Sajedeh Behnia

Abstract

The Copernicus Sentinel-3 Surface Topography Mission (S3 STM) provides critical surface elevation information for inland waters, sea ice, and land ice. This valuable data is acquired through its high-resolution radar altimeter and a unique orbit that reaches the polar regions. To ensure reliable measurements and maximize the mission's benefits, adequate validation is essential. This process involves comparing the mission's geophysical retrieval methods, processing algorithms, and corrections against independent observations known as Fiducial Reference Measurements (FRM). The St3TART project addresses the need for an operational framework for the provision of FRM to support validation activities and foster the exploitation of the Sentinel-3 SAR altimeter Hydro-Cryo Thematic data products. The project tackles the specific challenges associated with three types of surfaces: inland waters, sea ice and land ice. To achieve this, St3TART sets forth several objectives, including the identification and operation of super and opportunity sites, the acquisition, processing, and delivery of FRM for Calibration / Validation (Cal/Val) activities, and the characterization of uncertainties 171 associated with each FRM data product and measurand. It also involves the exploitation of FRM for Cal/Val activities, and the preparation of a roadmap for future Altimetry missions beyond S3 STM, focusing on the Cryosphere and Hydrology. These achievements pave the way for the successful implementation of operational FRM provision, ultimately contributing to the Sentinel-3 mission's goal of delivering accurate and reliable Earth observation data. We will present the project's objectives, tools, accomplishments, and future directions.

Abstract

Validation, including the determination of measurement uncertainties, is a key component of a satellite mission. Without adequate validation of the geophysical retrieval methods, of the processing algorithms and the corrections , the computed geophysical parameters derived from satellite measurements cannot be used with confidence. In this context, and in anticipation of the operational delivery of dedicated inland water products based on Copernicus Sentinel-3 measurements, the ESA St3TART project (Sentinel-3 Topography mission Assessment through Reference Techniques), prepared a roadmap and provided a preliminary proof of concept for the operational provision of Fiducial Reference Measurements (FRM) in support of the validation activities of the Copernicus Sentinel-3 (S3) radar altimeter over land surfaces of interest (inland water bodies, sea ice and land ice). In the framework of this project, the activities related to hydrology include a review of existing methodologies and associated ground instrumentation for validating and monitoring the performance and stability of the Sentinel-3 altimeter measurement via FRM. Methodologies and procedures have been defined considering the errors and uncertainties coming from 151 the measurements of in-situ sensors, satellite measurements and the environment of the validation site. Based on these protocols and procedures, a roadmap has been prepared for the operational provision of FRM to support the validation activities and foster exploitation of the Sentinel-3 SAR altimeter Land data products, over inland waters. Then, field campaign implementation and realization have been performed as demonstrators based on the procedures and protocols defined in the roadmap. In this project, a comprehensive review of altimeter uncertainties over inland water bodies was carried out on the basis of a literature review, leading to the identification of the different sources of error with their associated uncertainty level. A full review of all in-situ sensors that have been used for many years for Cal/Val activities for inland waters has also been performed, combined with an analysis of innovative sensors that can fulfil the needs and potentially be used in the framework of the St3TART project. Cal/Val “super-sites” have been carefully selected to implement the roadmap for operational FRM provision. Several campaigns have been performed on the different super sites. In addition of the super sites, opportunity sites from existing national hydrological networks have been studied to significantly increase the number of FRM. Finally, comparison with Sentinel-3 data and FRM have been conducted on all the super sites and the opportunity sites. We propose here to present the final results of these hydrology activities. A Follow-on of this project has been published by ESA. This new project aims to implement the RoadMap defined in the St3TART project. The consortium that worked on St3TART answered to this call. If the project is won, results from the regular production of FRM will be presented.

Abstract

The Copernicus Sentinel-3 Surface Topography Mission (STM) Land Altimetry provides valuable surface elevation information over inland waters, sea ice, and land ice, thanks to its synthetic aperture radar (SAR) altimeter and its orbit that covers high-latitude polar regions. To ensure that these measurements are reliable and to maximise the return on investment, adequate validation of the geophysical retrieval methods, processing algorithms, and corrections must be performed using independent observations. The EU-ESA project St3TART (started July 2021) aims to generalise the concept of Fiducial Reference Measurements (FRMs) for the Copernicus Sentinel-3 STM. This work has gathered existing data, made new observations during field campaigns, and ensured that these observations meet the criteria of FRM standards so that they can be used to validate Sentinel-3 STM Land Altimetry products operationally. A roadmap for the operational provision of the FRM, including the definition, consolidation, and identification of the most relevant and cost-effective methods and protocols to be maintained, supported, or implemented, has been developed. The roadmap includes guidelines for SI traceability, definitions of FRM measurement procedures, processing methods, and uncertainty budget estimations.