Analyze the error sources in GNSS positioning and their mitigation strategies.

GNSS error sources: satellite errors - clock drift (2m) mitigated by precise clock products, orbit errors (2.5m) by precise ephemeris. Atmospheric errors - ionospheric delay (5-15m) corrected using dual-frequency receivers or models, tropospheric delay (2.5m) using models and estimation. Receiver errors - clock solved as unknown, noise and multipath minimized by quality equipment and antenna placement. Geometric dilution of precision (DOP) affects solution - plan observations when DOP <3. Differential techniques eliminate common-mode errors. Integer ambiguity resolution critical for centimeter accuracy. Quality control monitors residuals and cycle slips.