In situ soil moisture data is used as the main reference for the validation of satellite soil moisture products. Although in situ measurements are often referred to as the “ground truth” and we have an understanding of the error sources, the magnitudes of the uncertainties associated with in situ measurements and methods to eliminate these uncertainties are hardly known. However, in order to achieve the best possible Return Of Investment (ROI) for a satellite mission, reliable and fully characterized in situ reference datatsets are crucial.ESA`s Fiducial Reference Measurement for Soil Moisture project (FRM4SM) was launched in 2021 to tackle the establishment of comprehensive and fully characterized, traceable uncertainty budgets for in situ soil moisture observations at the satellite footprint scale. The project aims to address the following scientific questions to facilitate the creation and exploitation of such Fiducial Reference Measurements (FRMs), using the International Soil Moisture Network (ISMN) as the in situ source and ESA’s Soil Moisture and Ocean Salinity (SMOS) mission as an example satellite product:(1) understand the status quo and means to establish an (SI-)traceable uncertainty budget for in situ soil moisture measurements(2) identify error sources that impact the in situ measurement(3) create quality indicators that allow to identify the most reliable “soil moisture FRMs” from the ISMN(4) verify and demonstrate the merit of these select soil moisture FRMs within validation case studies,(5) create protocols and procedures for the creation and use of such an FRM subset, which are built upon community=agreed standards and practices(6) integrate the established FRM dataset and all developed validation methods into the freely-accessible Quality Assurance for Soil Moisture (QA4SM) online validation serviceIn this presentation, we will introduce the FRM4SM project and highlight our latest achievements and ongoing developments. Furthermore, we will discuss future directions, and give insights into challenges that need to be overcome in order to achieve a traceable uncertainty budget calculation for in situ soil moisture data at the satellite footprint scale.

The Global Climate Observing System Essential Climate Variables (GCOS ECVs) requirements define a target threshold of 0.005 m³/m³ per decade for satellite soil moisture product stability. As admitted by GCOS, this threshold lacks robust justification in the scientific literature, prompting critical assessment. Moreover, no commonly-accepted method exists to assess satellite soil moisture product stability to begin with.In this study, we investigate the suitability of existing in situ soil moisture monitoring networks contained in the International Soil Moisture Network (ISMN) for stability assessment. The selection of such stable reference sites is based on two criteria: (i) sites that are considered “fiducial reference sites” as defined by the Fiducial Reference Measurements for Soil Moisture (FRM4SM) project; and (ii) sites that provide suitable temporal coverage for the time spans over which satellite product stability is required (i.e., 10 years or more). Using these select reference sites, we assess the stability of various common satellite soil moisture products (e.g., ASCAT, SMOS) using Theil-Sen slopes that are calculated for various validation metrics (e.g., median annual Pearson correlations or unbiased Root Mean Square Differences). In addition, we investigate the impact of data gaps and scarcity on the calculated stability metrics.Analyses were carried out using the the python toolbox for evaluating soil moisture observations (pytesmo; https://github.com/TUW-GEO/pytesmo). The goal is to include stability metrics as part of the QA4SM online validation service in the future (https://qa4sm.eu/).

The purpose of the Quality Assurance for Soil Moisture (QA4SM) service is to provide a central, cloud-based platform for soil moisture data validation. QA4SM is an easy-to-use graphical web interface that caters to both producers of satellite soil moisture data as well as users of such products. It provides the means to assess quality requirements for satellite products, as defined by the Global Climate Observing System (GCOS) for example, all the way to the validation and (inter)comparison of satellite data against (fiducial) reference measurements and land surface model data. QA4SM delivers reproducible validation results based on a consistent methodology and community-agreed best practices. Numerous well-known data products are readily available and periodically kept up to date. This includes satellite products of different levels from SMOS, SMAP, ASCAT, and Sentinel-1 missions. Further, data products from both the Copernicus Climate Change Services (C3S) and the ESA Climate Change Initiative (CCI) are provided, too. Also included is data from the International Soil Moisture Network (ISMN) and reanalysis model data such as NASA’s GLDAS-Noah or ECMWF’s ERA5(-Land). Beyond that, users can upload custom datasets to the platform in different formats.QA4SM offers a broad palette of processing tools such as: the filtering of datasets according to flags or versions; spatial and temporal scaling options; the selection of spatial and temporal subsets; temporal matching methods; and different metric and anomaly calculations for up to six datasets simultaneously. Means for a subsequent publication of the results, including the generation of a digital object identifier (DOI), are implemented as well. In this talk, we will present the functionalities and tools provided by QA4SM, and report on recent updates, the latest features, and planned future developments of the platform. Both scientific and technical aspects will be discussed.

