Planet is improving its algorithm for calculating Surface Reflectance in PlanetScope and RapidEye products. Planet is also now producing analytic_sr assets under the existing PSOrthoTile and REOrthoTile item types.
The new Surface Reflectance algorithm should help reduce scene-to-scene difference due to rapidly varying atmospheric conditions. Reference the updated white paper on the support page: https://support.planet.com/hc/en-us/articles/360012629573-Planet-Surface-Reflectance-Product
The new analytic_sr assets are available under the existing PSOrthoTile and REOrthoTile items listed in the Dev Center: https://developers.planet.com/docs/data/items-assets/