These images were captured by the NOAA series of polar-orbiting meteorological satellites (NOAA-15, 16, 17,18 or 19) operated by the U.S. National Oceanic and Atmospheric Administration) or the MetOP-series of satellities operated by European Organization for the Exploitation of Meteorological Satellites.
Polar-orbiting satellites revolve around the Earth along paths which pass roughly over the poles, and take pictures of the Earth along their paths. Normally, one to two images can be received at Hong Kong from each satellite every day. Orbiting several hundred kilometres aloft, these satellites are closer to the Earth than geostationary satellites and thus produce images of higher resolution.
The images are in the infra-red region (wavelength between 10.3 and 11.3 micrometres) showing temperatures of cloud tops. In general, the higher the cloud top, the lower its temperature will be. The colour scale in the picture provides a read-out of the cloud temperature.
There may be occasional signal interference and blockage by obstacles during image reception, causing black lines on the image.