This project aims to formulate, design , build and test a versatile, high-efficiency, low-resolution spectrograph to function as the G-CLEF (GMT-Consortium Large Earth Finder) exposure meter. G-CLEF, the first-generation Giant Magellan Telescope's (GMT) instrument, is a state-of-the-art, high-resolution, echelle spectrograph for the GMT, expected to be completed for the telescope's first light. The exposure meter plays a vital role for adjusting barycentric corrections of Doppler radial velocity (RV) by accounting for t Earth's chromatic atmospheric influences. Its significance becomes pronounced in Extreme Precision RV (EPRV) measurements, where the atmosphere's wavelength dependency contributes to errors at the scale of tens of centimeters per second, the same level of precision required for detecting Earth-analog planets orbiting stars similar to the Sun, aligning with one of the primary scientific objectives of G-CLEF. This paper explores the scientific motivation in detail, describes the designs trade-off analysis and the performance simulations aiming to achieve 1cm/s precision on EPRV measurements and outlines the resulting principal parameters derived from these analyses.
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