Versatile and Targeted Validation of Space-Borne XCO2, XCH4 and XCO Observations by Mobile Ground-Based Direct-Sun Spectrometers oleh André Butz, André Butz, André Butz, Valentin Hanft, Ralph Kleinschek, Matthias Max Frey, Astrid Müller, Marvin Knapp, Isamu Morino, Anna Agusti-Panareda, Frank Hase, Jochen Landgraf, Jochen Landgraf, Sanam Vardag, Sanam Vardag, Hiroshi Tanimoto