually determine background activity?  Some meteor
showers appear to be characterized by very low activity >>over many
days.  How can we be sure we really are looking at sporadic activity
(true background "noise")
>>without contamination by weak and/or even unknown long term meteor
showers ?
    This is a question for radio observers, so I will have to leave this
for our expert radio elves.  But the question as you pose it involves
"unknown" long term meteor showers, some of which are so weak that I
doubt we could ever differentiate them from "true" sporadics.

   Well, now that I've had a good taste of my shoe, I leave further,
more adequate replies in the hands of those who really know!
Good luck in you radio observations!



"John R. Meyer" wrote:

> Dear Meteorobs Net:
>
> Our radio observatory is at the point where we are collecting solid
> data 95
> per cent of the time.  System specifications and data for January,
> 2000 were
> posted to Meteorobs Net on Fri., Feb 18, 2000 and in the Meteorobs
> Digest
> V3, #298.
>
> It appears that our next step in data reduction is to determine the
> number
> of background sporadics and subtract this from total reflections
> observed.
> Presumably the residual will be attributable to meteor showers.
>
> It may be, however, that determining background sporadics will not be
> trivial.  Unlike the situation with visual observations, we have no
> easy way
> to determine if a given reflection is due to a sporadic or is part of
> a
> stream/shower.
> This occurs because we collect no data on the radiant.    We only
> determine
> total activity as seen by our directional antenna.  It will respond to
> any
> signal which obeys the laws of specularity.  That is, it will pick
> up any signal where both the transmitting and receiving antennas can
> both
> "see" the meteor trail at the same time, and where our antenna is at
> the end
> of the path where the angle of incidence of the VHF signal upon the
> meteor
> trail is equal to the angle of reflection.  On average, this accounts
> for
> roughly 3,000 meteor events in an normal 24 hour period.
>
> Several question arise with regard to this:
>
> 1.  If we are able to determine sporadic activity for a given hour
> during
> the day, or month, are these data valid for the same hour of other
> days,
> months, and years?  That is,  the level of sporadic activity constant
> for a
> given hour, within statistical limits?  Are there monthly variations
> in
> sporadics that are statistically significant?  How about yearly
> variations?.
> We know,  of course, that there is a cyclical pattern of radio meteor
> activity over the 24 hour period due to the earth's rotation and its
> path
> around the sun.  Our data clearly show this 24 hour activity pattern.
>
> 2.  How do we actually determine background activity?  Some meteor
> showers
> appear to be characterized by very low activity over many days.  How
> can we
> be sure we really are looking at sporadic activity (true background
> "noise")
> without contamination by weak and/or even unknown long term meteor
> showers ?
>
> I would very much appreciate input on the above questions, along with
> any
> suggestions on literature that might deal with this.
>
> Regards, John Meyer
> Van Andel Creation Research Center
> Chino Valley, AZ
>
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