that can identify thick plumes of ash
John
This appears to be the biggest problem we have with the current methods of determing ash in the atmoshere.
If its dense it can be seen both by the pilot and by satellites. Setting any very low acceptable ash levels is going to cause a major problem of locating where they are by the simple fact that they cannot be seen.
As such we rely on computer and mathematical modelling which may hold X ash concentrations but may also hold X+Y or X-Y or infact no X at all.
Without analysing millions of test shots of air over huge areas we dont know.
Maybe the best way would be to scrap the minimal acceptable levels altogether and to use the satellite visible charts with a safety area around those visible dense ash concentrations.
On the basis that if you cannot see it its unlikely to hurt you aircraft flying in the computer generated low ash areas which are not visible and where ash may or may not be present should be monitored on a more regular basis until we do know more? but with NO meaningless limits
Pace