A field intercomparison technique to improve the relative accuracy of longwave radiation measurements and an evaluation of CASES-99 pyrgeometer data quality

The least squares-based optimization technique uses a field intercomparison (i.e., a time period during which all the PIRs were upward looking and set up side by side) to determine a set of optimization coefficients for each PIR.

For the 10 CASES-99 PIRs, the optimization technique improved the standard deviation of the difference of downwelling irradiance between the PIRs from ±0.75 to ±0.4 W m⁻² (for nighttime data). In addition to presenting the optimization method, various PIR data quality checks are outlined and applied to the PIR data. Based on these quality checks, the measured case and dome temperatures of the CASES-99 PIRs were all reasonable.