Let's look at an example
In the image on the right, we can see there is an area of colder cloud tops (around -40°C) over the south of the South Island, but there is no information about the depth of the cloud layer. We can also see an area of relatively warm cloud tops along the South Island West Coast, and what appears to be a cloud free area off the Canterbury coast. One of the major limitations of infrared satellite imagery is that if the cloud tops are a similar temperature to the land or sea, they will not be easy to distinguish. A particular example of this to be aware of is when there is fog or stratus, because this will be a relatively thin layer, with a temperature very close to the surface below (sea or land). At night, when fog and stratus are more common, its presence cannot be determined from infrared images alone, however, once the first visible satellite image is available, the areas will become obvious.