This book describes the fundamental scientific principles  underlying high quality instrumentation used for environmental  measurements. It discusses a wide range of in situ sensors employed  in practical environmental monitoring and, in particular, those  used in surface based measurement systems. It also considers the  use of weather balloons to provide a wealth of upper atmosphere  data. To illustrate the technologies in use it includes many  examples of real atmospheric measurements in typical and unusual  circumstances, with a discussion of the electronic signal  conditioning,  data acquisition considerations and data  processing principles necessary for reliable measurements. This  also allows the long history of atmospheric measurements to be  placed in the context of the requirements of modern climate  science, by building the physical science appreciation of the  instrumental record and looking forward to new and emerging sensor  and recording technologies.