How many ship tracks can you see at night south of Alaska in this GOES-17 imagery?
By Jochen Kerkmann (EUMETSAT) and Dan Lindsey (CIRA)
As shown in the case study from 26 June 2015 ship trails can be tracked at night using the Night Microphysics RGB or the 24-hour Microphysics RGB.
Small droplets emit less radiation (lower emissivity) in the IR3.9 and IR8.4 bands (compared to large droplets), so that at night the brightness temperature difference (BTD) IR10.3–IR3.9 (or IR10.3–IR8.4) of ship trails is more positive than the brightness temperature difference of stratocumulus clouds with large droplets.
With the availability of new satellite instruments like the Advanced Himawari Imager (AHI) on Himawari-8/9 and the Advanced Baseline Imager (ABI) on GOES-16/17, the ability to detect ship trails has significiantly improved. The higher spatial resolution (2 km), and the higher radiometric resolution and lower noise, lead to a larger colour contrast between ship trails (green) and non-polluted stratocumulus clouds (light magenta).
Figure 1: GOES-17 Night Microphysics RGB, 5 Feb 02:00 UTC–09:00 UTC
This can be seen in the animation of the GOES-17 Night Microphysics RGB from 02:00 to 09:00 UTC (night). The ship trails appear as a bright green colour. It is possible to follow some of the ships by tracking the leading edges of the trails, resulting in speed estimates of around 18–20 kn.
Note: NOAA's GOES-17 satellite has not been declared operational and its data are preliminary and undergoing testing.