Phenomenology Imager and Nighttime Observer (PIANO): Low-light weather imagery from the ISS

The Phenomenology Imager and Nighttime Observer (PIANO) is a space based infrared imager deployed to the International Space Station in January 2022. The camera bandpass is 1.5 to 1.72 microns (H band), which is ideal for reflective imagery of cloud and surface features using illumination from the bright OH Meinel airglow emission. PIANO has a 34° x 34° FOV, sweeping out a 270 km swath from the ISS, with a native spatial resolution of ~65 meters. The camera utilizes a state-of-the-art 16 megapixel (4K x 4K, 15 micron pixel) Teledyne H4RG detector and custom optical assembly to obtain high spatial resolution, high-performance space-based imagery. The focal plane array has a long-wavelength cutoff of 1.72 microns, which precludes the need for cold optics and reduces cooling requirements (to ~ 180 K). The camera is fed by a custom optical telescope which compensates for orbital motion of the ISS during ~1.5s integration time and creates equal-area ground pixels. This allows smear-free, high-spatial resolution imaging from a moving platform.

The near infrared, see-to-the ground band in which PIANO operates allows imaging of Earth surface and cloud features in the absence of moonlight using ambient airglow. PIANO acquires images at ~10s cadence, with sequential images overlapping by about 70%, providing multiple views of the same scene. Tomographic analysis of overlapping images allows determination of cloud heights within a scene to ~500 m accuracy, depending on the number of overlapping images. Cloud heights in sunlit and moonlit scenes can be verified via analysis of cloud shadows. In this presentation we show examples of cloud cover and cloud characteristics, including comparisons to VIIRS DNB imagery, particularly for moon-down periods where the primary illumination source is airglow. The cloud height algorithm and the results from its application will also be discussed.