Tuesday, December 18, 2012

Fruit-Bat Tracking with Robin GPS Logger

I have recently received the results of an interesting experiment done with Robin, Cellguide's snapshot GPS tracker so I thought I should share it with the Community.

Figure 1: Yes, a fruit bat
Becuase of its size and weight Robin enables new applications of GPS technology, including wildlife tracking of course. Particularly of species on which was very difficult in the past.

Test Setup 
  • CellGuide Robin GPS Logger with 100mAh battery (2.2 grams): total weight 4.75 grams
  • Programmed to operate every day between 5pm to 5am
  • Total length of the experiment: 72 hours
  • Operating regime:
    • Fix every 3 seconds
    • Medium sensitivity (GPS snapshot length of 128ms)
The test was conducted by researches from Tel Aviv University. They packed Robin in a light weight plastic wrap along with a UHF beacon device, and attached everything to the bat using a special medical glue that only sticks for a few days.

Figure 2: A picture of the fruit bat with Robin on the back.
Figure 3: The test area.
During the first night, the bat visited three other trees along its path. On the second night, the bat took a bit of a different path but still quite similar to the one from the previous night and flew to the same tree. Then, pretty much as the two previous nights, the bat flew to his favorite tree again.

 Figure 4: From left to right: first, second, and third night

The Robin logger was found two weeks later inside the cave, using a UHF beacon device. A summary of the experiment is given below.

Figure 5: All nights on the same map.
Despite this experiment being simply very cool for a GPS passionate as I am, I shall probably mention here that I don't work for Cell-guide so for further information on the Robin GPS Logger please do contact the experts!



Ric said...

Hi Michele! Thanks for the post. Snapshot postioning is very interesting but I have a doubt. If I understand it correctly, the GPS device just records the raw pseudorange measurements, the actual positioning is done a posteriori in a computer using offline navigation messages. But in order to track the satellites, decode their PRNs and calculate the actual pseudoranges you still need to know the (at least approximate) satellite positions Do you know how this is tackled within the GPS chip? Many thanks - Ricardo.

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Michele said...


The GPS device does not record pseudorange measurements, just a digital copy of the GPS RF spectrum. Thus, both the raw observations calculation and the PVT are done in post-processing.
You only need to know the approximate position of the satellites for PVT. A receiver can acquire (decode PRNs), track, and calculate pseudoranges without knowledge of satellite orbits/clocks. Hope this helps.

Thanks for the kind words, will surely do!

Unknown said...

hello ,
I have read ur articles and i found them very intresting . i want to do a project on SOFTWARE BASED GPS RECEIVER ,, but i cant get the code for it...could u please help me????

Unknown said...

Hi Michele,
I'm a graduate student and just started working with SDR GPS Receivers. I'm using the NSL Stereo (GNSS RF Front end) to capture data. I am working on my own software right now but I have trouble understanding the format of the data captured by the receiver. The manual doesn't explain much neither does the website. Thankfully the NSL webpage directed me to your blog.

Your help would be much appreciated!

Michele said...

There are plenty of sources on the Internet, please search Google before posting.

I am not employed by NSL since two years! The last document I have on the hard-drive is the Stereo UM v1.2.
You may download it here:
In appendix A is explained the data packing and how to decompress the binary stream. PLease contact NSL for more details.

Adam Peck-Richardson said...

Hi Michele,

Thank you for your efforts to explore, test, and share the progression of this emerging technology. May I ask what your sources are for this article or what lab is conducting the research? I am interested in finding out more about this project and more about the researchers' experience with the Robin device. I have also read your post detailing your own tests with a Robin device. I am particularly interested in the device's success rate for obtaining a position. Do you have any data on the likelihood that the device will obtain a position during a given "snap" or how this success rate changes relative to the snap duration? Thank you in advance.

Michele said...

Dear Adam,

Snapshot GPS positioning is not exactly an emerging technology.. it has been around since at least 15 years. After the team at NXP software (then Geotate) was acquired by uBlox, I feared it would disappear forever. Only recently started again to be applied with success in ultra-low power applications that don't require a remote link with the GNSS tag fix.
With regards with the results posted above, it is the Cell-guide team that disclosed them to me so they should be taken as a reference for that kind of work.
The device success rate for a fix depends a lot on the signal conditions. I would say that availability is similar to the one of an old-fashioned low-sensitivity (-152dBm) GPS receiver, but the Cell-guide guys might have implemented a higher sensitivity algorithm without sharing it with me of course :)
Please do get in touch with them, I am sure they have all the information you need. By the way, the Memoto camera project uses a Cell-guide positioning core.. quite impressive.


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Unknown said...

It is very useful to have this kind of equipment.

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Unknown said...
This comment has been removed by the author.
Lupus said...

I would be interested in the accuracy of the heights the Robin loggers recorded. I'm involved in a bat project as wel, using the same gps units. Is it correct that i have to substract the geoid height from the received height in order to get the real flying height of the bats?