**5. Conclusion**

We discussed in this brief paper the pros and cons of the standard approach mapping functions + gradients to model the neutral delays of the atmosphere, and more specifically the wet delays caused by the presence of water vapor in the troposphere. If this standard approach is almost perfect for people doing positioning, deformation and VLBI studies, as they see the neutral delays as "noise", it is not so well adapted to people looking at these delays as signals to study atmospheric processes. In particular, the standard definition of gradients is too crude, and does not permit to have access to the horizontal turbulence/convection scales, that are key parameters to model these processes in high resolution NWM models. We therefore propose an alternative way to model the wet tropospheric delays, through a representation of the wet refractivity field as a perturbation over an exponential decay with altitude with a locally adjusted scale height and a time/space series expansion over a suitable basis of orthogonal functions. Our approach is computationally expensive, and maybe not suited for real-time applications, but its

*Beyond Mapping Functions and Gradients DOI: http://dx.doi.org/10.5772/intechopen.96982*

end-product are records of the total and wet refractivity values with high-resolution in time (minute-scale) and distance (sub km-scale), in accordance with the needs of future numerical weather models [38], the emerging field of the modeling of atmospheric rivers [100, 101] and besides does not require the additional step of water vapor tomography, with lower cost, better mobility and simpler operation [102].
