Measurement of Incoming Radiation below Forest Canopies: A Comparison of Different Radiometer Configurations

Clare Webster Department of Geography, Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne, United Kingdom, and WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland

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Nick Rutter Department of Geography, Faculty of Engineering and Environment, Northumbria University, Newcastle upon Tyne, United Kingdom

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Franziska Zahner WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, and Institute of Environmental Engineering, ETH Zurich, Zurich, Switzerland

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Tobias Jonas WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland

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Abstract

Ground-based, subcanopy measurements of incoming shortwave and longwave radiation are frequently used to drive and validate energy balance and snowmelt models. These subcanopy measurements are frequently obtained using different configurations (linear or distributed; stationary or moving) of radiometer arrays that are installed to capture the spatial and temporal variability of longwave and shortwave radiation. Three different radiometer configurations (stationary distributed, stationary linear, and moving linear) were deployed in a spruce forest in the eastern Swiss Alps during a 9-month period, capturing the annual range of sun angles and sky conditions. Results showed a strong seasonal variation in differences between measurements of shortwave transmissivity between the three configurations, whereas differences in longwave enhancement appeared to be seasonally independent. Shortwave transmissivity showed a larger spatial variation in the subcanopy than longwave enhancement at this field site. The two linear configurations showed the greatest similarity in shortwave transmissivity measurements, and the measurements of longwave enhancement were largely similar between all three configurations. A reduction in the number of radiometers in each array reduced the similarities between each stationary configuration. The differences presented here are taken to reflect the natural threshold of spatial noise in subcanopy measurements that can be expected between the three configurations.

Denotes Open Access content.

Publisher’s Note: This article was revised on 22 April 2016 to include the open access designation that was added after initial publication.

Publisher’s Note: This article was revised on 22 June 2016 to include the CCBY license that was added after initial publication.

This article is licensed under a Creative Commons Attribution 4.0 license.

Corresponding author address: Clare Webster, Department of Geography, Faculty of Engineering and Environment, Northumbria University, Ellison Place, Newcastle upon Tyne NE1 8ST, United Kingdom. E-mail: clare.webster@northumbria.ac.uk

Abstract

Ground-based, subcanopy measurements of incoming shortwave and longwave radiation are frequently used to drive and validate energy balance and snowmelt models. These subcanopy measurements are frequently obtained using different configurations (linear or distributed; stationary or moving) of radiometer arrays that are installed to capture the spatial and temporal variability of longwave and shortwave radiation. Three different radiometer configurations (stationary distributed, stationary linear, and moving linear) were deployed in a spruce forest in the eastern Swiss Alps during a 9-month period, capturing the annual range of sun angles and sky conditions. Results showed a strong seasonal variation in differences between measurements of shortwave transmissivity between the three configurations, whereas differences in longwave enhancement appeared to be seasonally independent. Shortwave transmissivity showed a larger spatial variation in the subcanopy than longwave enhancement at this field site. The two linear configurations showed the greatest similarity in shortwave transmissivity measurements, and the measurements of longwave enhancement were largely similar between all three configurations. A reduction in the number of radiometers in each array reduced the similarities between each stationary configuration. The differences presented here are taken to reflect the natural threshold of spatial noise in subcanopy measurements that can be expected between the three configurations.

Denotes Open Access content.

Publisher’s Note: This article was revised on 22 April 2016 to include the open access designation that was added after initial publication.

Publisher’s Note: This article was revised on 22 June 2016 to include the CCBY license that was added after initial publication.

This article is licensed under a Creative Commons Attribution 4.0 license.

Corresponding author address: Clare Webster, Department of Geography, Faculty of Engineering and Environment, Northumbria University, Ellison Place, Newcastle upon Tyne NE1 8ST, United Kingdom. E-mail: clare.webster@northumbria.ac.uk
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