Measurements and observations of the atmosphere (and especially the troposphere) are the most important pre-requisite to our understanding of weather and climate. Numerical models of the atmosphere have revolutionized the preparation of weather forecasts, although rather than reducing the need for observations such models have increased awareness of the importance of data through assimilation schemes. Indeed, the accuracy of forecasts relies crucially upon how well the initial state of the atmosphere can be described and this requires detailed measurements throughout the entire depth of the atmosphere.

Over the last half century, the increasing availability of low cost computers and sensors has enabled a move away from a reliance on the collection of weather data at traditional sites and enclosures. However, perhaps the greatest contribution to improving accuracy in weather prediction and monitoring is the advent of new observing systems based on satellite and airborne platforms. These technologies have completely revolutionized the networking of conventional meteorological instrumentation and have facilitated a colossal advance in both the spatial and temporal scale of weather measurement.

In this Special Issue of Meteorological Applications, a collection of papers has been assembled which details many of these new monitoring methods and how they can be used to measure the fundamental parameters of weather and climate in the troposphere: temperature, moisture and momentum. Papers include examples of ground based systems covering networks of surface based instruments for use in mesoscale meteorological studies as well as methods of using radar and lidar systems. Alongside these is a series of papers describing state of the art satellite systems, detailing the data produced and subsequent applications. Throughout the issue, reviews of past work set the scene for future developments, and new approaches to measuring tropospheric parameters show how measurements are opening up exciting opportunities to learn more about how the weather works. There is no doubt that observational techniques will continue to keep pace with the development needs of weather forecasting. Overall, this issue provides a window into many of the current observationsystems being used for research and operations.