Background

Soils, the upper layer of the Earth, is a mixture of organic matter, minerals, gases, liquids and organisms, and a key for life. Including peat and litter, they represent the largest carbon pool on land. It is the substrate allowing plants to grow, a means to water storage and purification, a modifier of the Earth’s atmosphere and a habitat for organisms. Soil processes are impacting ecosystems functioning and food, fibre and timber production. It regulates climate, the hydrological and nutrient cycle and provide resilience against floods and droughts. Several targets of Sustainable Development Goals (SDG) depend on healthy and functional soils.

Pressure on soils such as climate change, industrialization and urbanization, intensive agriculture and livestock farming, etc. lead to soil degradation (erosion, sealing, contamination, loss of organic matter, ….). Careful monitoring of this finite, non-renewable resource is therefore mandatory as stressed by many national and international treaties and policies, e.g. the Sustainable Development Goals, the UNCCD Land Degradation Neutrality, the RAMSAR Convention, the EU Thematic Strategy for Soil Protection and the Common Agricultural Policy, etc.

Publish IPCC Report on Land and Climate ¹ stresses that sustainable land management can be improved by increasing the availability and accessibility of data and information relating to the effectiveness, co-benefits and risks of emerging response options and increasing the efficiency of land use (high confidence). Some response options (e.g., improved soil carbon management) have been implemented only at small-scale demonstration facilities and knowledge, financial, and institutional gaps and challenges exist with upscaling and the widespread deployment of these options (medium confidence).

As emphasized by FAO ², Soil Organic Carbon (SOC) is the main component of Soil Organic Matter (SOM). As an indicator for soil health, SOC is important for its contributions to food production, mitigation and adaptation to climate change, and the achievement of the Sustainable Development Goals. A high SOM content provides nutrients to plants and improves water availability, both of which enhance soil fertility and ultimately improve food productivity. Moreover, SOC improves soil structural stability by promoting aggregate formation which, together with porosity, ensure sufficient aeration and water infiltration to support plant growth. With an optimal amount of SOC, the water filtration capacity of soils further supports the supply of clean water. Through accelerated SOC mineralization, soils can be a substantial source of greenhouse gas (GHG) emissions into the atmosphere. Although the overall impact of climate change on SOC stocks is very variable according to the region and soil type, rising temperatures and increased frequency of extreme events are likely to lead to increased SOC losses.

Within the Framework of the United Nations Framework Convention on Climate Change (UNFCCC), international agreements such as the Kyoto Protocol and the Paris Agreement have set the rules for GHG emission targets, as well as the necessity to regularly report on anthropogenic GHG emissions. As part of these efforts, accurate inventories on emissions due to SOC stock changes should be reported. The Intergovernmental Panel on Climate Change (IPCC) provides guidelines for measuring, reporting and verifying national SOC stock inventories following the Monitoring, Reporting and Verifying (MRV) Framework which ensures that these inventories fulfill the criteria of completeness, transparency, consistency, accuracy and thus comparability. To achieve greater specificity and accuracy, improved methods are required to measure, account, monitor and report on this specific carbon pool.

Spaceborne Earth Observation Data

Space-based EO systems provide a means to support the monitoring of some soil chemical and physical properties, directly or indirectly, through the interaction of radiance fields with the (mainly upper) soil layer (topsoil) as shown by many research projects. However, space-based EO data together with in-situ measurements and modelling are hardly been used today in an operational manner by national and international organizations with the mandate to map, monitor and report on soils. This may be related to the lack of adequate, available space-borne EO data (spectral and temporal coverage, restricted data access) as well as the lack of available processing capabilities. With the advent of operational EO systems such as the European Union Copernicus Program (including the high priority Copernicus expansion missions), the free and open EO data policies as well as cloudbased access and processing capabilities (e.g. DIAS) an EO based Soil Monitoring System appears feasible today.

A user consultation workshop on space-based EO tools for mapping and monitoring soils was organized by ESA with the aim to bring together stakeholders from the policy and user domain with remote sensing experts to discuss the necessary steps to develop such a system. The workshop took place from 02 – 03 July 2019 at ESA ESRIN, Frascati, Italy.

Following the findings and recommendation given at this workshop, the WORLDSOILS study has the overall objective:

To develop in close cooperation with users and stakeholders a global Earth ObservationSoil Monitoring System on a suitable cloud environment utilizing open source and information available from operational, in situ and reference data and additional variables and/or indices derived from EO data together with blending and modelling techniques. The development shall be based on monitoring top soil organic carbon (SOC) and implemented in a modular way allowing its future extension to additional soil indices. The system’s grid resolution supported by appropriate covariate information shall be 100m x 100m globally and 50m x 50m over Europe, shall provide appropriate confidence metrics and shall allow assessing temporal changes of the global top soil layer at least once per year.

In this context it is anticipated that an Earth Observation Soil Monitoring System will provide essential baseline information for manifold downstream research, institutional and commercial applications as e.g. for the implementation of urgently needed soil management systems and as such supporting national and international policy making and monitoring.