Some time ago we presented a free software mini-suite that can be useful to support UAV based survey tasks/general purpose operations.
The new Basic Air Data GSP Logger App release was tested at Centre for Geoinformatics, IIFM, Bhopal, India; the results were as expected.
They produced a pdf report and 15 minutes quick start up video-tutorial for GPSLogger. The pdf report contains the details about GPS Logger altitude correction.
You find everything in this link.