GRUAN depends critically on a wide variety of instrumentation for measuring upper-air essential climate variables. In addition, different instruments are often used to measure the same climate variable as such a variety of approaches allows us to validate different measurement systems through intercomparisons. The core GRUAN principle of ensuring traceability of measurements to SI units or community accepted standards, requires a deep understanding of how every instrument used in GRUAN functions.


Radiosondes provide high resolution in-situ data on the vertical profile of temperature, humidity, pressure and winds through the troposphere and into the lower stratosphere. Radiosondes form the backbone for balloon sounding in GRUAN. In addition to measuring high priority essential climate variables, the radiosondes also provides the means for transmitting data from additional sensors to the ground. Additional sensors are often coupled to radiosondes to provide measurements of other, or related, essential climate variables. These sensors include:

Ozone sensors

Additional sensors for measuring ozone concentrations through the troposphere and into the stratosphere. These are typically ozonesondes.

Water vapour sensors

Humidity sensors on radiosondes are seldom suitable for measuring the very low water vapour concentrations found in the stratosphere. Therefore, specialized instruments are often flown to measure water vapour concentrations in the stratosphere.

Temperature sensors

Although radiosondes do measure temperature, they may not always be suitable for very specific applications e.g. measuring extremely rapid changes in temperature that result from atmospheric turbulence. Therefore, additional fast response temperature sensors are sometimes flown together with radiosondes to provide such bespoke temperature measurements.

Aerosol sensors

Measuring aerosols size distributions, composition and concentrations is essential for understanding how the atmosphere absorbs and transmits radiation. Aerosols also play key roles in cloud formation by providing cloud condensation nuclei. Specialized sondes are often flown on balloons to make the required measurements to understand aerosols in Earth’s atmosphere.