Abstract:Spaceborne carbon monitoring is a crucial observational approach for achieving accurate global surveillance of anthropogenic carbon emissions and advancing climate change research, and it plays an important role in supporting greenhouse-gas mitigation and China′s "dual-carbon" goals. Owing to its broad spatial coverage, passive optical remote sensing has become one of the primary technical pathways for spaceborne monitoring of carbon point sources. Identifying carbon point sources and dynamically tracking their emission variations enable quantitative assessment of carbon emissions from cities and industrial sectors, thereby providing a scientific basis for emission-reduction policies. To address the demand for sub-kilometer spatial-resolution monitoring of carbon point sources, this paper first reviews the development status and recent advances of representative international instruments. Key performance characteristics are then systematically summarized in terms of spectral coverage, spectral resolution, spatial resolution, and swath width. Based on this review, we further outline the fundamental principles of several representative instrument architectures, including prism-based dispersion spectrometers, grating spectrometers, Fabry-Pérot interferometers, and spatial heterodyne interferometric imaging spectrometers. For each architecture, we summarize the corresponding scientific objectives, typical application scenarios, and the use of associated data products. The review indicates that sub-kilometer carbon point-source monitoring payloads are generally evolving toward coordinated improvements in "higher spectral resolution–higher spatial resolution–wider swath", so as to simultaneously meet the requirements of point-source detectability and the accuracy of quantitative emission retrieval. However, concurrent enhancement of these metrics is typically accompanied by trade-offs in optical throughput, system complexity, and engineering feasibility, and different architectures exhibit distinct boundaries in achievable performance and implementation cost. To meet the hotspot greenhouse-gas emission monitoring requirements of China′s next-generation carbon satellite, TanSat-2, we designed and developed a laboratory prototype based on a bidirectional heterogeneous-modulation spatial heterodyne spectroscopy (SHS) concept. Preliminary laboratory experiments demonstrate that, within the 1565 – 1585 nm spectral band, the prototype achieves a spectral resolution better than 0.125 nm. At an orbital altitude of 7 443 km, it attains a spatial resolution better than 500 m while maintaining a swath width exceeding 100 km. These results validate the feasibility of this approach in jointly achieving ultra-high spectral resolution, high spatial resolution, and wide-swath coverage, thereby providing key technical support for future deployment on TanSat-2 to enable quantitative greenhouse-gas column retrievals and point-source detection. Based on the proposed scheme and prototype verification, future spaceborne high-resolution carbon monitoring systems may further target multi-gas synergistic observations by advancing integrated and miniaturized designs of wide-swath, high-resolution spectrometers. Such systems could also benefit from satellite constellations to increase revisit frequency, and from the integration of cloud screening and aerosol correction methods to extend monitoring capability toward nearly all-weather conditions, offering guidance for subsequent engineering development and application system construction. Close-