Evaluating the uncertainties of satellite soil moisture (as SMOS or SMAP) is crucial for enhancing our comprehension of climate mechanisms, such as the water cycle or the energy balance. The commonly used method is to evaluate the agreement between the satellite data and a reference, which are often ground measurements. However, the measurand in the present case is soil moisture at the satellite footprint scale, which means a much larger spatial and temporal scale than the in situ one. Various methods are employed to address these scale mismatches, such as multiple spatial sampling with in situ measurements within the satellite footprint (dense networks with strategic location installation) or the probes’ classification with representativeness indicators (based on triple collocation analysis, for example). Within ESA's Fiducial Reference Measurement for Soil Moisture project (FRM4SM), we propose to investigate the level of heterogeneity within the SMOS satellite footprint due to its influence on the complexity of the retrieval model and also its influence on the scale mismatch with the reference. To do so, various indices are developed to i) quantify the footprint heterogeneity in terms of the spatial distribution of hydro-geophysical parameters, and ii) analyse the impact on the retrieval quality. We present the analysis using indices of diversity of surface conditions (Shannon and Gini indices), and indices based on the level of similarities of hydro-geophysical conditions between the probes’ environment and the satellite footprint. Results show that even though the Shannon index is not significantly related to the soil moisture retrieval performances, the index based on the similarities of surface conditions better correlates with the retrieval performances.

This study attempts to derive the uncertainty of the soil moisture estimation from passive microwave satellite mission at global scale. To do so, the approach is based on the sensitivity of the Soil Moisture and Ocean Salinity (SMOS) soil moisture retrieval quality to the land surface characteristics within its footprint (presence of forest, topography, open water bodies, sand, clay, bulk density and soil organic carbon content). First, we performed a global assessment of SMOS using in situ measurements from the International Soil Moisture Network (ISMN) as reference, with more than 1900 ISMN stations and 10 years of SMOS data. This assessment shows that the ubRMSD scores vary greatly between locations (with a mean of 0.074 m3m−3 and an interquartile range of 0.030 m3m−3). Second, the scores are analyzed for different surface conditions within the satellite footprint. The best agreement between the ground measurement and SMOS time series are obtained for low forest cover, low topographic complexity, and marginal presence of open water bodies within the SMOS footprint. Soil parameters also have an impact, with better scores for sandier soils with a high bulk-density and low soil organic carbon content. Finally, we propose to extrapolate the obtained relationships, using a multiple linear regression, in order to derive a global map of SMOS uncertainties based on surface conditions. This map of predicted uncertainties show a diverse range of ubRMSD values across the globe (with a mean of 0.076 m3m−3 and an interquartile range of 0.031 m3m−3) depending on the surface characteristics. At the ISMN site location, the predicted ubRMSD shows similar results than the comparison between SMOS and the in situ measurements. The map of predicted SMOS ubRMSD represents an upper bound estimate of the SMOS uncertainty, as it includes the uncertainties of the in situ sensor measurements and the scale mismatch. Further investigations will focus on the different components of this uncertainty budget to obtain a better assessment of the absolute uncertainties of SMOS soil moisture retrievals across the globe.

