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-reversable conditions.
* Help assess areas in Scotland where peatland could be regenerated.

Background
Peatlands are the most efficient terrestrial store of carbon (C) on Earth; in less than 3% of land area, they hold 600 Gt of carbon, almost as much as the total carbon in the atmosphere [1]. Peatlands play an important role in the global Carbon cycle, including the recovery from anthropogenic CO2 emissions. Peatlands also deliver a range of 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 [2]. Provision of these Ecosystem Services are closely linked to peat hydrology through complex feedback mechanisms [3] which are inherently resilient, as suggested by their persistence of peatlands as natural C sinks since the last glacial maximum. However, disturbance of hydrology through land use change (e.g. drainage, afforestation, over-grazing) can compromise the delivery of ecosystem services, with significant costs to society [4,5].

To monitor peatland condition, including vegetation cover and hydrology, this project we will use satellite Synthetic Aperture Radar (SAR), which 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 polarimetry (PolSAR), a cutting-edge radar technology. The advantage of PolSAR is that we can use the polarisation of the radar echo to obtain more images and therefore more information about objects in the scene [6]. In addition to using satellite data, we will be carrying out extensive experiments using ground radar which can simulate images obtained from satellites. Finally, we will make use of unmanned aerial vehicle (UAV; “drone”) based observations for field validation and rapid local assessment using low cost aircrafts. This will provide measurements related to the moisture content and vegetation cover of the peatlands.

A strong motivation for using satellite images is that we have entered a new era of freely available satellite data (e.g. the ESA Sentinel constellation missions [7]). 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. Although there is a richness in free data, we still face the challenge of interpreting information on peatlands over large areas on a regular basis to track their inter-seasonal and inter-annual dynamics.

The remote sensing development work will be accompanied by substantial fieldwork in Scotland with at least quarterly visits to peatlands of interest. We will be using water table loggers installed in several peatlands around Scotland (e.g. Flanders Moss) where regeneration has been carried out. If successful, the results will contribute to the monitoring and assessment of Peatland ACTION peatland restoration success.

Click on an image to expand

Image Captions

Flanders Moss as seen from the observation tower (credits: Nature Scot)

Methodology

Deliverables: In this project, we will set up a series of methodologies to provide weekly updates of peatland conditions (possibly water table) and soil moisture from images acquired from space. Work will focus on areas experiencing drastic changes in peatland condition following disturbance and recovery, land use change or restoration to develop remotely sensed products to identify areas in need of rapid intervention. We want also to develop a vulnerability index for peatlands

Novelty: PolSAR is a cutting edge technology capable of obtaining biophysical parameters of vegetation and soil. [6]. However, we are in urgent need of controlled experiments on the ground, performing the very first ground radar campaign for monitoring a raised bog. This 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 observations for leading actions.

Data (satellite): Archived PolSAR 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) and COSMO-Skymed comprising of varying wavelengths (L-band (23.6cm), C-band (5.6cm), and X-band (3cm)).

Data (ground): We will be using a ground radar built in the Stirling radar lab (based on a Vector Network Analyser architecture) to acquire images that emulate those acquired by satellites. This can be tuned at different frequencies and acquire data with polarimetric diversity. It can be easily transported and installed on a tripod and can acquire radar images of the bog when conditions are modified. For instance we could observe the change of signal when the water table is different, or perform experiments with metallic objects under the peat to observe the penetration of electromagnetic waves into the peat. This may require experiments in water wells too.

Data (drone): We will be using our UAV to collect multispectral observations 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. 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 [8]. The output of these algorithms will be used to train regression models (e.g. multiple regressions) and machine learning methodologies (e.g. Random Forest and Support Vector Machines).

Project Timeline

Year 1

Literature review of SAR, drone imaging, peatlands. Fieldwork collecting radar ground measurements and starting analysis of PolSAR data. Attendance of international training events. Target of submitting a journal paper on monitoring peatlands with PolSAR.

Year 2

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

Year 3

Use models to evaluate the sustainability of human activities based on temporal trends observed. Starting writing the thesis chapters. Expected submission of journal paper on sustainability assessment.

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; and (e) peatland hydrology and monitoring.

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) and Remote Sensing software; (e) peatland hydrology and ecology training.

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

References & further reading

[1] Ciais et al. 2013, Carbon and Other Biogeochemical Cycles. In: Stocker, et al. Climate Change 2013: The Physical Science Basis., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.;[2] Kimmel & Mander. 2010, Prog.Phys.Geogr. 34:491-514;[3] Waddington et al. 2015, Ecohydrology 8:113-127;[4] Parry et al. , 2014, J.Environ.Manage. 133:193-205;[5] IUCN. 2019, Commission of Enquiry on Peatlands: The State of UK Peatlands – an update, International Union for Conservation of Nature, Edinburgh;[6]: https://earth.esa.int/web/polsarpro/polarimetry-tutorial[7]: https://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Satellite_constellation[8]: Marino, A. and Hajnsek, I. (2014). A change detector based on an optimization with polarimetric SAR imagery. IEEE TGRS, 52(8).

Further Information

For additional information on the project please contact Dr Armando Marino, armando.marino@stir.ac.uk

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