Precipitation - measurements are made at the surface where the water is used by plants, runs off in rivers, soaks into the ground. Usually, a surface-based measurement is used to characterize the climatic conditions in weird locations and to characterize climatic differences between locations. Because of their long record these measurements provide a means to identify how various climate elements change over time. Potential changes in station location, exposure, observer techniques, obs time, equipment, etc. Measurements over oceans are generally sporadic.
Satellites represent a platform for remote sensing.
Scientists must keep the accuracy of these remote sensing instruments high or the measurements will not mean much and thus will not be used. Measurements are taken by a radiometer and generally for a few square kilometer area. Quite different from surface-based point measurements. Describe the climate for particular applications. Derived data is better than the actual observed data.