Abstract: Integrated path differential absorption (IPDA) light detection and ranging (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 XCO${}_{\mathrm{2}}$ products. And the validation of its v1.0 product against by 13 total carbon column observing network sites yielded mean error of 0.02×10^-6 and root mean square error of 1.4×10^-6, indicating that spaceborne greenhouse gas IPDA has entered the stage of on-orbit application validation. We examine progress and constraints in payload design, cross-scale validation, and multi-source 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-airborne-spaceborne 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.