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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - HYPERNETS (A new hyperspectral radiometer integrated in automated networks of water and land bidirectional reflectance measurements for satellite validation)

Teaser

Summary

Networking of automated instruments on unmanned platforms, e.g. AERONET-OC and RADCALNET, has proved to be the most effective way to provide validation data for Copernicus optical missions. The re-use of data from each site for many optical missions (S2, S3, PROBA-V, MODIS, VIIRS, L8, PlÃ©iades, ENMAP, PRISMA, SABIAMAR, etc.) gives a huge economy of scale. The existing AERONET-OC and RADCALNET networks are based on multispectral instruments; however these are expensive to acquire and require modelling of the associated uncertainties to cover all spectral bands of all sensors. Recent advances in opto-electronics facilitate the use of miniaturized hyperspectral spectrometers with reduced price. Industrial production of video surveillance cameras greatly reduces the price of pointing systems for scientific instruments. Improved LEDs provide a stable light source for relative calibration and continuous autonomous monitoring of radiometers. Webcams (for remote inspection of instruments and maintenance support) and data transmission have become cheaper reducing the running costs and improving the reliability of autonomous instrument systems. The general objectives of the HYPERNETS project are (1) developing a new lower cost hyperspectral radiometer and associated pointing system along with an embedded calibration device for automated measurements of water and land bidirectional reflectance, and (2) providing high quality in situ measurements at all spectral bands for the validation of the surface reflectance data issued from all optical Copernicus missions. The instrument will be tested in a prototype network covering a wide range of water types, land types, and operating conditions. Quality controlled data with associated uncertainty estimates will be provided automatically. In addition to the development of the HYPERNETS instrument and system, preparations are made for (1) the new instrument design (and associated calibration service) to be commercialized with an expected lifetime of at least 10 years and (2) the networks to be further expanded to become the main source of surface reflectance validation data for all spectral bands of all optical missions for at least the next 10 years.

Work performed

The main task achieved at the beginning of the project consisted of identifying the user requirements for the instrument- and system design, as well as for the in situ data for validation of land and water reflectance. These requirements were used as the basis for the design concepts of the (1) instrument (Fig. 1), (2) system and (3) network, which in turn were used for the development of the HYPERNETS instrument, system, and prototype network.

For the development of the HYPERNETS instrument design, a set of suitable components were selected based on two criteria: the instrument concept design and technical specifications from the manufacturers. Next, to identify the most appropriate components out of those selected, rigorous laboratory testing activities of the Visible-Near-Infrared (VNIR) and Short-Wave Infrared (SWIR) spectrometers and cosine collectors were conducted. These testing activities are still ongoing. In addition to the measurement module (i.e., VNIR and/or SWIR spectrometers and cosine irradiance collector), the HYPERNETS instrument design also includes a validation module with a thermally- and electrically-stabilised LED source. At the time of this first periodic report, short-term (hours) and long-term (weeks) tests of a few narrowband and broadband LEDs have been conducted.

For the development of the HYPERNETS system, several key (pan-tilt unit, rugged PC, ..) and auxiliary (rain sensor, GPS, cameras, ...) components were selected and tested which conform to the requirements for the mechanical, hardware and software design and the data management and transfer. In addition, actions have also been taken to prepare for the deployment of the instrument and system, and 24 test sites, that will form the prototype network, have already been described and characterized (Fig. 2). Instrument, data and network standardization have also been discussed (i.e., acquisition protocols, data storage, instrument maintenance and calibration, â€¦ ) and reported in the concept designs for both the land and water networks. A first version of the data management plan for research and operational data has also been created, ensuring there is a consistent approach to the treatment of data (including metadata) that is created by the instruments integrated in the network and that the data follows the â€˜findable, accessible, inter-operable and reusableâ€™ (FAIR) principles.

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.

Final results

The HYPERNETS project is developing a new hyperspectral radiometer instrument with enhanced performance with respect to existing COTS instruments, and lower acquisition and running costs, thanks to the use of new opto-electronic components and pointing systems. This in itself is ambitious â€“ the instrument is intended to become the worldwide market leader for radiometric validation activities for the next 10 years. The networks in which this instrument will be embedded 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. The pointing mechanism and inclusion of azimuth- and zenith-pointing in the water and land measurements will also very significantly improve the in situ measurements available for development and validation of bidirectional reflectance distribution function (BRDF) corrections and algorithms for satellite data. Space agencies and related validation entities confirmed, when HYPERNETS was mentioned or presented during meetings, workshops or other events, the need for hyperspectral validation data and, in particular, for the validation of future hyperspectral sensors.