摘要：Atmospheric delays are known to cause biases in Global Navigation Satellite System Refectometry (GNSS-R) altim‑ etry applications, such as for sea-level monitoring.The main quantity of interest is the refection-minus-direct or interferometric atmospheric delay.Recently, we have presented a rigorous raytracing procedure to account for linear and angular refraction in conjunction with refection as observed from near-surface platforms.Here, we demon‑ strate the feasibility of simplifying the ray trajectory by imposing a rectilinear wave propagation model.Two variants were assessed, based on the apparent or refracted satellite direction on the one hand and the geometric or vacuum conditions on the other hand.The former was shown to agree with rigorous results in terms of interferometric radio length while the latter agreed in terms of the interferometric vacuum distance.Upon a judicious combination of the best aspects of the two rectilinear cases, we have defned a mixed variant with excellent agreement with rigorous raytracing in terms of interferometric atmospheric delay.We further showed that mapping functions developed for GNSS positioning cannot be reused for GNSS-R purposes without adaptations.Otherwise, the total atmospheric delay may be underestimated by up to 50% at low elevation angles.The present work facilitates the adaptation of existing atmospheric raytracing software for GNSS-R purposes.
