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Alex,

The website, http://www.topozone.com/ has topographic maps covering
the U.S., from which you can extract your elevation to the nearest 20
feet or so, which is close enough.

Fred

On Oct 31, 2006, at 10:33 AM, Alexandre E Eremenko wrote:

>
>
> Jean-Philippe,
> Thanks.
> I have no problems with conversion of units,
> (though it is sometimes annoying with pressure
> for which at least 5 different units are commonly used:
> psi(=punds/square inch), millibar(=1000 dynes/square centimeter),
> Pascal (not to be confused with psi:-),
> inches of mercury and
> millimeters of mercury.
> And I almost forgot the sixth unit: the atmosphere:-)
>
> Most barometers on e-bay use one or two of these units,
> so one has to hand a conversion table besides the barometer:-)
>
> Is there a convenient source on the web to find one's altitude
> over the sea level, (I mean for those unfortunate ones
> who do not live on a sea shore)?
>
> Alex.
>
> On Tue, 31 Oct 2006, jean-philippe planas wrote:
>
>> If you know the elevation of your observation spot as well as the
>> atmospheric pressure reduced to sea level (QNH for the pilots) you
>> can determine the local pressure (QFE for the pilots) knowing the
>> fact that every 28 ft of altitude the pressure decreases by 1
>> millibar in the lower standard atmosphere . I'll look for the
>> formula in inches of mercury if its the way the weather channel
>> provides this info.
>>   JPP
>>
>> Fred Hebard  wrote:
>>
>> That's correct! I started looking into this, but gave up.
>> Hopefully, the physicists will jump in here.
>>
>> On Oct 31, 2006, at 8:59 AM, Alexandre E Eremenko wrote:
>>
>>>
>>>
>>> Fred,
>>> I see, this sounds reasonable.
>>> But then I need a barometer, or to correct
>>> the pressure from the Weather channel for
>>> my altitude, because,
>>> if I understand correctly, the pressure broadcast
>>> for the weather prediction is reduced to the sea level.
>>>
>>> Alex
>>>
>>> On Tue, 31 Oct 2006, Fred Hebard wrote:
>>>
>>>>
>>>>
>>>> Alex,
>>>>
>>>> Use the actual pressure. That is the determinant for the refraction
>>>> correction. The elevation above sea level has an insignificant
>>>> effect on parallax, when you consider that the radius of the
>>>> earth is
>>>> about 3400 nautical miles, but significantly reduces refraction via
>>>> the effect on barometric pressure.
>>>>
>>>> Fred
>>>>
>>>> On Oct 31, 2006, at 8:27 AM, Alexandre E Eremenko wrote:
>>>>
>>>>> Related question: the barometric pressure in the refraction
>>>>> formula.
>>>>> Should I use the actual pressure at my observation site,
>>>>> or should I "reduce it to the sea level"?
>>>>> The actual pressure at my site reflects not only the deviation
>>>>> from the standard atmosphere but also my altitude over the sea
>>>>> level.
>>>>>
>>>>> Alex
>>>>>
>>>>
>>>>
>>>>>
>>>
>>>
>>>>
>>
>>
>>
>>
>>
>>
>> JPP
>>
>> ---------------------------------
>> Get your email and see which of your friends are online - Right on
>> the  new Yahoo.com
>>
>>>
>
>
> >


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