The EarthCARE Commissioning Calibration and Validation Campaign in Ottawa (ECALOT) was a dedicated airborne and surface-based campaign designed to support the calibration and validation of Level 1 and Level 2 products from the EarthCARE satellite mission. The campaign was conducted between October 2024 and March 2025 in eastern Canada, primarily in the regions surrounding Ottawa and Montreal. Airborne observations were carried out using the National Research Council Canada (NRC) Convair-580 research aircraft, equipped with remote sensing instruments analogous to those flown on EarthCARE, including a nadir/zenith/side-looking 94 GHz cloud radar system with Doppler capability and zenith/nadir-pointing 355 nm elastic lidars, together with a comprehensive suite of in situ cloud and aerosol probes. Complementary surface-based observations were obtained at a primary site at the Ottawa Macdonald-Cartier International Airport and two additional climate sentinel stations in the Montreal region, providing continuous ground-based reference measurements of surface radiation, atmospheric thermodynamic profiles, precipitation, and other meteorological variables.</p> <p>A total of seven research flights were conducted, sampling a range of mid-latitude continental cloud conditions, including stratocumulus, multilayer cloud systems, and nimbostratus associated with liquid- or solid-phase precipitation. The ECALOT sampling strategy was designed to integrate airborne and surface-based in situ and remote-sensing observations collected along and offset from EarthCARE’s ground track, while accounting for temporal offsets relative to the satellite overpass. Together, the ECALOT campaign provides coordinated multi-platform observations that enable evaluation of active sensor measurements, radar-lidar-imager synergy, representation of liquid, ice and mixed-phase clouds, three-dimensional scene construction, and radiative closure across EarthCARE’s data processing chain, while also providing observational constraints for improving the representation of mixed-phase clouds and their radiative effects in numerical models.