Planetary cloud tracking

From a perspective of experimental fluid mechanics, this review describes cloud-tracking methods to extract high-resolution velocity fields from publically available images of planets (such as Jupiter, Saturn and Earth) obtained from ground-based and space-based observations. These methods include manual tracking, correlation image velocimetry (CIV) and optical flow method (OFM) that have been applied to various images of planets. The relevant issues such as image navigation, image registration and metric conversion are also discussed. The accuracy of the open-source cloud-tracking algorithms is evaluated based on simulated cloud images of Jupiter's Great Red Spot (GRS). As an example, the application of cloud tracking to the GRS cloud images obtained from NASA's space flight missions is discussed, progressively revealing the complex flow structures of the GRS. Although the cloud images of Jupiter and Saturn are mainly used in this paper, the cloud tracking methods are also applicable to satellite cloud images of Earth. As an extra example, OFM is applied to the satellite infrared images of Typhoon Rai to extract the flow structure of Rai's top layer. This review tries to open a window for experimental fluid dynamicists to explore intriguing planetary flows based on cloud images of planets. [GRAPHICS] .