Analysis of Down Looking GPS Occultation Simulated Data Using Least Squares and Abel Inversions

Abstract

Atmospheric refractivity profile can be retrieved from Down Looking (DL) GPS radio occultation data. The main observations are the bending angle of the ray as a function of the impact parameter. Abel inversion and least squares are the possible ways to invert the profile of bending angle to the vertical profile of refractivity. The current paper uses simulated GPS data to compare the merits and limitations of the least squares and Abel techniques. The simulation uses model refractivity from MSIS dry Model, wet model and radiosonde data. The result shows that it is possible to produce accurate vertical refractivity profile using either least squares or Abel inversion. Abel inversion is slightly more accurate than least squares. The percentage of the relative error of the two methods is in the range of 0.2-0.25. Least squares technique is more sensitive to biases than Abel inversion. Abel inversion solution requires much less computation time compared to least squares one.