Next message: Robert Eno: "Re: Refraction"
Marcel,
You can download copies of the Air Almanac from
<http://164.214.12.145/NAV_PUBS/SRTA/Pub249/>
Fred
On Aug 4, 2005, at 8:40 AM, Marcel E. Tschudin wrote:
> Hello Robert
>
> Thank you for your fast reply. Unfortunately I am not in possession of
> the Air Almanac; in addition I am for about an other year abroad in a
> country where I am not able to order copies from a library. May I
> therefore ask you, whether it would be possible for you to derive from
> the table you indicated one or the other benchmark value? As you
> mentioned this would at least give a clue. Thanks a lot!
>
>
> Like you I am still hoping that there is some one out there who really
> can provide a solution to this problem.
>
> Marcel
>> ----- Original Message -----
>> From: Robert Eno
>> To:
>> Sent: Saturday, September 03, 2005 2:37 PM
>> Subject: Re: Refraction
>>
>> Hello Marcel
>>
>> Refraction error makes the observed body appear to be higher than it
>> actually is, ergo the same correction rules for postitive
>> altitudes would apply to negative altitudes; only in this case the
>> negative numbers would be added. If, for example, your sextant
>> altitude was minus 5 degrees, and the refraction correction was (I am
>> just pulling a random number out of my head) minus 60 minutes
>> (refraction correction is always subtracted from the sextant
>> altitude), then your corrected altitude would be minus 6 degrees.
>>
>> Near as I can reckon, you would only experience negative altitudes
>> from an aircraft flying at high altitudes or in the polar regions in
>> winter.
>>
>> Have a look at Table # 6, HO 249, Sight Reduction Tables for Air
>> Navigation and the correction tables at the back of the Air Almanac.
>> These give you a bit of a clue as to what to expect. Other than these
>> tables, I know of no other tables which provide refraction
>> corrections for negative altitudes for observers at sea level. If
>> anyone out there is aware of such tables, do let me know. It is a
>> question I have not pondered for some time now.
>>
>> Robert
>>> ----- Original Message -----
>>> From: Marcel E. Tschudin
>>> To:
>>> Sent: Thursday, August 04, 2005 6:48 AM
>>> Subject: Refraction
>>>
>>> Hello
>>>
>>> While searching with Google, I came across this mail list. May be
>>> some one out here may be able to help me answering the following
>>> question:
>>>
>>> How do refraction values for negative elevations have to be
>>> calculated, such as e.g. the horizon from a plane? (I am interested
>>> in the range of 0° to approx. –5°.)
>>>
>>> Is Bennett’s approximation also valid for negative elevations? If
>>> not, what other approximation formulae should be used, or, where can
>>> one find some benchmark values?
>>>
>>> I am interested in formulae for both, refraction from apparent
>>> position and from physical position.
>>>
>>> Thank you for any input to my problem.
>>>
>>> Marcel
