Demonstration of Dual-Integration Spectroradiometer Operation by ARM for Enhanced Dynamic Range, Temporal Resolution, and Radiometric Accuracy

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 by the deployment 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 (< 1.7-2.1 microns, depending on instrument). We present results from a recent innovation implemented at the ARM sites after Sept 1, 2022. Previously, a significant limitation of these instruments is that the spectrometers apply a single integration time to all pixels with the result that one faces a trade-off between pixel-level signal to noise where signal is weak and pixel saturation where signal is strong.

By quickly alternating between two different integration times every half-second we mitigate this limitation. The instruments alternate between a long integration time designed to improve signal to noise for weak spectral regions and a short integration time selected to avoid saturation by bright targets. We demonstrate increased dynamic range, signal-to-noise, and temporal resolution for zenith radiances of sky and clouds. Additionally, we represent the zenith radiance spectra n terms of the Leblanc hyperspectral parameters, and subsequent cloud property retrievals at the ARM Southern Great Plains site (SGP) and ARM Mobile Facility Houston (HOU) deployments.