Papers by Steffen Dransfeld
Comparison of neural networks with other ocean colour algorithms and effects of noise on reflectance band weighting
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
SENTINEL-3 A, B, C, D: Development, Commissioning and Operations of an Environmental and Climate Monitoring Observation System
IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium
The Sentinel-3 (S3) mission is developed as part of the Copernicus Space Component (CSC) Programm... more The Sentinel-3 (S3) mission is developed as part of the Copernicus Space Component (CSC) Programme to fulfil the space-based observation requirements in response to European policy priorities with a particular emphasis on the Copernicus core services as identified by the Commission.
Radiometer (MFRSR) and freely available. The MFRSR infers the solar beam intensity by making succ... more Radiometer (MFRSR) and freely available. The MFRSR infers the solar beam intensity by making successive global and diffuse measurements and computing their difference. In this way it simulates measurements of a sun photometer. In processing the raw data, the cosine response of the instrument is accounted for, thus allowing for accurate calibration using the Langley method. MFRSR channels (nominally 415, 500, 614, 670 and 868nm) are calibrated using a linearized form of Beer's Law to produce Langley plots from which an extrapolation to zero path length represents the calibration, or what the instrument would measure at the top of the atmosphere. Therefore, absolute calibration of the channels is not necessary for the AOD application. The Angstrom exponent is computed with the AODs for the 500-nm and 868-nm channels.

We present the first extended validation of a new SYNERGY global aerosol product (SY_2_AOD), whic... more We present the first extended validation of a new SYNERGY global aerosol product (SY_2_AOD), which is based on synergistic use of data from the Ocean and Land Color Instrument (OLCI) and the Sea and Land Surface Temperature Radiometer (SLSTR) sensors aboard the Copernicus Sentinel-3A (S3A) and Sentinel-3B (S3B) satellites. Validation covers period from 14 January 2020 to 30 September 2021. Several approaches, including statistical analysis, time series analysis, and comparison with similar aerosol products from the other spaceborne sensor, the Moderate Resolution Imaging Spectroradiometer (MODIS), were applied for validation and evaluation of S3A and S3B SY_2 aerosol products, including aerosol optical depth (AOD) provided at different wavelengths, AOD pixel-level uncertainties, finemode AOD, and Angström exponent. Over ocean, the performance of SY_2 AOD (syAOD) retrieved at 550 nm is good: for S3A and S3B, Pearson correlation coefficients with the Maritime Aerosol Network (MAN) component of the AErosol RObotic NETwork (AERONET) are 0.88 and 0.85, respectively; 88.6 % and 89.5 % of pixels fit into the MODIS error envelope (EE) of ±0.05 ± 0.2 × AOD. Over land, correlation coefficients with AERONET AOD (aAOD) are 0.60 and 0.63 for S3A and S3B, respectively; 51.4 % and 57.9 % of pixels fit into MODIS EE. Reduced performance over land is expected since the surface reflectance and angular distribution of scattering are higher and Published by Copernicus Publications on behalf of the European Geosciences Union. L. Sogacheva et al.: Validation of the Sentinel-3 SYNERGY aerosol product (SY_2_AOD) products are within 0.02 for the study area (30 • S-60 • N, 80 • W-45 • E). The agreement is better over ocean; however, a difference up to 0.6 exists between syFMF and modFMF. Over bright land surface (Saharan desert) the difference in AOD between the two products is highest (up to 0.11); the sign of the difference varies over time and space. For both S3A and S3B AOD products, validation statistics are often slightly better in the Southern Hemisphere. In general, the performance of S3B is slightly better.

Validation of the Integrated Water Vapour (IWV) from Sentinel-3 Ocean and Land Colour Instrument ... more Validation of the Integrated Water Vapour (IWV) from Sentinel-3 Ocean and Land Colour Instrument (OLCI) was performed as a part of the "ESA/Copernicus Space Component Validation for Land Surface Temperature, Aerosol Optical Depth and Water Vapour Sentinel-3 Products" (LAW) project. High-spatial-resolution IWV observations in the near-infrared spectral region from the OLCI instruments aboard the Sentinel-3A and Sentinel-3B satellites provide continuity with observations from MERIS (Medium Resolution Imaging Spectrometer). The IWV was compared with reference observations from two networks: GNSS (Global Navigation Satellite System) precipitable water vapour from the SuomiNet network and integrated lower tropospheric columns from radio-soundings from the IGRA (Integrated Radiosonde Archive) database. Results for cloud-free matchups over land show a wet bias of 7 %-10 % for OLCI, with a high correlation against the reference observations (0.98 against SuomiNet and 0.90 against IGRA). Both OLCI-A and OLCI-B instruments show almost identical results, apart from an anomaly observed in camera 3 of the OLCI-B instrument, where observed biases are lower than in other cameras in either instrument. The wavelength drift in sensors was investigated, and biases in different cameras were found to be independent of wavelength. Effect of cloud proximity was found to have almost no effect on observed biases, indicating that cloud flagging in the OLCI IWV product is sufficiently reliable. We performed validation of random uncertainty estimates and found them to be consistent with the statistical a posteriori estimates, but somewhat higher.

