|Figure 1. -- 1-Wire Instrument, Rain Gauge, Radiation Shield (with Humidty and Temperature Sensor)
The software that runs this weather station
consists of a number of tasks, which run at specified intervals. Some tasks are responsible for reading the weather instruments;
other tasks are responsible for formatting the data and posting it to logs and weather web sites.
The wind speed task samples wind speed every three seconds and places each sample into a buffer, averaging over
a two-minute sliding window. It calculates the minimum and maximum wind speed every sample period.
The wind direction task samples the wind direction every five seconds and places each sample into a buffer, averaging
over a two-minute sliding window. The averaging algorithm uses consensus averaging
The temperature task samples the temperature sensor once a minute and places the data in a buffer, averaging over a ten-minute
sliding window, and calculating the minimum and maximum temperature every sample period.
Humidity and Dewpoint
The humidity task samples the humidity sensor every minute and places the data in a buffer, averaging over a ten-minute
sliding window, and calculating the minimum and maximum humidity every sample period. Dewpoint is calculated from the humidity
and temperature data.
The barometer task samples the air pressure sensor every minute and places the data in a buffer, averaging over a ten-minute
sliding window, and calculating the minimum and maximum air pressure every sample period.
The precipitation task samples the tipping-bucket rain gauge every minute and converts the number of bucket tips (0.01
inch each) into total accumulation since local midnight, and the number of bucket tips per minute as rainfall rate in inches
per hour summed over a 60-minute sliding window.
Posting Data to Weather Underground
Every ten seconds (a.k.a. "RapidFire
"), the weather underground task posts the average temperature, average humidity, rainfall rate, accumulated rainfall since
midnight, the average wind speed, the maximum wind speed recorded for the previous ten seconds and the average wind direction
to Weather Underground Data Exchange.
Posting Data to Citizen Weather Observer Program (CWOP)
Every ten minutes, the CWOP task posts the average temperature, average humidity, rainfall rate, accumulated rainfall
since midnight, the average wind speed, the maximum wind speed recorded for the previous ten minutes and the average wind
direction to CWOP.
Weather Instrument Specifications
To reduce solar warming effects on my thermometer/hygrometer, I built a radiation shield out of nested foil pie tins
(see figure 1, above). At this time, the pie tins are not painted, they're just natural aluminum. They started out shiny,
as pie tins do, but they have weathered down to dull aluminum, as pie tins also do.
The effectiveness of the radiation shield seems quite good. My temperature data quality typically rates "two thumbs up
" from MADIS. I have some maintenance scheduled for this summer, and I might paint them with some flat white epoxy at that
time, and see how that affects accuracy.
The Weather Underground is a respectable organization, providing useful weather information, hobbyist support and other
interesting services. They took their name as a tongue-in-cheek reference to the radical 1960s Weather Underground
political group. Both Weather Undergrounds got their start at the University of Michigan. It may have been tongue-in-cheek,
but during the 2008 election, I have become much more familiar with the radical Weather Underground and its co-founder, William Ayers
. These despicable people were domestic terrorists responsible for more than a few deaths in this country, and on 9/11, Ayers
expressed regret that he "hadn't done more".
I understand his frustration at social evolution when it doesn't go the way we think it should. I have felt that my whole
life. My principles happen to be diametrically opposed to Ayer's, but I understand his frustration nevertheless. That is why
I think, if he wants change, he should have to accomplish it in the free market of ideas like everyone else, and not by having
tantrums, or bombing, or trying to force everyone else to do things his way, just because he can't understand, or doesn't
like the status quo. Who anointed him dictator?
He avoided prison on a technicality, and is now a tenured professor at the University of Illinois, teaching the next
generation of educators how to indoctrinate the next generation of students. Disgusting. With this knowledge, I think it is
time that the new Weather Underground consider changing its name to something else. I get the joke, and it isn't funny anymore.