CyMISS (Cyclone Intensity Measurement from the ISS)
One of the most destructive natural phenomena known are powerful tropical cyclones (better known in the US as “hurricanes” when they originate in the Atlantic or eastern Pacific Oceans or in nearby seas). Their powerful winds, rain and associated storm surges can cause huge losses of life and property. While there have been great improvements made in recent decades in our ability to track and predict these destructive storms largely as a result of advances made in satellite remote sensing technology, there is still much room for improvement especially when these storms occur outside of the range of American hurricane-chasing aircraft whose patrols are limited to the Atlantic and northeastern Pacific Oceans.
Limitations of Today’s Methods
Today, the empirically-based Dvorak technique and its subsequent modifications are generally used to categorize the intensity of tropical cyclones in the absence of observations from surface ships or instrumented ocean buoys. Named after American meteorologist Vernon Dvorak who developed and refined the method between 1969 and 1984, the Dvorak technique relies on data from constellations of meteorological satellites in polar or geosynchronous orbit to estimate the strength of storms based on such attributes as their appearance, temperature and the apparent motion of cloud features over time. But the modified Dvorak technique can experience errors of at least 20% in estimating maximum sustained surface winds. A dangerous Category 3 tropical cyclone could be miscategorized as a weaker Category 1 storm or vice versa.
Image of Typhoon Haiyan taken by NASA;s Earth Observatory as it approached the Philippines on the left. (NASA)
One example of this was Typhoon Haiyan which hit the Philippines on November 8, 2013. It was not recognized that this typhoon was still intensifying as it approached landfall and this resulted in an estimated death toll of about 10,000 partly because the appropriate evacuation orders were never issued. A more recent example was the first hurricane of the 2014 season, Hurricane Amanda, which unexpectedly intensified but fortunately caused no loss of life or property since it remained far out at sea. A counterexample of a storm that never intensified as expected was tropical Cyclone Phailin which made landfall near Gopalupur, India on October 12, 2013. Expected to intensify to a dangerous Category 5 storm, the government of India evacuated 800,000 people along the vulnerable coast at great expense only to have the storm turn out to be a a much less dangerous low-end Category 4 storm. Obviously better methods are needed to help predict the strength of tropical cyclones.
CyMISS (Cyclone Intensity Measurements from the ISS)
Professor Kerry A. Emanuel of the Massachusetts Institute of Technology (MIT) developed the currently accepted theory that the thermodynamics of tropical cyclones are the equivalent of a Carnot engine. The Carnot cycle operates between the warm ocean and the cold stratosphere to power these storms’ powerful surface winds and intense rainfall. Emanuel’s model was subsequently extended with input from Dr. Paul C. Joss of MIT and Visidyne, Inc. in Burlington, Massachusetts in the late-1990s as part of an experiment of the RAMOS (Russian-American Observation Satellites) cooperative program with Russia.
Diagram demonstrating how the Carnot cycle powers cyclones. By accurately measuring the altitude and temperature of the clouds of the storm’s eye wall, the strength of the storm can be determined. Click on image to enlarge. (Visidyne)
Cancelled in 2004, the RAMOS program was to use a pair of Russian-built satellites carrying an American and Russian-built instrument suite to make stereo observations of clouds and other atmospheric phenomena at wavelengths ranging from the infrared to the ultraviolet with a nominal 100-meter pixel footprint (see this site’s RAMOS Page for more information). Dr. Joss and other members of the RAMOS program’s American science team had worked out an improved method of estimating the strength of tropical cyclones based on the Carnot engine model using information about the temperature of the cloud tops around the storm’s eye wall (derived from infrared measurements from the satellites) and the altitudes of those clouds (derived from a three dimensional reconstruction of the scene using stereo data from the pair of satellites). With cloud top temperature accuracy of ±1° K and altitude determinations of about ±100 meters, the observations by RAMOS coupled with this new Carnot engine model promised to provide estimates of tropical cyclone strength superior to those based on the Dvorak techniques using data from conventional meteorological satellites.
