A measurement system for generating ionospheric phase scintillation measurements based on at least one Global Navigation Satellite System (GNSS) signal from a satellite-borne transmitter of a GNSS, the measurement system comprising, in a ground-based receiver: a data acquisition module, a demodulator module and an atmospheric monitoring algorithms module arranged in an open loop configuration; wherein the data acquisition module is adapted to receive said GNSS signal and includes a reference clock and an analog-to-digital converter coupled to the reference clock, the ADC being adapted to generate a plurality of intermediate frequency samples (r) under the timing of the reference clock, each IF sample having an associated time tag derived from said reference clock; wherein the demodulator module is adapted to receive said IF samples (r) and associated time tags and auxiliary data related to said satellite system, the auxiliary data includes ephemeris information, and is adapted to generate correlator values (Y i) therefrom; and wherein the atmospheric monitoring algorithm module is adapted to receive said correlator values (Y i) and to generate therefrom said phase scintillation measurements (σ φ); and wherein the atmospheric monitoring algorithms module includes a phase process reconstruction algorithm, the phase process reconstruction algorithm comprising: de-rotating the current correlator values ( Y i) by the previous phase estimate; estimating the residual phase (Φ) using a discriminator; and computing the current phase (θ) as the sum of the previous phase and the current residual phase (Φ). a data acquisition module, a demodulator module and an atmospheric monitoring algorithms module arranged in an open loop configuration; wherein the data acquisition module is adapted to receive said GNSS signal and includes a reference clock and an analog-to-digital converter coupled to the reference clock, the ADC being adapted to generate a plurality of intermediate frequency samples (r) under the timing of the reference clock, each IF sample having an associated time tag derived from said reference clock; wherein the demodulator module is adapted to receive said IF samples (r) and associated time tags and auxiliary data related to said satellite system, the auxiliary data includes ephemeris information, and is adapted to generate correlator values (Y i) therefrom; and wherein the atmospheric monitoring algorithm module is adapted to receive said correlator values (Y i) and to generate therefrom said phase scintillation measurements (σ φ); and wherein the atmospheric monitoring algorithms module includes a phase process reconstruction algorithm, the phase process reconstruction algorithm comprising: de-rotating the current correlator values ( Y i) by the previous phase estimate; estimating the residual phase (Φ) using a discriminator; and computing the current phase (θ) as the sum of the previous phase and the current residual phase (Φ). de-rotating the current correlator values ( Y i) by the previous phase estimate; estimating the residual phase (Φ) using a discriminator; and computing the current phase (θ) as the sum of the previous phase and the current residual phase (Φ).