Data in today's dynamic world undergoes constant change and evolution, spanning various formats such as text, websites, tweets, and sensor readings. Storing and referencing these diverse data types pose significant challenges due to data movement, changes in content or structure, and limited availability. Efficient data identification is crucial for speeding up scientific discovery and result validation, especially when data accessibility is guaranteed. Recent years have witnessed progress in data citation practices, with conferences mandating the inclusion of utilized and generated data. However, existing solutions primarily cater to static datasets, rendering them ineffective for dynamically evolving ones. This paper addresses this gap by providing a tailored dynamic data citation prototype for the International Soil Moisture Network, one of the largest scientific in situ soil moisture databases. Our work encompasses the implementation and evaluation of different data versioning strategies and a query store architecture that enables the citation, reproducibility, and verification of large sets of SQL queries to recreate data requests by users. By applying the RDA Dynamic Data Citation Guidelines, we assess the necessary needs for such a system and further measure the performance and storage impact of our proposed approaches.

<p>To this day, in situ soil moisture data is viewed as ground truth by the satellite soil moisture (SSM) community. In general, little is still commonly known regarding the traceability of ground measurement uncertainty and their overall in uncertainty budget, which can impact satellite SSM product quality assessments.</p> <p>Within ESA’s “Fiducial Reference Measurement for Soil Moisture (FRM4SM, May 2021 - May 2023)” project, objectives are set towards building fully characterized and traceable (i.e., fiducial) in situ measurements following community-agreed guidelines from the GEOS/CEOS Quality Assurance for Soil Moisture (QA4EO) framework. These so called “fiducial reference data” (FRM) should have associated Quality Indicators (QI) attached to evaluate their fitness for purpose building upon agreed reference standards (SI if possible). Moreover, such data should be easily and openly accessible, validation case studies should demonstrate their utility and reliability, and protocols and procedures should be established for the usage of such FRM datasets to make scientific studies intercomparable and reproducible.</p> <p>As part of the FRM4SM project, the following questions were addressed using the International Soil Moisture Network (ISMN) as a ground reference database and the Soil Moisture and Ocean Salinity (SMOS) mission as an example satellite product:</p> <p>(1) What makes “fiducial reference data” fiducial?</p> <p>(2) Is the creation of a globally-representative FRM subset already feasible for SSM?</p> <p>(3) What are the current limitations of in situ observations that limit fiduciality?</p> <p>(4) What is needed to create a full traceability chain from in situ point measurements to the satellite footprint scale?</p> <p>In this presentation, we will discuss these questions in detail and report on related findings of the FRM4SM project.</p>

The aim of this presentation is to report on recent advances concerning the satellite based soil moisture validation done through the ESA project “Fiducial Reference Measurement for Soil Moisture (FRM4SM)”. The main objective of this two years project (May 2021 - May 2023) is to study the means to inform on the confidence in soil moisture data products for the whole duration of a satellite mission. Composed of three international partners (AWST, CESBIO and TU WIEN), it aims at the identification and creation of standards for independent, fully characterized, accurate and traceable (i.e., fiducial) in situ soil moisture reference measurements with corresponding independent validation methods and uncertainty estimations for a satellite mission. The ground reference data is drawn from the International Soil Moisture Network (ISMN). New quality indicators are created to better characterize the aptness of ISMN measurements for satellite soil moisture validation, and protocols provided to identify a select set of fiducial reference data. The satellite part, in charge of independent validation methods, focuses efforts towards the Soil Moisture Ocean Salinity (SMOS) mission from ESA. Finally, the easy-to-use interface for the comparison of satellite soil moisture data against land surface models and in situ data, the Quality Assurance for Soil Moisture (QA4SM), targets to implement all created FRM protocols from ground measurement to validation methods created within the FRM4SM project.

