From March 10 - 14, 2025, UMBC Atmospheric Physics graduate student Rachel Smith and ESI mechanical engineers CJ Escobar and Ian Decker calibrated ESI’s AirHARP2 ultraviolet spectrometer (AH2-UV) and shortwave-infrared imager (AH2-SWIR) instruments at the NASA Goddard Space Flight Center's (GSFC) Goddard Laser for Absolute Measurement of Radiance (GLAMR) laboratory. GLAMR is a specialized integrating sphere, a device that generates a spatially uniform and depolarized light field. GLAMR can also produce calibrated light fields from the ultraviolet to the shortwave-infrared, and at high spectral precision (1 nanometer steps or less!).
The ESI team took GLAMR measurements with the AH2-UV and AH2-SWIR to evaluate the spectral response function (SRF) of the instruments. The SRF tells us which wavelengths of light meaningfully contribute to information measured at the detector. The more accurately we can characterize the SRF, the more accurately we can use the measurements of the AH2-UV and AH2-SWIR to infer climate-relevant properties of Earth’s atmosphere and surface.
The AirHARP2 suite contains four compact remote sensors that can all image the same scene on the ground at the same time. The lead instrument is a copy of the HARP2 polarimeter on the NASA Plankton Aerosol Cloud ocean Ecosystem (PACE) mission. The combination of all four instruments, which also includes a spectrometer that images in the visible and near-infrared, increases the amount of information content that is possible in a single observation of clouds, aerosol, land, ocean, or atmosphere. The four instruments took over 75 legs of data (i.e., uninterrupted stretches of data) during NASA’s PACE-PAX campaign last fall. ESI members are currently hard at work converting this calibration data into meaningful and physical imagery for the climate community to use.
This work also was supported by ESI chief engineer Dominik Cieslak, UMBC Atmospheric Physics graduate student Noah Sienkiewicz, and ESI scientist Dr. Brent McBride, as well as GSFC calibration faculty led by Dr. Julia Barsi.
Interested in the data from the AirHARP2 suite during PACE-PAX? The ESI team is releasing science-ready datasets from the polarimeter on Monday, March 31, 2025 via the NASA Langley Atmospheric Science Data Center. Data from the other instruments will come at a later date.
Photo (left): The AH2-UV instrument (gold box) is centered on the aperture of the GLAMR integrating sphere at NASA GSFC prior to calibration. Credit: GLAMR Team.
Photo (right): A preliminary SRF for one of the spectral filters in the AH2-SWIR instrument. Black curve is for visual guidance only. Credit: B. McBride/ESI.
