Assisting peatland restoration using satellite radar data

Overview

In this novel research, we want to improve the management and protection of peatland in Scotland by using satellite images. Our objectives are:
• Aid assessment of regeneration activities in Scottish peatlands.
• Provide real time tools to assess if peatland are approaching un-reversible conditions.
• Help assess areas in Scotland where peatland could be regenerated.
The project will include processing satellite data, but also performing experiments in Scottish bogs with a ground radar and drones.

Background
Peatlands are the most efficient terrestrial store of Carbon on Earth [Alexandrov et al. 2020]. In less than 3% of the land area, they hold 600 Gt of carbon, almost as much as the total carbon in the atmosphere [Creis et al 2013]. Over long periods of time, they cool the Earth’s climate and play an important role in global Carbon cycle recovery from anthropogenic emissions. Peatlands in good condition also deliver other important benefits to society, such as flood prevention, provision of fresh water, support of biodiversity, natural archives for past climate and history, recreation opportunities and provision of fuel. Ultimately, the flows of energy, material and information in peatland (e.g. carbon & nutrient transfer between trophic levels, water and solar energy transfer in the soil, direct signalling between and within biota) are strongly modulated by hydrology through complex feedback mechanisms [Waddington et al. , 2015] and are inherently highly resilient, as suggested by their persistence as a natural C sink since the last glacial maximum.

However, land use change (e.g. drainage, afforestation, over-grazing) can push peatlands outside of their resilience boundaries, altering the tight eco-hydrological coupling and compromising the delivery of ecosystem services, with significant costs to society [IUCN, 2019]. Disturbance such as heavy rainfall, droughts or wildfires, which are exacerbated by climate change will further decrease peatland resilience. In the UK, peatlands cover approximately 3M ha (12%) of the land area, with blanket bog (a globally rare habitat) being the most widespread peatland type. Yet, up to 80% of UK peatlands are degraded to some degree and net greenhouse gas (GHG) emissions are estimated to be 18-23 Mt of CO2-equivalent per year. This figure on its own is sufficient to shift the entire UK Land-Use and Land-Use Change inventory from net sink to net source of GHGs [Evans et al 2017].
In this project we will use satellite Synthetic Aperture Radar (SAR). SAR is able to obtain images of the environment from space using microwaves. It allows us to acquire images independent of weather condition and solar illumination, which is very valuable in areas with frequent cloud cover. We will also use a cutting edge radar technology called polarimetry interferometric (Pol-InSAR). The advantage of PolIn-SAR is that we can use the polarisation and interferometric information of the radar echo to obtain more images and therefore more information about objects in the scene [ESA-PolSAR]. Beside using satellite data we will be carrying out extensive experiments using a ground radar which can simulate the images obtained from satellites. Finally, we will make use of the emerging technology of UAV (“drone”) based observation for field validation and rapid local assessment using low cost aircraft.
A strong motivation for using satellite images is that we entered a new era of freely available satellite data (e.g. the ESA Sentinel constellation missions [ESA-Sentinel]). We are experiencing a rapid growth of activities in the Space industry and the Earth Observation sector. When paired to the exponentially growing sector of unmanned aerial monitoring, this opportunity not only supports businesses activities but also provides many state of the art tools to the environmental management community.

The development work will be accompanied by large fieldwork in Scotland with at least quarterly visits to peatlands of interest. We will be using water table logger installed in several peatlands around Scotland (e.g. Flanders Moss) where restoration has been carried out. This work is in the framework of the Scotland’s International Environment Centre (SIEC) [SIEC 2021] and if successful, will feed into the Nature Scot management strategy.

Methodology

Deliverables: In this project, we will set up a series of methodologies that starting from images acquired from space, will be able to provide weekly update of water table and soil moisture. Among other products we are interested in monitoring drastic changes in peatland which could help rapid intervention.

Novelty: PolIn-SAR is a cutting edge technology and is very useful to retrieve biophysical parameters of vegetation and soil [ESA-PolSAR]. It has been recently seen that differential interferometric SAR can be used to monitor the “breathing” of bogs from space across the different seasons (i.e. vertical displacement of the bog consequence of different water retention). However, we are in urgent need of controlled experiment on the ground, which will allow a much better understanding of the satellite signal over peatlands. Additionally, the research work carried out in this project puts the management at the core of the project, developing mechanisms that use satellite observation for leading actions.

