Errors caused by long-term drifts of magnetron frequencies for refractivity measurement with a radar: Theoretical formulation and initial validation

International audience ; Refractivity measurements in the boundary layer by precipitation radar could be useful for convection prediction. Until now such measurements have only been performed by coherent radars but European weather radars are mostly equipped with non-coherent magnetron transmitters, for which the phase and frequency may vary. In this paper, we give an analytical expression of the refractivity measurement by a non-coherent drifting-frequency magnetron radar and we validate it by comparing with in-situ measurements. The main conclusion is that, provided the necessary corrections are applied, the measurement can be successfully performed with a non-coherent radar. The correction factor mainly depends on the local-oscillator frequency variation, which is known perfectly. A second-order error, proportional to the transmitted frequency variation, can be neglected as long as this change remains small.