Although the RAMOS program was cancelled, work has continued on this improved method at Visidyne with the hope that we would one day have an opportunity to implement it. Since 2013, a team from Visidyne working in cooperation with engineers at Utah State University’s Space Dynamics Laboratory in Logan, Utah (the former prime contractor of the RAMOS program) has developed the proposed CyMISS (Cyclone Intensity Measurements from the ISS) project. Selected by CASIS (Center for the Advancement of Science in Space which manages the US National Laboratory on the International Space Station), we are developing a relatively inexpensive demonstration of our technique for an initial daytime-only implementation called CyMISS-D (with “D” for “daytime”). Astronauts on the ISS are currently gathering images of tropical cyclones with hand-held cameras as part of their CEO (Crew Earth Observation) program to support development of this project.
Example of a 3D reconstruction of a thunderstorm using pseudo-stereo. Click on image to enlarge. (NASA & A.J. LePage/Visidyne)
CyMISS-D will use a camera operating at visible wavelengths with precisely known pointing mounted on the ISS to obtain a sequence of images of tropical cyclones as the space station passes overhead. Building on earlier work done as part of the RAMOS program, these images will then be analyzed using a new pseudo-stereo technique developed at Visidyne to determine the altitude of the clouds associated with the eye of a tropical cyclone. Instead of using a pair of satellites to provide stereo information about a scene, a single platform is used in the pseudo-stereo technique with the orbital motion providing the baseline required for stereo.
The accuracy of earlier attempts to derive cloud altitudes using pseudo-stereo analysis of satellite images have been limited because of the motion of the clouds being measured – a problem especially severe in powerful cyclonic storms. In order to get the required altitude accuracy of 100 to 200 meters, information from the analysis of a sequence of images acquired by the CyMISS-D camera on ISS will be combined with information on cloud motions derived from a sequence of high frame-rate, visible-band mesoscale images acquired by the ABI (Advanced Baseline Imager) to be carried by the new GOES-R geosynchronous meteorological satellite slated for launch in 2015. For the CyMISS-D demonstrations, infrared data from ABI will also be used to derive cloud top temperatures.
The ABI (Advanced Baseline Imager) to be carried by the new GOES-R satellite. Images from this instrument will be combined with image sequences from CyMISS-D in low Earth orbit to accurately determine the strength of tropical cyclones. (NOAA/NASA)
The uncertainty in the sea level pressure at the center of the storm is expected to be ±5 hPa with the uncertainty in the surface wind speed of ±20 knots (±10 m/s) – a significant improvement over the existing Dvorak-based techniques. The addition of an infrared imager to our ISS-based instrument package in the future would allow CyMISS to derive its own cloud top temperatures at higher spatial and temporal resolution independently of ABI as well as allow the system to make nighttime observations.
After the concept has been demonstrated on ISS, we currently envision deploying a constellation of four or more miniaturized satellites based on Cubesat or similar technology that will allow storms to be observed every two to five hours. Information derived from CyMISS could then be incorporated into storm forecast models which are updated every six hours and promise to greatly improve forecasting of the strongest tropical cyclones.
The Tropical Cyclone Experiment on ISS – 2014 Results
While the crew on the ISS have been performing handheld photography of tropical cyclones for years, unfortunately these images are typically of limited use for meeting our goals. They are usually acquired at irregular intervals using a zoom lens employing widely varying focal lengths over a range of poorly known or completely unknown pointing angles. Too many parameters are varying by too much and frequently in unknown ways with too wide a field of view to meet our needs. Images need to be acquire in a very specific way that maximizes their usefulness to us.
Typhoon Vongfong as viewed from the Cupola of the ISS on October 9, 2014. (Earth Science and Remote Sensing Unit NASA-JSC)
After months of working through the appropriate channels in the ISS program office at NASA to institute specific photographic protocols, the Tropical Cyclone Experiment is now an officially approved ISS experiment under their CEO (Crew Earth Observation) activities. When an appropriate target has been identified, the ISS crew will fix-mount one of the digital cameras they have available in the ISS Cupola to acquire a sequence of images at one-second intervals for several minutes as the ISS passes over a tropical cyclone. Because of the technical limitations of such photography, performing meaningful, quantitative pseudo-stereo reconstructions of the storms observed will not be possible using these images. But these image sequences can be used to meet the following, more limited objectives:
– Characterize the scene structure near the eye of a tropical cyclone on spatial scales of 100 meters or better.
