Characterization of GNSS Observables from LuGRE Lunar Surface Operations

This paper presents a characterization of the precision of raw GNSS code-pseudorange, carrier-phase, and Doppler-shift observables collected by the Lunar GNSS Receiver Experiment (LuGRE) during lunar-surface operations. Detrended observable time series are used to derive empirical standard-deviation curves as a function of carrier-to-noise density ratio (C/N0), separately for each of the four tracked signals (GPS L1 C/A, GPS L5, Galileo E1 OS, Galileo E5a). These curves are modeled according to a compact exponential model, yielding an analytical, C/N0-conditioned representation of observable precision over the signal-strength range experienced during LuGRE surface operations. The adequacy of this description is assessed by standardizing the de-trended samples using the fitted models and re-binning them against two geometry-related descriptors: the transmit off-boresight angle and the grazing altitude of the line-of-sight path. Results show that the C/N0-conditioned models capture the dominant structure of observable dispersion over the well-sampled portion of the dataset. Local departures from unit normalized dispersion are observed for some signal-observable pairs, particularly at high off-boresight angles and within specific grazing-altitude intervals; however, no consistent geometry-dependent trend emerges across signals. The available data therefore do not support the introduction of a general additional geometry-dependent variance term. The resulting flight-derived precision models provide empirical inputs for measurement weighting in cislunar navigation filters and for realistic simulations supporting future lunar missions.