Traditional techniques, such as Simultaneous Nadir Overpasses (SNOs) and vicarious inter-calibration over Pseudo-Invariant Calibration Targets (PICTs), have been widely used for this purpose. The work focused on three inter-calibration approaches: Simultaneous Nadir Overpasses (SNO), Opportunistic Constant Target Matching (OCTM), and vicarious inter-calibration over Pseudo-Invariant Calibration Targets (PICTs). AWS-12, AWS-14 Lower/mid-tropospheric temperature sounding SNO using ATMS-5 or ATMS-6 OCTM using ATMS and SEVIRI water-vapor channels SNO provides the most stable uncertainty performance. AWS-21 89 GHz window Vicarious, using ATMS-16 SNO using ATMS-16 Vicarious is primary because it provides a broader dynamic range (163.4-297.8 K) than SNO (163.4-270.2 K). AWS-31 166 GHz window / pseudo-window SNO using ATMS-17 Vicarious using MHS-2 SNO has substantially lower propagated uncertainty, but vicarious calibration covers a wider dynamic range and should be retained for scene-representativeness checks.