I've been looking into this for a couple of organisations, and came across
this paper by the inventor of this device. I also discovered that he was sacked by an Australian Research institute in 2006 because they didn't see any point in the research, which is how he ended up in Norway.
The basic technology seems to be an infra red radiometer, using some form of particle generated diffraction, or possibly even laser backscatter, to detect particles.
Matching the experience in Europe over chasing the unpronouncable volcano's ash cloud, they found that the ash signal was obscured by ice particle content, or high water content. UK scientists' experience have found it possible to some extent to differentiate between ice/water/ash from backscatter lidar returns. However, this has only really been possible above the planetary boundary layer (which generally runs from surface to around FL60), and by taking results from multiple instruments and running it through the brain of a bloke with a PhD in aerosol chemistry and half a dozen years subsequent practice in doing this sort of thing.
No current instrumentation exists that does this horizontally, and no current instrumentation exists that reliably does this all remotely. Also Prata's own paper does say that routinely telling the difference between volcanic ash and (less hazardous) desert dust. He further says that inversions (which are pretty common over Europe!) can give false positives.
From all that, and a certain amount of personal experience in this, I'd reckon that this technology could go somewhere. However, from what I can find out this chap Prata has been a voice in the wilderness for years - telling everybody that the world needed some form of remote volcanic ash detection system: and mostly being treated as a bit of an amiable lunatic by the aviation community. Suddenly, it turns out that he was probably right and the rest of the aviation world were wrong - he must feel great about that!
However, he is coming at this from a bit of a standing start, and there are going to be some massive technological problems to solve in getting this sort of system working on an aeroplane.
Here's my best guess - if you throw enough research funding at this; let's say around £10-£20m over a shortish period of time, and get some of the world's better airborne instrument people onside: labs like Met Office OBR, DMT, Manchester University, FAAM, NCAR... - you may get a flying prototype giving order of magnitude information by about the end of 2011 and something fittable onto in-service aircraft by the end of 2012. It'll not just involve a lot of instruments by the way, but stacks of computing power on board, and probably very regular ground based calibration which will be a high maintenance overhead.
And IF it works, frankly this chap Prata deserves a handful of medals and to retire rich and famous. The question is I think whether beyond some inspiring press releases, somebody's prepared to shove this much cash into it (plus the several tens of thousands of dollars and tens or hundreds of kilos per aeroplane) that this sort of system is likely to cost per airliner that eventually such a system will cost. There's got to be a significant risk that it won't except in conditions clear of cloud and above about 6,000ft.
However, doubtless something cobbled together will fly shortly on Toulouse's A340-600 test hack, it'll generate some dubious data which impress company executives and leave the scientists who really understand this stuff very critical. That may nonetheless be worthwhile if it gets the enormous research funding that something like this needs.
G