Applying the geodetic detrending technique for investigating the consistency of GPS L2P(Y) in several receivers

Abstract

Global Navigation Satellite System signals have been used for years to study high-frequency fluctuations (f > 0.1 Hz) in the ionosphere. The customary procedure uses the geometry-free (GF) combination of L1 and L2 carriers, for which it is necessary to acquire the L2 GPS signal. Initially, L2 had to be acquired from a codeless signal, L2P(Y), using several techniques, some of them requiring the aid of L1. New GPS satellites transmit the new C2 civil code, which can be used to acquire directly L2, i.e. L2C. Several publications have reported differences in the GF combination when it is computed from L2P(Y) or L2C. Using two ionospheric scintillation monitoring receivers (ISMRs), these differences were shown to be related to how they acquire L2, i.e. if the receiver acquires L2 with the L1 aid. However, ISMRs are scarce, so the extension of such a study is not straightforward. The present work uses the geodetic detrending technique to identify whether a conventional geodetic-grade receiver acquires L2 with the aid of L1. The study employs six different receiver types with measurements stored in RINEX formats version 2 and 3. In both formats, we are able to identify if L2 signal is acquired with L1 aid. In this way, we show that some receiver types heavily underestimate high-frequency ionospheric fluctuations when using the GF combination. Our results show that the ionosphere-free combination of these carrier phases is not free from high-frequency ionospheric fluctuations, but in some receivers, almost 90% of the high-frequency effects in L1 remain in such combination.