Cheap electret microphones for environmental noise measurements

[env.noise]

I'm a Ph.D. student and I need to make some long term environmental noise 
measurements. I need to deploy a noise measurement network using small nodes 
equipped with a microphone and a radio interface (for transmiting measurements).

I don't need very accurate results, but as I will have to deploy a lot of 
measurement nodes, I need each of them to be very cheap. Electret microphones 
such as Panasonic WM-61 are enough for my purposes. My only concern with them 
is that as I need to do measurements for a year or more, I need the microphones 
to last as much as possible.

Does anybody know (and if backed with data, better) if these microphones can 
last when placed outdoors without breaking or suffering severe 
sensitivity/frequency response deviations? How can I properly (and cheaply) 
protect them? I can correct measurements with temperature data, and maybe also 
with humidity. Any other advices are welcome!

Please avoid expensive commercial solutions (such as Class1/Class2 outdoor 
microphones).

Thanks,

John 

 PS: This topic is not 100% related to this group, as it deals with 
environmental noise, and not with nature sounds, but I think people in this 
group has for sure the experience and knowledge necessary to solve my problem, 
and the community might be interested in how to record sounds for long term 
with cheap microphones.
 

 Sorry if I bother someone.









"While a picture is worth a thousand words, a 
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.



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