Student Pyranometer Data

Insolation Data from School Sites

These data have been collected with an Apogee Instruments Model PYR silicon solar cell-based pyranometer (www.apogee-inst.com) or with "homemade" pyranometers that use commercial photodetectors. Data are recorded with an Onset Computer Corporation U12-series 12-bit data logger (www.onsetcomp.com), one sample per minute (except as noted below). The numbers shown over each day are the maximum and daily average insolation, rounded to the nearest Watt per meter squared. The Excel files containing these data are available from David Brooks.

The data from the University of Northern Iowa started in late January, 2005. From the outset, these data were characterized by a very noisy signal that is especially evident at night, with spurious voltage signals that translated into as much as 30 W/m² and, occasionally, even higher. (The Waterloo CMS values have always been zero at night.) The UNI nighttime values have manually been set to 0 so they will not affect the daily average. Without this "fix" the daily average is as much as 5 W/m² too high. The noise problem doubtless affects the daytime readings, too, but it is not feasible to remove this noise signal from individual samples. Therefore, take care when using individual values from these data. If the noise is really random, the daily averages should not be seriously affected even though the data logger does not record negative voltages that might be seen when the true signal is small. (This conclusion turned out to be false! See link to discussion below.) Data exhibiting this noise problem are graphed in blue rather than red.

Initially, the UNI data were sampled at 3-minute intervals. This was changed to 1-minute sampling on the afternoon of 18 February, 2005, in order to be compatible with the Waterloo CMS data. In the graphs, 3-minute data are plotted with "+" symbols rather than a solid line.

Up through the end of March, the maximum daily insolation value for the UNI pyranometer is always an even multiple of 5 W/m². The reason for this is that the UNI instrument, which is a newer model than the Waterloo CMS instrument, is calibrated so the calibration constant is always exactly 5000 W/m²/V, and the older Greenline software used to process these data exports voltages rounded to the nearest millivolt. Newer HOBOWare software has fixed this problem, as the actual resolution for 12-bit digital-to-analog conversion is about 0.0006V.

Graphs of daily average and maximum insolation, and a discussion of the CMS and UNI data through the end of 2005 can be found here.

Site	Longitude	Latitude
Waterloo Central Middle School, Waterloo, Iowa All 2004 data from Waterloo Central Middle School All 2005 data from Waterloo Central Middle School	92.3706 W	42.5293 N
University of Northern Iowa, Cedar Falls, Iowa	92.4586 W	42.5122 N
West High School, Waterloo, Iowa	92.351 W	42.471 N
Bellaire High School, Bellaire, Texas	95.469 W	29.692 N
Arrie Goforth Elementary School, Norfork, Arkansas (includes air temperature and relative humidity}	92.2688 W	36.1972 N
The Chinquapin School, Highlands, Texas	95.02 W	29.82 N
The Institute for the Promotion of Teaching Science and Technology (IPST), Bangkok, Thailand	100.584 E	13.719 N
California Trail HS, Olathe, Kansas	94.746 W	38.886 N