Hi all,
I am a hang-glider pilot in the SF bay area and have been doing the sport for a couple of years. For this reason I have taken much greater interest in the weather than in the past.
The biggest factor determining whether there is a chance of soaring is a favorable lapse rate which gives rise to thermals. So we free flight pilots are always looking at the measured lapse rate and ground temperature to see how a good a given day may be.
I was surprised to find out that the lapse rate is only really measured in a few places daily, and the data is used for a huge area! In the SF Bay they send up a balloon in Oakland, and we have to use that sounding data for flying sites as far away as Dunlap California, which is all the way in the foothills of the Sierras, east of Fresno.
This lead me to research about methods to determine lapse rate , and I came across something called "Radio Acoustic Sounding". Basically a low frequency sound wave is projected into the air. The air temperature at different places in the sound wave's upward progress changes the local speed of sound, and thus the sound wave wavelength. This wavelengths can be measured by backscattering from a tuned radio wave (Bragg scattering condition). The temperature at a given altitude is then determined by timing of backscattering and frequency. Depending on frequency of sound wave, power, etc etc. lapse rate can be measured up to a few thousand feet above ground level.
It seems like an ideal system to place at a local site, and run automatically. However, all I was able to find on the method was scientific papers describing one-off systems built by the researchers. It does not seem like they are commercially sold from what I can tell, nor could I find much talk about them on forums. The papers are rather short on details needed to actually build one.
Is anyone familiar with these RAS systems, has built one, worked with one, or knows what manufacturers sell them? Are there better ways to measure lapse rate that don't involve sending up a balloon?
Regards,
Mark G
