Sensitivity Studies for Argus 1000 Micro-Spectrometer: Measurements of Atmospheric Total Column Carbon Dioxide By Reflected Sunlight
Alsalem, Naif Zaid M.
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A sensitivity analysis of the atmospheric boundary layer (ABL) and the atmospheric total column carbon dioxide was performed. The absorption of reflected solar radiation from the atmosphere and Earths surface near 1.58 m is utilized in this study. The CO_2 near infrared (NIR) bands at 1.58 m and 1.60 m are located within the Argus 1000 spectrometer spectral range, 1.0-1.7m. The model findings suggest that Argus 1000 spectrometer signal-to-noise ratio (SNR) must be 2000:1 to detect a 1% CO_2 change in the boundary layer (0-2 km). Argus 1000 spectrometer with its current SNR (~ 1520:1) can detect approximately 1.31% CO_2 change in the boundary layer (ABL). Two solar radiance paths were considered using GENSPECT, a line-by-line radiative transfer model, to examine the solar radiance spectra seen by the sensor. In path one, sunlight is assumed to travel through a longer path length in the atmosphere and reflect off the ground back to space. In path two, the solar beam is assumed to travel through a shorter path length and reflect off a cloud layer that is 4 km above the ground. The model findings suggest that the ratio between the solar radiances in both paths is approximately 4.5. The radiance change in both paths was examined for a 1% CO_2 perturbation in the boundary layer. The effect of the presence of clouds on both solar radiation and CO_2 absorption is also analyzed using flight data collected by the Argus 1000 spectrometer over cloudy and cloud-free scenes. The finding shows that CO_2 absorption in a clear sky condition is approximately 5.3% higher than when clouds are present.