We are balloon mapping the receding shoreline of the Salton Sea in Southern California. This is California's largest inland lake and now has a shoreline projected to recede by several hundred feet over the next 10 years. We are mapping the shore over time to show the increase of playa and potential increase in airborne dust. I am a professor working from Loma Linda University, but partnering with local organizations, notably the Alianza of Coachella Valley.
We have had successful mapping missions before: https://mapknitter.org/maps/yachtclubtest
We were mapping yesterday with 3 mylar balloons filled with commercial grade helium. The mylar ballons were made from emergency sleeping bags taped with foil tape and held the helium well. They are very light and have lifted the camera rig in the past. The camera is a Canon SX260 on a picavet suspended underneath the cluster of three mylar balloons.
There were 15 of us at the Salton Sea yesterday and it was 110 degrees at 5pm at the seashore yesterday and the balloon would only rise about 20feet at the most. It was the same rig that lifted the balloon successfully in February and earlier days of the year when it was much cooler. The helium was much cooler when it came from the tank and I think the temperature of the helium gas may have kept the balloon from rising. From researching solar balloons, I know that the gas in the balloon needs to be hotter than the ambient air temperature.
Is the helium lift a function of temperature? Has anyone else dared to balloon map in such heat?
Yes, any gas will be less dense when it is hotter and therefore will have more lift. If the gas inside the balloon is the same as the gas outside (e.g., a hot air balloon) then the gas inside must be hotter (less dense) than the gas outside. Helium is much less dense than air, so helium in a balloon can be cooler than the air outside and still have lift. The helium in the balloon does not have much thermal mass so it would warm up quickly. So the temperature difference between February and July probably cannot explain your lack of lift.
Are your balloons pumped full of helium (plump) or just partly filled? If they were partly filled (both in July and February) then differences in the amount of helium (the volume of the balloons) could explain the difference between now and then.
If the balloons were pumped to plumpness in both February and July, then the difference in lift could be caused by a difference in helium. Did you use pure helium or helium from a party store? Party store helium is not guaranteed to be pure helium.
If the balloons, payload, gas, and balloon volume were identical between February and July, you have an interesting mystery.
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Thank you @cfastie for answering this and mentioning that that helium "does not have much thermal mass". The temperature was my main hypothesis. Now I can rule that out and evaluate the source of the helium gas. It is not pure helium, it is not from a party store, but it is from a University gas supplier.
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