Taking an image of the Calibrated Reflectance Panel is a very important part of data collection, as these images help calibrate your data based on the day's lighting conditions.
We recommend imaging the reflectance panel immediately before and after each flight, with the panel flat on the ground in an open area from about 1m in height. This is best done by holding the aircraft with the sun to your back such that the sun is hitting the panel but light isn't reflected onto the panel from your clothes or from any surrounding objects.
To capture the panel use the button on front of the camera or the WiFi interface, as these ensure special exposure rules are used which are optimized for panel capture.
When capturing images of the panel under cloudy skies, take care not to block the incident light from the clouds from showing up on the panel. In cloudy conditions, the aircraft may cast a shadow on the panel but the shadow may not be apparent.
Imaging the panel using the camera by itself outside of the aircraft may be required in the aircraft is very large and blocks a significant portion of the light.
When deciding which panel image to use for processing in Pix4D or other third-party image processing software, choose the panel image taken at a time that best represents the average illumination of the flight. For example, if it was sunny when you took the first panel image but then clouds moved in and covered the sky for the majority of the flight, you would want to ensure you use a panel image that was taken under the cloudy sky.