Abstract. 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.

Abstract. 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., 2011a, b). The ISMN brings together in situ soil moisture measurements collected and freely shared by a multitude of organisations, harmonizes 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). 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 December 2020, the ISMN now contains data of 65 networks and 2678 stations located all over the globe, with a time period spanning from 1952 to present.The number of networks and stations covered by the ISMN is still growing and many of the data sets contained in the database continue to be updated. 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 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.

<p>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. </p><p>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.</p><p>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.</p><p>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.).</p><p>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.</p><p>In this session, we give an overview of the ISMN, its unique features and its benefits for validating satellite soil moisture products.</p>

<p><span>The International Soil Moisture Network (ISMN, </span><span></span><span>) is an international cooperation to establish and maintain an open-source global data hosting facility, providing in-situ soil moisture data as well as accompanying soil variables. This database is an essential means for validating and improving global satellite soil moisture products as well as land surface -, climate- , and hydrological models.</span></p><p><span>For hydrological validation, the quality of used in-situ data is essential. The various independent local and regional in situ networks often do not follow standardized measurement techniques or protocols, collect 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.</span></p><p><span>The ISMN was created to address the above-mentioned issues. 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. </span></p><p><span>Since its establishment in 2009 and with continuous financial support through the European Space Agency (ESA), the ISMN evolved into a widely used in situ data source growing continuously (in terms of data volume and users). Historic measurements starting in 1952 up to near–real time are available through the ISMN web portal. Currently, the ISMN consists of 60 networks with more than 2500 stations spread all over the globe. With a </span><span><span>steadily growing user community more than 3200 registered users strong</span></span><span> the value of the ISMN as a well-established and rich source of in situ soil moisture observations is well recognized. In fact, the ISMN is widely used in variety of scientific fields (e.g. climate, water, agriculture, disasters, ecosystems, weather, biodiversity, etc.). </span></p><p> <span>Our partner networks range from networks with a handful of stations to networks that are composed of over 400 sites, are supported with half yearly provider reports on statistical data about their network (e.g.: data download statistic, flagging statistic, etc.). </span></p><p><span>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 (GROW observatory ) collected by citizen scientists, holds the potential of closing this gap, thus providing new information and knowledge.</span></p><p><span>In this session , we want to give an overview of the ISMN, its unique features and its support of data provider, who are willing to openly share their data, as well as hydrological researcher in need of freely available datasets.</span></p>

<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>

<p>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.</p> <p>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).</p> <p>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.</p>

<p class="western" lang="en-US" align="justify"><span lang="fr-FR">The aim of this presentation is to report on recent advances concerning the satellite based soil moisture validation done through t</span>he ESA project “Fiducial Reference Measurement for Soil Moisture (FRM4SM)”<span lang="fr-FR">. T</span>he main objective<span lang="fr-FR"> of this </span>two years project (May 2021 - May 2023) <span lang="fr-FR">is </span>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), <span lang="fr-FR">it </span>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 (<span id="OBJ_PREFIX_DWT19829_com_zimbra_url" class="Object" role="link"><span id="OBJ_PREFIX_DWT19832_com_zimbra_url" class="Object" role="link">ISMN</span></span>). 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 (<span id="OBJ_PREFIX_DWT19830_com_zimbra_url" class="Object" role="link"><span id="OBJ_PREFIX_DWT19833_com_zimbra_url" class="Object" role="link">SMOS</span></span>) 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 (<span id="OBJ_PREFIX_DWT19831_com_zimbra_url" class="Object" role="link"><span id="OBJ_PREFIX_DWT19834_com_zimbra_url" class="Object" role="link">QA4SM</span></span>), targets to implement all created FRM protocols from ground measurement to validation methods created within the FRM4SM project.</p> <p class="western" lang="en-US" align="justify"> </p>

<p>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. </p><p>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.</p><p>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).</p><p>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.</p><p>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.).</p><p>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).</p><p>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).</p><p> </p>