MEASUREMENT PRINCIPLE
A scintillometer is an instrument that measures the 'amount' of scintillations by emitting a beam of light over a horizontal path. The scintillations 'seen' by the instrument can be expressed as the structure parameter of the refractive index of air (Cn
2 ), which is a representation of the 'turbulent strength' of the atmosphere. The turbulent strength describes the ability of the atmosphere to transport heat and water vapour. The LAS and X-LAS measure the structure parameter of air using a near-infrared light source of 880 nm. At this wavelength temperature fluctuations are dominant. Therefore, Cn
2 measurements and standard meteorological observations (wind speed, air temperature and air pressure) can be used to derive the surface sensible heat flux (H), representative of areas of several square kilometres.
SOFTWARE SCINTILLATION
The recorded Cn
2 data from the LAS or X-LAS can be processed using the included WINLAS software. This is a Windows™ program that calculates the sensible heat flux, using additional wind speed, air temperature and pressure data, for both unstable (day-time) and stable (night-time) conditions. WINLAS displays the input data file and the results using a simple viewer. The results are written in an output file that can be imported into spreadsheet programs. At extra cost the user can upgrade to the specially developed Kipp&Zonen 'EVATION' software package. This software provides installation, set-up, configuration and help files for a complete Kipp&Zonen Evapo-Transpiration (E-T) system comprised of the LAS or X-LAS, comprehensive meteorological
sensors and data loggers. EVATION calculates and displays sensible heat flux, evapo-transpiration and other parameters in a graphical environment. The scintillation technique to determine the path-averaged structure parameter of the refractive index of air is based on the propagation statistics of electromagnetic radiation through the atmosphere. When an electromagnetic beam of radiation propagates through a turbulent atmosphere it is distorted by a number of processes, which remove energy from the beam leading to signal attenuation. The most dominant of these are small fluctuations in the refractive index of air (n) caused by temperature and humidity variations. These refractive index fluctuations lead to intensity changes, which are known as scintillations.
SOLAR & ATMOSPHERIC SCIENCE
