(meteorobs) Accounting for airmass in LM

• To: meteorobs@atmob.org
• Subject: (meteorobs) Accounting for airmass in LM
• From: Mike Linnolt <mlinnolt@alum.mitdot edu>
• Date: Sat, 18 Aug 2001 12:11:03 -1000
• Delivered-To: meteorobs-mh@atmob.org
• Delivered-To: meteorobs@atmob.org
• Reply-To: meteorobs@atmob.org
• Sender: owner-meteorobs@atmob.org

In followup to my last post, there is an optimum elevation for your
comparison star field to be used for LM estimate.

You should use a star field at an elevation that corresponds to the
weighted average airmass over your FOV. This way the LM
estimate best represents the overall condition, not an inflated value.

This optimum elevation is given by: arcsin(1/weighted mean
airmass).

For some typical FOV elevations, here is the optimum comparison
star field elevation to be used (100° wide field assumed):

FOV elev.  Weighted mean airmass   Star field elev.
--------------  -----------------------------------   --------------------
   75°                     1.18                           58°
   70°                     1.24                           54°
   65°                     1.32                           49°
   60°                     1.45                           44°
   55°                     1.67                           37°

Mike Linnolt

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