with various DIY UV and PAR sensors.
The most interesting results from these logging projects came during one of my annual
trips to calibrate instruments at Hawaii’s
Mauna Loa Observatory (MLO). Prior to the
trip, I modified 16 Onset Hobo loggers with the
op-amp circuit in Figure B and photodiodes
fitted with UV-B filters (Figure D).
I hid the modified loggers around the Big
Island in places with full sunlight. Several days
later I retrieved the loggers, which provided a
record of solar UV-B between sea level and the
11,200-foot elevation of MLO. The MLO logger
showed that cumulus clouds near the sun
caused UV-B increases of up to 15%. Figure E
shows the data on a clear day and on a day
with clouds during the afternoon. This finding
led to a report in a leading scientific journal
(F.M. Mims III and John E. Frederick, “Cumulus
Clouds and UV-B,” Nature 371, 1994).
In Hawaii I’ve also measured the sun’s UV-B
underwater and reflected by surf. Figure F
shows a typical result when the sensor was
mounted on a 12-foot pole and held over the
surf: significant UV-B is reflected from ocean
surf. When I repeated these measurements
over a turbulent waterfall in Colorado, very
little UV-B was reflected.
During the May 10, 1994, annular eclipse of
the sun, one of my modified Hobos monitored
the sun’s UV-B. During peak annularity, the
sun formed a thin ring of brilliant light around
the moon for about five minutes. The highly
diminished solar UV during this time is indicated by the bottom of the dip in Figure G.
NASA twice sent me to Brazil to monitor the
ozone layer and other atmospheric parameters during that country’s annual burning
seasons. Hobo data loggers modified to measure UV and PAR silently monitored whatever
sunlight managed to leak through the smoky
sky, allowing me to concentrate on measuring
smoke and ozone. Figure H shows the PAR
measured at Alta Floresta on a very smoky
day and a cleaner day. When I left Alta Floresta
for a remote camp on the Cristalino River, a
concealed Hobo with a DIY sensor provided an
important record of PAR during my absence.
Figure I shows two pyranometers (solar
radiation sensors) at Hawaii’s Mauna Loa
Observatory connected to an Onset U12-006.
My recent work with these remarkable 12-bit
loggers has led to new findings I hope to publish. The pyranometers were designed by my
colleague Dr. David Brooks of the Institute
for Earth Science Research and Education
(IESRE) and are available as kits or assembled units at makezine.com/go/pyrano.
Get Started Logging
If you want to do serious amateur science,
data logging has huge potential. I recommend
you acquire a basic temperature-sensing logger and start experimenting. The experience
might inspire you to find entirely new logger
PAR (arbitrary units)
6:00 8:00 10:00 12:00 14:00 16:00 18:00
; Fig. H: The photosynthetic radiation (PAR)
responsible for plant growth on a very smoky day
(blue) and a cleaner day (red) at Alta Floresta, Brazil.
Sharp dips indicate clouds at the sun.
; Fig. I: The sunlight intensity measured by
two solar pyranometers at Hawaii’s Mauna Loa
Observatory is being logged by two of the four
channels in an Onset 12-bit data logger.
Forrest M. Mims III ( forrestmims.org), an amateur scientist
and Rolex Award winner, was named by Discover magazine
as one of the “ 50 Best Brains in Science.” His books have sold
more than 7 million copies.
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