First comparison of XCO₂ products from DQ-1 ACDL and passive optical satellites

Abstract. Spaceborne active CO₂ IPDA lidar provides an active remote-sensing approach for XCO₂ observations that differs from passive NIR/SWIR remote sensing. However, comparisons between DQ-1 ACDL and passive optical satellite XCO₂ products remain limited. Here we compare DQ-1 ACDL with OCO-2, OCO-3, GOSAT, and GOSAT-2 XCO₂ products from June 2022 to December 2024 using a unified framework that combines CAMS-based spatiotemporal coherence assessment, satellite sampling availability, daily 2° aggregation, spatiotemporal collocation, and XCO₂ column-definition correction. The results show that DQ-1 is broadly consistent with OCO-2 and OCO-3 over coherent and well-sampled regions, with mean differences mostly below 0.5 ppm and similar spatial distributions, meridional structures, and regional monthly variations. Nighttime DQ-1 XCO₂ is also consistent with CAMS-derived XCO₂, indicating stable performance relative to an external model reference. Independent validation against TCCON shows that daytime DQ-1 XCO₂ has a correlation coefficient of 0.92, a mean bias of 0.21 ppm, and an RMSE of 1.49 ppm, with statistics comparable to GOSAT. Regional results further indicate that DQ-1 does not simply duplicate existing passive satellite observations, but provides complementary XCO₂ observational coverage under high aerosol loading, at high latitudes, and in regions where passive observations are limited. Overall, DQ-1 ACDL is comparable to passive satellite XCO₂ products under the unified framework, and can serve as an important complement to existing passive satellite XCO₂ observations, supporting future active–passive joint XCO₂ constraints, regional carbon flux inversions, and emission monitoring.