– Characterize the persistence of scene structure and how it evolves over the course of 100 to 200+ seconds with a temporal resolution on the order of one second.
– Provide realistic image sequences to support the development of pseudo-stereo reconstruction software that will be capable of absolute altitude accuracies of 100 meters.
ISS crew photography is currently the only practical means of providing the data we require. The resolution and imaging rate from weather satellites are too low while commercially provided satellite imagery has more resolution than we require and covers too small an area.
A montage of images showing the eyes of tropical cyclones observed from the ISS during 2014 that met our project’s selection criteria. Each image has been remapped to approximate an overhead view covering an area of 100×100 kilometers. On the top row (left to right) are Hurricane Arthur on July 3, Typhoon Neoguri on July 8 and Hurricane Edouard on September 16. Bottom row are Hurricane Edouard on September 17, and two views of Typhoon Vongfong on October 9 and on October 10. Click on image to enlarge. (A.J. LePage/Visidyne/NASA-JSC)
While we were working our way towards getting our tropical cyclone imaging procedures approved, we were able to use existing channels to direct the astronauts to photograph various storms during the course of this past summer on an “as-available” basis. In the end, a limited set of images from four TCs observed on a total of seven passes between July 3 and October 10 satisfied our selection criteria well enough to allow us to meet some of our near-term objectives. The observations of Hurricane Edouard and Typhoon Vongfong have proved to be especially useful for our work.
Hurricane Edouard
On September 16 and 17, ISS crew were able to acquire images for us of Hurricane Edouard on three different passes as it churned away in the North Atlantic. Here is a typical image of Edouard taken by the astronauts. It was acquired on September 16 at 13:51:49 GMT.
An oblique view of Hurricane Edouard taken at 13:51:49 GMT on September 16, 2014 from the ISS. (Earth Science and Remote Sensing Unit NASA-JSC)
The images the astronauts acquired were taken using two different cameras with zoom lenses with focal lengths ranging from 28 to 200 mm. A subset of the images with focal lengths longer than 40 mm and with the horizon visible to provide a pointing reference were selected for further study. In order to aid in our analysis, we had to reprocess the images to take out the huge variations in the focal length settings used as well as the changes in the viewing geometry as the ISS passed the storm. Here is a montage of a dozen images acquired over 82 seconds remapped into a common nadir-viewing projection. For this particular montage, each image uses just the red-channel of the original color image and covers 100 by 100 kilometers roughly centered on the eye of Edouard.
A montage of images of Hurricane Edouard acquired on September 16, 2014 from ISS that have been reprojected to a common scale and view. Each image tile covers 100X100 km. Click on image to enlarge. (A.J. LePage/Visidyne/NASA-JSC)
Such image sequences will be useful in characterizing the scene structure on spatial scales of hundreds of meters and how it changes over the course of tens of seconds. Subsequent observations of Hurricane Edouard on the subsequent orbit of the ISS on Spetember 16 and again on the following day clearly show that the appearance of the eye of this storm change greatly over the course of an 98 minutes and 23 hours 12 minutes.
A selection of three red-channel images of Hurricane Edouard illustrating how the appearance of the storm’s eye changed 98 minutes (center) and 23 hours 12 minutes (right) after the image on the left was acquired. Each of the images covers 100X100 kilometers and was remapped to a common image scale of 100 meters/pixel. Click on image to enlarge. (A.J. LePage/Visidyne/NASA-JSC)
Typhoon Vongfong
On October 9 and 10, ISS crew acquired images of Typhoon Vongfong in the western Pacific Ocean as it was heading towards Asia. Here is a Terra-MODIS image of Vongfong acquired on October 10 that provides an overview of the storm as it approached the Asian mainland.
