Below is the verbatim report of Windsond during a big ballooning event.
Wind measurements during Swiss National Hot Air Balloon Championship (SMHL 2014) in Bischofszell, May 28th – June 1st. 31 balloon teams from 6 European nations started at the Swiss National Hot Air Balloon Championship (SMHL 2014). For more details of the competition see www.smhl.ch.
Claude Weber (Luxemburg) leaded the competition as Event Director and Daniel Gerstgrasser was consulting meteorologist. We did at least one wind measurement for the task setting of each flight. All wind measurement were done with windsondes .We started the measurements typically two hours before the task briefing. Daniel Gerstgrasser presented the results of the wind measurements in his meteo report to the pilots during the briefings. For some flight we also measured the wind after the briefing near the launch fields of the hot air balloons and the pilots have been invited to consult this data. Most of the pilots used this opportunity.
Claude Weber and Daniel Gerstgrasser have been very impressed by the good quality of the wind measurements.
The new Windsond website marks the introduction of a logotype for Windsond. The unassuming and stylish dandelion seed represents floating with the winds, low weight and ease of use. Like the dandelion seed, the Windsond radiosonde is its own parachute. Many thanks to my friend the game and graphics designer Martin Magni for the logo work!
Windsond was used during the Australian National Balloon Championships on April 22-27. The organizer released at least one sonde before each morning and evening flight to get the most up-to-date data to plan fun and challenging tasks for the pilots. In total 15 soundings were made, up to 9700 ft AGL. All sondes were recovered – with one exception closer than 10 m from the reported GPS landing co-ordinates.
The people operating Windsond during the competition reports the following:
In summary the use of windsond was very well received by pilots, event directors and the event professional meteorologist. Readings correlated well with forecast conditions above 5000 ft agl and provided detailed information on conditions below 5000 ft where winds were more difficult to forecast due to localised drainage. To operate the system was simple and intuitive, with an average turn around from launch to return of 45 minutes to 1 hour for reading to around 7500 ft agl with data, maps and recovery of the windsond (up to 10 km from launch). Recovery was often straightforward thanks to the remote cut down feature, allowing us to accurately target landing adjacent to access roads thanks to the live tracking & rolling updated predicted landing points. By the end of the week we could confidently land it within 100 m of a road and the reported landing locations were within 10 m of the actual landing location. We made 15 soundings in total up to a maximum altitude of 9727ft agl and all sonds were recovered. We’ll definitely be using windsonds again in the future.
One of the soundings proved problematic, when the altitude reported by the sonde GPS suddenly reported a big drop in altitude although the sonde was still rising. This fooled the sonde to believe the balloon had burst and the sonde was falling, causing it to behave as though going through a landing. The sonde stopped updating the GPS position to save power, as it usually does after a landing. The sonde could still be recovered.
This was clearly a software bug. The altitude reported by the GPS system has proved to be inaccurate in general, and in this rare case particularly unreliable. That’s why all sondes also are equipped with a barometric pressure sensor, which the system usually trusts more than GPS. I’m now modifying the algorithm to inspect air pressure change instead of GPS altitude change also in this case, to avoid such errors in the future.
The Windsond software has matured a lot over the winter. For example, the software can now generate a range of different file formats for the weather data. The settings dialog of this is pictured below. All generated files can be viewed within the application, even while the sounding is still progressing.
Here’s a quick breakdown of the major changes:
- Better curve smoothing algorithm that preserves air layer transitions
- Altitude axes start at the current ground altitude
- Support generating nine different weather data formats
- Select generated data formats in the Settings dialog and inspect the result in the Report panel.
- Dewpoint and lapse rate are plotted
- Plot history of sensor readings and GPS/pressure altitude
- Winds are reported starting at 10m height
- Bugfix in improving cut-down altitude accuracy when using the default cut-down altitude
- Name of launch site can be entered by hand or selected in list
The software update is available without charge to all customers.
In Abu Dhabi, I visited the International Exhibition for Security and National Resilience (ISNR) on April 1. (No, it’s not an April fool.) This is a big trade show held every two years at the grand National Convention Centre in Abu Dhabi, UAE. The 400 exhibitors cover topics such as security, surveillance, terror prevention and counter-measures, emergency services like ambulance and fire-fighting, etc.
At the show I met with several interesting companies where Windsond would serve a valuable role. The small size and ease of deployment of Windsond makes it possible to gather local wind profiles in scenarios where this was previously unpractical. My goal is to continue exploring such alternative use cases in cooperation with these companies. I extend a thank you to exhibitors and fellow visitors from all over the world for the friendly reception!
I’m happy to announce that Kiwi Embedded has sold a Windsond system to Burkan Munitions Systems LLC, based in the United Arab Emirates. Burkan develops various types of ammunition and will use Windsond for gathering wind data during field tests. The company also uses a traditional weather sounding system and find Windsond to be a perfect complement for the lower atmospheric conditions. Advantages include portability, convenience, cost of operation and control over flight path.
