Development of upper air simulator for the calibration of solar radiation effects on radiosonde temperature sensors

Abstract

For the accurate measurement of temperature in the upper air by using radiosondes, one prerequisite is the compensation of solar radiation effects that cause sensor heating. The development at the Korea Research Institute of Standards and Science (KRISS) of an upper air simulator (UAS) that can simulate radiation effects is reported. The UAS can independently control four environmental parameters: irradiance, temperature, pressure and air speed. An entire radiosonde can be installed in the test chamber and the measurement data transmitted remotely via an antenna. Solar irradiance is mimicked by using a solar simulator that irradiates the radiosonde sensor. The temperature of the test chamber is controlled from −70 to 20°C by placing it inside a climatic chamber. The pressure and ventilation speed in the test chamber are modulated using combinations of sonic nozzles, a mass flow controller and a vacuum pump. A ventilation speed of 5 m·s−1, which mimics the speed of ascent of the radiosondes when lifted using a balloon, is achieved at pressures as low as 7 hPa. The capability of controlling the environmental parameters independently and the stability of each parameter are presented. As a proof of concept, the radiation‐induced bias on the temperature sensor of a commercial radiosonde Vaisala RS41 is measured. The effect of each parameter is investigated by varying it while keeping the other parameters fixed. Radiosonde calibration using the UAS at the KRISS will help improve the traceability of upper air measurements to the International System of Units.

Radiation correction and uncertainty evaluation of RS41 temperature sensors by using an upper-air simulator

“…The UAS developed at KRISS provides a unique opportunity to correct the solar radiation effect on commercial radiosondes by reproducing the environments that may be encountered by radiosondes by simultaneously controlling T, P, v, and S. The following ranges of T, P, and v are considered in this study: -67 °C to 20 °C, 5−500 hPa, and 4−7 m•s -1 , respectively, with a fixed S0 = 980 W•m -2 . The functionalities of rotating and tilting the sensor boom are added considering the previous report on the UAS (Lee et al, 2020) to investigate the effect of the radiosonde motions with respect to the solar irradiation direction during ascent. The correction formula for the radiation effect on a Vaisala RS41 temperature sensor is derived through a series of experiments with varying environmental parameters and motions/positions of the radiosonde sensor.…”

Reply on RC1

“…The temperature rise due to irradiation (ΔTrad) is defined as the difference in the temperatures with irradiation (Ton) and without irradiation (Toff); ΔTrad = Ton − Toff. It has been reported that ΔTrad significantly increases as the pressure (P) decreases from 100 hPa to 7 hPa in the UAS (Lee et al, 2020). This phenomenon occurs because the convective cooling process is weakened as the air density decreases at low pressures.…”

“…However, these experiments were conducted at room temperature, and thus, the temperature effect on the sensors was not considered. Notably, the existing studies based on other chamber systems reported that the solar-irradiation-induced temperature rise of sensors increases as the air temperature is decreased (Lee et al, 2018a;Lee et al, 2020).…”

Laboratory characterisation of the radiation temperature error of radiosondes and its application to the GRUAN data processing for the Vaisala RS41

“…This chamber generated an internal airflow that is comparable to the ventilation experienced during a radiosonde ascent, at pressures between ambient and 3 hPa. Another, similar, setup was used in the development of the data processing for the Meisei RS-11G (Kizu et al, 2018), and recently Lee et al (2020) built a setup to investigate the radiation temperature error at temperatures that prevail in the stratosphere, but so far the latter setup was not applied for GDP development. Several restrictions concerning the orientation of the sensor with regard to the light source and the air flow limited the ability of the chamber used by Dirksen et al (2014) to realistically render the in-flight conditions, and this prompted the construction of the custom-build Simulator for Investigation of Solar Temperature Error of Radiosondes (SISTER) setup at Lindenberg observatory, which is described in this paper.…”