Diffraction-limited Titan Surface Imaging from Orbit Using Near-infrared Atmospheric Windows

The selection of Dragonfly enables regional Titan surface science, but global Titan geophysics, geology, hydrology, and meteorology require an orbiter. We consider the sources of signal and noise that would contribute to near-infrared surface imaging from such an orbiter both analytically and numerically. The fraction of light arriving at an orbiting camera directly from Titan's surface, and therefore conveying full-resolution surface information, decreases at shorter wavelengths as additive atmospheric scatter and light blurred on the way out increase with higher haze optical depths. We apply the Monte Carlo radiative transfer model SRTC++ and show that up to 75% of observed flux in Titan's 5 mu m window comes directly from the surface, up to 47% comes directly at 2 mu m, and up to just 7% comes directly in the 0.94 mu m window. We find that diffraction-limited surface imaging with 10 m pixels is possible with a signal-to-noise ratio for surface features of 100 in the near-infrared at 5 and 2 mu m using a 50 cm aperture. A Titan orbiter camera could image in color using 5 mu m, 2 mu m, and potentially other wavelengths using a pushbroom strategy with time-delay integration.