Undifference ambiguity resolution for GPS-based precise orbit determination of low Earth orbiters using the new CODE clock and phase bias products.

Introduction • GNSS-based Precise Orbit Determination (POD) of Low Earth Orbiters (LEOs) has nowadays become a standard application for high-quality GNSS products as provided by the IGS, or its individual analysis centers. For many LEOs, e.g., for altimetry missions, the centimeter absolute orbit precision and accuracy achieved by carrier phase-based GNSS positioning is mandatory and could hardly be obtained by other tracking data.