Research project Long-term operation of the AERONET-OC station Palgrunden in Lake Vänern for validation of Sentinel-3
The NASA Aerosol Robotic Network (AERONET) is a global network of about 600 autonomous ground-based remote sensing validation and aerosol monitoring stations that measure aerosol optical properties, such as Aerosol optical thickness and the Ångström coefficient.
For validation of ocean colour data, the network has been extended to support marine and aquatic applications, and an additional sub-network was established by NASA, the AERONET – Ocean Color (AERONET-OC) network.
This network component provides the additional capability of measuring the radiance emerging from the sea or lake surface (i.e. the water-leaving radiance) with a network of CIMEL sun-photometers (Cimel Electronique, France) installed on offshore platforms such as lighthouses, oceanographic towers and oil platforms. AERONET-OC is instrumental in satellite ocean colour validation activities through highly standardized measurements which are performed at different sites with a single measuring system and protocol.
The instruments are all calibrated against an identical reference source and method, and the data is processed with the same code. The data from each station is transmitted to NASA via GSM or satellite transmission and is freely available on the NASA AERONET-OC web site.
Project description
The AERONET-OC station Palgrunden in Lake Vänern was established by ESA and SNSA in 2008. It is a vital component for the development and validation of Sentinel-3 (S3) mission data at high latitudes and over boreal lakes with high humic content (highly absorbing waters). The station is crucial for the Copernicus ocean colour mission as the retrieval of ocean colour products over highly absorbing waters still poses a challenge. Our Marine Remote Sensing Group (MRSG) at the Department of Ecology, Environment and Plant Sciences (DEEP) has been part of the MERIS validation team since 2001 and is also part of the Sentinel-3 validation team, although the data from the AERONET-OC station Palgrunden has already be used for the validation of Sentinel-2 mission data.
As the data from AERONET-OC is generally regarded as state-of-the-art for the validation of Ocean Colour (OC) satellite data the Palgrunden station is vital for the success of the Copernicus missions and for validation of Sentinel-3 as well as Sentinel-2 processors and products in Swedish waters. The satellite processors and products can be improved and validated for Lake Vänern, and thereby become also applicable for other highly absorbing waters, such as the Bothnian Sea.
The Palgrunden station performs high-frequency measurements, and thereby offers a possibility to monitor short- and long-term changes in water quality and atmospheric composition. The station can thus be considered an important national infrastructure of great relevance for Swedish research and development, and, additionally, for demonstrating that Earth Observation data can be a reliable part of freshwater management programs.
In 2017, the Swedish National Space Agency decided to fund the AERONET-OC project as a national space infrastructure of international importance through to 2029 which allowed us to continue the measurements. Since then, we have upgraded the station with a new CIMEL CE-318-T series of instruments with support from the Joint Research Centre (JRC) in Ispra, Italy. The CE-318-T series of instruments is state of the art and the only one accepted for future AERONET-OC deployments. JRC also give us high quality technical support in terms of instrument calibration in a dedicated optical calibration laboratory. NASA supports the project by yearly intercalibration against the same source, and by acting as data host and making the data available via the AERONET-OC web site.
Project members
Project managers
Susanne Kratzer
Forskare, Docent
