H2020 Copernicus CalVal Solution CCVS

The objective of the Copernicus H2020 Cal/Val Solution (CCVS) project is to define a holistic solution for all Copernicus Sentinel missions to overcome current limitations for both current and upcoming Sentinel-missions. This includes improved calibration of currently operational or planned Copernicus Sentinel sensors and the validation of Copernicus core products generated by the payload ground segment. While high-resolution optical missions are out of scope of the project, most of the recommendations coming from the project could be applicable or beneficial to these missions. This presentation will focus on those aspects and highlight possible synergies between Copernicus missions and high-resolution missions. The first aspect concerns R&D on models. Models of natural targets (PICS, Moon, Deep Convective Clouds) need to be further improved in terms of spectral coverage, SI traceability and uncertainty estimates. Validation methodologies using models of complex scenes (e.g. urban or vegetated scenes) with 3D Radiative Transfer should be developed. Progress on atmospheric Radiative Transfer Models is critical to improve uncertainty of surface reflectance measurements. Development of open-source models and cross-comparison activities should be encouraged, and community-agreed guidelines on best practices for modelling should be issued. Validation of surface reflectance is currently limited by the lack of suitable reference measurements (FRM). The CCVS project supports the development of an operational network of automatic hyperspectral radiometers on a set of representative and fully characterized sites (including BRDF and spatial homogeneity). The measurements should be SI traceable and provided with uncertainties. These sites should be regularly compared with a well characterised travelling standard that is controlled by across network body. Such network could be of interest for VHR-missions for the radiometry CalVal activities. Regarding geometry CalVal, in addition to the project support of a public reference grid such as the Sentinel-2 GRI at Level-1C, the project identified a lack of suitable geometric reference for nigh-time thermal infra-red imaging. R&D activities should explore the possible use of reference features such as gas flares or contrasted scenes (water/land interfaces). Finally, the reliability of cloud and cloud shadow masks is an important factor for the quality of optical surface measurements. Therefore, any improvement on the masking algorithms would be an asset to the VHR-missions products. To achieve this objective, it could be useful to develop a public cloud mask reference database and to harmonize validation methodologies

Ground-based measurements for validation of L2A-products

Multispectral Copernicus Sentinel-2 and hyperspectral DESIS and EnMAP missions serve for observation of land-cover change and deriving biophysical variables related to agriculture and forestry, monitor coastal and inland waters and are useful for risk and disaster mapping. Level-2A (L2A) data contain Bottom-of-Atmosphere (BOA) surface reflectance (SDR) products together with Aerosol Optical Thickness (AOT) and Integrated Water Vapour (WV) maps. A pre-condition for validation of SDR, AOT and WV data are in-situ measurements collocated spatially and in time with Satellite overpasses over the test site. AERONET provides such data for validation of AOT and WV retrievals for a large number of locations around the globe. Similarly, for the validation of SDR, permanently operating stations with standardized equipment are required. Such sites like the established RadCalNet sites have the advantage to provide data for each cloud screened satellite overpass. However, sites with permanent operating instruments measuring SDR are focusing on few homogeneous sites with typically low AOT, which are perfectly suitable for radiometric Cal/Val. They don’t offer the diversity of land surface types and aerosol conditions necessary for validation of L2A-products. Therefore, this validation data source has to be supplemented by in-situ measured SDR data from ad-hoc campaigns, as identified in projects such as Copernicus Cal/Val Solutions (CCVS). Ad-hoc campaigns are limited to quite short time range but provide reference data for substantially more surface types. DLR has a long-time experience in performing ground-based reference measurement campaigns for validation of multispectral and hyperspectral L2A products of, for example, Sentinel-2, Landsat, Rapid-Eye, DESIS and EnMAP data, as well as Cal/Val for airborne hyperspectral sensors. This covers all of SDR, AOT and WV retrieval. In this presentation we explain our measurement protocol applied for measuring SDR, AOT and WV on ground which was refined over years following own experience and recommendations from publications about best practices. It is necessary to know the instruments and sites used and to understand the measurement process and uncertainties involved. It is necessary to include into the measurement protocol the upscaling approach from the small footprint of instruments used near the ground to the size of satellite pixels. The completion of the validation procedure includes to convolve spectrally the ground reference measurements to the satellite-sensor-bands, to consider directional effects of surface reflection on the ground and careful geolocation of measurement positions in satellite image with respect to the selection of image pixels for spatial averaging. Application of the complete procedure is demonstrated on example of Sentinel-2 L2A-products, EnMAP data are used to demonstrate progress in accounting for BRDF-effects and open questions are discussed

A Holistic Perspective on the Calibration and Validation of Sentinel-2 L2A products: Contribution From the CCVS Project

In this presentation, we report on the preliminary findings of the H2020 project “Copernicus Cal/Val Solution” (CCVS), whose objective is to define a holistic solution to the cal/val of the Copernicus Sentinel missions. We focus more specifically on synergies of the Sentinel-2 mission with other Sentinel or third-party missions, in terms of cal/val requirements as well as reference data sources. Regarding the first aspect, CCVS will consolidate cal/val requirements for all missions with a unified approach. For instance, we compare validation requirements for Sentinel-2 L2A AOD and Water Vapour products to other optical missions like Sentinel-3 OLCI and SLSTR, as well as atmospheric composition missions. In addition, user-driven inter-operability requirements could lead to specific calibration or validation needs. A first example concerns the radiometric inter-calibration between Sentinel-2A and B, which could be ensured with better accuracy than the absolute calibration of either satellites. Geometric co-registration with other optical missions like Landsat could be also monitored. In terms of data sources, CCVS will first establish a survey of existing sources, including natural targets and in-situ data acquired in the frame of systematic measurement programs or ad-hoc campaigns. In a second step, we investigate potential data sources needed for calibration and validation, with a specific focus on directional surface reflectance and cloud mask

