Specify the expected background

The user is offered to select parameters of zodiacal light, namely to specify the value of surface brightness for zodiacal light. This can be done in two ways:

1. Select the following surface brightness value in V filter:

High level, $m_V = 22.1$ mag/arcsec$^2$

Medium level, $m_V = 22.7$ mag/arcsec$^2$

Low level, $m_V = 23.3$ mag/arcsec$^2$

In this case, spectral distributions for zodiacal light taken from work (Diaz, 2015) and indicated in the Figure below will be used.

Figure. Spectral distribution of zodiacal light, normalized to different surface brightness in V filter. Figure taken from work (Diaz, 2015)

2. Specify the surface brightness in V filter:

$$F_{zodi}(\lambda) = SED_{zodi}(\lambda) \times 10^{(-0.4 \ (m_V - 22.1))}$$

Earth's airglow in ultraviolet spectral range: The calculations also use the spectrum of Earth's airglow in the ultraviolet spectral range, specified according to the STIS Instrument Handbook of the Hubble Space Telescope [https://hst-docs.stsci.edu/stisihb/chapter-6-exposure-time-calculations/6-6-tabular-sky-backgrounds]. The most intense geocoronal spectral lines are taken into account: HI Lyα (1206 Å), OI triplet (1302.2, 1304.9 and 1306.0 Å), OI (1356 Å), OII (2471 Å)