Still image from video captured from the top of the Ameriflux tower at Niwot Ridge (left), and the sway frequency measured from video collected from this same vantage point (right)

RAL has tested three methods of measuring snow and rain intercepted water content at Niwot Ridge, CO in 2016. The first method uses measurements of the tree stem compression to quantify changes in water stored in the canopy.  This system was shown to be highly sensitive to freezing temperatures and a paper is in review documenting these measurements (Gutmann et al., 2016). The second system uses the same equipment measured at 10Hz, or accelerometers measured at 10Hz, to quantify the magnitude and frequency of trees swaying in the wind.  Initial analyses have shown these measurements have been shown to be less sensitive to freezing temperatures, and changes in the tree’s intrinsic sway frequencies appear to be related to changes in water storage.   The third system uses video cameras to measure tree sway frequencies.  This system was just installed and tested this year.  Initial results show that this system can measure the sway frequency of all trees that are well resolved in the video (figure).

The sway frequency measurements from both individual trees, and the video of the forest will be documented in a publication to be submitted in 2017. The sway magnitude data will also be investigated for their use in understanding momentum transfer from the atmosphere to the surface.  Relevant measurements of wind speeds at multiple heights are available from the Ameriflux tower for comparison.