Refractivity and Refractivity Gradient Estimation From Radar Phase Data: A Least Squares Based Approach. - Rubén Nocelo López; Brais Sánchez-Rama; Veronica Santalla del Rio; Sérgio Barbosa; Paulo Narciso; Román Pérez-Santalla; Alberto Pettazzi; Paulo Pinto 004; Santiago Salsón; Tânia Viegas (IEEE Trans. Geosci. Remote. Sens., 2023)