Here we present a compact LED-based source designed within the framework of the EMPIR project 19 ENV04 MAPP “Metrology for aerosol optical properties” for monitoring responsivities of the AERONET Europe radiometers. The aim of the task was to design an LED source flangeable to an integrating sphere that would allow to track responsivity changes of the network instruments. For this purpose the spectral flux of the source must cover the bands of the Cimel sun photometers used in this network and be stable and reproducible at a level of ~0,1%. The design includes 9 LEDs in surface-mount device (SMD) package, one for each band of the sun photometer, soldered on a printed circuit board (PCB). The temperature of the LEDs is accurately controlled by a Peltier device attached to the other side of the PCB. The LEDs are connected in series and operated in stabilized current (CC) mode. Several such LED boards have been built. The devices have been investigated with respect to the spectral properties, stability, and reproducibility. First measurements showed the spectral flux of the LEDs coupled to an integrating sphere to be sufficiently high for being detected by the sun photometers. This report shows the validation of the stability of the flux of the LEDs and gives an outlook about the implementation of the LED source.

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