A Terra-MODIS image of Typhoon Vongfong as it appeared on October 10, 2014. Click on image to enlarge. (GSFC.NASA)
Of particular interest to us was a long, six-minute sequence of images acquired using a fixed-mounted camera looking out one of the windows in the Cupola. Although the images were taken with a wide-angle lens and have less than half the resolution we would like, it is proving to be an excellent series of images nonetheless. Here is a typical image in the sequence showing an oblique view of Vongfong not long after the eye of the storm became visible in the sequence. It was acquired at 8:13:51 GMT when ISS was at an altitude of about 418 kilometers with the eye of the storm at a nadir angle of about 51°.
One of a sequence of 361 images acquired on October 10, 2014 giving an oblique view of Typhoon Vongfong from the ISS. (Earth Science and Remote Sensing Unit NASA-JSC)
One of the first steps in our analysis requires that all of these images be reprojected to a common perspective and scale. Here is the above oblique view of Vongfong reprojected to appear as if it is being viewed from directly above. This image covers about 2100 by 1400 kilometers.
The previous image of Typhoon Vongfong reprojected to appear as if being viewed from above. This image covers an area of 2100X1400 km. Click on image to enlarge. (A.J. LePage/Visidyne/NASA-JSC)
Here is a close up view of the eye of Vongfong from the same image. This reprocessed image covers an area of 210 by 140 kilometers at a pixel footprint of 200 m/pixel (close to the resolution limit of the original color image but five times better than typical GOES weather satellite images).
A reprojected close up image of the eye of Typhoon Vongfong covering 210X140 km. Click on image to enlarge. (A.J. LePage/Visidyne/NASA-JSC)
Since we have a long sequence of images, it was also possible to use two of these images to produce a very preliminary anaglyphic stereo image of the eye of Vongfong. The two images used for this sample were acquired about 18 seconds apart over a baseline of about 125 km. Like the image above, it covers an area of 210 by 140 kilometers at a pixel footprint of 200 m/pixel. The black area in the upper right represents the part of the scene that was not viewed in both image pairs. While cloud feature motions and image distortions are mixed in with the parallax resulting from variation in the altitude of the clouds in the scene, there is enough stereo information present to provide a convincing 3D effect:
An anaglyphic stereo image (left eye – red/right eye – cyan) of the eye of Typhoon Vongfong. Click on image to enlarge. (A.J. LePage/Visidyne/NASA-JSC)
Reprocessing the 165 images in sequence from this pass that offer an unobstructed view of the eye to a common nadir-view and scale has allowed us to characterize how features near the eye of tropical cyclones move and change over time. While the effective resolution of these reprocessed images becomes quite poor late in the sequence due to the increasing slant range and oblique viewing geometry, we should be able to meet our near-term objectives using the images from the first half of the sequence.
A montage of selected remapped versions of the images of Typhoon Vongfong acquired during the ISS overpass on October 10, 2014. Each of the images has been reprojected to approximate an overhead view which covers 100X100 kilometers with a common image scale of 200 meters/pixel. This sample of images are spaced at regular ten-second intervals from 8:13:30 (upper left) to 8:16:00 GMT (lower right). Note the decrease in image resolution over time. Click on image to enlarge. (A.J. LePage/Visidyne/NASA-JSC)
These images have been used to produce a video which clearly shows how the cloud features near the eye of the storm move and change over time. Analysis of the images in this sequence will be useful for mapping the apparent velocity of cloud features near the eye of this powerful storm.
Over the course of the next several months, we will be continuing to analyze the images acquired during the 2014 hurricane/typhoon season which should help meet all three of our near-term objectives. And now that we have an officially approved ISS experiment, with luck we will be acquiring images using our new procedures as the tropical cyclone season opens in the southern hemisphere.
General References
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]
“The Cyclone Intensity Measurements from the ISS (CyMISS) (TROPICAL CYCLONE)”, NASA ISS Web Site, [Link]
“Weekly Recap From the Expedition Lead Scientist – December 18, 2014″, NASA Space Station Research & Technology Web Site, [Link]