Data (satellite): Archived Pol-InSAR data are already available. Future acquisitions will be carried out synchronised to fieldwork. The datasets used will include at least the following satellite missions: ALOS-2 (Japanese Space Agency); Sentinel-1 (European Space Agency).

Data (ground): We will be using a ground radar built in the Stirling radar lab (based on a VNA architecture) to acquire images that emulates satellites. This can be tuned at different frequencies and acquire quad-polarimetric and interferometric data. It can be easily transported and installed on a tripod. One of the experiments will consider inserting a metal pipe in the moss and evaluate the depth the radar signal can reach. This will tell us about the capability of microwaves to monitor ground water level.

Data (drone): We will be using our DJI Phantom-4 drone to collect aerial images of the peatlands during fieldwork.

Algorithm development: In this project we will develop algorithms that exploit weekly available PolSAR images combined with sporadic ground measurements to monitor water table, soil moisture, changes in vegetation cover and more generally peatland dynamics.
1) We will monitor changes, in water table, soil moisture and vegetation cover, by applying scattering models and change detectors. One of the methodologies will be based on the use of optimisations of polarimetric data [Marino et al 2014].
2) Analysis of time series. This will allow to evaluate trends in biophysical parameters of soil and moss.

Project Timeline

Year 1

Preparing a literature review on the topics: SAR, drone imaging, peatlands. Fieldwork. Start working on ground measurements and monitor of soil moisture changes with Pol-InSAR. Attending international training events. Expected submission of a journal paper on monitoring peatlands with Pol-InSAR.

Year 2

Monitor multi-year changes in water level and vegetation cover. Expected submission of a journal paper on retrieving biophysical parameters with Pol-InSAR and drone data.

Year 3

Develop a processing chain to assess the impact of restoration. Starting writing the thesis chapters. Expected submission of journal paper on restorations assessment in Scotland.

Year 3.5

Complete thesis, submission and viva.

Training
& Skills

This is a multi-disciplinary project including topics related to (a) satellite Earth Observation; (b) drone surveys; (c) physical models (electromagnetic scattering); (d) data analysis; (e) floods, peatland and grassland; (f) programming.

The successful candidate will have the opportunity to gain valuable skills in the context of: (a) analysing and processing satellite and drone images using Python; (b) planning and accomplishing ground radar and drone campaigns; (c) developing analytical and empirical models to measure biophysical parameters of the environment; (d) using Geographical Information Systems (GIS) software.

The training will also include the attendance of major international training events such as the training on polarimetric SAR data, provide by ESA in Italy

References & further reading

[Alexandrov et al. 2020] Alexandrov, G. A., Brovkin, V. A., Kleinen, T., and Yu, Z. (2020): The capacity of northern peatlands for long-term carbon sequestration, Biogeosciences, 17, 47–54, https://doi.org/10.5194/bg-17-47-2020..[Ciais et al. 2013], Ciais et al. (2013), Carbon and Other Biogeochemical Cycles. In: Stocker, et al. Climate Change 2013: The Physical Science Basis., Cambridge University Press.[ESA-PolSAR]: https://earth.esa.int/web/polsarpro/polarimetry-tutorial[ESA-Sentinel]: https://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Satellite_constellation.[Evans et al. , 2017], Evans at al (2017) Implementation of an emission inventory for UK peatlands. Report to the Department for Business, Energy and Industrial Strategy, Centre for Ecology and Hydrology, Bangor;[IUCN, 2019], Commission of Enquiry on Peatlands: The State of UK Peatlands – an update, International Union for Conservation of Nature, Edinburgh;[Marino et al 2014]: Marino, A. and Hajnsek, I. (2014). “A change detector based on an optimization with polarimetric SAR imagery”. IEEE TGRS, 52(8).[SIEC 2021] https://www.stir.ac.uk/about/scotlands-international-environment-centre/[Waddington et al. , 2015] M. Waddington,P. J. Morris,N. Kettridge,G. Granath,D. K. Thompson,P. A. Moore, (2015) Hydrological feedbacks in northern peatlands, Ecohydrology 8:113-127;

Further Information

This project is in the framework of the Scotland’s International Environment Centre and it will feed in the Nature Scot project Peatland ACTION.

Apply Now