This is a review of the Optical-Microwave Scintillometer （OMS） system newly developed in last two decades， which can measure area averaged sensible and latent heat fluxes over a scale of 1 -10 km， especially over heterogeneous surfaces such as cross a valley or over urban areas.Among the methods of area averaged flux measurements， such as eddy-covariance based multi-point observations， air craft observations， satellite， and surface remote sensing etc.， scintillometry is probably the most feasible technique in getting areal fluxes up to 10 kilometers.The basic theory of scintillometry includes electromagnetic wave propagation， atmosphere turbulence， and micrometeorology， which are more sophisticated than that of the popular eddy covariance （EC） system.Based on the introduction of concepts such as refractive index， structure parameter and turbulence spectra etc.， basic scintillometer theories and equations are presented briefly， including： （1） calculation of structure parameter of refractive index via the variance of received light log-intensities； （2） the understanding of the working scale of scintillometry via the light-path weighting function， the spatial spectral weighting function， and the temporal spectral characteristics； （3） the derivation of structure parameters of temperature and humidity via the structure parameters of refractivity； （4） the calculation of fluxes by using the typical functions of Monin-Obukhov similarity； （5） the footprint analysis of scintillometry.A comparison between scintillometry and EC are presented in three aspects： ‘Characteristics’， ‘Advantages’ and ‘Weakness’.It is clear that a combined use of EC & Scintillometry can provide better area averaged fluxes， and， refined flux aggregation schemes.Then， the application of scintillometry is introduced for rather homogeneous surfaces， complicated surfaces， urban areas， and， the ‘ground truth’ for remote sensing and the application of areal averaged fluxes in atmospheric models.The example utilizations of the OMS systems in the Arou alpine-meadow station and the Zhangye oasis station， of the Heihe River basin， clearly show the advantages of scintillometry over the EC in the measurements of larger scale evapotranspiration.Nowadays there are hundreds flux stations operating over various climate regions and surface states of the world.Upscaling of the spatial representativeness of these stations becomes a key point to better understanding the land surface processes， and improving the spatial matching between land surface models and meso/large scale atmospheric models.Comparatively， the time of development of scintillometry， particularly the microwave scintillometers in measuring water vapor fluxes， are still short.Further improvements of relevant hardware， data sampling， and data processing software etc.are still needed.
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