M. Heinonen

Validation of a calibration set-up for radiosondes to fulfil GRUAN requirements

Interest in the precise measurement of water vapour in the upper-air is growing along with the consciousness of climate change. Because better knowledge of high altitude humidity levels improves the accuracy of climate models and weather forecasts, the Global Climate Observing System (GCOS) is putting more effort into the quality of these measurements. The GCOS established the Reference Upper-Air Network (GRUAN) and set the requirements for its measurements accuracy and traceability to the International System of Units (SI). To fulfil these requirements, improved radiosondes and methods to calibrate them are being developed. This paper presents a new calibration system for radiosondes based on mixing air flows from two independent dew-point generators. The system operates in the air temperature range down to −80 °C. Our results show that the new calibration set-up is able to provide calibrations for radionsondes at the uncertainty level of 2% in terms of the water vapour mixing ratio as required by GRUAN. A complete calibration covering the whole temperature and humidity range lasts less than three days. Additionally, the apparatus provides an option to characterize the behaviour of a radiosonde in changing temperatures and water vapour concentrations.

A new challenge for meteorological measurements: The meteoMet project-Metrology for meteorology

Climate change and its consequences require immediate actions in order to safeguard the environment and economy in Europe and in the rest of world. Aiming to enhance data reliability and reduce uncertainties in climate observations, a joint research project called MeteoMet-Metrology for Meteorology started in October 2011 coordinated by the Italian Istituto Nazionale di Ricerca Metrologica (INRiM). The project is focused on the traceability of measurements involved in climate change: surface and upper air measurements of temperature, pressure, humidity, wind speed and direction, solar irradiance and reciprocal influences between measurands. This project will provide the first definition at the European level of validated climate parameters with associated uncertainty budgets and novel criteria for interpretation of historical data series. The big challenge is the propagation of a metrological measurement perspective to meteorological observations. When such an approach will be adopted the requirement of reliable data and robust datasets over wide scales and long terms could be better met.

Atomic force microscope adhesion measurements and atomistic molecular dynamics simulations at different humidities

Due to their operation principle atomic force microscopes (AFMs) are sensitive to all factors affecting the detected force between the probe and the sample. Relative humidity is an important and often neglected—both in experiments and simulations—factor in the interaction force between AFM probe and sample in air. This paper describes the humidity control system designed and built for the interferometrically traceable metrology AFM (IT-MAFM) at VTT MIKES. The humidity control is based on circulating the air of the AFM enclosure via dryer and humidifier paths with adjustable flow and mixing ratio of dry and humid air. The design humidity range of the system is 20–60 %rh. Force–distance adhesion studies at humidity levels between 25 %rh and 53 %rh are presented and compared to an atomistic molecular dynamics (MD) simulation. The uncertainty level of the thermal noise method implementation used for force constant calibration of the AFM cantilevers is 10 %, being the dominant component of the interaction force measurement uncertainty. Comparing the simulation and the experiment, the primary uncertainties are related to the nominally 7 nm radius and shape of measurement probe apex, possible wear and contamination, and the atomistic simulation technique details. The interaction forces are of the same order of magnitude in simulation and measurement (5 nN). An elongation of a few nanometres of the water meniscus between probe tip and sample, before its rupture, is seen in simulation upon retraction of the tip in higher humidity. This behaviour is also supported by the presented experimental measurement data but the data is insufficient to conclusively verify the quantitative meniscus elongation.

Moisture Measurement Setup for Wood Based Materials

Abstract: We are developing a novel gravimetric moisture measurement system for wood based materials. The measurement principle is based on combining the Loss on Drying (LoD) method with complementary water loss detection systems. In our setup, air flows through a sample container containing sample material from 5 g to 400 g. The sample container is placed in a thermally controlled enclosure, which can be heated up to 200 °C. The mass loss of water is studied by weighing the sample before and after heating, and by monitoring the humidity of the air exiting the sample container with a capacitive sensor. The amount of evaporated water is also studied by trapping the water from the through-passed air in a separately weighed cold trap. The material samples can be exposed to different heating cycles in order to study different binding degrees of the water. This paper presents the measurement concept and the setup.