Windsond altitude record

The Mountain Meteorology Group at the University of Utah is evaluating Windsond for their meteorology research. During one test, the sonde failed to detach from the balloon. They continued to track the balloon to an altitude of 9700 m MSL, at which point the sonde battery was drained. This is close to the altitude of the tropopause, the important point where the temperature reaches a local low point.

Sounding wind speed

The last message before the sonde shut down was transmitted at a distance of 49 km, where the sonde was still rising at 1.5 m/s and travelling at 17 m/s. This is a great result for the basic whip receiver antenna. The reception was becoming increasingly spotty towards the end and the contact wouldn’t be possible without the error-correcting code used in the radio link. The range could easily be improved a lot by using a directional antenna.

To reaching high altitudes on purpose, a bigger balloon would be used to gain a higher vertical speed and to allow the contained helium to expand the balloon further before the balloons bursts. A high-altitude radiosonde commonly use a balloon weighing 100 g, compared to the 8 g balloon commonly used for Windsond. Officially supporting high altitudes would also require proper testing of all components in a climate chamber.

I’m now doing all I can to avoid the mishap from repeating:

  • Cut-down is done by heating a thin metal wire until it melts the wire tethering the sonde to the balloon. The duration of the heating will get progressively longer if the detaching fails.
  • Before launch, the sonde will detect if the mechanism is broken to alert the user.
  • There’s now support for backup cut-down hardware.
  • If the sonde still continues to fail to detach it will eventually stop trying. That will save the battery from draining as it did this time. The balloon will eventually pop and with battery to spare it’s still possible to recover the sonde.

European hot air ballooning championships 2013

The European hot air ballooning championships took place in Wloclawek, Poland on September 6-14. The Swiss teams used Windsond to help them plan their flights. They fared well; all four Swiss teams scored in the top third of the field of 81 competitors (see the results). A part of this favorable result is attributable to Windsond.

Here is an account of how the Swiss teams had good use of Windsond during one of the tasks, as told by participant Léon André.

The flight No. 3 of the 18th FAI Hot Air Balloon Europeans Championship was an evening flight with three tasks. The second task was a “Maximum Distance Double Drop” (MDD).

Part of the task sheet for flight No. 3, with the description of MDD

The distance between entrance point into the scoring area and exit point should be as long as possible. The task before the MDD was a “Hesitation Waltz” (the pilot had to fly as near as possible over one of thee goals). For the following MDD the pilot had to enter as near as possible at the optimal entrance point and to fly without leaving the scoring area in direction of the optimal exit point. Of course it helps a lot, if the pilots know exactly the winds in the different altitudes.

Drawing of the scoring area (overlap of the two circles) on the competition map

We measured with a Windsond a short time before the pilots completed the “Hesitation Waltz”. So they had the time to plan the best way thru the scoring area with the existing winds.

The way of the sounding balloon during the measurement

We sent the wind data to our teams in the following form: [Note by Anders: This view is created by the Swiss teams and not part of Windsond]

The measured wind data

The scoring area ended at 2000 ft. But between 1500 ft and 2000 ft there was a wind layer approximately in the direction of the axis of the scoring area.
In the ranking of task 12 our pilots Stefan Zeberli and René Erni has been on place 1 and 2.
– Léon André

Swedish Ballooning Championship

The Swedish Hot Air Ballooning Championships is taking place now between April 27 and May 1. The pilots and crew of nine hot air balloons compete for the top position. The hosting organization is Dalslands ballongklubb. The location is the plains and forests around Kroppefjäll, to the west of Sweden’s biggest lake Vänern.

Windsond is used by the competition meteorologist along with other data sources to get a picture of the expected conditions for the next flight. Each flight of the competition needs to be planned ahead to be challenging and fair for all teams, and the weather conditions play an important role in the decision. Here’s a picture gallery in Swedish of how they use Windsond.

Two of the teams also cooperate in using Windsond to get detailed weather information during their flight. Up to four receivers are used to get real-time wind data to pilots and crews at the same time.

Of the seven soundings made so far, all sonds have been recovered and set up for new soundings. Predicting and controlling the landing location is working out well. At one point the competition organizers saw a sond drifting towards lake Vänern and could abort the sounding to save the sond.