Copernicus Cal/Val Solution - D3.2 - Recommendations for R&D on Cal/Val Methods

This document presents a gap analysis of the methods used in the calibration and validation of Earth Observation satellites relevant to the Copernicus programme and suggests recommendations for the research and developments required to fulfil this gap when/where possible. The document identifies the gaps and limitations of the CalVal methods, used for calibration and validation (CalVal) activities for the current Copernicus missions. It will also address the development needs for future Copernicus missions. Four types of missions are covered based on the division used in the rest of the CCVS project: optical, altimetry, radar and microwave and atmospheric composition. Finally, it will give a prioritized list of recommendations for R&D activities on the CalVal methods. The information included is mainly collected from the deliverables of work packages 1 and 2 in the CCVS project and from the consortium experts in CalVal activities

Copernicus Cal/Val Solution - D3.6 - Copernicus Cal/Val Solution

This document presents the synthesis of activities performed in Task 3 of the CCVS project. It gathers the main identified gaps and recommendations regarding: • Instrumentation technologies • Development of Cal/Val methods • In-situ measurement networks and field campaigns • Data distribution services The recommendations are selected in order to form a consistent plan to improve cal/val activities for all Sentinel missions, trying to find an overall balance across the main domains (optical observations, radar imaging, altimetry and atmospheric composition missions). Finally, we provide some recommendations regarding coordination, organization and processes involving the different actors of the Copernicus programme. Programmatic and sustainability aspects are not addressed in this document (cf. Task 4 documents)

Copernicus Cal/Val Solution - D3.1 Recommendations for R&D activities on Instrumentation Technologies

The Document identifies the gaps in instrumentation technologies for pre-flight characterisation, onboard calibration and Fiducial Reference Measurements (FRM) used for calibration and validation (Cal/Val) activities for the current Copernicus missions. It also addresses the measurement needs for future Copernicus missions and gives a prioritised list of recommendations for R&D activities on instrumentation technologies. Four types of missions are covered based on the division used in the rest of the CCVS project: optical, altimetry, radar and microwave and atmospheric composition. It also gives an overview of some promising instrumentation technologies in each measurement field for FRM that could fill the gaps for requirements not yet met for the current and future Copernicus missions and identifies the research and development (R&D) activities needed to mature these example technologies. The Document does not provide an exhaustive list of all the new technologies being developed but will give a few examples for each field to show what efforts are being made to fill the gaps. None of the examples is promoted as the best possible solutions. The selection is based on the authors' knowledge during the preparation of the Document. The information included is mainly collected from the deliverables of work packages 1 and 2 in the CCVS project. The new technologies are primarily from the interviews with various measurement networks and campaigns carried out in tasks 2.4 and 2.5. Reference documents can be found in section 1.3

Assessment of the Performance of the Atmospheric Correction Algorithm MAJA for Sentinel-2 Surface Reflectance Estimates

International audienceThe correction of atmospheric effects on optical remote sensing products is an essential component of Analysis Ready Data (ARD) production lines. The MAJA processor aims at providing accurate time series of surface reflectances over land for satellite missions, such as Sentinel-2, Venμs, and Landsat 8. The Centre d’Études Spatiales de la Biosphère (CESBIO) and the Centre National d’Études Spatiales (CNES) share a common effort to maintain, validate, and improve the MAJA processor, using state-of-the-art ground measurement sites, and participating in processor inter-comparisons, such as the Atmospheric Correction Intercomparison Exercise (ACIX). While contributing to the second ACIX-II Land validation exercise, it was found that the candidate MAJA dataset could not adequately be compared to the main reference dataset. MAJA reflectances were corrected for adjacency and topography effects while the reference dataset was not, excluding MAJA from a part of the performance metrics of the exercise. The first part of the following study aims at providing complementary performance assessment to ACIX-II by reprocessing MAJA surface reflectances without adjacency nor topographic correction, allowing for an un-biased full resolution comparison with the reference Sentinel-2 dataset. The second part of the study consists of validating MAJA against surface reflectance measurements time series of up to five years acquired at three automated stations. Both approaches provide extensive insights on the quality of MAJA Sentinel-2 Level 2 products

Sentinel-2 Calibration and Validation: from the Instrument to Level 2 Products

Sentinel-2 is an optical imaging mission devoted to the operational monitoring of land and coastal areas. It is developed in partnership between the European Commission and the European Space Agency. The Sentinel-2 mission is based on a satellites constellation deployed in polar sun-synchronous orbit. It will offer a unique combination of global coverage with a wide field of view (290km), a high revisit (5 days with two satellites), a high resolution (10m, 20m and 60m) and multi-spectral imagery (13 spectral bands in visible and shortwave infra-red domains). The first satellite is planned to be launched by mid-2015. CNES is in charge of the geometric and radiometric calibration of the instrument during the commissioning phase in collaboration with ESA. The combination of vicarious and in-situ calibration techniques associated to on-board diffuser acquisitions is expected to provide very well calibrated L1C products. A review of the sentinel-2 radiometric calibration methods will be described in this presentation. Moreover, CNES will operate a Sentinel-2 level 2 processing chain in the frame of THEIA land data center. We will introduce THIEA, the level-2 production methodology and then review the product validation strategy. The latter is based on reflectance and AOT in-situ measurements, and products and masks cross comparisons