Soil moisture is recognized as an Essential Climate Variable (ECV), because it is crucial to assess water availability for plants and hence food production. Having long time series of freely available and interoperable soil moisture data with global coverage enables scientists, farmers and decision makers to detect trends, assess the impacts of climate change and develop adaptation strategies.The collection, harmonization and archiving of in situ soil moisture data was the motivation to establish the International Soil Moisture Network (ISMN) at the Vienna University of Technology in 2009 as a community effort. Based on several project funding periods by the European Space Agency (ESA), the ISMN became an essential means for validating and improving global land surface satellite products, climate and hydrological models.Permanent funding for the ISMN operations was secured through the German Government (Ministry of Digital and Transport) and therefore the ISMN has successfully migrated at the end of 2022 to its new host the International Centre for Water Resources and Global Change (ICWRGC) and the German Federal Institute of Hydrology (BfG). Furthermore, the ISMN was recognized by WMO in their latest State of Global Water Resources report.To improve the data service delivery, ISMN users can now benefit from a newly developed dataviewer which features functionalities such as data archives and advanced filter options (e.g. for climate and landcover types, for data quality) developed in synergies with the ESA project Fiducial Reference Measurements for Soil Moisture (FRM4SM). This presentation aims at showcasing these latest upgrades as well as new network contributions to the ISMN.

Soil moisture is recognized as an Essential Climate Variable (ECV) because it is crucial for assessing water availability for plants and hence food production. Having long time series of freely available soil moisture data with global coverage enables scientists, farmers and decision makers to detect trends, assess the impacts of climate change, and develop adaptation strategies. The collection, harmonization and archiving of in situ soil moisture data was the motivation to establish the International Soil Moisture Network (ISMN) at TU Wien, with the financial support of the European Space Agency (ESA), in 2009 as a community effort. The ISMN became an essential source for validating and improving global satellite products, and climate, land surface, and hydrological models. In 2021 permanent funding for the ISMN operations was secured through the German Government (Ministry of Digital and Transport). The transfer of the ISMN to its new host, i.e., the International Centre for Water Resources and Global Change (ICWRGC)/German Federal Institute of Hydrology (BfG), took place during 2021/2022. The takeover posed the challenge to migrate an operational service between two different teams, locations/hardware and organisations. Finally, the ISMN started serving data from its new host in December 2022 while keeping the service continuously running throughout the migration. In parallel the team in Vienna developed and launched a new dataviewer. This presentation aims at showcasing new ISMN features as well as recent data contributions as well as next evolution of the ISMN based on synergies and science outcome of the Research and Development activities performed by ESA in the context of the Fiducial Reference Measurements for Soil Moisture (FRM4SM) project.

Quality assessment is an integral part of creating climate data records. Producers of satellite based records want to evaluate whether their products fulfill certain quality requirements, such as the ones set by the Global Climate Observing System (GCOS) of the World Meteorological Organization (WMO) or by the Committee on Earth Observation Satellites (CEOS). Users of these data, on the other hand, are usually interested in their fitness-for-purpose in terms of specific applications, temporal/spatial subsets, and how different data sets of the same variable compare to each other.Quality Assurance for Soil Moisture (QA4SM) is an online validation service for (inter)comparing soil moisture records and assessing their quality, incorporating best practices, in a standardized, traceable way via an easy-to-use graphical user interface. The processing chain includes automatic preprocessing (filtering, temporal/spatial matching, scaling) of input data and computation of a set of quality metrics (e.g., correlation, bias, signal-to-noise-ratio). It provides an open and flexible framework in which users can upload their own data for comparison to state-of-the-art records that are already integrated in the service. These include reference data from the International Soil Moisture Network (ISMN), reanalysis data from ERA5 and GLDAS Noah, and various satellite based records such as SMOS, SMAP, Sentinel-1, ESA CCI, and C3S. In this presentation we give insight into the scientific and technical background of developing a cloud-based validation service and its current capabilities. We explain the advantages a service like this has, and how it can benefit users of climate data records with minimal effort.The service was launched as part of the Quality Assurance for High Spatial and Temporal Resolution Soil Moisture Data (QA4SM-HR) project through the Austrian Research Promotion Agency (FFG) and is currently developed within the framework of the European Space Agency’s Fiducial Reference Measurement for Soil Moisture (FRM4SM) project. It can be accessed at: https://qa4sm.eu

