Relationship between ground levelling measurements and radar satellite interferometric estimates of bog breathing in ombrotrophic northern bogs
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Date
2023
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Mcode
Degree programme
Language
en
Pages
28
Series
Mires and Peat, Volume 29
Abstract
Understanding the seasonal oscillation of peatland surface height initiated by changes in water table level (known as ‘bog breathing’) is key to improving spatial models of the water balance of bogs and their greenhouse gas exchanges with the atmosphere. Bog breathing has been studied locally via point-based measurements by telmatologists as well as over wider areas by the remote sensing community, in the latter case often without or with limited ground-truth validation. We aim to bring the two disciplines together by assessing the feasibility of validating Synthetic Aperture Radar (SAR) data from the Sentinel-1 satellite with in situ ground levelling data from nanotopes with different drainage status in two hemiboreal raised bogs. We demonstrate the continuous measurement of bog breathing using automatic ultrasonic levelling devices which shows that, during one growing season, bog breathing amounted to 11.6–14.7 cm in hollows, 6.9–7.5 cm in hummocks and 9.5–11.6 cm in haplotelmic nanotopes. Accounting for such relatively large vertical surface deformations remotely using the SAR Differential Interferometry (DInSAR) technique is prone to estimation errors owing to the so-called estimation ambiguity that occurs when deformation exceeds half the wavelength of the radar signal (2.77 cm for Sentinel-1). We approach the ambiguity problem by estimating deformation between consecutive SAR acquisitions (time separation 6 or 12 days) only. Remote and in situ measurements of bog breathing correlate moderately to very strongly (rs = 0.82–0.93 in hummocks) even though, from time to time, all nanotopes except hummocks show surface deformations in just a single day that exceed the ambiguity threshold. This indicates that DInSAR surface deformation estimates contain useful information despite under-estimating larger changes, and DInSAR has high potential for the assessment of bog breathing. Our findings imply that DInSAR estimates in peatlands without ground validation should be interpreted with caution. To take full advantage of the plentiful data from Sentinel-1, the introduction of contextual information (e.g. temperature, precipitation and/or evapotranspiration data) could guide ambiguity resolution, as we demonstrate up to moderate correlation (rs = 0.59 in a hollow) between precipitation and bog surface height.Description
Funding Information: This study formed part of a PhD project supported by the European Union from the European Regional Development Fund. The research was funded by Estonian Environmental Investment Centre grants SLOOM12006 and SLOOM14103, Estonian State Forest Management Centre grant LLTOM17250, and national scholarship program Kristjan Jaak which is funded and managed by the Archimedes Foundation in collaboration with the Ministry of Education and Research (Estonia). The authors thank Karsten Kretschmer (DLR) for helping with Python, Philip Conroy for giving a native speaker’s touch to the manuscript, and the SarProz team for their excellent software and extremely flexible student licensing. Publisher Copyright: © 2023, IMCG and IPS. All rights reserved.
Keywords
bog drainage, InSAR, peatland, Sentinel-1, surface deformation
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Citation
Tampuu, T, Praks, J, De Zan, F, Kohv, M & Kull, A 2023, ' Relationship between ground levelling measurements and radar satellite interferometric estimates of bog breathing in ombrotrophic northern bogs ', Mires and Peat, vol. 29, 17 . https://doi.org/10.19189/MaP.2022.OMB.Sc.1999815