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General Calibration: Optical Frequently Asked Questions

FAQ Legend:All Products
Product Class (UV Radiation)
This Product (Calibration: Optical)

1. General

1. What kind of optical interference filters do the MFR, UVMFR, and SPUV use?

The MFR, UVMFR, and SPUV all use new technology "Ion Assisted Deposition" interference filters. The slit width and effective center wavelength are exceptional and stable. However, while the throughput/transmission of IAD filters is far superiror compared with previous generations of optical filter technologies, we still recommend that yearly factory calibrations.

2. Why is data from a narrowband UV radiometer more useful than that from a broadband pyranometer?

This question could apply to most areas of the electromagnetic spectrum, but in the UV portion of the spectrum its sharp structure is essentially lost in the integrated nature of a broadband detector. Narrowband UV radiometers such as the SPUV-10, UVMFR-7 and UVRSS-1024 measure either discrete lines or the entire spectrum, respectively. This comes at a price in terms of complexity; hence the market popularity of broadband pyranometers.

3. Can I run YES instruments from batteries alone for portable operation?

Yes, for most instruments except for the TSI-880 and RSS/UVRSS-1024 systems which have internal heaters.

YES products can be setup to run on DC. Use a lead-acid type RV/marine-type deep cycle battery. YESDAS-2 (which runs the UVMFR, MFR, SDR), will keep a battery float charged while plugged into the line. But if run "barefoot" a small wire jumper needs to be added from the "B+" to the "P+" terminal.

Keep in mind that depending on the model, DC current requirements can be significant. Refer to the product data sheet to determine the maximum current drain for each sensor.

If you will be making long term, remote measurements (off the AC power grid), you will need to plan how to keep the batteries charged. If you plan to back up the batteries with solar panels or a wind generator, this is possible but you will want to carefully size the system based on expected solar insolation and/or wind levels at your site. The technology for providing off-grid power tends to be well developed and often invoves a wind-diesel hybrid solution. We know of several excellent companies that can provide commercial-quality turn-key DC power systems - contact Yankee technical support for more guidance.

4. What do I need to know before selecting an radiometer for outdoor use?

You need to know whether you want spectral or broadband data, and whether you want measurements in the thermal Infrared, NIR/visible, UV-A or UV-B.

Next, decide whether you want direct-normal and/or total (global) radiation measurements.

Finally, decide if you need continuous unatended measurements of "campaign mode" measurements. In campaing mode, the instrument is kept out of inclement weather and setup for brief periods of time, such as making ground-truth measurements during a a satellite fly-by. All YES systems work well in both applications because they are weatherproof and thermally stabilized. However, other instruments (e.g. telescopes) are only suitable for campaign mode.

5. Why do we have to measure UV radiation? Why can't we just model it?

Our UV_Calc package (which is included with each UVB-1 pyranometer we sell) uses a simple model called Green's model and does quite a good job modeling clear sky UV irradiance. However, for non-clear skies Green's model does not work well at all. In typical non-clear conditions, UV-B radiation is quite difficult to model due to its strong dependence on changing cloud conditions, aerosols and stratospheric (column) ozone levels. Since accurately modeling the dynamic and random behavior of clouds is extremely difficult, modeling the UV-B is difficult as well. Note that established atmospheric radiation modeling tools do exist for the visible and infrared spectrum (LOTRAN / MODTRAN), but most models for UV-B are quite complex and still experimental. NCAR has more information on atmospheric models at their web site: http://www.ncar.ucar.edu/.

6. Why should we choose a UVB-1 over a competitve product such as a Solar Light 501?

YES, Eko and Solar Light broadband UV radiometers were extensively tested by NIST. See


for more information.

7. The internal operating temperature of the UVB, MFR, UVMFR, SPUV, RSS is about 45 C. Why is this?

To eliminate effects of changing ambient air temperature and solar loading, we thermally stabilize the internal optics of our instruments to above ambient temperature, between 38 C and 45 C, depending on the instrument. The exact temperature is not as important as knowing that the temperature is stable and has been stable since the most recent calibration.

8. Can I get non-standard filters for the MFR, UVMFR, or SPUV?

Yes, at additional cost and only as long as the filters are 10 nm FWHM wide and on 10 nm increments. For the MFR-7 and SPUV, the longest practical wavelength is 1040 nm due to the silicon detector's lack of quantum efficiency beyond this. Remember that the radiometric calibration accuracy may suffer as the bandwidth increases. Beyond 40 nm wide, calibration with FEL lamps becomes a problem.

The RSS/UVRSS instruments provide continuous spectral measurements and are excellent solutions for special requirements.



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This page was last updated on Monday, September 11, 2006 .