I fly my UAVSonde flights once per week, usually on the weekend, to gather temperature, pressure, and relative humidity once a day. I began to wonder how these conditions changed throughout the day. I know the ground temperature increases until around 4:00 PM before it begins falling again. But does this hold true 400 feet above the ground? I am investigating conditions at an altitude of 400 feet because that's how high my drone can legally fly.
So I ran the same sensors and collected data the same way five times on Sunday, July 9th. Now it was stinking hot on Sunday. My part of Idaho broke a temperature record with highs above 100 degrees. Also, the quadcopter lifted off from my driveway. That driveway was extra toasty. It was obviously the case if you looked at the driveway and the neighboring lawn with the thermal imager. Anyway, once I completed the first flight, I was committed to repeating the rest of the flights in the same manner. Below are the results I got from the flights. The time is in 24 hour time.
The first chart shows that the ground temperature did indeed increase throughout the day and began cooling at around 3:00 PM. It then spiked in temperature later in the evening. The air temperature at 400 feet AGL lagged behind the surface temperature by 7 to 10 degrees before cooling off by 7:00 PM.
The second chart shows the air pressure at 400 feet AGL is always lower than the surface pressure, but that amount of difference changes throughout the day. Also that the surface pressure spiked at around 7:00 PM. Meanwhile, the air pressure at 400 feet AGL spiked earlier at around 2:30 PM.
I really need to repeat this experiment again when it's not quite so hot. I'll also experiment with calibrating the pressure sensor with temperature in order to remove this possible effect. Finally, I'll launch the quadcopter from the lawn.
It's said you can look up lots of information on the Internet these days. It's probably true that someone already knows how the temperature of the air several hundred feet above the ground changes throughout the day. But I say why look it up when you could find out for your self. In the process, you learn more STEM and the importance of measurement. And you'll develop more skills and hone the ones you already have. An that's not a bad way to spend a Sunday afternoon.