Before each acquisition survey, Helica carries out the calibration and adjustment of the onboard sensors. The operation involves a number of flights over target areas,
the position and dimensions of which have been surveyed very accurately at ground level with traditional methods.
This way systematic errors carried by the instruments are determined. GPS ground stations are required as integration to the corresponding airborne data for the processing of the flight trajectories
in order to georeference the data with centimetric accuracy.
As an on-ground reference Helica uses GPS stations belonging to a regional permanent GPS network and/or its own stations. In case of using a GPS-station network, Helica operates a preliminar check of its functioning and accuracy. In case of incomplete coverage or unreliability of the local GPS station network, Helica uses its own GPS systems. These double frequency (L1-L2) GPS receiving systems allow data recording with a sampling frequency over 1 Hz. The master stations are placed within a 30 km radius of the survey area and positioned on points with known coordinates.