An exoplanet mission based on a high-altitude balloon is a next logical step in humanity’s quest to explore Earthlike planets in Earthlike orbits orbiting Sunlike stars. The mission described here is capable of spectrally imaging debris disks and exozodiacal light around a number of stars spanning a range of infrared excesses, stellar types, and ages. The mission is designed to characterize the background near those stars, to study the disks themselves, and to look for planets in those systems. The background light scattered and emitted from the disk is a key uncertainty in the mission design of any exoplanet direct imaging mission, thus, its characterization is critically important for future imaging of exoplanets. Cook, Cahoy, Chakrabarti, Douglas, Finn, Kuchner, Lewis, Marinan, Martel, Mawet, Mazin, Meeker, Mendillo, Serabyn, Stuchlik, and Swain: Planetary Imaging Concept Testbed Using a Recoverable Experiment–Coronagraph (PICTURE C)

Micro-Electro-Mechanical Systems (MEMS) Deformable Mirrors (DMs) enable precise wavefront control for optical systems. This technology can be used to meet the extreme wavefront control requirements for high contrast imaging of exoplanets with coronagraph instruments. MEMS DM technology is being demonstrated and developed in preparation for future exoplanet high contrast imaging space telescopes, including the Wide Field Infrared Survey Telescope (WFIRST) mission which supported the development of a 2040 actuator MEMS DM. In this paper, we discuss ground testing results and several projects which demonstrate the operation of MEMS DMs in the space environment. The missions include the Planet Imaging Concept Testbed Using a Recoverable Experiment (PICTURE) sounding rocket (launched 2011), the Planet Imaging Coronagraphic Technology Using a Reconfigurable Experimental Base (PICTURE-B) sounding rocket (launched 2015), the Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) high altitude balloon (expected launch 2019), the High Contrast Imaging Balloon System (HiCIBaS) high altitude balloon (launched 2018), and the Deformable Mirror Demonstration Mission (DeMi) CubeSat mission (expected launch late 2019). We summarize results from the previously flown missions and objectives for the missions that are next on the pad. PICTURE had technical difficulties with the sounding rocket telemetry system. PICTURE-B demonstrated functionality at >100 km altitude after the payload experienced 12-g RMS (Vehicle Level 2) test and sounding rocket launch loads. The PICTURE-C balloon aims to demonstrate ${10}^{-7}$ contrast using a vector vortex coronagraph, image plane wavefront sensor, and a 952 actuator MEMS DM. The HiClBaS flight experienced a DM cabling issue, but the 37-segment hexagonal piston-tip-tilt DM is operational post-flight. The DeMi mission aims to demonstrate wavefront control to a precision of less than 100 nm RMS in space with a 140 actuator MEMS DM.

Radiometric calibration of the Dual-Wavelength Echidna^® Lidar (DWEL), a full-waveform terrestrial laser scanner with two simultaneously-pulsing infrared lasers at 1064 nm and 1548 nm, provides accurate dual-wavelength apparent reflectance (ρ_app), a physically-defined value that is related to the radiative and structural characteristics of scanned targets and independent of range and instrument optics and electronics. The errors of ρ_app are 8.1% for 1064 nm and 6.4% for 1548 nm. A sensitivity analysis shows that ρ_app error is dominated by range errors at near ranges, but by lidar intensity errors at far ranges. Our semi-empirical model for radiometric calibration combines a generalized logistic function to explicitly model telescopic effects due to defocusing of return signals at near range with a negative exponential function to model the fall-off of return intensity with range. Accurate values of ρ_app from the radiometric calibration improve the quantification of vegetation structure, facilitate the comparison and coupling of lidar datasets from different instruments, campaigns or wavelengths and advance the utilization of bi- and multi-spectral information added to 3D scans by novel spectral lidars.

We describe the capabilities and performance of a terrestrial laser scanning instrument built for the purpose of recording and retrieving the three-dimensional structure of forest vegetation. The dual-wavelength Echidna^® lidar characterizes the forest structure at an angular resolution as fine as 1 mrad while distinguishing between leaves and trunks by exploiting their differential reflectances at two wavelengths: 1 and 1.5 $μ$m. The instrument records the full waveforms of return signals from 5 ns laser pulses at half-nanosecond time resolution; obtains $±$117 deg zenith and 360 deg azimuth coverage out to a radius of more than 70 m; provides single-target range resolution of 4.8 and 2.3 cm for the 1 and 1.5 $μ$m channels, respectively (1$σ$); and separates adjacent pulse returns in the same waveform at a distance of 52.0 and 63.8 cm apart for the 1 and 1.5 $μ$m channels, respectively. The angular resolution is in part controlled by user-selectable divergence optics and is shown to be $<$2 mrad for the instrument’s standard resolution mode, while the signal-to-noise ratio is 10 at 70 m range for targets with leaf-like reflectance for both channels. The portability and target differentiation make the instrument an ideal ground-based lidar suited for vegetation sensing.

The Journal of Astronomical Telescopes, Instruments, and Systems (JATIS) publishes peer-reviewed papers reporting on original research in the development, testing, and application of telescopes, instrumentation, techniques, and systems for ground- and space-based astronomy.