Estimating active layer thickness at the high Arctic study site Zackenberg from remotely sensed ground subsidence
(2021) In Student thesis series INES NGEK01 20202Dept of Physical Geography and Ecosystem Science
- Abstract
- The active layer thickness (ALT) is an indicator of permafrost thaw, which potentially leads to the release of large amounts of greenhouse gases under global warming, and thus could further amplify climate change. The thaw depth of the active layer also governs seasonal surface deformation, caused by the volume change between ice to water, which poses risks for slope stability and infrastructure foundations. Currently, the monitoring of the ALT is accomplished through modelling and field measurements. This thesis aims at testing a recently introduced remote sensing method for ALT monitoring by comparing the estimated ALT to ALT field measurements and environmental parameters. The method is based on remotely sensed seasonal ground... (More)
- The active layer thickness (ALT) is an indicator of permafrost thaw, which potentially leads to the release of large amounts of greenhouse gases under global warming, and thus could further amplify climate change. The thaw depth of the active layer also governs seasonal surface deformation, caused by the volume change between ice to water, which poses risks for slope stability and infrastructure foundations. Currently, the monitoring of the ALT is accomplished through modelling and field measurements. This thesis aims at testing a recently introduced remote sensing method for ALT monitoring by comparing the estimated ALT to ALT field measurements and environmental parameters. The method is based on remotely sensed seasonal ground subsidence, derived through the differential interferometric synthetic aperture radar technique (DInSAR). By estimating the ice content in the soil, the ground subsidence can be related to ALT development, which was used to determine the ALT throughout the thawing season 2017 at Zackenberg valley, Greenland. The ice content was derived by combining saturation fraction with porosity. The saturation fraction was determined based on a linear regression between the normalized soil moisture index and soil moisture measurements. The porosity was obtained through organic matter field measurements and a mineral soil database. The resulting ALT estimate was statistically similar to the ALT field measurements, both considering ALT maximum (p-value = 0.55) and temporal development (agreement to ideal fit: p-value = 0.33). The ALT distribution is plausible considering environmental factors (aspect, topography, vegetation). Yet, the method was found to perform best in water-saturated areas and showed more variable results in drier areas. For future applications it is recommended to incorporate modelling of the subsurface ice content, as the ALT result in drier soils is especially dependent on a correct estimate of the ice content. If this is accomplished, and if the subsidence retrieval considers 3D-ground displacement, the tested method is promising for the ALT monitoring at high spatial resolution during the snow-free season. (Less)
- Popular Abstract
- Permafrost covers 14 % of Earth’s land surface and is defined as soil which has been continuously frozen for at least two years. Due to global warming, permafrost soils experience thawing. This has to be monitored because the thawing could release greenhouse gases from previously frozen organic soil as well as affect ground stability and thereby infrastructure. Permafrost thaw is indicated by a deepening of the upper soil layer, which thaws during the summer. This so-called active layer and its thickness (ALT) can be monitored through modelling or field measurements. Yet, these methods are limited by data resolution and available labour.
This thesis aimed at testing a new method presented by Liu et al. (2012) for ALT estimation. For... (More) - Permafrost covers 14 % of Earth’s land surface and is defined as soil which has been continuously frozen for at least two years. Due to global warming, permafrost soils experience thawing. This has to be monitored because the thawing could release greenhouse gases from previously frozen organic soil as well as affect ground stability and thereby infrastructure. Permafrost thaw is indicated by a deepening of the upper soil layer, which thaws during the summer. This so-called active layer and its thickness (ALT) can be monitored through modelling or field measurements. Yet, these methods are limited by data resolution and available labour.
This thesis aimed at testing a new method presented by Liu et al. (2012) for ALT estimation. For this, the method was applied across Zackenberg valley in NE Greenland to estimate the ALT during the thaw season of 2017. Then, the result was evaluated through comparison with field measurements and relationships to environmental factors.
The tested method is based on ground subsidence estimated through radar satellite imagery. As ground subsidence during the thawing season is a result of the volume change of water from ice to liquid in the soil, the ALT can be estimated if subsidence and ice content are known.
In this study, the relationship between a satellite-based soil moisture index and soil moisture measurements was used to map the saturation across the study area. The porosity of the soil was estimated from field measurements and a soil database. By combining ground subsidence with ice content based on saturation and porosity, the ALT development and maximum ALT could be estimated.
Both the resulting maximum estimated ALT and the temporal development were statistically similar to the field measurements. The estimated ALT was deepest on southern slopes, which aligns with more available energy for thawing due to more incoming solar radiation compared to other slope directions. Shallower ALT was found in wetlands, which thaw slower due to insulating peat layers and high ice content. The error in ALT estimate was largest in drier areas, shown by larger differences to field measurements. This was also supported by larger discrepancies of the ALT estimate in dry vegetation types to the expected values from literature. The error can be related to increased sensitivity of the method to accurate ice content estimates in drier soils.
The method is promising for intermediate-scale ALT mapping and can be applied in water-saturated areas. For other areas, it is recommended to refine the method by including soil saturation modelling and to evaluate the estimate with more extensive field measurements. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9038935
- author
- Wendt, Lotte LU
- supervisor
- organization
- course
- NGEK01 20202
- year
- 2021
- type
- M2 - Bachelor Degree
- subject
- keywords
- active layer thickness, DInSAR, subsidence, permafrost, Zackenberg, CALM
- publication/series
- Student thesis series INES
- report number
- 537
- language
- English
- id
- 9038935
- date added to LUP
- 2021-02-01 11:21:04
- date last changed
- 2021-02-01 11:21:04
@misc{9038935,
abstract = {{The active layer thickness (ALT) is an indicator of permafrost thaw, which potentially leads to the release of large amounts of greenhouse gases under global warming, and thus could further amplify climate change. The thaw depth of the active layer also governs seasonal surface deformation, caused by the volume change between ice to water, which poses risks for slope stability and infrastructure foundations. Currently, the monitoring of the ALT is accomplished through modelling and field measurements. This thesis aims at testing a recently introduced remote sensing method for ALT monitoring by comparing the estimated ALT to ALT field measurements and environmental parameters. The method is based on remotely sensed seasonal ground subsidence, derived through the differential interferometric synthetic aperture radar technique (DInSAR). By estimating the ice content in the soil, the ground subsidence can be related to ALT development, which was used to determine the ALT throughout the thawing season 2017 at Zackenberg valley, Greenland. The ice content was derived by combining saturation fraction with porosity. The saturation fraction was determined based on a linear regression between the normalized soil moisture index and soil moisture measurements. The porosity was obtained through organic matter field measurements and a mineral soil database. The resulting ALT estimate was statistically similar to the ALT field measurements, both considering ALT maximum (p-value = 0.55) and temporal development (agreement to ideal fit: p-value = 0.33). The ALT distribution is plausible considering environmental factors (aspect, topography, vegetation). Yet, the method was found to perform best in water-saturated areas and showed more variable results in drier areas. For future applications it is recommended to incorporate modelling of the subsurface ice content, as the ALT result in drier soils is especially dependent on a correct estimate of the ice content. If this is accomplished, and if the subsidence retrieval considers 3D-ground displacement, the tested method is promising for the ALT monitoring at high spatial resolution during the snow-free season.}},
author = {{Wendt, Lotte}},
language = {{eng}},
note = {{Student Paper}},
series = {{Student thesis series INES}},
title = {{Estimating active layer thickness at the high Arctic study site Zackenberg from remotely sensed ground subsidence}},
year = {{2021}},
}