We now take the next steps, after building the Mauna Loa system and operating it: into Space with NASA!
The reason is simply that, from space we can avoid the variability due to observing through an atmosphere and do not need a global network of earth-bound telescopes – one suitable instrument will do it all from orbit.
Even from NOAA’s Mauna Loa Observatory (MLO) — one of the best observatories anywhere on Earth — we could easily see variability in our results due mainly to very thin high-altitude clouds. Extinction at MLO is low of course, but variable. Sure, the ‘bad seeing nights’ can be eliminated by detecting the variability each night, but then you end up with not very many good data!
When we noticed a small Earth-Observing student satellite ( @flying_laptop on Twitter) from University of Stuttgart — we asked if they would try to catch some images of the Moon for us — and they did! The images were interesting and taught us the importance of optimized optical design — optimization for the sake of driving down ‘scattered light’ (really, a phrase covering aperture diffraction as well as various internal scattering processes). We worked with the students and reported on what we found at the 2019 annual European Geophysical Union meeting in Vienna, in the “Earth radiation budget, radiative forcing and climate change” session that Martin Wild, and others, organize each year. See our poster here.
Building on that experience, we are now looking at more ways to go into space, and also to improve on the earthshine instruments we can orbit.
One such effort is with the SAIL (Space and Atmospheric Instrumentation Lab) at Embry-Riddle Aeronautical University in Daytona Beach, Florida. With three friends there we are putting together a NASA Instrument Incubator Proposal (IIP) for development of an optical system optimized for the task at hand: observing high-contrast targets with quite extreme requirements for performance.
In our present ground-based approach we are never really observing the Moon without a contribution from the atmosphere, and must resort to various ‘subtraction schemes’ to get rid of either a ‘halo around the Moon’ (which is light scattered along the path to the image sensor) or a ‘flat sky level’ which can be due to such things as airglow, or the Moon-light scattering up from the ground onto particles in the atmosphere (this is not a ‘halo contribution’). Both kinds of contributions have to be removed before the faint earthshine can be used for terrestrial albedo studies. From space, both of these contributions would be omitted automatically, leaving only a faint contribution due to aperture diffraction — our goal is therefore to study how to build a telescope that has as little diffraction as possible.
With our group of experts in optics and satellite payloads at Embry-Riddle we are considering refractive optics, advanced sensors and ‘baffling’ to minimize unwanted light reaching the image sensor. Our IIP proposal is being submitted this week!
We have tried NASA proposals before, and this is the second try, building on reviews of our first attempt. The opportunities — the proposal call aims — vary, so emphasis is different this time: First time we focused on the sensors, now we are working on the optics.