As regular readers of Drew Ex Machina are probably aware, in addition to being a writer, I am also a physicist specializing in the processing and analysis of remote sensing data from satellites and other platforms. One of the projects in which I have participated over the past few years is called CyMISS (Tropical Cyclone Intensity Measurements from the ISS). The purpose of this project is to develop an Earth orbiting system that determines the altitudes and temperatures of cloud tops near the eye of powerful tropical cyclones in order to estimate the strength of these storms much more accurately than can be done using existing remote sensing methods (see “A New Satellite-Based Method to Determine Hurricane Strength”). In our implementation, the temperature information is derived using infrared measurements of the cloud field while the cloud altitudes are determine using a new pseudo-stereography technique which takes advantage of the motion of the orbiting platform to provide a stereo baseline.

In order to gather data to help support the development of this system, our project team has been analyzing images of tropical cyclones acquired by the crew of the International Space Station (ISS) using specific photography protocols designed to maximize their value to us. Only imagery from the ISS, which has a low Earth orbit similar to one we wish to use in our deployed system, has the spatial and temporal resolution required to meet our current objectives. Since 2014, this work has been performed under NASA’s Tropical Cyclone Experiment on the ISS and funded, in part, by a grant from CASIS (Center for the Advancement of Science In Space). A sample of the more interesting observations made during 2014 that were analyzed by the CyMISS team has already been presented (see “ISS Tropical Cyclone Experiment” and “New Tropical Cyclone Videos from ISS”). But before we start our recently approved 2016 observation campaign, I wanted to share a sample of our results from 2015.

Sample from the 2015 Campaign

Of the dozens of tropical cyclones observed by the crew of ISS during 2015, a total of five met our requirements of storm intensity and the quality of the image sequence needed for more detailed analysis. Of these, the observations of two powerful Category 4 typhoons were especially noteworthy.

The first was Typhoon Soudelor which formed on July 29, 2015 in the Pacific Ocean. As the storm moved westward towards Asia, it quickly intensified and by August 3 was a Category 5 super typhoon. The crew of the ISS secured a long sequence of images during an overpass on August 4 at approximately 08:00 GMT after the storm had been downgraded to Category 4. A subset of 177 images acquired at a rate of once each second were remapped into a common projection and assembled into a 1,500 by 1,000-kilometer color mosaic to give a synoptic view of this powerful storm as viewed from ISS.

Out of this superb series of images, a total of 65 gave an unobstructed view of the eye of Soudelor. In order to aid analysis and remove the effects of the changes in viewing geometry as the ISS passed by, these images were reprojected into a common-scale overhead view with a nominal pixel footprint of 120 by 260 meters – about a factor of five better than the nominal spatial resolution of the current generation of GOES meteorological satellites.

The original color images and their processed versions were assembled into a video. The loop of close up images of the eye, in addition showing some motion as the ISS crew member made a slight adjustment, displays the signs of some rapid cloud motion especially in the lower half of the eye. On going analysis of these images in combination with complementary data returned from the newly commissioned Japanese satellite, Himawari 8, in multiple wavelength bands will provide much needed data for the development of a CyMISS system.

The second storm of note observed as part of our project from the ISS during 2015 was Typhoon Atsani. This storm formed on August 14 in the western Pacific like Soudelor a fortnight earlier. Atsani intensified and was imaged for our project from the ISS at about 01:11 GMT on August 19 just before it had grown into a Category 5 super typhoon.

Out of the long sequence of images acquired by the ISS crew during this overpass, a total of 44 provided unobstructed views of the storm’s eye. As before, these images were processed into a common scale and projection that approximated an overhead view of the storm. The resulting images have a pixel footprint of about 100 by 220 meters – among the highest resolution views of a powerful tropical cyclone obtained to date for the Tropical Cyclone Experiment. While the eye looked somewhat subdued in the original color images, the reprojected close-ups show a wealth of detail including what appears to be lower altitude clouds deep inside the eye.

As was done for the earlier storm, the original ISS images and their processed versions were used to create a short video of this spectacular storm. With the view of the sequence of close up images in this video focused on the center of the storm, what is immediately noticeable is the large apparent motion of the high-altitude deck of cloud surrounding the eye. This apparent motion is dominated by parallax effects caused by the motion of the ISS .

With this strong parallax present, a pair of reprojected close up images from this sequence were combined to produce a stereo image of the eye of this storm. Although there is insufficient information to accurately determine the absolute altitudes of the clouds in this view, it is apparent that the clouds inside the eye of Atsani are at a much lower altitude than the cloud deck surrounding the eye. Close inspection also reveals much vertical structure in this cloud deck as well.

The CyMISS team is continuing to study data from these two storm along with the others observed in 2015 and earlier in 2014 in support of our project. As we are gearing up for the upcoming 2016 tropical cyclone seasons in the northern hemisphere, the ISS crew has already been busy acquiring new image sequences of promising storms as they occur elsewhere around the globe. With luck, we will secure sufficient data during the course of this year to help us move to the next phase of our project.

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Related Reading

A description of the CyMISS project and a sample of some of its results can be found on this web site’s CyMISS Page. Related posts include:

“New Tropical Cyclone Videos from ISS”, Drew Ex Machina, March 13, 2015 [Post]

“ISS Tropical Cyclone Experiment”, Drew Ex Machina, November 10, 2014 [Post]

“A New Satellite-Based Method to Determine Hurricane Strength”, Drew Ex Machina, June 18, 2014 [Post]

General References

Paul Joss, A.T. Stair and Andrew LePage, “Looking Into the Eye of the Hurricane”, On Station, February 19, 2016 [Article]

“The Cyclone Intensity Measurements from the ISS (CyMISS) (TROPICAL CYCLONE)”, NASA ISS Web Site, [Link]

P.C. Joss, A.T. Stair, J.G. DeVore and G.E. Bingham, “A New Method for Accurate Remote Measurement of Tropical Cyclone Intensities”, Poster at AGU Science Policy Conference (Washington, DC; June 16-18, 2014), Poster # NH-12, 2014 [Poster]