Windsond evaluated

A customer deeply involved in hot air ballooning and gas ballooning sent me the story of his first test of Windsond. Naturally the system has already undergone a lot of testing but it’s reassuring to read his account.

The launch

Today it looked like a nice evening for a test launch, so I readied my balloon chase car, got my old ACER Travelmate C312XMI charged – and brought my 220v inverter with me.

It is pretty dark out, but nonetheless, I would not need to rely on visual contact with the sond, since the system would tell me exactly where this device is floating.

Ok, system running in the car, antenna mounted, external power supply working, GPRS mobile data service, map loaded, all systems green, one more beep – and release (for flight)!

As I have hoped, very slow wind conditions.
As I have feared with saving precious helium, a very slow ascent (1 m/sec), but that doesn’t hurt.

Ok, we now see clearly in physical reality — and on the Google earth display — the typical fine weather easterly flow, my first Windsond drifting very gently to the west. Daddy was the driver, I was glued to the Laptop Display, my mother in the back row.

Now it was easy to predict where we should go (read the position off GEarth ;-)
We went to a dark place, since then we would be able to observe (visually) better.
Then hopped to a next further stopping point, near the estimated landing positions, if we would release soon.

Bad thing was the local Fussball-game with its bright lights, and we were on the wrong side of the stadium, blinded by those beams. Anyway, I could not wait for the set altitude of 1500m AGL and sent the ‘cut’ command at about 1600 MSL or thereabouts. Too bad the wind shifted in those last 20 seconds of flight, although still slow, the track curved towards the stadium (we imagined trying to find the Windsond among 4.500 white foam cups of the visitors of the game …. ;-)

So cutting was sensible, or wait for the Windsond to go over the city – I did not want to climb to any roofs in the night. We could even follow the fall quite nicely, the flashing makes sense (for night trainings, anyway)

The recovery

Then repositioned the car to a closer road, hopped out (with Laptop, GPRS Modem but no external power supply) and got our feet dirty… Estimated landing was about 90 meters short, but no problem, we could even hear the “find me” sound and see the flashing of the Windsond.

Retrieved in no time, it was like finding lost markers, better than Easter anyway.IT IS A GREAT SYSTEM, I TIP MY HAT FOR YOU, THE CREATOR, DESIGNER, THINKER.
It is well thought through, it is reliable, it is usable, it is a dream come true – for me.

The customer suggested some improvements for the software which I’ll incorporate. I’ll also look into improving the 90 m inaccuracy of the landing prediction.

Launching Windsond by a condom

The team and I launched a sond a few days ago by inflating a condom with helium. Condoms are much lighter than regular balloons but above all they improve the mood of the mission participants considerably. ;) The helium volume was estimated to 17 liters. This gave an average ascent rate of 1.5 m/s. The ascent rate given the neck lift 15.1g should be 1.0 m/s so the shape of the condom probably helped to improve the speed.

The condom burst a bit prematurely at 2400m AGL, a few hundred meters before the sond was instructed to let go. The temperature had dropped from 0*C on the ground to -12.4*C at this altitude. Although it’s doubtful condoms are designed to “operate” at freezing temperatures, the gas expansion at the altitude is the probable cause of the burst. On the other hand, a ground test showed a condom of the same model could contain over 40 liters of air before popping but maybe there are variations between copies. I considered to write a complaint to the manufacturer over this blatant product failure. ;-)

The launch was done in the evening, after dark. While the sond was still falling, I activated the beacon strobe by a button in the GUI. We were still 3-4 km away from the falling payload but the brief flashes of light were clearly visible, like a shooting star. The sond landed 65 m from the location originally predicted at 2400m altitude. In the dark, the blinking was very effective to locate the sond. The whole enclosure lit up and illuminated a meter of the ground around it. In the open landscape, the beeping was faintly audible at 200 m distance.

Another Windsond was also launched to compare the results of two data sources. They coincided very closely. The profiles of wind direction, wind speed, temperature and humidity were found to agree within tight margins. The second sond was launched while the first was still in the air which also demonstrated the ability of the system to handle multiple soundings at the same time. For the second sond I picked a landing location on a field close to a minor road. We picked up the sond 50 meters from the estimated position.

