To test this feature, visit your live site.

GPS-Sync Settings -- Can files be saved when GPS fails to acquire fix?

Hi, all -

I'm trying to use an array of 28 AudioMoth Dev units with GPS+GLONASS modules to capture 12-hour continuous recordings using the GPS-Sync firmware.

What I am finding is that the recorders get their initial fix (on being switched on) very quickly, and the first recording in the program is typically successful in both getting a fix and recording until the maximum file length. After that, however, most attempts to record - both continuing on during that initial recording session, and on subsequent days - fail because a GPS fix is never acquired. All recorders do not fail all of the time, but most recorders fail most of the time.

I have tried giving the recorders 900 seconds to get a fix (recordingFixDuration: 900) but this hasn't helped. And I've noted that when the recorders are first switched on, they do acquire a fix quickly, typically within 30s. I have also tried breaking the recording period into shorter recordings (ranging from 15 minutes to 1.5 hours) with breaks in between to allow more time for acquiring a GPS fix; this hasn't resolved the issue either.

If there is something else I should try to correct the GPS issue I would love to hear ideas. Alternatively I am wondering if it is possible to program the units to carry on recording (and saving the recordings) even if a fix isn't acquired? That way I would at least have the recordings even though I won't be able to sync them.

Thanks for any help and ideas!

Cheers, Laura

4 comments

4 Comments

Laura Molles

Hi, Alex - I'll try that and see if it helps, in the meantime I am also deploying a set with the standard firmware today. We'll have a look at the results in a few days and go from there.

Thanks again for your help!

Cheers,

Laura

Laura Molles

Hi, Alex -

Thanks so much for your fast and comprehensive reply!

Here is some more information:

-Initial voltages for the first recordings (always successful) are 3.9-4.1V. In cases where one or more later recording attempts have been successful, the range was 3.6-3.9V. I had one recorder get to the point where recording stopped due to low supply voltage. The voltage value in the metadata for that file was 3.4V.

-Powerex 2700mAh rechargeable batteries

-Samsung ProPlus 128GB MicroSD cards

-Recorders are in a rural area, mostly in the open with a large hedge alongside one row of recorders. The row that has the least clear view of the sky (due to the hedge) has actually performed better on average than those with a totally unobstructed sky view

-I'm in New Zealand and suspect our satellite coverage is not as comprehensive as it will be in many places, but during the day when I'm setting them up the recorders reliably get a fix within a minute

I'll check with my colleague who has been fine-tuning his sound localisation code regarding the sync accuracy, and will have a go with the standard firmware approach and see if that works for us.

I've attached both the settings file I've been using, plus a few recorder logs: one for a recorder which only made one successful fix + recording, one that made multiple recordings (and probably failed due to a low battery before making a final recording), and one that got a fix at every recording attempt and stopped solely due to low voltage. These three recorders were operating within 10m of one another at the same time.

Thanks again for your help, hopefully the standard firmware approach will be the solution but I do appreciate any advice on where I've gone wrong with the sync firmware.

Cheers,

Laura

Alex Rogers

Replying to

Hi Laura, I think the GPS fix issue must be due to the battery voltage dropping. I double checked with a device here and there is no firmware issue that prevents a fix if the file is restarted due to the file size limit being exceeded. I think it would be worth trying the sleep/record cycle so that the battery gets a short recovery period before acquiring a new recording fix. With a sleep time of 300 seconds and a record time of 2 x 3600 - 300 = 6900 you would get recordings that start on the hour, last just less than 2 hours, and have a five-minute gap between them. It should also mean that the start time of all the recordings are the same as at the moment they will vary depending on how long it takes the GPS to acquire a fix. If the recordingFix is 120 seconds, you will give the battery about three minutes to recover between recordings. We'll look at modifying the firmware, as if you don't get an initial fix, it is probably worth at least getting an unsynchronised recording, rather than no recording.

Alex

Edited

Alex Rogers

Hi,

Can you share the configuration that you are using. The AudioMoth-GPS-Sync firmware needs to have a continuous fix in order record the necessary PPS time signal alongside the WAV file.

In the case where the later recordings are successful, can you check the voltage in the WAV file. The GPS takes quite a lot of power when running continuously so I wonder if the batteries are running down which is affecting the ability of the GPS module to get a fix. What make and model of battery are you using? Also, what make and model of SD card are you using?

How accurate do you need the synchronisation to be? The AudioMoth-GPS-Sync firmware will synchronise to about 1us which is much better than required. If you use the standard firmware and use the GPS on either side of 1-hour recordings, then the synchronisation will typically be to within a couple of milliseconds which is good for most application. In the case that the GPS does not acquire a fix the recording will still be present and can be synchronised, with a bit less accuracy.

https://github.com/OpenAcousticDevices/Application-Notes/blob/master/New_Support_for_GPS_Synchronisation_in_the_Standard_Firmware/New_Support_for_GPS_Synchronisation_in_the_Standard_Firmware.pdf What type of environment are the devices deployed in?

Alex

Edited