GOES-8 Imagery as a New Source of Data to Conduct Ocean Feature Tracking

Sequential imagery from the AVHRR has been used to conduct ocean feature tracking since the early 1980s. One of the primary limitations of AVHRR data for feature tracking is the lack of temporal continuity, since it is only possible to obtain coverage from the same satellite once every 12 hours. Thus, for the highly variable flows that are often encountered in coastal areas, undersampling can be a serious problem. With the availability of imagery every half hour from the new imager on the GOES-8 and -10 satellites, the possibility of tracking features on shorter time scales should be considered. Also, the higher sampling rate of the GOES imager could be particularly beneficial in obtaining cloud-free coverage of the ocean. However, unlike the AVHRR, which has 1-km resolution, the new imager on GOES has 4-km resolution in the infrared channels. Thus, even for relatively vigorous currents, it will take at least several hours for a feature to be advected over a distance of one pixel, and considerably longer to generate displacements that can be estimated reliably. Also, one of the basic assumptions in conducting ocean feature tracking has been that it is the submesoscale features that serve as the primary tracers of the flow. As pixel size increases, the ability to resolve and track features at these scales clearly comes into question. Additionally, as with AVHRR imagery, the ability to accurately navigate successive images is crucial to making reliable estimates of the feature displacements. These and other related issues are discussed, and three examples of feature tracking using imagery from the imager on GOES-8 are presented, together with qualitative verifications in each case. Finally, a new method for rapidly renavigating satellite imagery is presented.