Simulating the Profile of a Radio Altimeter Echo Signal

Abstract

Introduction. Radio altimeters are used for remote monitoring of the Earth and sea surface based on the signal power profile, i.e. the dependence of echo signal power vs time, averaged over a set of sounding measurements. Calculation of the power profile in the presence of sea waves requires information about the probability distribution density (PDD) of sea surface applicates. The existing applicate PDD models (linear, Gram-Charlier, combined model) are characterized by certain drawbacks leading to errors in assessing sea surface parameters based on the signal power profile. In this work, the echo signal of a radio altimeter is simulated using the nonlinear Creamer model for calculating sea surface applicates.Aim. To test the validity of the non-linear Creamer model for obtaining the PDD of sea surface applicates in the problem of simulating the power profile of a radio altimeter echo signal while providing an unambiguous relationship between the statistical parameters of PDD and wind speed.Materials and methods. A two-dimensional sea surface of finite dimensions with an Elfohaily spatial spectrum was simulated in the MATLAB environment based on both linear and non-linear Creamer models.Results. Under small wind speed values of up to 3 m/s, the PDD of sea surface applicates formed by the non-linear Creamer model obey the Gauss law. For the non-linear model, an increase in the duration of an radio altimeter echo signal along with an increase in the wind speed was shown to be 5.47 % slower on average compared to that for the linear model. The time shift of the leading edge of an echo signal for the nonlinear model relative to the linear model due to the PDD transformation may reach 70 ns, which is equivalent to 10.5 m. The conducted study confirmed the validity of the non-linear Creamer model for obtaining the PDD of sea surface applicates when simulating the power profile of a radio altimeter echo signal.Conclusion. The non-linear Creamer model can be recommended for simulating an echo signal power profile for use as input data when estimating the parameters of a radio altimeter echo signal at the stage of post-processing.