Langley Calibration

Last Updated: January 2016

The Langley calibration method can be used to convert the instrument's voltage to irradiances watts / (m2 * nm) by:

irradiance = mV measured x (ET/Langley Voltage Intercept)

ET (extra-terrestrial irradiance) calculation:

ET (extra-terrestrial irradiance) is calculated for each channel of the instrument for each deployment period by weighting the Susim 3 spectrum by the most recent filter function determined by the calibration facility (YES or CUCF or CSU) prior to the deployment.

Our Langley Voltage Intercept can be obtained from an instrument's deployment at Mauna Loa, Hawaii(MLO calibration) or while the instrument is deployed at one of our locations(In-situ calibration). For more information about the intercept please see the menu item .

For more information about the Langley calibration method, see Slusser, J.R., J.H. Gibson, D.S. Bigelow, D. Kolinski, P. Disterhoft, K. Lantz and A. Beaubien, 2000, Langley Method of Calibrating UV Filter Radiometers, J. Geophys. Res. 105, 4841-4849.

Lamp or Langley Calibration. Which is Better?

For most time periods, data calibrated by the Langley method are now available. Whereas lamp calibrated or MLO calibrated data typically become available the next day after collection, Langley calibrations are updated monthly, so data is available for periods up to the previous month only. During the time immediately following an instrument rotation, the lag time for Langley calibrated data may be greater than 5 weeks, if sufficient calibration information has not yet been collected. This will affect the relatively turbid sites more frequently than sites that are typically dry and sunny.

Due to lack of funds for calibrating the Vis-MFRSR and UV-MFRSR instruments, their lamp-calibration information is very outdated. Therefore, the Langley calibrated data (in-situ) from those instruments should always be considered more accurate than the lamp-calibrated data. There may, however, be periods for some sites when Langley calibration is not possible due to very short instrument residence times and/or too few clear days during the time a given instrument was operating. If available the MLO Langley calibrated could be used. The calibration date for these instruments can be found under Monitoring Network, Sites Information, . If the lamp calibrated is within 18 months of the requested date then the lamp calibrated will also be accurate.