## 5 Outlook
### Future Work and Landsat 9  
The remote sensing field is growing exponentially. In response, commercial companies have launched cube satellites with remarkable spatial and temporal resolutions at the expense of low orbital stability and radiometric consistency. In addition to Landsat's deep historical archive, Landsat data can act as a radiometric reference, thus mitigating the limitations of data collected by cube satellites. Currently, the application of data acquired by these new satellites has been relatively limited, largely due to price, but remains a potential avenue for future work. This can be more feasible if and when these datasets become more easily accessible. In recent years, cloud platforms have been developed with a focus on planetary-scale products and applications. Most of these platforms rely on free availability of data collected by sensors such as Landsat. However, due to costs and policies, many of these cloud platforms are not commonly used in studies. The inclusion of regional, national, and local reference data sets in these platforms would be of great support to up-and-coming projects. Landsat-9 is planned to be launched in September 2021 and will provide long-term data production (sustainability), meet the Landsat archive performance standard for monitoring decadal landscape changes (continuity), and continue the long-running Landsat observational record (reliability). Landsat-9 will take the orbital place of Landsat-7, continuing the trend of 8 days of data provision with Landsat-8. Landsat-9 shares many similarities with Landsat-8, including spatial resolution and a sun-synchronous orbit. There are, however, some significant improvements and enhancements. Similar to Landsat-8, Landsat-9 is required to provide at least 400 scenes per day to USGS. However, the collection of as many as ~740 scenes per day is supported by a 4 Tb onboard data recorder and a ground system, designed to allow for control of Landsat-9 in orbit and manage data transmission. The major updates of Landsat-9 are to the OLI-2 and TIRS-2 sensors. OLI-2 data will be downlinked with the full 14-bit radiometric resolution, improving the signal-to-noise ratio in darker areas. The TIRS-2 absolute radiometric accuracy is improved, and the scene-select mirror mechanism has been redesigned for more precise geolocation. Both sensors and the spacecraft were designed with five-year lifetimes. However, consumable resources carried by Landsat-9 are sufficient for 10 years of operation, which is only feasible if the satellite survives its early operation stage. The Landsat Collection 2 became available in December 2020 and prior to the launch of Landsat-9, representing the second major reprocessing of the Landsat data archive. Collection 2 offers improved geometric accuracy by joining ground control points with Copernicus Sentinel-2 global reference images. Additionally, Collection 2 benefits from updated 3-arc-second digital elevation modeling and radiometric improvements of some satellites. Collection 2 will also provide per-pixel quality assurance (QA) bands shared by Collection 1, including cloud and cloud shadow confidence, snow and ice confidence, radiometric saturation, and terrain occlusion, with the addition of surface reflectance aerosol and surface temperature QA bands. After the public release of Collection 2, Collection 1 will remain accessible for at least one year and Landsat-9 data will be processed only into Collection 2. It is worth noting that Landsat-4-Landsat-9 Collection 2 will include single-channel atmospheric compensation for surface temperature products to ensure time series consistency. However, Landsat-8 and Landsat-9 dual separated thermal channels grow expectations for future Collection 3 reprocessing to enable atmospheric correction via split-window technique [54]. Landsat Collection 2 surface reflectance/temperature products, as the best input for change detection studies, will be available in 25-27 days after Landsat-7 and 15-17 days after Landsat-8 data acquisition.