weather station- what is being attached to the ballon--- mcu with temp probe?

HTH

Tauno Voipio tauno voipio @ iki fi

Years ago, I happend to see one. AFAIR, the temperature was measured with a bimetal. What I don't remember is how the temperature was transmitted. It was almost infinitely simple. Eg passive, by tuning a microwave resonator that it appears as sidebands on the tracking radar. Eg active, by tuning a HF resonator, ... The barometic unit worked similar, the displacement was made into clicks.

The whole ballon measuring unit was incrediby simple, incredibly cheap to manufacture and incredibly durable. Definitely no processor.

Rene

Go away, Mylinux.

I went to school with a lot of farming folk. They would quite frequently find met probes on their property. I asked them to collect them over the holidays bring them to me at the beginning of every school term, because they were cool free techno-stuff :)

The units they used (this was in the late 1980s) were a cylindro-conical styrofoam body with two projecting "wings", and a barometric sensor mounted on the outer end of one of those wings. The wings were angled so that the device would spin in any significant airflow, somehow I think this was used to measure wind speed.

A short antenna (stiff wire) poked directly out of the center of the "pointy end" of the device. In other words, it looked something like a propeller with a greatly elongated boss.

There was a 28-pin IC in the device with markings filed off, which I presume was a microcontroller. There was also a thermistor and some kind of hygrometric sensor. The device was powered by a 9V battery.

I would imagine they were probably made or at least designed by the CSIRO, since this was in Australia. Not terribly long ago, I saw some of these radiosonde casings (not exactly the same, but VERY similar) up on a web site that does US Government surplus auctions.

thanks, pals.

Interesting. I happened to see my described devices in Australia in the mid 80ies. They were in a rectangular styrofoam box. The costal wheather stations used to send them off to gather their pressure and temperature profile. They were attached to those rubber hydrogen baloons. Not the stratospheric type, just round rubber. The baloon would burst at some height, and the dispensable(?) measurement box would fall down. The position was continously measured with a doppler radar, so they got the wind directions and the wind speeds depending on the heights. Since they measured three times a day, the units had to be cheap, and since most of them probably fell into the sea, was not regarded as recoverable. There may be different type of units depending on whatever.

Oh, I guess normal wheather stations don't have a radar. This radar was also used to detect and track cyclones. At the northern coast somewhere.

AFAIK, a ballon cannot measure side winds, as it always moves with the side wind.

Rene

--- 8< clip clip ---

It has been done for decades with a thing called a radio-theodolite: a multi-channel receiver with a specially formed antenna field which is able to determine the azimuth and elevation angles of the incoming signal from the radiosonde. With altitude information from the pressure sensor in the sonde, it is possible to plot the travel of the balloon in three dimensions.

A more modern method includes a suitable GPS transponder at the sonde, which enables the tracking with the GPS signals.

Again, for details, see

Tauno Voipio tauno voipio @ iki fi

Sorry, Somewhat unclear. Below a baloon, a measurement unit will not detect side winds, as the baloon always moves with the wind. Whoever made a baloon flight is amazed as no wind can be felt. From the ground such a measurement is possible.

Aha, interesting. The radio approach. The radar approach works somewhat different. There, measuring the barometric pressure is not for the height. The height is calculated from the delay of the radar pulse. The barometric pressure is measurement data and belongs to the height. Usually, for standard applications, such as air traffic, the height is taken from the barometric pressure as is follows some exponential function, at least in theory. There it is calibrated from the QNH. Meteorological measurements take the deviation of the pressure from the theoretical values into account. A tracking radar, recognizable from the vibrating feeder, can output a 3D path by itself.

Sure, GPS. But not really cheap. Also not in numbers. You have to recover such a unit.

Rene

It depends how much processing you do on the probe and how much on the ground. It would be sufficient to rebroadcast the actual received data and the "phase" difference between the PRN chip clocks from various satellites and do the actual position determination on the ground. Depending on the availability of suitable integrated circuits, this does not have to be very expensive.

An other option is to install a 100 kHz Loran-C receiver and rebroadcast the signal received from multiple Loran-C stations. Again, the _difference_ between the signals from various transmitters are summed at the balloon and the time difference between the pulses can be determined on the ground and the location of the balloon determined. Since the spectrum of these pulses are quite wide and the SNR from some stations can be quite bad, the down link requires a wide bandwidth and good SNR in order to not degrade the signal very much more. Of course this method requires that some Loran-C chains are in the region.

Other radio navigation systems can be used on the balloon and rebroadcast the raw signal to the ground station for processing, simplifying the electronics on the probe. Multifrequency systems, such as the discontinued Decca, are much more problematic, if the carrier frequency and phase must be maintained through various heterodyning processes.

Paul

which

No need - a cleverly designed GPS transponder is inexpensive enough to be disposable.

(I'm not going to repeat the URL)

Tauno Voipio tauno voipio @ iki fi

Hmmm, I can't see how you can get any airflow, let alone any significant airflow, over any part of a free balloon. You might be able to read the difference between the airflow at the instrument and the average airflow over the entire balloon, but I'm not sure how this would be useful.

The climb of the balloon creates a hefty vertical wind over the sonde, suspenede well below the balloon. It was used in earlier (1930's to 1960's) Vaisala sondes to turn the mechanical multiplexor switch inside the sonde.

Tauno Voipio tauno voipio @ iki fi

I've no idea, I'm just recollecting how they were shaped :) Once the balloon burst, these things would have been spinning RAPIDLY by the time they hit the ground.

Ah, yes of course. I forgot the vertical component. Still, that's not "wind speed" as I'd refer to it.

Trev

Very observant.

Their function is to keep fall rate below an injurious value if the ballon breaks or deflates.

Ah, d'you mean they make it spin like a sycamore seed as they fall?

There was no price to be found. A GPS receiver outputting NMEA code and subsequent retransmission is hardly to be done below say 200$. Then on the other hand it depends on the project what is considered cheap. Letting them up three times a day, daily, is different to a one time experiment where you can write half a dozend papers afterwards.

Rene

Nahhh, GPS chipsets cost around $10 in large volume. You can buy complete modules outputting NMEA for $50-$70. A uBlox GPS module costs around EUR 70-80 in single qty.

Meindert

Yup. IIRC, some birch trees use a similar, if asymetrical, technique.