For over a decade, the International Soil Moisture Network (ISMN) has been providing free in-situ soil moisture data for validating and improving global satellite soil moisture products, weather prediction, agricultural activities, research and training as well as for the development of hydrological models. The ISMN is a community-wide effort and aggregates soil moisture observations from several organizations, harmonizes them and provides a centralized platform where end users can access them. Presently, the ISMN consists of over 72 soil moisture networks and more than 2800 stations spread across the globe. For more than a decade, the ISMN has been funded by European Space Agency and established, developed and maintained by Vienna University of Technology (TU Wien), Austria. For continuing development, outreach and maintenance of the ISMN, a sustainable and long-term support is required. In order to achieve such long-term support, the ISMN will be transferring to the German Federal Institute of Hydrology (BfG) and connected International Center for Water Resources and Global Change (ICWRGC) in Germany within 2022. While BfG and ICWRGC (operating under the auspice of UNESCO and WMO) will host and maintain the ISMN data facility, long-term financial support will be provided by the German Federal Institute of Hydrology through the Federal Ministry of Digital Infrastructure and Transport. The ICWRGC has being coordinating the Global Terrestrial Network – Hydrology (GTN-H) as well as Global Environment Monitoring System for Freshwater (GEMS/Water Data Center) for several years. Hence, the center has an extensive experience, resources as well as scientific advisory support for a long-term sustainable operation and maintenance of the ISMN. As we look forward to a new future of ISMN, we also want to maintain, even improve on the great community support the project has received. Therefore, our presentation aims to give an overview of the contribution of ISMN to research and training development, provides recent updates regarding the data service and ongoing technical developments. Furthermore, we want to introduce the new host as well as presenting the future outlook of the ISMN, which include setting up scientific advisory board with members from relevant UN organizations, key data providers and data users that would help promote and develop the ISMN further. Through the connection to UN organizations, member states could be encouraged to share their operational soil moisture data with the ISMN for continuing support of global climate and water resources observations. We also look forward to gaining new collaborations that will help in extending the ISMN database, initiate discussion between stakeholders to improve visibility and scientific advancement of the ISMN as well as promoting the importance of soil moisture within global earth observations data products.

With its steadily growing provider and user community (4000 active users), the International Soil Moisture Network (ISMN, https://ismn.earth) is a unique centralized global data hosting facility, making in-situ soil moisture data easily and freely accessible. The main goal of the ISMN in the past decade was to build up the harmonized and quality-controlled in-situ soil moisture source it is today. The ISMN provides benchmark data for several operational services such as ESA CCI Soil Moisture, the Copernicus Climate Change (C3S) and Global Land Service (CGLS), and the online validation tool QA4SM (https://qa4sm.eu). ISMN data is widely used for support of algorithm development and validation of different satellites, evaluation of soil moisture products, as a training set for various data-driven approaches, model developments, drought monitoring and diverse meteorological applications (Dorigo et. al 2021). In this presentation, we will provide an overview of the ISMN scientific achievements accomplished in the last decade, show recent scientific and service developments, and present foreseen future developments. We provide a review of hundreds of papers making use of ISMN data to identify major scientific breakthroughs facilitated through the ISMN. We also identify current limitations in data availability, functionality and challenges in data usage (e.g., in-situ data inclusion in data sparse regions, in-situ data inclusion from official governmental observation networks, data and measurement traceability, etc.). One of the major successes has been the achievement of long-term financial support for the ISMN through the German Ministry of Digital Infrastructure and Transport. Therefore, the ISMN operations is currently transferred from Vienna Austria (TU Wien) to the new host in Koblenz, Germany (International Center for Water Resources and Climate Change - ICWRGC, Federal Institute for Hydrology – BfG). This evolution not only opens up a stable future for the ISMN but also gives TU Wien once more the opportunity to focus on the scientific development of the ISMN as currently proceeded within the ESA project “Fiducial Reference Measurement for Soil Moisture (FRM4SM)”. Within this two-year project (May 2021 – May 2023) the goal is also to identify and create standards for independent, fully characterized, accurate and traceable in-situ soil moisture measurements (from the ISMN) with corresponding uncertainty estimations and independent validation methods (inserted in the QA4SM service: https://qa4sm.eu).

