Hi Jessica,
Just an idea, but to aid in the interpretation of the plots, you should connect successive tag hits from a given antenna with a line.
Tara Crew may have already responded, but I think she was working on localizing birds in situations with simultaneous tower detections.
Some of the variability in your signal strengths can result from a bird flying across an antenna beam, and/or variation in the birds flight behavior (e.g., climbing or dropping in altitude). Flights across an antennae beam tend to look fairly smooth. Given that you have similar peaks between two separate antenna, it suggests to me that some of the variability in the plot you sent is the result of flight behavior of the bird. My interpretation of this track is that the bird departed in a SW direction and probably departed somewhere west of the tower.
Any other thoughts?
Greg
--
http://motus-wts.org/
---
You received this message because you are subscribed to the Google Groups "Motus Wildlife Tracking System" group.
To unsubscribe from this group and stop receiving emails from it, send an email to
motus-wts+...@googlegroups.com.
To post to this group, send email to
motu...@googlegroups.com.
Visit this group at https://groups.google.com/group/motus-wts.
To view this discussion on the web visit
https://groups.google.com/d/msgid/motus-wts/bb0b7253-2296-4f06-b2de-e5eee9719538%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
Hi Jessica,
Jim makes a really good point about the lobes and the link he sent around is great. Some of the dips in strength could be the result of the bird passing through multiple lobes.
Three quick points:
1) the last antenna to receive a signal will *most* of the time give you an approximate vanishing bearing, i.e. N, SE, or SW in the example you provided if the bird has departed on a migratory flight. I believe this is the approach taken by the references you originally provided.
2) generally, when I have been tracking migratory departure flights, I am able to track the birds for an average of 15 minutes, but this varies with ground speed and the size of the antenna, and so I am curious how long the track is from the bird for which you provided the plot?
3) based on the additional information you have provided, I am wondering if the departure you are describing is really a migratory flight? If you picked up a bird a couple minutes later at a tower north of the tower in question, you would likely have had simultaneous detections on both towers (they sound like they are quite close together). I would also expect that you would have picked up the bird on the north facing antenna if it ultimately began climbing in altitude during departure in a northerly direction.
Happy to follow up off-line if you want to discuss further.
Best,
Greg
From: Jim Moore [mailto:j...@marshlands.org]
Sent: September 1, 2016 10:31 AM
To: Jessica Howell; Motus Wildlife Tracking System
Cc: jeho...@gmail.com; Mitchell, Gregory (EC)
Subject: Re: [motus-wts] Determining Flight Direction of Birds Detected on Towers
One factor that needs to be considered in these sort of calculations is the beam pattern of the Yagi antenna. It is multimodal with lobes proportional to the number of elements in the Yagi antenna. For any given received amplitude the beam pattern can be thought of as a locus of all possible positions of the bird for that signal strength. An article by Cisco "Antenna Patterns and their Meaning" is worth taking a look at.
I am planning on deploying two SG receivers about 0.9 Km apart this fall to get some field test data on signal vs. location that may be useful for answering questions about location vs. relative signal strength.
Cheers
-jim, W3ASA
Jim Moore
34 Moore's Rd.
Elverson, PA
19520
610.286.5187 (Home)
215.500.7525 (Cell)
----- Original Message -----
From: Jessica Howell
Sent: Wednesday, August 31, 2016 5:13 PM
Subject: Re: [motus-wts] Determining Flight Direction of Birds Detected on Towers
To view this discussion on the web visit https://groups.google.com/d/msgid/motus-wts/6e175ea6-eb0a-433f-b269-ae071325cc7d%40googlegroups.com.
From: Jessica Howell
Sent: Wednesday, August 31, 2016 5:13 PM
To view this discussion on the web visit https://groups.google.com/d/msgid/motus-wts/6e175ea6-eb0a-433f-b269-ae071325cc7d%40googlegroups.com.