how many to plan for, thinking about in-situ processing and Iridium data transmission

[jerabaul29]

Hi @jvoermans ,

A few questions:

• how many instruments do you plan on building / deploying?

• I am trying to think about the in-situ processing and Iridium data transmission. Do you think it would be ok to have separately "IMU boxes" of the old model with only the IMU and GPS as we used to, and "Geoduino boxes" with all the new stuff but not the IMU, and to maybe deploy both boxes together (if 2 boxes are deployed a couple of meters from each other I think the probability is quite high that they will stay together and have the same fate). This would make it quite a bit easier to design the Geoduino boxes, and reduce the testing needed. Of course this is a bit of extra cost (extra box, battery, etc), but I think that compared with the headache of re-designing the IMU analysis questions and moving it to the Due it would be much simpler. The difficulty is in adapting hardware and software with moving "specifications" that were not thought for at the time when I first built things. The situation will be much better with the "super new" instruments I plan on building if I get the new project accepted :)

[jvoermans]

Svalbard: 3x Geo, 2x IMU + 3x IMU are still in Svalbard (UoM owned) Antarctic: 3x Geo, 2x IMU + 2x IMU still there.

Regarding Svalbard, we have quite a few IMU's. What about below Layout? In principle, geophones need to be in triangle. If data quality is good enough, we should be able to identify the approximate location from which vibrations are coming from. If in a fjord, waves are not too directional, thus ideally they are along a line.

[jerabaul29]

That is really nice, this is a lot of instruments. I think your figure looks very good.

Crossing fingers that the recovery part of the geophones will go well :) This is the only real challenge - we need the raw data for the correlation geophone analysis.

The GPS positioning is not super accurate, so make sure to have ample distance between the geophones :) What do you think would be reasonable? 25 meters between the geophones? 50m?

[jvoermans]

I was thinking of a bit more, perhaps 300 meters? Speed of sound in the ice is ~3000 m/s, so for 300 meters this would mean a difference of 0.1 s.

Yes, I actually was hoping if the geophone data could be removed every few days. I tested an sd-card extender: https://www.adafruit.com/product/3688

a while back using the sketch with geophone logging only, and it didn't seem to have any problem. It is unnecessarily long though. But I plan to put the electronics in a separate weatherproof box inside the Pelican, so perhaps it can be opened in the field then.

[jerabaul29]

300 meters sounds good. Then you need to find a location with a large piece of landfast ice :) Also, you will have to check that the sound does not get damped over these distances. May be interesting to change from few days to few days with the distance, and maybe to try 100m / 50 m / 25 m?

The clocking signal is really accurate thanks to the GPS receivers. Like, the PPS output from the GPS should be a few 100s of ns accurate (absolute accuracy), and it is logged with an interrupt, so a few clock cycles of accuracy in the arduino timestamps; this means that in theory, sub-micro second accuracy about timing differences should be very attainable (in practice, this will be microsecond accuracy, as the Arduino as is now does not have some sub microsecond accurate timer; I could fix this, but would be a bit of work; so since this would be overkill, I think I will not implement it). So should be still possible to measure time differences and triangulate still for distances of 30 meters, maybe even less.

Getting data each few days sounds excellent. Nice SD extenders, sounds like a really cool idea to have a "double box" for easy checking of the SD card. That sounds excellent, will be extremely exciting to see how the data will look like :) .

A small note: I wonder if it may be a good idea to try to have 1 or 2 spares of geoduino in each deployment if it is possible. Otherwise we are a bit vulnerable to single instrument failures... Of course this is dependent on cost and time available for building though...

[jvoermans]

Yes, homogeneity is an assumption that has to be made. Any discontinuities in the ice are a problem too (cracks, ice ridges...)

I'm already happy with ms accuracy :) my initial problem was the 1s accuracy of the GPS unit in the most elementary sketches, so its great you got that working.

We don't really have budget for more instruments unfortunately, we budgeted for hydrophones as well, but have to pass for this deployment. The geophone is perhaps the most expensive element, but other than that, we can arrange back-up electronics? It might be possible to simply swap the 'electronics box' inside the pelican by itself and keep the battery and geophone as is... I don't think this will be the most likely source of instrument failure though...

[jerabaul29]

Do we drop iridium for the geoduinos altogether? ...

[jerabaul29]

I think maybe for the first deployment logging is the only true option, as we do not know what kind of signal we will be looking for.

[jvoermans]

Yes, for this deployment better to drop Iridium. The only reason it could be handy is to determine if the Geophone is not drifting away on the ice. But if other buoys are deployed nearby then we already have that info

[jerabaul29]

Sounds good. Then closing this issue.