A Study of IR Loss Correction Methodologies for Commercially Available Pyranometers
Authors
Chuck N. Long (deceased) — NOAA- Earth System Research Laboratory
Afshin Michael Andreas — National Renewable Energy Laboratory
John Augustine — National Oceanic and Atmospheric Administration
Mike Dooraghi — National Renewable Energy Laboratory
Emiel Hall — Cooperative Institute for Research in Environmental Science
Mark Carl Kutchenreiter — National Renewable Energy Laboratory
Allison C. McComiskey — Brookhaven National Laboratory
Ibrahim Reda — National Renewable Energy Laboratory
Manajit Sengupta — National Renewable Energy Laboratory
Description
IR loss from pyranometers is a known phenomenon that introduces a bias in solar irradiance measurements, most detectable at night producing a night time offset. Whether pyranometers are operated with or without active ventilation using alternating current (AC) or direct current (DC) fans, and with what flow volume, has been investigated for its impact on this offset and the results submitted for publication (Michalsky et al., 2017). A methodology that was developed by ARM specifically for the Eppley PSPs that ARM uses is currently applied to correct for the IR loss in unshaded (global) shortwave measurements (Younkin and Long, 2004). This method was developed back when ARM ventilators used 110V AC fans that have been shown to produce larger-magnitude IR losses (Michalsky et al., 2017), which begs the question whether that methodology is still as relevant now that ARM uses higher-volume DC fans. Additionally, a separate methodology is applied using average longwave net responsivity (RSnet) to account for IR loss during the ARM Broadband Outdoor Radiometer Calibration (BORCAL) process with the pyranometers operated ventilated or unventilated (Reda et al., 2005). Other common makes and models of pyranometers are widely used by the international community, each with its own IR loss characteristics and operational ventilation paradigms.
Several of the more commonly used makes/models of pyranometers operating in free air and forced ventilation modes are being studied with respect to their nighttime offsets, and application of differing permutations of IR loss correction methodologies with respect to IR loss-free reference measurements. With analysis of these data we expect to study:
1) The nighttime offsets versus daytime magnitudes of IR loss by make/model and ventilation paradigm
2) The effectiveness of the various permutations of IR loss correction methodologies compared to the IR loss-free reference, especially during daylight hours
3) How well using an average RSnet during the BorCal procedure mitigates the IR loss effects on obtaining an accurate and consistent calibration of only the solar (shortwave) sensitivity of the pyranometer.
We present preliminary results of these studies, with initial findings.
