The importance of humidity measurement in meteorology

How to ensure reliable humidity measurement in harsh environments

The science of meteorology – the study of processes and phenomena within the atmosphere – has advanced dramatically in recent years. The advent of super-computers, earth-orbit satellites and new monitoring and measurement technologies, combined with advances in data modelling and deeper understanding of atmospheric physics and chemistry, is leading to fresh insights into the conditions that drive our climate and weather systems.

We’re now able to forecast future weather events with far greater accuracy. We’re also able to use atmospheric modelling as the basis for activities that range from agriculture and biosecurity, to the prediction of demand for power generation and the development of strategies to combat the impact of climate change.

Sensors for remote weather stations

A critical factor in the advance of meteorological science has been the availability of a new generation of sophisticated, multi-function automated weather stations, designed for use in remote locations. These exploit the latest GPS, cloud-based communications and solar power technologies to provide scientists with data from multiple sensors and measuring instruments, often in real-time.

Although a variety of sensors are used in different types of weather stations, common to almost all is the requirement to measure temperature and humidity. The latter is especially important if accurate weather predictions are to be made. This is particularly true in the agricultural sector, as humidity is one of the most important factors affecting crop growth, the risk of infestation from pests and changes in weather conditions. When it is used in conjunction with measurements of soil moisture, temperature and wind and rain conditions, accurate humidity monitoring allows farmers to determine the best time to plant seeds, apply pesticides or harvest crops. It also helps reduce waste, increase yields and minimise carbon emissions.

Demanding conditions require tough sensors

Meteorological applications, by their very nature, tend to be extremely demanding. Widely fluctuating temperatures, storm-force winds, high levels of rain, snow and ice, plus dust, sand, salt and agricultural chemicals, are commonplace. As an example, our relative humidity and temperature sensors are currently being used in weather stations on the summit of Mount Everest, at a height of over 8,000m and in some of the harshest environmental conditions to be found anywhere on the planet.

Humidity sensors therefore have to be designed to withstand tough conditions, while providing accurate, consistent and repeatable data. Perhaps as importantly – especially where weather stations are at sites that are remote or difficult to access – they have to be small, lightweight and consume minimal power.

One of the additional challenges for instrumentation engineers is to design a sensor mechanism that is free from drift – or at least as free as possible. Drift, or the tendency for sensor accuracy gradually to change over time, affects all humidity sensors. The degree of drift will depend on a range of factors, of which the operating conditions and quality of sensor construction are the most important.

In simple terms, a humidity sensor consists of three layers, with a moisture-detecting dielectric material sandwiched between two charged electrodes. Changes in humidity affect the impedance of the dielectric material and thus the current that flows across the sensor. As the dielectric needs to be at least partially exposed to the surrounding atmosphere its performance can deteriorate over time, especially if aggressive chemicals are present.

The best sensors, and therefore those with the optimum drift characteristics, such as our latest HC2A-S3A, use specialised coatings to protect the sensor layers without affecting performance, in terms of accuracy, hysteresis, speed of response and reliability. This results in drift that is less that 1% rh/year, in clean air, an accuracy of ±0.8% rh at 23°C, and a response time of under 15 seconds. It also significantly reduces drying time after condensation.

The technology employed in products such as the HC2A-S3A ensure that the challenges of sensor drift are successfully overcome, while advanced onboard electronics offer intelligent sensor adjustment, data management and external communication. These instruments are compact, lightweight and require minimal power, making them ideal for harsh meteorological environments, where they will continue to play a valuable role in advancing our knowledge of weather patterns and climate change.

With over 55 years of experience in the development of innovative precision instruments, we are the application experts in humidity measurements for harsh meteorological environments. Contact us to discuss your application.

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