ESA's Sentinel-3 Mission - Status and Performance
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
The Sentinel-3 mission forms part of the Copernicus Space Component. Its main objectives are to m... more The Sentinel-3 mission forms part of the Copernicus Space Component. Its main objectives are to measure sea-surface topography, sea- and land-surface temperature and ocean- and land-surface colour in support of ocean forecasting systems, and for environmental and climate monitoring. The series of Sentinel-3 satellites will ensure global, frequent and near-real time ocean, ice and land monitoring, with the provision of observation data in routine, long term (up to 20 years of operations) and continuous fashion, with a consistent quality and a high level of reliability and availability. The Sentinel-3 mission addresses these requirements by implementing and operating the following instruments, building on experience and heritage from the ERS and ENVISAT missions: •A dual frequency, delay-Doppler Synthetic Aperture Radar Altimeter (SRAL) instrument supported by a dual frequency passive microwave radiometer (MWR) for wet-tropospheric correction, and a Precise Orbit Determination package. This combined package provides measurements of sea-surface height and topography measurements over sea ice, ice sheets, rivers and lakes. •A highly sensitive Ocean and Land Colour Imager (OLCI) delivering multichannel wide-swath optical measurements for ocean and land surfaces. With 21 bands, compared to the 15 on Envisat's MERIS, a design optimised to minimise sun-glint and, a resolution of 300 m over all surfaces, OLCI marks a new generation of measurements over the ocean and land. The swath of OCLI and nadir SLSTR fully overlap. •A dual-view Sea and Land Surface Temperature Radiometer (SLSTR) delivering accurate surface ocean, land, and ice temperature, with an accuracy better than 0.3 K. SLSTR measures in 9 spectral channels and two additional bands optimised for fire monitoring. SLSTR has a spatial resolution in the visible and shortwave infrared channels of 500 m and 1 km in the thermal infrared channels.

SENTINEL-3 A and B Optical Payload: Early Results From Commissioning and Tandem Flight Activities
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
The Sentinel-3 (S3) mission is developed as part of the Copernicus Space Component (CSC) Programm... more The Sentinel-3 (S3) mission is developed as part of the Copernicus Space Component (CSC) Programme to fulfil the space-based observation requirements in response to European policy priorities with a particular emphasis on the Copernicus core services as identified by the Commission. The Sentinel-3 main objectives are to measure sea-surface topography, sea- and land-surface temperature and ocean- and land-surface colour in support of ocean forecasting systems, and for environmental and climate monitoring. A series of Sentinel-3 satellites will ensure global, frequent and near-real time ocean, ice and land monitoring, with the provision of observation data in routine, long term (up to 20 years of operations) and continuous fashion, with a consistent quality and a high level of reliability and availability. Sentinel-3 carries an Ocean and Land Colour Instrument (OLCI), a Sea and Land Surface Temperature Radiometer (SLSTR), a SAR Radar altimeter (SRAL) supported by a Microwave Radiometer (MWR) and a suite of orbit determination instruments. A full description of Sentinel-3 can be found in [Donlon et al (2012)]. The paper will focus on S3 optical payloads described in Nieke et al (2015) and Coppo et al (2015).

Context Sentinel-3A (S3A), carrying the Ocean and Land Colour Instrument (OLCI), was successful... more Context Sentinel-3A (S3A), carrying the Ocean and Land Colour Instrument (OLCI), was successfully launched on February 16 th 2016 OLCI dedicated to land and ocean colour, continuity with MERIS, inheriting algorithmic evolutions from MERIS 4 th reprocessing, this talk only on ocean SVC It is essential to ensure product quality prior public release for operational services such as Copernicus Marine Environment Monitoring Service Radiometric validation results demonstrate that OLCI absolute radiometric calibration is comparable with its heritage instrument, MERIS, and that OLCI has a positive bias of about 2 to 3 percent, OLCI being too bright. Actions are in place to achieve OLCI radiometric compliancy (2% absolute accuracy < 900 nm). As for any ocean colour mission, proper system vicarious calibration (or "adjustment") must be made using fiducial reference measurements (i.e. high quality targets) at surface level "Adjustment" stands here for sensor (residual L1 calibration) + L2 processor adjustment

Proba-V cloud detection Round Robin: Validation results and recommendations
2017 9th International Workshop on the Analysis of Multitemporal Remote Sensing Images (MultiTemp), 2017
This paper discusses results from 12 months of a Round Robin exercise aimed at the inter-comparis... more This paper discusses results from 12 months of a Round Robin exercise aimed at the inter-comparison of different cloud detection algorithms for Proba-V. Clouds detection is a critical issue for satellite optical remote sensing, since potential errors in cloud masking directly translates into significant uncertainty in the retrieved downstream geophysical products. Cloud detection is particularly challenging for Proba-V due to the presence of a limited number of spectral bands and the lack of thermal infrared bands. The main objective of the project was the inter-comparison of several cloud detection algorithms for Proba-V over a wide range of surface types and environmental conditions. Proba-V Level 2a products have been distributed to six different algorithm providers representing companies and research institutes in several European countries. The considered cloud detection approaches are based on different strategies: Neural Network, Discriminant Analysis, Multi-spectral and Mult...
Application of AATSR aerosol retrieval to new data from SLSTR onboard Sentinel-3 satellite

Status of copernicus Sentinel-2A and Sentinel-3A optical calibration and validation activities
2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2017
The Copernicus Programme, being Europe's Earth Observation and Environment Monitoring Program... more The Copernicus Programme, being Europe's Earth Observation and Environment Monitoring Programme led by the European Union, aims to provide, on a sustainable basis, reliable and timely services related to environmental and security issues. The Copernicus Programme uses multiple source data and comprises a service component, a space infrastructure component and an in-situ component. The objective of the Copernicus Space Component (CSC) Programme is to fulfil the space-based observation requirements in response to European policy priorities with a particular emphasis on the Copernicus core services as identified by the European Commission. It aims at developing a fully operational capability in view of feeding Copernicus services with satellite data. The CSC Programme also aims at the operational provision of satellite data for other European and national services. The main data source for the CSC Programme are the Sentinels, dedicated missions providing continuity to past or prese...

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
Continuity to the Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index (M... more Continuity to the Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index (MTCI) will be provided by the Sentinel-3 Ocean and Land Colour Instrument (OLCI), and to ensure its utility in a wide range of operational applications, validation efforts are required. In the past, these activities have been constrained by the need for costly airborne hyperspectral data acquisition, but the Sentinel-2 Multispectral Instrument (MSI) now offers a promising alternative. In this paper, we explore the synergetic use of Sentinel-2 MSI data for validation of the Sentinel-3 OLCI Terrestrial Chlorophyll Index (OTCI) over the Valencia Anchor Station, a large agricultural site in the Valencian Community, Spain. High retrieval accuracy (RMSE = 0.20 g m+2) was obtained by applying machine learning techniques to Sentinel-2 MSI data, highlighting the valuable information it can provide when used in synergy with Sentinel-3 OLCI data for land product validation.

OLCI/SLSTR SYN L2 Algorithm and Products Overview
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018
The Sentinel-3 SYNERGY (SYN) processing branch has been designed as a combination of the acquisit... more The Sentinel-3 SYNERGY (SYN) processing branch has been designed as a combination of the acquisition of the two optical instruments, the Ocean and Land Color Instrument (OLCI) and the Sea and Land Surface Temperature Radiometer (SLSTR), with the main objective to provide surface vegetation products similar to those obtained from the VEGETATION instrument on SPOT. Synergistic and collocated measurements from both OLCI and SLSTR are ingested in an aerosol retrieval module. Then for each 300m pixel, Aerosol optical thickness data and Surface directional reflectances are retrieved and outputted in S3 SYNERGY L2 products. A description of the whole processing chain from OLCI/SLSTR L1 products to SYN L2 ones will be provided followed by a detailed description of the SYN L2 products. Quality assessment of these products, performed by the S3 MPC consortium and using in situ comparisons with AERONET data and with PROBA-V data will be discussed. Finally, a third section will be dedicated to the development of a future global aerosol products and the possible evolutions of this SYNERGY processing branch. More details about the whole S3 algorithms and products can be found in the Sentinel 3 Handbook [1]

Remote Sensing, 2021
To validate the iCOR atmospheric correction algorithm applied to the Sentinel-3 Ocean and Land Co... more To validate the iCOR atmospheric correction algorithm applied to the Sentinel-3 Ocean and Land Color Instrument (OLCI), Top-of-Atmosphere (TOA) observations over land, globally retrieved Aerosol Optical Thickness (AOT), Top-of-Canopy (TOC) reflectance, and Vegetation Indices (VIs) were intercompared with (i) AERONET AOT and AERONET-based TOC reflectance simulations, (ii) RadCalNet surface reflectance observations, and (iii) SYN Level 2 (L2) AOT, TOC reflectance, and VIs. The results reveal that, overall, iCOR’s statistical and temporal consistency is high. iCOR AOT retrievals overestimate relative to AERONET, but less than SYN L2. iCOR and SYN L2 TOC reflectances exhibit a negative bias of ~−0.01 and −0.02, respectively, in the Blue bands compared to the simulations. This diminishes for RED and NIR, except for a +0.02 bias for SYN L2 in the NIR. The intercomparison with RadCalNet shows relative differences < ±6%, except for bands Oa02 (Blue) and Oa21 (NIR), which is likely relate...

Remote Sensing, 2020
The Ocean and Land Colour Instrument (OLCI) on-board Sentinel-3 (2016–present) was designed with ... more The Ocean and Land Colour Instrument (OLCI) on-board Sentinel-3 (2016–present) was designed with similar mechanical and optical characteristics to the Envisat Medium Resolution Imaging Spectrometer (MERIS) (2002–2012) to ensure continuity with a number of land and marine biophysical products. The Sentinel-3 OLCI Terrestrial Chlorophyll Index (OTCI) is an indicator of canopy chlorophyll content and is intended to continue the legacy of the Envisat MERIS Terrestrial Chlorophyll Index (MTCI). Despite spectral similarities, validation and verification of consistency is essential to inform the user community about the product’s accuracy, uncertainty, and fitness for purpose. This paper aims to: (i) describe the theoretical basis of the Sentinel-3 OTCI and (ii) evaluate the spatiotemporal consistency between the Sentinel-3 OTCI and the Envisat MTCI. Two approaches were used to conduct the evaluation. Firstly, agreement between the Sentinel-3 OTCI and the Envisat MTCI archive was assessed ...

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2019
Continuity to the Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index (M... more Continuity to the Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index (MTCI) will be provided by the Ocean and Land Colour Instrument (OLCI) on-board the Sentinel-3 missions. To ensure its utility in a wide range of operational applications, validation efforts are required. In the past, direct validation has been constrained by the need for costly airborne hyperspectral data acquisition, due to the lack of freely available high spatial resolution imagery incorporating appropriate spectral bands. The Multispectral Instrument (MSI) on-board the Sentinel-2 missions now offers a promising alternative. We explored the synergetic use of MSI data for validation of the OLCI Terrestrial Chlorophyll Index (OTCI) over the Valencia Anchor Station, a large agricultural site in the Valencian Community, Spain. Using empirical and machine learning techniques applied to MSI data, in-situ measurements were upscaled to the moderate spatial resolution of the OTCI. An RMSECV of 0.09 g m-2 (NRMSECV = 20.93%) was achieved, highlighting the valuable information MSI data can provide when used in synergy with OLCI data for land product validation. Good agreement between the OTCI and upscaled in-situ measurements was observed (r = 0.77, p < 0.01), providing increased confidence to users of the product over vineyard dominated Mediterranean environments.
2010 IEEE International Geoscience and Remote Sensing Symposium, 2010
Measuring Land subsidence in Ha Noi city by means of Radar Interfeometry technique
In the past 10 years, the speed at which Hanoi has been urbanized is so fast that it has brought ... more In the past 10 years, the speed at which Hanoi has been urbanized is so fast that it has brought some bad influences on the environment. One of such problems is the collapse of the land in some area of the city, resulting from the under-water exploition (according to the research of the Institute of Hanoi Technological architecture, the number
The German SMOS project office - CAL/VAL activities
The SMOS remote sensing mission planned to be launched in July 2009 is part of the opportunity mi... more The SMOS remote sensing mission planned to be launched in July 2009 is part of the opportunity missions of the European Space Agency's (ESA) Earth Explorer programme. The role of the German SMOS project office (funded by the BMBF/DLR) is to inform the scientific community and the public about the current mission status as well as to promote the use
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Papers by Steffen Dransfeld