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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 20, issue 6
Hydrol. Earth Syst. Sci., 20, 2309–2315, 2016
https://doi.org/10.5194/hess-20-2309-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Hydrol. Earth Syst. Sci., 20, 2309–2315, 2016
https://doi.org/10.5194/hess-20-2309-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Technical note 15 Jun 2016

Technical note | 15 Jun 2016

Technical note: Improving the AWAT filter with interpolation schemes for advanced processing of high resolution data

Andre Peters, Thomas Nehls, and Gerd Wessolek Andre Peters et al.
  • Institut für Ökologie, Technische Universität Berlin, Berlin, 10587, Germany

Abstract. Weighing lysimeters with appropriate data filtering yield the most precise and unbiased information for precipitation (P) and evapotranspiration (ET). A recently introduced filter scheme for such data is the AWAT (Adaptive Window and Adaptive Threshold) filter (Peters et al., 2014). The filter applies an adaptive threshold to separate significant from insignificant mass changes, guaranteeing that P and ET are not overestimated, and uses a step interpolation between the significant mass changes. In this contribution we show that the step interpolation scheme, which reflects the resolution of the measuring system, can lead to unrealistic prediction of P and ET, especially if they are required in high temporal resolution. We introduce linear and spline interpolation schemes to overcome these problems. To guarantee that medium to strong precipitation events abruptly following low or zero fluxes are not smoothed in an unfavourable way, a simple heuristic selection criterion is used, which attributes such precipitations to the step interpolation. The three interpolation schemes (step, linear and spline) are tested and compared using a data set from a grass-reference lysimeter with 1 min resolution, ranging from 1 January to 5 August 2014. The selected output resolutions for P and ET prediction are 1 day, 1 h and 10 min. As expected, the step scheme yielded reasonable flux rates only for a resolution of 1 day, whereas the other two schemes are well able to yield reasonable results for any resolution. The spline scheme returned slightly better results than the linear scheme concerning the differences between filtered values and raw data. Moreover, this scheme allows continuous differentiability of filtered data so that any output resolution for the fluxes is sound. Since computational burden is not problematic for any of the interpolation schemes, we suggest always using the spline scheme.

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The AWAT (Adaptive Window and Adaptive Threshold) filter routine for high-resolution lysimeter data is improved. The threshold scheme with original step interpolation yields unrealistic fluxes for high temporal resolution. Improvement applies linear and spline interpolation schemes so that fluxes in high temporal resolution are automatically calculated. The spline scheme allows continuous differentiability of filtered data so that any output resolution for the fluxes is sound.
The AWAT (Adaptive Window and Adaptive Threshold) filter routine for high-resolution lysimeter...
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