Yes, polarization filters vary constantly with the angle to the sun; the maximum affect is achieved at 90 degrees to the sun (photographers have a trick using their thumb and index finger). Linear polarizers are more effective than circular polarizers but most autofocus cameras that use through-the-lens focusing require circular polarizers. That said, for aerial SfM work at infinity focus distance, manual focus is preferred if you can fix (tape) the lens in place so linear polarizers can be used (they are also less expensive to purchase). Lastly, even if you use a circular polarizer, be sure to tape the adjustment ring so it doesn't rotate during your photo survey.