Bumped into acoustic array during fieldwork - localisation issue?

Question

While walking backwards in the dark, I bumped into my 4-channel inverted T-shaped acoustic array placed on a tripod. The array has a central mic with 3 peripheral mics at 60 cm Radius at 120 deg intervals. (See sketch below).

(Quick sketch of a 60 cm radius inverted T shape array geometry, photo to come. Red dots indicate mic positions on the frame.).

The frame shook a bit, but seemed to remain more or less in the same position as it was. I'm a little worried now. The frame is rigid, and the inter-mic distances will remain the same. The 'pose' of the frame is my concern.

How much will this change the final coordinates of the localised bat calls?

What do you do in case something like this happens?

Answer 1

Always useful to calibrate your array now and then, by playing back a sound from a known position, whereby you can verify array geometry. In air, useful sound sources are training clickers, which will make a sharp sound transient when you press them, very useful for testing arrays. Some array positioning algorithms are optimized for bat calls (FM-sweeps) and perform poorly with transient signals, so in those cases you will have to design your own artificial bat call device.

In water, a gillnet pinger is similarly handy to deploy at known positions from your array to verify geometry.

Answer 2

This has happened every now and then to me, and the solutions ate a combination of using clickers like @Jakob Tougaard suggested, and also taking measurements as commented by @etgriffiths.

By measurements, I mean taking distances to landmarks with a laser range finder or tape. If the landmarks are slightly far away, you won't pick up small alterations in distance, but can realize bigger ones.

In addition to distance, you can also additionally take 'tilt-measurments' every now and then. Some range-finders come with tilt measurements in built too, which reduces the number of things you need to carry in the field.