How will Icarus aboard the ISS track bird migration?

Question

The question Is it possible to see animals from space? has several answers, and they are all based on optical imaging.

In this answer I describe and show images from the

• First count of individual birds from space
• First complete count of an entire species population from space

That worked because the birds were known to be roosting on open ground in a very specific, localized area that offered good imaging contrast.

Now I've just read in Spaceflight Now's article Spacewalkers toss nanosatellites into orbit, hook up bird migration monitor

Clad in pressurized spacesuits, two Russian cosmonauts headed outside the International Space Station on Wednesday and hand-released four tiny CubeSats and installed hardware for a German experiment to track animal migration.

[...]

Called Icarus, the project aims to reveal changes in migratory routes, animal connections and other animal behavior. The antenna for Icarus was carried aloft in February, and a computer launched on a Russian Progress mission last year to help process the signals coming from tracking units tagged to animals on Earth.

“Icarus is a global collaboration of research scientists that are interested in life on the globe, and once we put together all the information on mobile animals, then we have a different and new understanding of life on Earth,” said Martin Wikelski, lead scientist on the Icarus project, director of the Max Planck Institute of Ornithology, and professor the University of Konstanz in Germany.

The spacewalkers set up an antenna boom, routed and mated numerous cables and connectors, and installed the Icarus antenna.

So rather than optically imaging the bird migrations as I'd first imagined, Icarus receives signals in Space from tracking transmitters attached to individually tagged birds.

Question: How does this work? Do the trackers each have GPS and transmit their locations to the receiver on the ISS, or does the special antenna and signal processing pick up beacon signals from much simpler tags on the birds, and reconstruct each signal's direction using the antenna as perhaps a phased array?

note: While the title of the article says bird migration, the body of the article only talks about animal migration. Land mammals can support heavier trackers than migrating birds, so they might have on-board GPS.

I suppose the birds could grip the GPS units "by the husk" or two could cary it together using a strand of creeper, held under the dorsal guiding feathers...

Answer 1

It seems they have very small miniaturized tags on animals that do include GPS along with other sensors and they can transmit up to 800km.

See the technical pdf at the end of this page

Direct link to pdf: https://icarusinitiative.org/sites/default/files/MP_ICARUS_Flyer-EN-lowQ.pdf

From the pdf, page 3:

Animal Tag

The main challenge of ICARUS is the implementation of a low-volume data link between the tags on the animal and the transmitter-receiver on the ISS. A miniaturized animal tag provides the capability of communicating up to 800 km with the ICARUS equipment at the ISS, to measure its absolute position in regular intervals using GPS and to acquire local temperatures, acceleration and magneto-meter values that give indications of the behaviour of the animal – all with a mass of the tag less than 5 grams and a volume of approximately 2 cm3. To achieve this challenging objective, the essential functions of the tag are concentrated within miniaturized electronic units that are optimized for low power consumption, the main power consumers being the radio frequency communication system and the GPS. The design life time of the tag is at least one year.

---

The system works a little bit like GPS in that the signal from the ISS received by each tracker contains a "mini ephemeris" with updated information about the ISS' orbit, so that the tracker can calculate when next to "wake up" and use it's limited battery power to transmit again to the ISS during it's overhead pass. This is key to conserving power and keeping the mass of the battery small. From the PDF:

1. The tag is in the hibernation mode, i.e. in the mode with the lowest power consumption, waiting for the internal timer to awake the system to life at the time of the expected ISS appearance.

2. After wake-up, the receiver starts listening intermittently in order to detect the presence of the ISS downlink radio frequency signal.

3. This intermittent operation will be continued until the detection is successful. With the successful reception of the ISS downlink signal, the tag will extract the most recent information about the ISS orbit from the received signal.

4. With the received ISS orbit data the tag will determine its relative position to the ISS using its own GPS based position on the ground. Based on this information the tag calculates its presence within the field of view of the ISS receive antennas. Until then the receiver will go back into stand-by mode.

5. Upon reaching the predicted receive window the tag will transmit the stored position and sensor data.

6. After data transmission, the tag will remain in receive mode for a predefined time to listen for a configuration command that may be sent by the ICARUS on-board equipment.

7. Before falling back into hibernation mode, the tag calculates the time gap until the next scheduled ISS contact. The hibernation mode is interrupted periodically for position determination and acquisition of sensor data.