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Weather Monitoring Frequencies Subject to Pollution
jd writes "In a case of technology vs. technology, the ICU (the body governing the use of radio frequencies around the globe) has been asked to secure radio frequences used for weather monitoring. In-car radar, mobile phones and other commercial and military applications are now using these same frequencies. However, weather satellites can't simply be re-tuned. There is only one very narrow band that detects water vapor but not liquid water, for example. This frequency has been sold to developers of car radar systems. The more this happens, the less useful weather radar and weather satellites will be. The noise will simply swamp the data, making what is collected useless. The article doesn't give a 'doomsday' timeframe, when we'll have no better ability to forecast the weather than they did in the 1800s, but that is what they are talking about."
Well, I am not sure how great we are at predicting the weather now.
A kid at my son's school collected and analyzied common RSS weather feeds for a science project.
He collected the data and used it to judge how accurate the weatherman's predictions were.
Within 5 degrees and 25% chance of rain, he gave them credit. They got credit 50ish percent of the time.
He then analyzied other ways of predicting the weather.
By just saying that the weather today will be the same as the weather yesterday, he got credit 50ish percent of the time.
I don't say this to belittle the weather people. I do this to say that the techniques we use now are not the greatest in the world. If we need those frequencies because they are the only ones that work, then maybe the gov't should buy them back. However, if those frequencies are used because that's the old school way of doing it, well, they aren't working at that great now.
Ok, water vapor sensing is exactly what I did for my master's thesis. I'm going to keep it brief though.
Water vapor has an absorption line centered at 22.235 GHz while liquid water's absorption increases with frequency^1.95. Vapor sensing radiometers do not generally measure at 22.235 GHz because the peak of the absorption line curve is extremely sensitive to pressure. There are points to either side where the curve is insensitive to changes in pressure allowing measurement throughout the entire atmosphere without having to know the pressure profile. That is why the scientists in the article want to keep the 23.6 to 24.0 GHz band for their measurments.
My radiometer measured the emission spectrum at 21.6, 22.235, and 31.6 GHz. 21.6 and 31.6 GHz were the measurements of vapor and liquid water, respectively. 31.6 GHz is a window between the 22.235 GHz vapor line and the group of oxygen lines around 60 GHz. This makes liquid the strongest contributor to the noise temperature at that frequency. The 22.235 GHz was to experiment with. By using 22.235 and 21.6 I tried to see if I could get reasonably similar results even though both frequencies were more sensitive to vapor than liquid. Two close frequencies are measureable using one antenna thereby making the radiometer less expensive and available for more widespread use. I showed that the measurement could be made, but a lot more data needed to be taken to refine the data processing. Enough information was there in the measurements, but there were factors I couldn't account for in the time I had. Hopefully in time, radiometers could become a much more common piece of weather sensing equipment. You can get a lot more data on vapor with a radiometer than you can with a weather balloon, but radiometers are currently expensive and therefore limited in usability. Water vapor is the single biggest driving factor in the weather, we NEED to be able to measure it. Cheaper radiometers would let us get more data and improve weather modeling.