On the Computation of Secondary Electron Emission Models

Secondary electron emission is a critical contributor to the charge particle current balance in spacecraft charging. Spacecraft charging simulation codes use a parameterized expression for the secondary electron (SE) yield delta(Eo) as a function of the incident electron energy Eo. Simple three-step physics models of the electron penetration, transport, and emission from a solid are typically expressed in terms of the incident electron penetration depth at normal incidence R(Eo) and the mean free path of the SE lambda. In this paper, the authors recall classical models for the range R(Eo): a power law expression of the form b1Eo n1 and a more general empirical double power law R(Eo)=b1Eo n1+b2E o n2. In most models, the yield is the result of an integral along the path length of incident electrons. An improved fourth-order numerical method to compute this integral is presented and compared to the standard second-order method. A critical step in accurately characterizing a particular spacecraft material is the determination of the model parameters in terms of the measured electron yield data. The fitting procedures and range models are applied to several measured data sets to compare their effectiveness in modeling the function delta(Eo) over the full range of energy of incident particle

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

Copernicus Cal/Val synergy among current and future optical missions

Operational Calibration and Validation (Cal/Val) is required to ensure the quality of and build confidence in Copernicus data. However, current Cal/Val activities are limited and insufficiently harmonized between different missions. 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 both for 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. CCVS started with an overview of existing calibration and validation sources and means, identified gaps in the current cal/val practise and is proposing long-term solutions to address the currently existing constraints in the Cal/Val domain. An objective is also to exploit existing synergies between the missions. The analysis performed within the CCVS project is based on experience from many experts in the Cal/Val domain and on feedback from different working groups gathering European Space Agencies, Copernicus Services, measurement networks and International partners. This presentation will give an overall assessment of Copernicus Cal/Val maturity in the optical mission component both for sensor calibration and characterization and for product quality. Required developments in terms of technologies and instrumentation, Cal/Val methods, instrumented sites and dissemination service are addressed. One of our findings is the need for ground-based hyperspectral reference measurements in particular to prepare the validation of CHIME

Observations and Recommendations for the Calibration of Landsat 8 OLI and Sentinel 2 MSI for Improved Data Interoperability

Combining data from multiple sensors into a single seamless time series, also known as data interoperability, has the potential for unlocking new understanding of how the Earth functions as a system. However, our ability to produce these advanced data sets is hampered by the differences in design and function of the various optical remote-sensing satellite systems. A key factor is the impact that calibration of these instruments has on data interoperability. To address this issue, a workshop with a panel of experts was convened in conjunction with the Pecora 20 conference to focus on data interoperability between Landsat and the Sentinel 2 sensors. Four major areas of recommendation were the outcome of the workshop. The first was to improve communications between satellite agencies and the remote-sensing community. The second was to adopt a collections-based approach to processing the data. As expected, a third recommendation was to improve calibration methodologies in several specific areas. Lastly, and the most ambitious of the four, was to develop a comprehensive process for validating surface reflectance products produced from the data sets. Collectively, these recommendations have significant potential for improving satellite sensor calibration in a focused manner that can directly catalyze efforts to develop data that are closer to being seamlessly interoperable

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 - D4.1 - Roadmap and Sustainability Analysis

This document analyses funding and schedule aspects of the Copernicus Cal/Val Solution

Time series noise of Copernicus Sentinel-2 operational L2A-Products of year 2022

Copernicus Sentinel-2 is the main European land surface observing mission. It serves for observation of land-cover change and deriving biophysical variables related to agriculture and forestry, monitors coastal and inland waters and is useful for risk and disaster mapping. Data quality of the provided data products is a critical point for all these applications. The Sentinel-2 mission consists of a constellation of two polar orbiting satellite units. Both Sentinel-2A and Sentinel-2B are equipped with an identical optical imaging sensor MSI (Multi-Spectral Instrument) which samples 13 spectral bands: four bands at 10 m in the Visible Near Infrared (VNIR) region, six bands at 20 m and three bands at 60 m spatial resolution in the VNIR to Shortwave Infrared (SWIR) region. Sentinel-2 Level-2A (L2A) data contain Bottom-of-Atmosphere (BOA) surface reflectance products together with Aerosol Optical Thickness (AOT), Integrated Water Vapour (WV) and Scene Classification (SCL) maps. They are generated with Sen2Cor which is the operational atmospheric correction processor that removes the effect of the atmosphere from Top-of-Atmosphere Level-1C data. ESA started the complete reprocessing of the Sentinel-2 data archive named Collection-1 which is tagged with the processing baseline (PB) 5.00. The previous processing baseline PB 4.00 has equivalent evolutions and is very close to the PB 5.00 of Collection-1. Operational L2A products with PB 4.00 were generated from end of January 2022 to beginning of December 2022. In this presentation we propose to study surface reflectance time series smoothness, for several test sites, using L2A products from year 2022. The smoothness of that time series is used as an indicator of data quality of the reprocessed products. Test sites are selected representing different climate zones with different AOT retrieval performance 0.03 ≤ RMSDAOT ≤ 0.20 and different WV retrieval performance 0.12 g/cm2 ≤ RMSDWV ≤ 0.40 g/cm2

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 Sentinel-2 Collection-1: A Consistent Dataset of Multispectral Imagery with enhanced Quality

The Copernicus Sentinel-2 satellite mission, with its Sentinel-2A and Sentinel-2B units, offers since several years now a massive quantitative and qualitative resource for the Earth Observation community. Since the launch of Sentinel-2A in 2015, and Sentinel-2B in 2017, many lessons have been learnt leading to continuous improvements of the radiometric and the geometric performances. However, the current archive is composed of heterogenous processing baselines with inconsistent product formats and uneven data quality, which limits its use for multi-temporal monitoring applications. To overcome this limitation, the Copernicus program has undertaken a complete reprocessing with the latest processing baseline (05.00). It concerns the L1C (Top-OfAtmosphere reflectance) and L2A (Surface Reflectance) products. This paper recalls the features of Collection-1 products and gives an overview of the first validation results