Ground-based observatory operations optimized and enhanced by direct atmospheric measurements

Earth's atmosphere represents a turbulent, turbid refractive element for every ground-based telescope. We describe the significantly enhanced and optimized operation of observatories supported by the combination of a lidar and spectrophotometer that allows accurate, provable measurement of and correction for direction-, wavelength- and time-dependent astronomical extinction. The data provided by this instrument suite enables atmospheric extinction correction leading to "sub-1%" imaging photometric precision, and attaining the fundamental photon noise limit. In addition, this facility-class instrument suite provides quantitative atmospheric data over the dome of the sky that allows robust real-time decision-making about the photometric quality of a night, enabling more efficient queue-based, service, and observer-determined telescope utilization. With operational certainty, marginal photometric time can be redirected to other programs, allowing useful data to be acquired. Significantly enhanced utility and efficiency in the operation of telescopes result in improved benefit-to-cost for ground-based observatories. We propose that this level of decision-making will make large-area imaging photometric surveys, such as Pan-STARRS and the future LSST both more effective in terms of photometry and in the use of telescopes generally. The atmospheric data will indicate when angular or temporal changes in atmospheric transmission could have significant effect across the rather wide fields-of-view of these telescopes. We further propose that implementation of this type of instrument suite for direct measurement of Earth's atmosphere will enable observing programs complementary to those currently requiring space-based observations to achieve the required measurement precision, such as ground-based versions of the Kepler Survey or the Joint Dark Energy Mission.