The Instrument

The optical components of the Brewer spectrophotometer are comprised of three parts: (1) the fore-optics, (2) the spectrometer, and (3) the photomultiplier housing, as illustrated in Fig. 6.1 (from Fig. 2.5 of the Brewer Instruction Manual, courtesy of Kipp and Zonen). Additional information regarding the optical components can be found in Fig. 2.4 of the Brewer Instruction Manuals. The fore-optics direct incoming radiation onto the entrance slit of the spectrometer. The spectrometer disperses and focuses a spectrum of the incident radiation across a set of exit slits. For the Mark II and Mark IV instruments, the photomultiplier counts photons of radiation that pass through the exit slits. The Mark EI version of the instrument has a second spectrometer (recombining spectrometer) that mirrors the dispersing spectrometer of the Mark II and Mark IV versions.

Figure 6.1 Optical layout of the single monochromator (Mark II and Mark W) versions of the Brewer Spectrophotometer. This diagram shows the foreoptics, the spectrometer, and the photomultiplier components of the instrument. For the Mark III double monochromator, the dispersing spectrometer is the same as that shown here and the recombining spectrometer is the mirror image located behind (beneath) the base plane of the spectrometer illustrated above. The photomultiplier housing for the Mark III is located beneath the foreoptics. (Illustration from Brewer Instruction Manual, courtesy of Kipp and Zonen)

Figure 6.1 Optical layout of the single monochromator (Mark II and Mark W) versions of the Brewer Spectrophotometer. This diagram shows the foreoptics, the spectrometer, and the photomultiplier components of the instrument. For the Mark III double monochromator, the dispersing spectrometer is the same as that shown here and the recombining spectrometer is the mirror image located behind (beneath) the base plane of the spectrometer illustrated above. The photomultiplier housing for the Mark III is located beneath the foreoptics. (Illustration from Brewer Instruction Manual, courtesy of Kipp and Zonen)

A photograph of the Mark EI version is shown in Fig. 6.2. The optical components and supporting electronics of the Brewer instrument are enclosed in a weatherproof container that is painted white to minimize radiative heating. The cover for the instrument has a sloping quartz window to allow UV radiation onto the fore-optics of the instrument for direct sun, direct moon, and zenith sky measurement. Mounted on the top of the instrument is a Teflon diffuser covered by a quartz dome for measurements of global irradiance. The enclosed instrument sits on top of an azimuth drive box, which rotates the instrument in azimuth with a precision of about 0.025 ".Normally the azimuth drive aligns the instrument so that the quartz window faces the sun.

Figure 6.2 Photograph of the Mark III version of the Brewer Spectrophotometer (Courtesy of Kipp and Zonen)

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