What if we wish to see objects smaller than the resolution  of the sensor?

We cannot see objects smaller than the resolution of a sensor, but we can infer whether they are there or not by applying methods called "mixed pixel classification" to multispectral images.

What is a mixed pixel?

A mixed pixel is a pixel that contains radiation reflected by more than one type of object. For example, Fig 3 shows a typical orchard "scene" with trees planted far from each other (an element in this image corresponds to 1m²). When this scene is imaged with a sensor of 5m resolution, we may have some pixels of pure soil, but most of the pixels will have received reflected  radiation by both the soil and the trees.

Figure 3