Sensitivity and offset changes of a fast-response open-path infrared gas analyzer during long-term observations in an arctic environment

Abstract

We examined sensitivity and offset changes of a fast-response open-path gas analyzer in an Arctic environment. Output voltage from the gas analyzer was compared to water vapor density calculated from a slow-response thermometer and hygrometer, and then sensitivity and offset were determined. This procedure serves as an effective calibration of the gas analyzer. In this study, changes in sensitivity caused over- or underestimation of up to 10% in water vapor flux. An effective strategy was established for calibrating a gas analyzer in the field in the Arctic environment. The strategy comprises the following main points: 1) Parallel observation with a stable slow-response sensor is needed to calibrate a fast-response gas analyzer. The slow-response sensor should be calibrated as necessary. 2) The appropriate period length for applying the effective calibration should be determined, considering the data availability, the stability of sensors used, and the local environment, to obtain a statistically robust sensitivity and offset. 3) Rain events may cause a step change in offset, but not in sensitivity. Periods for applying effective calibration should be carefully determined in order to account for possible step changes in the sensitivity and offset. Additionally, this methodology may be applied to other environments in principle. © 2012, The Society of Agricultural Meteorology of Japan. All rights reserved.