Abstract: Integrated path differential absorption (IPDA) LiDAR retrieves atmospheric column absorption from the power ratio of online and offline dual-wavelength hard-target returns. Active IPDA observations are independent of solar illumination and provide narrow footprints and enhanced sensitivity to the lower atmosphere, complementing passive greenhouse gas remote sensing with wide coverage and mature product chains. As the first on-orbit greenhouse gas IPDA LiDAR, DQ-1/ACDL has generated global XCO₂ products. Validation of its v1.0 product against 13 TCCON sites yielded a mean error of 0.02 ppm and a root mean square error of 1.4 ppm, indicating that spaceborne greenhouse gas IPDA has entered the stage of on-orbit application validation. This review examines progress and constraints in payload design, cross-scale validation, and multisource fusion as spaceborne greenhouse gas IPDA advances from payload validation toward operational carbon monitoring. Operational applications require balancing measurement performance and effective coverage under platform resource constraints and closing the ground-airbornespaceborne validation chain. Active-passive product fusion also requires harmonized weighting functions, averaging kernels, spatiotemporal scales, surface elevation, and meteorological inputs, with random errors and correlated systematic biases propagated from Level 2 products to Level 4 applications. A three-stage development roadmap is proposed, comprising single-satellite application validation, cross-sensor fusion, and constellation-based continuous operational services, with end-to-end performance from Level 1 returns to Level 4 fluxes used to assess operational maturity.