Periodic Reporting for period 3 - HYPERNETS (A new hyperspectral radiometer integrated in automated networks of water and land bidirectional reflectance measurements for satellite validation)
Berichtszeitraum: 2021-01-01 bis 2023-04-30
A new hyperspectral radiometer, the HYPSTAR®, has been designed based on an innovative design, combining high performance and moderate cost. Various optical components were tested and a final selection was made based on actual performance with respect to the user requirements. A first batch of 7 radiometers (Fig. 3) was constructed and delivered to partners for testing and performance evaluation. Using feedback from partners to improve the design, a second batch of 7 radiometers and a final batch of 17 radiometers (Fig 4) were constructed and delivered.
The new HYPSTAR® radiometer is embedded within the HYPERNETS host system, which integrates radiometer pointing, data acquisition and data transmission via a rugged PC and includes auxiliary sensors (rain, GPS, etc.) and site-specific power management. A first batch of 7 host systems was constructed and delivered to partners for testing and performance evaluation. Using feedback from partners to improve the design, a second and a third batch of host systems was delivered to partners.
A demonstration video (https://youtu.be/dfUAPYxg5Cc) has been produced for users showing the HYPSTAR® radiometer and host system.
The HYPERNETS network processor software receives data acquired by instruments in the field and processes to the level of water and surface reflectance with their uncertainties (Fig 5). This software integrates closely land and water processing branches and is now functioning in prototype form for automated daily processing of the data from the validation sites.
The HYPSTAR® radiometer and host system have been tested at 8 water (Fig. 6) and 12 land sites (Fig 7) covering a wide range of biogeophysical and environmental conditions. These validation sites form the core of a network that is appropriate for long-term radiometric validation of all optical imaging satellite missions.
HYPERNETS is now a well-known project throughout the international land and water remote sensing community, including the space agencies and validation entities. The project consortium has been very active in promoting the project by presenting the main objectives of the project at different meetings, conferences and other events. The user need is clear and the community is now waiting for this new instrument to become mature and commercially available.
The network of water and land sites where the instrument is being tested will give significantly more useful data than comparable existing networks, for example providing hyperspectral data for validation of all optical bands on all satellite missions instead of the current limited number of multispectral bands available from the AERONET-OC network. With its multi-site, multi-mission, all-band approach HYPERNETS aims to surpass the already impressive achievements of the AERONET-OC network for water reflectance validation and will reproduce this success for land reflectance validation over diverse surface conditions not currently covered by RadCalNet.
Space agencies and related validation entities have confirmed, when HYPERNETS was mentioned or presented during meetings, workshops or other events, the need for hyperspectral validation data, in particular, for the validation of the next generation of hyperspectral sensors (PRISMA, ENMAP, CHIME, PACE ...) but also for existing broadband sensors (Sentinel-2/MSI, Landsat-8/9, Planetscope/Doves …). Early results, using HYPERNETS data for the validation of the Sentinel-3/OLCI WFR product and CMEMS MULTI L3 MED water reflectance product and water and land surface reflectances from Sentinel-2 and Landsat-8/9 suggest that the instrument is fit for this purpose. The radiometer has also been used to estimate top of atmosphere reflectance at the Gobabeb and Antarctica sites at seems suitable also for vicarious calibration applications.
As a spin-off application, data from one validation site has been found useful for direct monitoring of algae in a drinking water reservoir (https://doi.org/10.3390/rs14215607) thus expanding the user community/customer base for the instrument and the data.
Full scientific results of the project will appear in a Special Issue of the journal Frontiers in Remote Sensing on “Optical Radiometry and Satellite Validation” (https://www.frontiersin.org/research-topics/55073/optical-radiometry-and-satellite-validation).
The first datasets from the project are distributed via ZENODO.