INTRODUCTION
Solar radiation at Earth’s surface is typically defined as total radiation across a wavelength range of 280 to 4000
nm (shortwave radiation). Total solar radiation, direct beam and diffuse, incident on a horizontal surface is defined
as global shortwave radiation, or shortwave irradiance (incident radiant flux), and is expressed in Watts per square
meter (W m-2, equal to Joules per second per square meter).
Pyranometers are sensors that measure global shortwave radiation. Apogee MP series solar radiation meters
incorporate silicon-cell pyranometers, and are only sensitive to a portion of the solar spectrum, approximately
350-1100 nm (approximately 80 % of total shortwave radiation is within this range). However, silicon-cell
pyranometers are calibrated to estimate total shortwave radiation across the entire solar spectrum. Silicon-cell
pyranometer specifications compare favorably to specifications for World Meteorological Organization (WMO)
moderate and good quality classifications and specifications for International Organization of Standardization (ISO)
Class C classification, but because of limited spectral sensitivity, they do not meet the spectral specification
necessary for WMO certification.
Typical applications of silicon-cell pyranometers include incoming shortwave radiation measurement in
agricultural, ecological, hydrological weather networks, and solar panel arrays.
Apogee Instruments MP series solar radiation meters consist of a handheld meter and a dedicated pyranometer
that is integrated into the top of the meter housing (MP-100) or connected by cable to an anodized aluminum
housing (MP-200). Integrated and separate sensors consist of a cast acrylic diffuser (filter), photodiode, and are
potted solid with no internal air space. MP series meters provide a real-time irradiance reading on the LCD display
that determines the radiation incident on a planar surface (does not have to be horizontal), where the radiation
emanates from all angles of a hemisphere. MP series meters include manual and automatic data logging features
for making spot-check measurements or calculating daily solar insolation.
