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RE: Compute Elevation

In the formulas developed for Quiktrak, based on Pedro Escobal's
work (also used in NOVA),  Obscura elevations are easily added to
the search algorithm.  This was a pain back on the old DOS days
with too little real memory, but nowadays, this could easily
be added.  Why not suggest this to NLSA for their next version
of NOVA?   I see no difficulty in adding this kind of computation
and making it as fine or as coarse a description of your horizon
as you might like.  Then you would get Newton's method search
times for AOS/LOS with a "filter" based on your real horizon.


-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of Ken Ernandes
Sent: Friday, August 09, 2002 4:31 PM
To: amsat-bb@AMSAT.Org
Subject: RE: [amsat-bb] Compute Elevation

Lance -

Let me give you some insight as to how we handle this problem in software
used by the Air Force Satellite Control Network (AFSCN) and others -- I am a
consultant for a company located in your neck of the woods.

What we have is an "Obscura" table for each of the Remote Tracking Sites
(RTSs) -- a single site would be analogous to your antenna farm.  An obscura
table is a discrete listing (from 0 to 359 degrees of Azimuth in one degree
increments) of the minimum unobscured elevation for the particular site.
The rough visibility computations are performed using the lowest unobscured
elevation to get the approximate horizon break time.  These times are then
adjusted the obscura Elevation corresponding to the Azimuth of the horizon
break.  This is perhaps more elaborate than you might want to code into your

There are more elegant ways I've developed if you don't need a precise
answer and have only a few blocking obstructions.

73, Ken N2WWD

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