Abstract
The overall reflectance of sunlight from Earth is a fundamental parameter for climate studies. We have designed and implemented small aperture, remote control telescopes in Big Bear Solar Observatory in California and in Tenerife in the Canary Islands. These telescopes observe the earthshine to obtain a global mean terrestrial reflectance utilizing a coronagraph‐like design for long exposures of the dark of the Moon and have internal moving parts in the optical train, which presented some design and control problems.
Highlights
For a decade, we have been measuring the Earth’s reflectance by observing the earthshine, which is sunlight reflected from the Earth to the Moon and retroflected to the nighttime Earth
The most important historical program of earthshine measurements was carried out by Danjon [3, 4] from a number of sites in France. Danjon estimated his uncertainty at roughly 5%
Our measurements are about an order of magnitude more precise than his estimates, in large part because we have better measurement technologies. We have eliminated his systematic error by correctly measuring the scattering from the Moon as a function of the phase of the Moon [1]
Summary
We have been measuring the Earth’s reflectance by observing the earthshine, which is sunlight reflected from the Earth to the Moon and retroflected to the nighttime Earth. An absolutely calibrated, large-scale albedo can be determined by measuring the amount of sunlight reflected from the Earth and in turn, back to the Earth from the dark portion of the face of the Moon (earthshine) and taking the ratio of that to the brightside (moonshine) signal; see Figure 1 [1, 2]. The most important historical program of earthshine measurements was carried out by Danjon [3, 4] from a number of sites in France Danjon estimated his uncertainty at roughly 5% (ignoring his appreciable systematic error from an incorrect determination of the Moon’s reflectivity). If funding is available we plan to increase our network to a maximum of 6–8 telescopes
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