Understanding ‘saturation’ of radar signals over forests

Neha Joshi; Edward Mitchard; Matthew Brolly; Johannes Schumacher; Alfredo Fernández-Landa; Vivian Kvist Johannsen; Miguel Marchamalo; Rasmus Fensholt

doi:10.1038/s41598-017-03469-3

Understanding ‘saturation’ of radar signals over forests

Neha Joshi, Edward Mitchard, Matthew Brolly, Johannes Schumacher, Alfredo Fernández-Landa, Vivian Kvist Johannsen, Miguel Marchamalo, Rasmus Fensholt

Research output: Contribution to journal › Article

Abstract

There is an urgent need to quantify anthropogenic influence on forest carbon stocks. Using satellite-based radar imagery for such purposes has been challenged by the apparent loss of signal sensitivity to changes in forest aboveground volume (AGV) above a certain ‘saturation’ point. The causes of saturation are debated and often inadequately addressed, posing a major limitation to mapping AGV with the latest radar satellites. Using ground- and lidar-measurements across La Rioja province (Spain) and Denmark, we investigate how various properties of forest structure (average stem height, size and number density; proportion of canopy and understory cover) simultaneously influence radar backscatter. It is found that increases in backscatter due to changes in some properties (e.g. increasing stem sizes) are often compensated by equal magnitude decreases caused by other properties (e.g. decreasing stem numbers and increasing heights), contributing to the apparent saturation of the AGV-backscatter trend. Thus, knowledge of the impact of management practices and disturbances on forest structure may allow the use of radar imagery for forest biomass estimates beyond commonly reported saturation points.

Original language	English
Journal	Scientific Reports
Volume	7
DOIs	https://doi.org/10.1038/s41598-017-03469-3
Publication status	Published - 14 Jun 2017

Bibliographical note

© The Author(s) 2017. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Matthew Brolly

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School of Environment and Technology - Principal Lecturer

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Cite this

Joshi, N., Mitchard, E., Brolly, M., Schumacher, J., Fernández-Landa, A., Johannsen, V. K., Marchamalo, M., & Fensholt, R. (2017). Understanding ‘saturation’ of radar signals over forests. Scientific Reports, 7. https://doi.org/10.1038/s41598-017-03469-3

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abstract = "There is an urgent need to quantify anthropogenic influence on forest carbon stocks. Using satellite-based radar imagery for such purposes has been challenged by the apparent loss of signal sensitivity to changes in forest aboveground volume (AGV) above a certain {\textquoteleft}saturation{\textquoteright} point. The causes of saturation are debated and often inadequately addressed, posing a major limitation to mapping AGV with the latest radar satellites. Using ground- and lidar-measurements across La Rioja province (Spain) and Denmark, we investigate how various properties of forest structure (average stem height, size and number density; proportion of canopy and understory cover) simultaneously influence radar backscatter. It is found that increases in backscatter due to changes in some properties (e.g. increasing stem sizes) are often compensated by equal magnitude decreases caused by other properties (e.g. decreasing stem numbers and increasing heights), contributing to the apparent saturation of the AGV-backscatter trend. Thus, knowledge of the impact of management practices and disturbances on forest structure may allow the use of radar imagery for forest biomass estimates beyond commonly reported saturation points.",

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