Validation practices for satellite soil moisture retrievals: What are (the) errors?

Gruber, Alexander; de Lannoy, Gabriëlle J.M; Albergel, Clément; Al-Yaari, Amen; Brocca, Luca; Calvet, Jean-Christophe; Colliander, Andreas; Cosh, Michael H.; Crow, Wade T.; Dorigo, Wouter Arnaud; Draper, Clara Sophie; Hirschi, Martin; Kerr, Yann H.; Konings, Alexandra G.; Lahoz , William A.; McColl, Kaighin Alexander; Montzka, Carsten; Muñoz-Sabater, Joaquín ; Peng, Jian; Reichle, Rolf H.; Richaume, Philippe; Rüdiger, Christoph; Scanlon, Tracy; van der Schalie, Robin; Wigneron, Jean Pierre; Wagner, Wolfgang