Compass bearings of antennas at Motus stations

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Mary Anne McLeod

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Nov 17, 2023, 1:26:34 PM11/17/23
to Motus Wildlife Tracking System
Hi all,
I've noticed that the compass bearings that are listed for antennas at Motus stations (in the pop-up window when you click on a station on the Receiver Locations map) do not line up exactly with the estimated antenna ranges displayed on the map. For the couple of stations I'm interested in along the Lower Colorado River, the oval of the estimated antenna range points at a bearing that is 10 degrees or so more than the listed compass bearing.  I checked a couple of stations in the northeastern U.S. and the reverse is true; the oval of the estimated antenna range points toward a compass bearing that is 10-15 degrees less than the listed compass bearing. Are the compass bearings listed relative to true north or magnetic north? If it's magnetic north, declination would explain the discrepancy. 

Thanks for your insights,
Mary Anne

Pat Lorch

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Nov 18, 2023, 1:16:42 PM11/18/23
to motu...@googlegroups.com
It is my understanding that Motus converts magnetic north readings entered when you deploy to true for display. Both are shown on the deployment form. 

Patrick Lorch

On Nov 17, 2023, at 10:26 AM, Mary Anne McLeod <fiddlin...@gmail.com> wrote:

Hi all,

I've noticed that the compass bearings that are listed for antennas at Motus stations (in the pop-up window when you click on a station on the Receiver Locations map) do not line up exactly with the estimated antenna ranges displayed on the map. For the couple of stations I'm interested in along the Lower Colorado River, the oval of the estimated antenna range points at a bearing that is 10 degrees or so more than the listed compass bearing.  I checked a couple of stations in the northeastern U.S. and the reverse is true; the oval of the estimated antenna range points toward a compass bearing that is 10-15 degrees less than the listed compass bearing. Are the compass bearings listed relative to true north or magnetic north? If it's magnetic north, declination would explain the discrepancy. 

Thanks for your insights,
Mary Anne

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The Motus Wildlife Tracking System (Motus) is an international collaborative research network that uses coordinated automated radio telemetry to facilitate research and education on the ecology and conservation of migratory animals. Motus is a program of Birds Canada in partnership with collaborating researchers and organizations. Learn more at https://motus.org
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