Standards Development

Scope

The document specifies a test method for estimating the magnitude of radiosonde temperature sensor warming, induced by direct solar radiation, based on variations in air pressure, temperature, ventilation speed, tilt angle of its supporting sensor boom, and light illumination angle on the boom through a laboratory evaluation. This document will describe the following:

a) Technical requirements for a laboratory setup to measure the effect of direct solar radiation on radiosonde temperature measurement under simulated sounding conditions;

b) A test procedure for estimating radiosonde temperature measurement errors due to direct solar radiation in the air pressure range of 3 hPa ~ 1,000 hPa, temperature range[1] of −70 °C ~ 50 °C, ventilation speed range of 3 m∙s-1 ~ 7 m∙s-1 at a predefined irradiance (e.g. 1,000  or higher), sensor boom tilt range[2] from 0° to 45° with respect to the air ventilation direction and the range of light illumination[3] angle from 0° to 90° with respect to the sensor boom plane;

c) A method to evaluate uncertainty in the results under the test conditions.

The essential components of the laboratory setup are a climate chamber, wind-tunnel, a test cell, thermometers, pressure and vacuum gauges, a laser anemometer and a solar simulator. These components are summarised in Clause 5. Clauses 6–8 provide details on test preparation, the procedure for installing a radiosonde in the test cell, the operation of the laboratory setup, the experimental range and sequence, and data processing. In Clauses 9 and 10, a method to evaluate and report uncertainty of the determined radiation errors on the temperature using the uncertainty propagation law, based on a mathematical model, is proposed.

NOTE 1 Since the test method is limited by the use of ground-based facilities, radiative cooling effect of radiosonde temperature sensors observed in stratosphere may not be reproduced and represented in the test result.

NOTE 2 The light source spectrum may be limited in the infrared (IR) region compared to that of the visible light solar spectrum. As recommended by the WMO guide by SC-MINT,[1] the heat exchange in infrared radiation (IR) needs to be avoided by using sensor coatings that have low emissivity in the IR. Otherwise, the effect of IR can be underestimated in the test.NOTE 3 Due to potential limitations in the number of test setups or laboratories capable of conducting this test, peer-reviewed reports or papers published online or offline resulting from research activities conducted by academia or meteorological institutes can be utilized as a test report when following this test procedure.