The International Soil Moisture Network (ISMN, ) is a unique centralized global and open freely available in-situ soil moisture data hosting facility. Initiated in 2009 as a community effort through international cooperation (ESA, GEWEX, GTN-H, WMO, etc.), with continuous financial support through the European Space Agency (formerly SMOS and IDEAS+ programs, currently QA4EO program), the ISMN is more than ever an essential means for validating and improving global satellite soil moisture products, land surface -, climate- , and hydrological models.Following, building and improving standardized measurement protocols and quality techniques, the network evolved into a widely used, reliable and consistent in-situ data source (surface and sub-surface) collected by a myriad off data organizations on a voluntary basis. 66 networks are participating (status January 2021) with more than 2750 stations distributed on a global scale and a steadily increasing number of user community, > 3200 registered users strong. Time series with hourly timestamps from 1952 – up to near real time are stored in the database and are available through the ISMN web portal for free (), including daily near-real time updates from 6 networks (~ 1000 stations).About 10’000 datasets are available through the web portal and the number of networks and stations covered by the ISMN is still growing as well as most datasets, that are already contained in the database, are continuously being updated.The ISMN evolved in the past decade into a platform of benchmark data for several operational services such as ESA CCI Soil Moisture, the Copernicus Climate Change (C3S), the Copernicus Global Land Service (CGLS), the online validation service Quality Assurance for Soil Moisture (QA4SM) and many more applications, services, products and tools. In general, ISMN data is widely used in a variety of scientific fields with hundreds of studies making use of ISMN data (e.g. climate, water, agriculture, disasters, ecosystems, weather, biodiversity, etc.).In this session, we want to inform ISMN users about the evolution of the ISMN over the past decade, including a description of network and dataset updates and new quality control procedures. Besides, we provide a review of existing literature making use of ISMN data in order to identify current limitations in data availability, functionality and challenges in data usage in order to help shape potential future modes in operation of this unique community- based data repository.

The International Soil Moisture Network (ISMN, https://ismn.earth) is international cooperation to establish and maintain a unique centralized global data hosting facility, making in-situ soil moisture data easily and freely accessible (Dorigo et al., 2021). Initiated in 2009 as a community effort through international cooperation (ESA, GEWEX, GTN-H, GCOS, TOPC, HSAF, QA4SM, C3S, etc.), the ISMN is an essential means for validating and improving global satellite soil moisture products, land surface-, climate-, and hydrological models. The ISMN is a widely used, reliable, and consistent in-situ data source (surface and sub-surface) collected by a myriad of data organizations on a voluntary basis. The in-situ soil moisture measurements are collected, harmonized in terms of units and sampling rates, advanced quality control is applied and the data is then stored in a database and made available online, where users can download it for free. Currently, 71 networks are participating with more than 2800 stations distributed on a global scale and a steadily increasing number of user communities. Long term time series with mainly hourly timestamps from 1952 – up to near-real-time are stored in the database, including daily near-real-time updates. Besides soil moisture in our database are stored other meteorological variables as well (air temperature, soil temperature, precipitation, snow depth, etc.). The ISMN provides benchmark data for several operational services such as ESA CCI Soil Moisture, the Copernicus Climate Change (C3S) and Global Land Service (CGLS), and the online validation tool QA4SM. ISMN data is widely used in a variety of scientific fields (e.g., climate, water, agriculture, disasters, ecosystems, weather, biodiversity, etc). To validate the land surface representations of meteorological forecasting models soil moisture from the ISMN has often been used. The development of various generations of TESSEL models used both in the Integrated Forecasting Systems and reanalysis products of ECMWF, greatly profited from soil moisture and temperature data from the ISMN. Using ISMN data several studies assessed the soil moisture skill of the Weather Research and Forecasting Model (WRF) and assessed the forecast skill or new implementations of numerical weather prediction models. We greatly acknowledge the financial support provided by ESA through various projects: SMOSnet International Soil Moisture Network, IDEAS+, and QA4EO. To ensure a long-term funding for the ISMN operations, several ideas were perused together with ESA. A partner for this task could be found within the International Center for Water Resources and Global Change (ICWRGC) hosted by the German Federal Institute of Hydrology (BfG). In this session, we want to give an overview and future outlook of the ISMN, highlighting its unique features and discuss challenges in supporting the hydrological research community in need of freely available, standardized, and quality-controlled datasets.