The double test was a big success and also very fun! A big thank you goes out to the team.

Windsond in Swedish winter

Gränna saw the gathering of hot air balloons during the weekend Andrée Memorial Meet in February 2013. The cloud base was on the low side but turned out quite ok for a nice competition.

A Windsond sounding right before the morning briefing gave us the details of the wind conditions. As an anonymous pilot said afterwards; “I should have trusted the wind sounding more”.

Windsond ascent and fall in Gränna

Weather sounding before the flight

The system has matured a lot lately. The Windsond description is updated with the latest specifications.

Developing the next Windsond

Since the last update, I’ve developed most of the next version of Windsond. It will incorporate a great number of improvements:

  • Higher altitude
  • Longer radio range
  • Many concurrent units, both receivers and weather balloons
  • Lower weight
  • Longer battery life
  • Proper encasing
  • Optionally measure air pressure and humidity
  • Better adapted to automated production
  • … and more

Pictures and test results to follow.

Windsond graphics

So far I haven’t talked much about the computer software that controls Windsond and visualizes the data. The software is still not completely polished but I can give an idea of what it looks like.

For each launched sond, there are three views.

The first view shows individual data updates from the sond and gives control over sond settings such as detach altitude, radio output power, LED blinking and loudspeaker output. This part is receiving an overhaul right now so I’ll show a screenshot later.

The second view visualizes the status of the sond. This includes the present whereabouts such as battery voltage, altitude and distance travelled, but also graphs that show how radio reception, altitude and ascending speed has developed over time. There’s also a draft graph showing the shape of the flight path as seen from above.

View of sond status. In this example, the altitude curve shows how the sond ascended, then descended more quickly (after detaching from the balloon). When close to the ground, the radio reception was cut off until the chase car came within a few hundred meters of the landing site.

The third view shows weather data as measured by the sond by plotting wind direction, wind speed and temperature against altitude. The Y axis maps altitude and X axis the data at that altitude. The two right-most graphs have additionally a black curve-fitting function overlayed to disregard the uncertainty in individual measurements. The experimental left-most plot visualizes the wind direction at different altitudes using a polar representation, with radius being the altitude.

View of weather data

The sond can be tracked in real-time in Google Earth, something that proved very useful during the World Championship. Google Maps caches recently viewed areas and ready-made maps can also be loaded to enable viewing without mobile internet access.

Path of one launch, showing launch site at top and detach position, predicted landing and actual landing at bottom. This particular launch revealed vertical turbulence over the hill that a regular pibal couldn’t show.

The Windsond software also supports reviewing old sessions, either immediately or replaying the progress at different speeds.

After the Balloon World Championship

Early morning with Windsond and traditional theodolite

The Balloon World Championship is over and I’ve made my way back to Sweden. It was a great experience and I’d like to thank all the people that made it possible. The locals were also very hospitable and cheerful.

Windsond worked out well. It provided detailed wind readings to an altitude of our choice and immediately provided the pilot with a clear visualization. When other teams gazed in concentration on a pibal forming a dot in the sky, we could release a prepared balloon through the car side window and drive on.

Path of one launch, showing launch site at top and detach position, predicted landing and actual landing at bottom. This particular launch revealed vertical turbulence over the hill that a regular pibal couldn’t show.

Out of 13 launches, only 3 sonds were lost. The first landed deep in a thick corn field and we got tired of searching when we couldn’t even see a meter in front of us. After this experience, I improved the software to make such unfortunate landings improbable in the future. I’ll talk more about this in a future blog post.

The second sond had a faulty release mechanism and just sailed away. Having the first two sonds disappear was discouraging but after that we got the hang of it and could recover all of them except one which we lost radio contact with, probably from radio interference. Had I remembered to check the frequency before launch, I could have switched frequency and avoided the whole problem.

If you’re a balloonist reading this, I’d love to get in contact with you. The system works well as it is but there are many ideas for extensions and improved software. Knowing the level of interest and your needs helps me to motivate further development and drive down costs.

Reach me at anders@kiwiembedded.com or telephone +46 707 312608.