A few days ago I conducted an on-site training with the professional and hospitable team. For the occasion I travelled to the UAE for the first time. We spent a day out in the desert for a hands-on walkthough of the system and two short soundings. They had no problem understanding how to operate the system and complimented the ease-of-use and set of features. I was happy to see that Windsond will fit well into their workflow, after I make a small software adaptation.
This marks the start of Kiwi Embedded offering services in on-site training. Please contact me to discuss your case.
Some data formats include a field for the ground wind speed and direction. At first glance, Windsond should be able to report this… but it can’t, since the wind is sensed by the balloon floating with the air movements (i.e. winds) as it rises. Before the balloon starts rising it’s anchored (typically by someone holding it…) and can’t measure winds.
But wait a moment, what exactly is meant by winds on the ground? Due to the physics of fluid mechanics, wind movement very near the ground will be much lower than expected, even approaching zero extremely close to the surface. The ground drag is felt up to 200-400m height, depending on the type of terrain. As it turns out, the standard is to measure ground wind at 10 meters height. Here’s another discussion, by Belfort Instrument. It takes Windsond several seconds to reach 10m height so the GPS has time to sense the change in speed and direction.
Still, the wind close to the ground is more turbulent than at altitude, so a single reading from Windsond cannot capture average conditions like a ground-based weather station can.
By the way, the GPS senses the movement by doppler effect. This is more accurate than calculating heading and distance between successive position reports — GPS position reports may experience sudden jumps and even at the best of times they have a degree of uncertainty that would severely limit the time resolution possible.
At the moment Windsond measures wind once a second and makes an average over the last three seconds when sending data to the ground station. A software extension could transmit all three values to the ground station. A future experiment is to measure five times a second and save this to on-board storage for downloading after the sounding finished.
From now on, Windsond sondes use a mini connector for the battery, and the battery itself is fastened by velcro. To charge the battery, remove it from the sonde and connect it to the USB charger. Previously, the battery was soldered in the sonde and the USB charger connector needed to extend down into the sonde encasing.
This change removes the concern whether a particular sonde is charged and even enables the same sonde to be launched multiple times in succession by changing to a fresh battery. The battery can be removed for repairs, or replaced in case it’s damaged from deep discharge. For different trade-off between weight and running time, other battery sizes can be employed.
Another issue was the strict shipping regulations for LiPo batteries that affect world-wide shipping since Jan 1, 2013 to handle the risk of spontaneous battery combustion that have occurred aboard aircrafts. The rules are complex and cause headaches for many businesses. Even though the Windsond battery is miniscule and hardly constitutes a risk for anything, limitations may that apply — depending on whether you turn to the Swedish Postal Service, DHL, UPS or Fedex. Separating the battery gives the option to dropship the batteries directly from China which bypasses the problem altogether since China has less strict shipping regulations than Europe.
The battery assemby is custom-made for Windsond and I’m happy about how this change makes the system more modular and easier to handle.
The past weekend some friends and I tried attaching a Windsond to a sky lantern. Sky lanterns are made of a light paper bag over a suspended piece of wax that burns to fill the bag with hot air, creating a small hot air balloon. Sky lanterns are very light-weight and don’t carry much fuel to keep them afloat — would it be able to lift a Windsond?
Winter had finally arrived in Sweden and it was about -6 °C with fresh snow covering the landscape. Beautiful as it was, a wind of 5 m/s made the open landscape less pleasant to experience this day. We huddled behind one of the cars to light up the sky lantern. The Windsond was attached with a thin thread.
After a couple of minutes, the sky lantern was filled in spite of the chilling wind and we let it go. It had a hesistant start, then rose by a full 2 m/s as the wind carried it away. It rose to 110 m AGL, then appeared to run out of steam and started to sink again. Unfortunately it never recovered and continued to descend back to ground level by about 1 m/s. The flight was over in 3 minutes but the sonde still travelled 1 km.
Since the flight was over so quickly, we didn’t get a chance to cut-down the sonde and we couldn’t choose the landing location. Knowing the GPS coordinates, with maintained radio contact and the sonde blinking and beeping, it was no problem to find the sonde after walking across a snowy field. The sonde must have been attached to the sky lantern all the way to the ground since the fall was so slow, but we didn’t find the sky lantern and may never learn what happened of it.
The sonde carried the new high-accuracy humidity and temperature sensor which performed perfectly. The sonde was also equipped with an extra memory that logged more data than the radio link has capacity to carry. The firmware was extended to log a number of parameters with timestamps; full GPS readings, different types of temperature readings inside and outside the sonde, pressure, battery voltage and error conditions (although none occurred).
All in all, the results are mixed. Windsond did prove light enough to be carried by a sky lantern. It’s not necessary to bring a helium canister and the price of helium and sky lantern is about the same. On the other hand, sky lanterns are sensitive to winds and high humidity. The open flame presents a risk of starting a fire on the ground. And not least, the altitude of a standard sky lantern is very limited.
A video clip of the launch: