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Ground-based measurements for validation of L2A-products

Pflug, Bringfried and Bachmann, Martin and de los Reyes, Raquel and Marshall, David and Holzwarth, Stefanie and Goronno, Javier and Meygret, Aimé (2023) Ground-based measurements for validation of L2A-products. LPVE - Workshop on Land Product Validation and Evolution, 12-14 June 2023, Frascati, Italien.

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Official URL: https://az659834.vo.msecnd.net/eventsairwesteuprod/production-nikal-public/cc11f67cb84c4c75a4d54cbf4602a7e4


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.

Item URL in elib:https://elib.dlr.de/196024/
Document Type:Conference or Workshop Item (Speech)
Title:Ground-based measurements for validation of L2A-products
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Pflug, BringfriedUNSPECIFIEDhttps://orcid.org/0000-0002-4626-9393UNSPECIFIED
Bachmann, MartinUNSPECIFIEDhttps://orcid.org/0000-0001-8381-7662138874062
de los Reyes, RaquelUNSPECIFIEDhttps://orcid.org/0000-0003-0485-9552UNSPECIFIED
Marshall, DavidUNSPECIFIEDhttps://orcid.org/0000-0002-4765-8198UNSPECIFIED
Holzwarth, StefanieUNSPECIFIEDhttps://orcid.org/0000-0001-7364-7006UNSPECIFIED
Goronno, JavierUniv. of Valencia, SpainUNSPECIFIEDUNSPECIFIED
Meygret, AiméCentre National d’Etudes Spatiales (CNES)UNSPECIFIEDUNSPECIFIED
Date:June 2023
Refereed publication:No
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:Atmospheric Correction, Surface reflectance, validation, reference measurements, Sentinel-2, DESIS, EnMAP
Event Title:LPVE - Workshop on Land Product Validation and Evolution
Event Location:Frascati, Italien
Event Type:Workshop
Event Dates:12-14 June 2023
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Optical remote sensing
Location: Berlin-Adlershof , Oberpfaffenhofen
Institutes and Institutions:Remote Sensing Technology Institute > Photogrammetry and Image Analysis
German Remote Sensing Data Center > Land Surface Dynamics
Deposited By: Pflug, Bringfried
Deposited On:18 Jul 2023 12:57
Last Modified:16 Aug 2023 16:59

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