Figure 1 - Stand Layout
UV-B Network Instrumentation History
The 36 network stations, such as the one shown above, have been instrumented to measure solar irradiation at wavelengths of interest to the agricultural and atmospheric science communities: [instruments as numbered in figure 1]:
Figure 2 - Instrument Coverage of Electromagnetic Spectrum Originally, at the time of the USDA’s workshops, the primary instrument available for measuring UV radiation was a broadband-type pyranometer, shown as instruments 2 and 9 in the figure 1. Such instruments only measure global (or total) irradiance, which includes both the direct rays from the Sun as well as the diffuse rays as scattered by clouds and other atrospheric constituents. What was needed in addition was the ability to measure the direct and diffuse components separately and directly, as this facilitates measurement of the turbidity of the atmosphere due to aerosols and other contaminants. Fortunately, a new type of instrument, the Multifilter Rotating Shadowband Radiometer (MFRSR) had just been developed by scientists at Battelle Laboratories in Washington State. The capacity to manufacture these instruments was awarded to Yankee Environmental Services (YES) of Turners Falls, Massachusetts. The MFRSR is equipped with a shadowband that enables the separation and measurement of the total (global), diffuse horizontal, and direct normal components of solar irradiance (as depicted in figure 3) within a single instrument.
Figure 3 - Example of Total, Diffuse and Direct measurments This capability to inexpensively and reliably capture the direct component has a side benefit, in that it allows for periodic in-situ calibration checks of the instruments using the Sun as a source [the Langley method], independent of the laboratory calibration (Slusser, et al., 2000). Since visible wavelengths are more energetic, and thus easier to measure, than those of the UV range, the vis-MFRSR (instrument 1 in figure 1) was the first instrument on the market in the early 1990’s. The UV-MFRSR (instrument 4 in figure 1) followed in the mid-1990’s. The growth of the UVMRP network was directly influenced by this, as can be seen in figures 4 and 5, where the sharp rise in 1996 and 1997 illustrates the arrival of the UV-MFRSR instruments.
Figure 4 - Annual Instrument Growth
Figure 5 - Active Instrument Count Growth since then has been steady, with the addition of one to three climatological sites in most subsequent years. The ‘research’ instruments are those undergoing field testing after laboratory calibration and those operated by UVMRP which are owned by other agencies – UVMRP has the network infrastructure to collect, process and distribute shadowband data, so this service is offered to other owners of MFRSR instruments. The ‘short term’ instruments are those that were operated by UVMRP or another agency for specific data gathering and/or research purposes. All of this data is available through this web site.
- (1) visible (nominal 415, 500, 615, 673, 870, and 940 nanometers (nm));
- (2) Broadband (280 – 320 nm erythemal [DNA] damage weighted);
- (3) PAR (400 – 700 nm quantum weighted); and
- (4) UV-B (nominal 300, 305, 311, 317, 325, 332, and 368 nm).
- (5) surface reflectance;
- (6) air temperature;
- (7) relative humidity;
- (8) pressure (at 14 sites); and
- (9) UV-A biometer (at 7 sites).
Figure 2 - Instrument Coverage of Electromagnetic Spectrum Originally, at the time of the USDA’s workshops, the primary instrument available for measuring UV radiation was a broadband-type pyranometer, shown as instruments 2 and 9 in the figure 1. Such instruments only measure global (or total) irradiance, which includes both the direct rays from the Sun as well as the diffuse rays as scattered by clouds and other atrospheric constituents. What was needed in addition was the ability to measure the direct and diffuse components separately and directly, as this facilitates measurement of the turbidity of the atmosphere due to aerosols and other contaminants. Fortunately, a new type of instrument, the Multifilter Rotating Shadowband Radiometer (MFRSR) had just been developed by scientists at Battelle Laboratories in Washington State. The capacity to manufacture these instruments was awarded to Yankee Environmental Services (YES) of Turners Falls, Massachusetts. The MFRSR is equipped with a shadowband that enables the separation and measurement of the total (global), diffuse horizontal, and direct normal components of solar irradiance (as depicted in figure 3) within a single instrument.
Figure 3 - Example of Total, Diffuse and Direct measurments This capability to inexpensively and reliably capture the direct component has a side benefit, in that it allows for periodic in-situ calibration checks of the instruments using the Sun as a source [the Langley method], independent of the laboratory calibration (Slusser, et al., 2000). Since visible wavelengths are more energetic, and thus easier to measure, than those of the UV range, the vis-MFRSR (instrument 1 in figure 1) was the first instrument on the market in the early 1990’s. The UV-MFRSR (instrument 4 in figure 1) followed in the mid-1990’s. The growth of the UVMRP network was directly influenced by this, as can be seen in figures 4 and 5, where the sharp rise in 1996 and 1997 illustrates the arrival of the UV-MFRSR instruments.
Figure 4 - Annual Instrument Growth
Figure 5 - Active Instrument Count Growth since then has been steady, with the addition of one to three climatological sites in most subsequent years. The ‘research’ instruments are those undergoing field testing after laboratory calibration and those operated by UVMRP which are owned by other agencies – UVMRP has the network infrastructure to collect, process and distribute shadowband data, so this service is offered to other owners of MFRSR instruments. The ‘short term’ instruments are those that were operated by UVMRP or another agency for specific data gathering and/or research purposes. All of this data is available through this web site.