SASZe Dual-Integration Mode: Double the Value in Half the Time for Clouds, Aerosols, and Clear Sky
Authors
Connor J. Flynn — University of Oklahoma *
J.-Y. Christine Chiu — Colorado State University
Alexander Marshak — NASA - Goddard Space Flight Center
Samuel LeBlanc — NASA - Ames Research Center
Sebastian Schmidt — University of Colorado, Boulder
Jens Redemann — University of Oklahoma
Derek Hopkins — Pacific Northwest National Laboratory
Timothy B Onasch — Aerodyne Research
Herman E Scott — Aerodyne Research, Inc.
Stephen Jones — Aerodyne Research
Guoyong Wen — Morgan State University
Category
ARM infrastructure
Description
The U.S. Department of Energy’s Atmospheric Radiation Measurements program (ARM) has collected spectrally resolved measurements of short-wave zenith radiance since 2006 with the deployment of NASA Ames’s SWS (Shortwave Spectral Radiometer) instrument at SGP. These measurements were expanded on with the deployment of two DOE-designed SAS-Ze instruments in 2010. Each of these instruments uses grating array spectrometers to provide measurements of zenith radiance over the contiguous wavelength range from the UV (> ~325 nm) to the SW IR (< 1.7 or 2.1 microns, depending on instrument). A significant limitation of these instruments is that a single spectrometer applies the same integration time to all pixels with the result that one balance signal to noise at pixels where signal is weak and saturation where signal is strong. This frequently results in an imperfect compromise yielding insufficient signal to noise for some spectral regions and swamped pixels for other regions.
We present results from a newly developed dual integration time implementation that seeks to mitigate this limitation by alternating between two different integration times; one selected to improve signal to noise for weak spectral regions, and the other selected to avoid saturation by bright targets. We show quantitative comparisons to concurrent zenith radiance measurements from AERONET’s Cimel sun photometer, Aerodyne’s TWST zenith spectrometer, and ARMS NFOV2 radiometer. The SASZe exhibits increased dynamic range for bright scenes at the original temporal resolution and double that rate for all other scenes. We present representation of this robust zenith radiance measurement in terms of the LeBlanc hyperspectral parameterization, and example cloud property retrievals at the ARM Southern Great Plains site (SGP) and ARM Mobile Facility Houston (HOU) deployments. The improved SASZe will provide more accurate zenith radiances for studying cloud, aerosol, and cloud-aerosol interactions.
Lead PI
Connor J. Flynn — University of Oklahoma