[NLRS] ND Baloon Launch - August 27th

[Ford Peterson]

Andy wrote:

...snip...

> Many of those balloon flights reach 70,000 ft, sometimes even 100,000 
> ft, so you should have no trouble getting a line-of-sight path to it.  
> In fact, you can use the RainScatter program to see what a 70,000ft 
> footprint looks like.  Just enter one of the locations and draw the 
> 70,000ft "fisheye" from the menu.  I have an equasion around here 
> somewhere that can caluculate elevation angle from distance and altitude 
> if anyone is interested.  Assuming flat earth and using some simple trig 
> will get you in the ballpark, though.  This is afterall VHF and UHF....
> 
> Andy K0SM/2

I have studied the wx balloon data provided by NOAA and conclude that the achievable 'height' is quite variable.  A wx balloon has a payload of a few ounces.  True, they do get quite high from time-to-time.  But this is very unpredictable.  

The balloon is filled at ground level using current air pressure at ground level, estimating the amount of expansion required to 'burst' the balloon at altitude.  Although the 'science' is well understood, all balloons are different.  Slight variations on the thickness of the balloon can cause havoc at altitude.  Also, the air pressure at 30,000' is unknown, much less the pressure at 80,000'.  Likewise, accurately injecting an accurate 'volume' of helium is difficult to measure since the balloon pressure at ground level is really meaningless.  The volume of helium at a given pressure induces the burst.  Accurately measuring volume is almost impossible.

When I looked at the 100's of launches done by NOAA every day (twice a day actually), I could see that the altitude achieved was variable by more than 300%.  Some would only make it to 13km, others would make it to 44km and even higher.  And it was all-over-the-map in terms of 'in-between.'

Couple these notions with the fact that the payload is undoubtedly heavier than the NOAA payload of only a few ounces and you have an unpredictability of maybe 5:1 or more.  The longer the flight (slower rate of climb), the more likely it will burst low as the balloon continues to stretch itself out even if outside pressure remains the same.

If I were a gambler, I would put my money on <30,000'.  

Ford-N0FP
ford at cmgate.com