Atmospheric Gravity Wave and Instability Observations From the International Space Station Using the Near InfraRed Airglow Camera (NIRAC)

Abstract

AbstractThe Near Infrared Airglow Camera (NIRAC) is an imager that was deployed to the International Space Station (ISS) in May 2019. NIRAC's bandpass (1.5–1.72 microns) and field of view (∼23° × 23°) are ideal for observations of the bright OH Meinel airglow emission. NIRAC utilizes a 4‐megapixel Teledyne H2RG detector, a custom‐designed rectilinear lens, and a newly developed motion compensation system to obtain a spatial pixel‐resolution of about 83 m (66 m) at the ground (airglow layer). This design allows smear‐free, high (>50) signal to noise (S/N) imaging (of the ground or airglow layer) over the whole detector during multi‐second image acquisition times, even though the ISS is moving >7 km/s. NIRAC nominally acquires imagery at an ∼7.5 s cadence resulting in image sequences with significant overlap. These can be analyzed for wavelike features (gravity waves and instabilities) at 85 km using the relative displacement of these features as viewed from the two different viewing angles. This technique removes tropospheric cloud backgrounds and Earth background surface features that otherwise make identification of wavelike difficult in this band, an issue with remote sensing satellite instruments. Examples of imagery are presented that show how this technique can distinguish wavelike features that originate at ∼85 km from surface and tropospheric cloud features. This limited data set shows that complex wavelike dynamics are seen in the airglow directly over weather fronts. Because these regions are often cloudy and remote these dynamics have not been well‐studied.