Early Observations of Aerosols from the SAGE III ISS Instrument

Abstract:

The Stratospheric Aerosol and Gas Experiment III (SAGE III) was delivered to the International Space Station on 23 February 2017 in the unpressurized trunk of the SpaceX CRS-10 Dragon spacecraft. The SAGE III ISS payload was installed on ELC‑4 on the S3 Truss. SAGE III ISS represents an opportunity to extend the historical record of SAGE and SAGE II measurements of stratospheric aerosol. The SAGE record includes observations of major stratospheric aerosol loading events including El Chichón and Mount Pinatubo and spans a time period from 1979 beginning with the Stratospheric Aerosol Measurement (SAM) II through 2005 with the end of the SAGE II and SAGE III Meteor‑3M missions. SAGE III utilizes a charge-coupled device (CCD) of 857 pixels in the spectral dimension of which 809 pixels correspond to approximately 1 nm wide wavelength bands ranging from 282 nm to 1038 nm. The remaining 48 pixels characterize readout noise on a per-measurement basis. An additional InGaAs photodiode collects a wider passband centered at 1543 nm. The CCD readout is table-configured to provide 86 channels for solar occultations and 340 channels for lunar occultations and limb scatter measurements. Limb scatter measurements are further configurable with two on-board tables which can be switched at-will. A final spectral survey mode is capable of producing the full CCD data capture. Of the 86 pixels used for solar occultation data collection at 64 Hz, 10 are reserved for aerosol retrievals centered at 520 nm, 676 nm, 756 nm, 869 nm, a range spanning 1019 nm to 1024 nm. Recent attempts to bridge previous and current SAGE measurements using alternate satellite inputs have shown sudden increases of up to 100% of retrieved aerosol optical depth which present validation difficulties absent the better than 10% uncertainty observed through the SAGE II record. To answer questions regarding the state of this long-standing aerosol record, an initial look at SAGE III ISS aerosol observations in both the troposphere and stratosphere during the first year of operation are presented. Data quality and comparisons with other satellite observations of stratospheric aerosol are also shown. SAGE III ISS presents an excellent opportunity to begin a new period of highly accurate and precise measurements of aerosols per the proven SAGE technique and SAGE II standard.