Measuring solar radiation from a swaying balloon platform

Incoming solar radiation is a fundamental atmospheric quantity, typically measured at the surface using pyranometer devices, with thermopile or semiconductor sensors. During its passage through the atmosphere, solar radiation is absorbed and scattered. One method for removing the atmospheric effects on the measured solar irradiance is Langley extrapolation, but its effectiveness for determining the top-of-atmosphere irradiance is highly dependent on the measuring circumstances. It is preferable to make in situ atmospheric measurements using an airborne platform, such as an aircraft or balloon system. A practical difficulty, however, with small platforms is their motion, for which complex stabilization approaches may be needed. An alternative approach is to monitor the platform’s motion, using the additional information to correct for the varying orientation of the sensor. To evaluate the effectiveness of this approach, a small self-contained data logger was developed to capture solar radiation measurements across a wide dynamic range, using a photodiode as a sensor. The package included an orientation sensor to allow position fluctuations to be monitored and accounted for. The system was carried on a radiosonde flight to 30 km altitude, with both solar radiation and orientation measured throughout. Combining the data streams shows that improved solar irradiance measurements can be obtained using the orientation information, without the need for physical stabilization of the carrier platform.