Multiple sensors, and alternate statistical estimators, were tested for measuring canopy transmittance in four stands under a variety of sky conditions. On a given day, stand average transmittance estimates were insensitive to degree of synchronization of the sensors used to measure under-canopy and incoming radiation. In comparisons to periodic measurement of incoming radiation with a single radiometer, the use of an additional sensor in the open does not automatically improve the estimates of stand average transmittance.
Smith, E.R.; Riitters, Kurt H. 1994. A comparison of forest canopy transmittance estimators. Can. J. For. Res., Vol. 24: 188-192