Formal uncertainties (σ) of gravity field coefficients derived from combined 2W and SST mode under varying SST mode noise levels, 1, 0.1, and 0.01 mm/s, while the 2W mode remains fixed at 0.05 mm/s. Red and blue squares denote the positive and negative values of the reference J_n coefficients, respectively. Lower SST noise significantly reduces formal errors, improving sensitivity to both large-scale and fine-scale gravitational features.