In 2009, the International Soil Moisture Network (ISMN) was initiated as a community effort, funded by the European Space Agency, to serve as a centralised data hosting facility for globally available in situ soil moisture measurements (Dorigo et al., 2011b, a). The ISMN brings together in situ soil moisture measurements collected and freely shared by a multitude of organisations, harmonises them in terms of units and sampling rates, applies advanced quality control, and stores them in a database. Users can freely retrieve the data from this database through an online web portal (https://ismn.earth/en/, last access: 28 October 2021). Meanwhile, the ISMN has evolved into the primary in situ soil moisture reference database worldwide, as evidenced by more than 3000 active users and over 1000 scientific publications referencing the data sets provided by the network. As of July 2021, the ISMN now contains the data of 71 networks and 2842 stations located all over the globe, with a time period spanning from 1952 to the present. The number of networks and stations covered by the ISMN is still growing, and approximately 70 % of the data sets contained in the database continue to be updated on a regular or irregular basis. The main scope of this paper is to inform readers about the evolution of the ISMN over the past decade, including a description of network and data set updates and quality control procedures. A comprehensive review of the existing literature making use of ISMN data is also provided in order to identify current limitations in functionality and data usage and to shape priorities for the next decade of operations of this unique community-based data repository.

QA4SM validation of soil moisture data: ESA CCI SM combined v05.2 vs ISMN 20191211 global. URL: https://qa4sm.eu/result/5f6ae4c5-5115-4022-b489-99f4dda1089f/. Produced on QA4SM (https://qa4sm.eu)

The International Soil Moisture Network (ISMN, https://ismn.geo.tuwien.ac.at/) is an international cooperation to establish and maintain a unique centralized global data hosting facility, making in situ soil moisture data easily and freely accessible. This database is an essential means for validating and improving global satellite soil moisture products, land surface -, climate- , and hydrological models. In situ measurements are crucial to calibrate and validate satellite soil moisture products. For a meaningful comparison with remotely sensed data and reliable validation results, the quality of the reference data is essential. The various independent local and regional in situ networks often do not follow standardized measurement techniques or protocols, collecting their data in different units, at different depths and at various sampling rates. Besides, quality control is rarely applied and accessing the data is often not easy or feasible. The ISMN has been created to address the above-mentioned issues and is building a stable base to assist EO products, services and models. Within the ISMN, in situ soil moisture measurements (surface and sub-surface) are collected, harmonized in terms of units and sampling rates, advanced quality control is applied and the data is then stored in a database and made available online, where users can download it for free. Founded in 2009, the ISMN has grown to a widely used in situ data source including 61 networks with more than 2600 stations distributed on a global scale and a steadily growing user community > 3200 registered users strong. Time series with hourly timestamps from 1952 – up to near real time are stored in the database and are available through the ISMN web portal, including daily near-real time updates from 6 networks (> 900 stations). With continuous financial support through the European Space Agency (formerly SMOS and IDEAS+ programs, currently QA4EO program), the ISMN evolved into a platform of benchmark data for several operational services such as ESA CCI Soil Moisture, the Copernicus Climate Change (C3S), the Copernicus Global Land Service (CGLS) and the online validation service Quality Assurance for Soil Moisture (QA4SM). In general, ISMN data is widely used in a variety of scientific fields (e.g. climate, water, agriculture, disasters, ecosystems, weather, biodiversity, etc.). About 10’000 datasets are available through the web portal. However, the spatial coverage of in situ observations still needs to be improved. For example, in Africa and South America only sparse data are available. Innovative ideas, such as the inclusion of soil moisture data from low cost sensors (eventually) collected by citizen scientists, holds the potential of closing this gap, thus providing new information and knowledge. In this session, we give an overview of the ISMN, its unique features and its benefits for validating satellite soil moisture products.