LYRA Radiometric Model

Latest document on Radiometric Model: RadiometricModel_R1V4.doc (report 1, version 1.2)

Photons from the sun with an energy distribution E(λ) (Watts per square meter as a function of wavelength) enter the LYRA instrument through a circular aperture of 3mm diameter, resulting in an aperture size of A = 7.06858e-08 square meter, pass one of a set of filters of a certain transmissivity F(λ) (throughput as a function of wavelength), and are converted to an electric current by a detector with a certain spectral responsivity D(λ) (Ampere per Watt as a function of wavelength).

Based on simulations with filter transmissivities F(λ) and detector responsivities D(λ) measured in the laboratory, the 12 heads in the 3 channels have been equipped with detectors as summarized in the table below (to do the simulations, click here for an interactive table). The table lists resulting signals i and purities from measurements of the assembled channels ( = filters+detectors together, whereas the data in the interactive table are individually measured filter transmissivities and detector responses). The used solar irradiances E(λ) are based on two TIMED-SEE measurements. The resulting current i at the detector (Amperes, integrated over all wavelengths) is calculated according to

The purity is defined as the ratio of the flux in the interesting wavelength range to the total signal (ideally close to 100%).

Table: expected output signals and purities in all LYRA channels for solar minimum and solar maximum. Each signal and purity entry is a link to a graphical representation of the result.

Head Channel Detector signal and purity
@ solar minimum 		signal and purity
@ solar maximum

1 1 - Lyα 122XN MSM12 240.497 pA 24.4% 266.917 pA 30.2%
2 - Herzberg PiN10 12.565 nA 83.3% 12.587 nA 83.2%
3 - Aluminium MSM11 85.880 pA 58.3% 4.945 nA 2.5%
4 - Zirkonium AXUV20 D # 699.189 pA 99.8% 19.091 nA 100.0%

2 1 - Lyα 122 XN MSM21 103.870 pA 21.1% 113.883 pA 26.4%
2 - Herzberg PiN11 13.745 nA 83.6% 13.761 nA 83.6%
3 - Aluminium MSM15 74.020 pA 59.3% 3.837 nA 2.7%
4 - Zirkonium MSM19 94.822 pA 99.6% 2.772 nA 100.0%

3 1 - Lyα 122XN + Lyα 122N AXUV20 A #56 112.539 pA 80.6% 147.553 pA 84.3%
2 - Herzberg PiN12 10.145 nA 83.3% 10.156 nA 83.2%
3 - Aluminium AXUV20 B #59 1.090 nA 71.6% 36.827 nA 5.3%
4 - Zirkonium AXUV20 C #44 709.525 pA 99.8% 19.311 nA 100.0%

Link to the interactive table to combine any filter and detector