Introduction
Weather balloon photography is a my latest project idea and one I am very keen to presue. In a nutshell, a camera is strapped to the bottom of a weather balloon, the balloon is filled with helium and off you go! If you're lucky the camera takes photos at period intervals and you get your camera back in one piece when it eventually returns. That's the theory at least. If you're really lucky, your phone ends up thousands of feet into the air; one mission reported a bursting altitude of 52 000 feet — that's almost 16 kms into the sky! Commercial airliners fly at 40,000 feet; many amateur balloonists report getting up to 60,000 feet! At this height, the sky is no longer blue, and looking down you can see the curve of the earth and the boundary between sky and darkness. Most exciting indeed!
The attraction for me is that it involves many interesting and challenging aspects, yet is still relatively straight-forward and hopefully quite achievable.
Ingredients
- A balloon — A chance search of TradeMe found a perfectly good weather balloon, going for a perfectly good price ($NZ 16). As luck would have it, the seller is also intersted in aerial photography.
- A camera — God bless the Chinese for mass-produced electronic gadgets, that are both cheap and hackable. I have found a plentiful source of relatively good quality cameras, with the following features:
- Lost cost — < $NZ 100
- External SD/MMC card slot, allows virtually unlimited shots
- 2MP (non-interleaved) resolution, perfectly adequate images with no lens distortion, blurring, bleeding, reasonable white balance and gain
- Small and light weight
- Takes 3AA batteries (4.5 V) and can use USB power (5.0 V), making it quite easy to power externally
- A power source — Nokia phones all use nice little Li-ion batties that are small, light, powerful (3.7 V, 1000 mAh), readily available, and very cheap — just $NZ 12.00 in single quantities. Finally, I already have a Nokia phone, so I have a charger as well (Li-Ion batteries are weird to charge)
- A controller — A simple controller is required to trigger the camera's shutter periodically. A small 555 and relay would suffice, but why go simple when you can go high-tech? Most likely I will use one of the simple excellent PicAxe series controllers, which make such trivial control tasks, well, trivial!
Stages
1: Stage 1 is to get the balloon aloft with a camera and fire off a few pictures. For this I plan to have the balloon tethered and not go up too high. It will give me a good idea of the basics, such as how to fill the balloon, how much lift is required, how to trigger the camera, how reliable things are and what shots look the most impressive.
2: Stage 2 is to get a little more creative. I would like to add GPS and remote telemetry to the system. My thoughts are to use a simple cell phone, controlled through its serial port and either sending regular SMS messages to a predefined number, or streaming data through a GSM modem interface to a remote webserver. An alternative approach would be to use a low power (~1 W) amateur radio device. At this stage however the system would still be tethered.
SMS Pros and Cons
The advantage of using SMS is that it is relatively straight-forward and doesn't require any special support beyond being able to write standard AT commands to the phone's USART.
The disadvantage of using SMS is that (here in NZ at least) it can cost up to 20c per message, making the process potentially quite costly. However updates need not be frequent, and over the course of a flight message charges are not likely to become prohibitive. In addition, promotions and other special deals further reduce the cost of SMS messages.
WAP Pros and Cons
By using a live modem connection, a wide range of exciting possibilities are made available. For example, by using a powerful Blackfin DSP running uClinux, live image rescaling of the captured images could be performed, allowing a streaming preview to be sent over the GSM link to a remote machine. It would also allow a higher degree of control of the remote system, although in the end a simple SMS interface will accomplish many of the same things as a more complicated WAP interface.
Cellphone Coverage
In New Zealand, GSM appears to have larger coverage areas, especially around mountanous areas and out to sea. However GSM has an technological limit of 35 km range from any cell site. CDMA, on the other hand, has no such limit, however is more prone to interference and congestion at higher altitudes. CDMA coverage within the south island is good, however falls behind GSM.
Amateur Radio
An alternative / supplimentary approach to using a cellphone is instead to use
- Pros — No reliance on external companies for coverage, therefore cheaper in the long run.
- Cons — Need amateur radio license (though that looks easy), need specialised transmit and reciving equipment, though prices are well within reach
GPS Module
If going untethered, GPS is (I feel) essential, lest the whole lot get lost in the wilderness somewhere!
3: Stage 3 is to go completely untethered, although how practical this is in a country as small as New Zealand I don't know. Much of the country (especially the South Island) is open, with little in the way of roads and cellphone infrastructure. We are also surrounded by sea and have very strong winds much of the time. Oh well, time will tell.
References / More Info