ExifTool will do a piecewise linear time synchronization if you give it multiple calibration points (one from each PDC picture). The command syntax looks like this:
exiftool -geotag=mylog.gpx -geosync=10:03:04@pdc_pic1.jpg -geosync=10:20:11@pdc_pic2.jpg -geosync=10:35:32@pdc_pic3.jpg DIR
where DIR is the name of the directory containing images to geotag, and the geosync arguments are the time from the PDC clock and the corresponding picture (used to obtain the camera time).
See http://owl.phy.queen...ool/geotag.html for more help.
This could do what you want if you can arrange the PDC to write a GPX file with the depth information stored as a GPS altitude. Then ExifTool will calculate the interpolated altitude for the proper synchronized time. I hope this helps.