Solar Spectral Irradiance Measured from 11.58 km with a Leiss Monochromator and a Photoelectric Filter Radiometer.

Area of Science:

• Atmospheric Science
• Radiometry
• Solar Physics

Background:

• Accurate measurement of solar spectral irradiance is crucial for understanding Earth's energy balance and atmospheric processes.
• Previous measurements have shown variability, necessitating precise in-situ data collection above most of the atmosphere.

Purpose of the Study:

• To measure solar spectral irradiance from high altitude using two distinct instruments.
• To compare measurements from a Leiss double prism monochromator and a GSFC modified Eppley Mark V radiometer.
• To establish solar spectral curves and a solar constant value with minimal atmospheric interference.

Main Methods:

• Conducted six research flights aboard NASA's Convair 990 aircraft at 11.58 km altitude over the Pacific and western US.
• Utilized a Leiss double prism monochromator and an Eppley Mark V radiometer for spectral irradiance measurements (0.3-1.1 micrometers).
• Performed in-flight calibrations using a NBS type quartz-iodine standard and extrapolated data to zero air mass.

Main Results:

• Achieved excellent agreement between the two dissimilar instruments across the measured wavelength range.
• Generated solar spectral curves that differ significantly from previously published data (e.g., Johnson's).
• Determined a solar constant of 0.1351 W cm(-2), approximately 3.3% lower than Johnson's, but consistent with other recent values.

Conclusions:

• High-altitude aircraft measurements provide reliable solar spectral irradiance data.
• The study validates the performance of the employed instruments and calibration methods.
• The derived solar constant and spectral curves offer updated reference values for solar radiation studies.