Measuring aerosol optical thickness with a helicopter-based sunphotometer

The use of airborne sunphotometers and radiometrically calibrated sensors with fixed wing remote sensing platforms is a reliable method for obtaining atmospherically corrected surface reflectance. The authors describe a variation of such an instrument for use with helicopters. This system tracks the Sun once positioned within 30° of the solar disk. The electronics sample fast enough to collect data between passes of the rotor blades. Calibration for converting voltages to atmospheric transmittance was via the Langley plot method and by intercomparison with calibrated surface sunphotometers. Aerosol optical thickness can be inferred at discrete wavelengths in the visible and near-infrared portions of the spectrum. Aerosol optical thickness data collected with the system agrees reasonably well with data collected using other surface-based sunphotometers