Energy transfer through horizontal layers is characterized by multiple airborne zenith- and nadir-viewing radiometers. Two Zeiss spectrometers provide spectrally resolved irradiance measurements in the visible to near-infrared spectral range (0.26 – 2.2 µm). Supplementing these spectrally resolved measurements of irradiance is a set of (broadband) pyranometers and pyrgeometers which extend the observations into the infrared portion of the spectrum (0.2 – 42 µm). Manufactured by Kipp & Zonen, these sensors have been adapted in-house for airborne operations. In addition, zenith- and nadir-viewing radiation pyrometers in the 9.6-11.5 µm band (Heitronics KT19.85) are available to measure radiometric surface temperature. Finally, measurements of energy flux through a sphere (actinic flux) are accomplished with a set of radiometers designed to be equally responsive to photons from all directions at wavelengths of 280 – 680 nm.
The quality of airborne irradiance measurements is compromised by variations in aircraft attitude (with respect to horizontal) when sensors are rigidly mounted. Pitch and roll rotations by the aircraft introduce artificial fluctuations into the data, making interpretation of irradiance measurements difficult. This problem is being addressed with an effort to design and test stabilized platforms on which the radiometers are mounted. Integrated on the top and bottom of the aircraft, these systems actively level the sensors to compensate for aircraft pitch and roll angles of up to ±5° and ±10°, respectively, based on input from the aircraft Inertial Navigation System.
The various sensors and calibration methods will be described in this presentation. Data examples and applications from recent field experiments will also be shown.