It’s been a while since we last looked at some tropical cyclones with VIIRS. If you don’t keep up to date on tropical activity, you might not know there that have been a few. Granted, since Debby dumped a bunch of rain on Florida three weeks ago, the Atlantic basin has been pretty quiet. The East Pacific basin, however, has had one storm after another. The national media has largely ignored them since they have posed no threat to any landmasses. See this article from the L.A. times. Boring! Unless you can capture video of Jim Cantore struggling to stand upright, it isn’t a hurricane, right?
Wrong! First of all, eastern Pacific hurricanes affect some major shipping lanes. Second, and this is true of all hurricanes: they transport energy and moisture and help moderate the temperature imbalance between the tropics and mid-latitudes. They are important components of global energy transport.
In this post, we are going to compare the view of hurricanes provided by VIIRS against the view provided by GOES (specifically GOES-15). On 9 July 2012, there were two storms in the East Pacific: Daniel and Emilia.
Here is the GOES-15 view of Daniel followed by the VIIRS view of Daniel in their respective visible channels:
GOES-15 visible image (channel 1) of Hurricane Daniel, taken 22:45 UTC 9 July 2012. Image courtesy John Knaff.
VIIRS visible image (channel I-01) of Hurricane Daniel, taken 22:29 UTC 9 July 2012
Both images have the same latitude and longitude lines printed on them for reference and they both use the same color scales. If you zoom in, you’ll notice that the VIIRS image, with ~375 m resolution at nadir shows a bit more detail than the 1 km (1000 m) resolution GOES image. The additional detail provided by VIIRS really stands out in the infrared (IR) window channels, where GOES has 4 km resolution and VIIRS still has ~375 m resolution:
GOES-15 IR image (channel 4) of Hurricane Daniel, taken 22:30 UTC 9 July 2012
VIIRS IR image (channel I-05) of Hurricane Daniel, taken 22:29 UTC 9 July 2012
Now, it is worth noting that the high resolution IR image of VIIRS shown above comes from channel I-05, which is centered at 11.45 µm. The GOES image was produced from Imager channel 4, which is centered at 10.7 µm, so the two channels don’t exactly have the same spectral properties. VIIRS has a 10.7 µm IR channel as one of its moderate resolution bands (M-15). Here’s what that image looks like:
VIIRS IR image (channel M-15) of Hurricane Daniel, taken 22:29 UTC 9 July 2012
There isn’t a big difference between the two VIIRS channels, although you can see a bit more detail in the higher resolution (I-05) image.
On the previous orbit, VIIRS caught images of Hurricane Emilia, which was also in the view of GOES-15. Here’s how the images compare:
GOES-15 visible image (channel 1) of Hurricane Emilia, taken 21:00 UTC 9 July 2012. Image courtesy John Knaff.
VIIRS visible image (channel I-01) of Hurricane Emilia, taken 20:48 UTC 9 July 2012
GOES-15 IR image (channel 4) of Hurricane Emilia, taken 20:48 UTC 9 July 2012
VIIRS IR image (channel I-05) of Hurricane Emilia, taken 20:48 UTC 9 July 2012
In addition to the resolution differences, there is also a time difference of ~15 minutes between the VIIRS images and the GOES images. If you were to overlap these images, you would see that Emilia rotated a bit during that time. Emilia was not willing to hold the same pose for that long when having her picture taken. Once again, the M-15 image from VIIRS looks pretty similar to the I-05 image, so there’s no pressing need to show it.
Finally, let’s compare GOES-15 with VIIRS on Hurricane Fabio, which formed about a week after Daniel and Emilia were hurricanes.
GOES-15 visible image (channel 1) of Hurricane Fabio, taken 20:30 UTC 15 July 2012. Image courtesy John Knaff.
VIIRS visible image (channel I-01) of Hurricane Fabio, taken 20:36 UTC 15 July 2012
GOES-15 IR image (channel 4) of Hurricane Fabio, taken 20:30 UTC 15 July 2012
VIIRS IR image (channel I-05) of Hurricane Fabio, taken 20:36 UTC 15 July 2012
The GOES and VIIRS images of Fabio were taken only 6 minutes apart, so there is less movement to impede the comparison.
In all three hurricanes, you can see a lot more structure to the VIIRS images in the both the visible and IR channels. It’s as if GOES represents a standard definition TV camera, and VIIRS represents a hi-def TV camera. All those wrinkles GOES is smoothing over are showing up in VIIRS. Daniel, Emilia and Fabio are going to need more makeup. (Or, they would if they weren’t already dead.)