Error reduction for different observational configurations in scenario 1. Varying the number of sites and the Root Mean Square Error (RMSE-R) at each site defines the first four observational configurations in Table 2: (1) 5 sites (towers 1, 2, 3, 5 and 9) with 1 ppm observation error, (2) 12 sites with 1 ppm observation error, (3) 12 sites with 3 ppm observation error, and (4) 5 sites (towers 1, 2, 3, 5 and 9) with 1 ppm observation error and the other 7 sites with 3 ppm observation error. The same prior flux error (RMSE-B is 2 μmol m^–2 s^–1 and SCL is 5 km) is used for all these observational configurations. The domain and coordinates in each panel are same as Figure 1. DOI: https://doi.org/10.1525/elementa.138.f6