Carleton College Weather
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  Instruments and Setup
 
Carleton College has a long history of weather collecting. In years past, recording the weather consisted of reading thermometers and barometers three times a day, as well as estimating cloud cover. With the advent of digital technologies, we have been able to expand our data collecting quite a bit.
Currently, the weather is monitored continuously by a network of computers and instruments mounted atop Olin Hall, near the center of the Carleton College campus.
 
The core of our weather sensor setup is a Capricorn II Digital Weather Station. This commerical weather station displays barometric pressure, temperature, wind speed and wind direction in real time.

The temperature gauge is in a special housing that shields it from direct sunlight, but allows wind to flow past it. This insures that our temperature reading is accurate to 0.9 degrees F from -67 to +257. The temperature gauge has a resolution of 0.01 degrees F.
The Barometer is accurate to 0.03 inches Hg, has a range from 27 to 33.96 inches Hg, and has a resolution of 0.01 inches Hg.
The wind speed accuracy is 5 percent or better from 20-125 mph; 1 mph from 5 to 20 mph. The speed range is from 0 to 125 mph, with higher gusts possible, but not guaranteed. Thre are 16 compass points in the wind direction mechanism.
weather station
Anemometer, wind direction indicator, and
display case for Capricorn Weather Station
 
tipping bucket
The USW Tipping Bucket Rain Gauge
In addition to the Capricorn station, we have a Tipping Bucket Rain gauge. Our gauge is a TR-525 USW Tipping Bucket from Weatherama Weather Instruments. It has an 8-inch collector funnel, which complies to the standard set up the U.S. Weather Service. It consists of a gold anodized collector funnel with a knife edge that directs precipitation into the tipping bucket mechanism. Each tip represents 0.01 inches of rainfall.
This system has a accuracy of 1.0 percent at 1 inch per hour or less. The maximum bounce settling time is 0.75 ms.
 
To detect the brightness of the enviroment, we have a solar radiation detector. This sensor is a silicon photodiode, with a 100 mV/Wm^2 sensitivity. It has a response time of 1 second and a temperature range from -22 to +158 F.
 
We also have a Humiter® relative humidity sensor from Columbia Weather Systems, Inc. It has a 3% accuracy at 68 degrees, and an operating range from 0 to 100 percent relative humidity.

With temperature and humidity data, we are able to calculate both heat index and dewpont. Both of these weather measurements are actually just calculations that depend only on the temperature and humidity, in the same way that wind chill depends only on temperature and wind speed.
 
We then read the data into a computer using a custom LabView script. Even though we recieve data from our sensors continuously, we only record data once a minute. The exception to this is wind speed and direction, which is recorded 6 times a minute. From that computer we transfer the data to our database, which is accessed through these web pages.