0 Calculation Methods for Radio Pulses from High Energy Showers

We present an approximation for the numerical calculation ofČerenkov radio pulses in the Fraunhofer limit from very high energy showers in dense media. We compare it to full Montecarlo simulations in ice studying its range of applicability and show how it can be extended with a simple algorithm. The approximation reproduces well the angular distribution of the pulse around thě Cerenkov direction. An improved parameterization for the frequency spectrum in thě Cerenkov direction is given for phenomenolgical applications. We extend the method to study the pulses produced by showers at distances at which the Fraunhofer limit does not apply, and give the ranges of distances and frequencies in which Fraunhofer approximation is good enough for interpreting future experimental data. Our results are relevant for the detection of very high energy neutrinos with this technique.