Earlier this week Hurricane Daniel was churning westward across the Eastern Pacific, trailed not far behind by Emilia, which remains an active storm. The last advisory related to Daniel was issued by the Central Pacific Hurricane Center on Wednesday, July 11, while Emilia remains a Category 3 storm. In the early morning hours of July 9, then-Hurricane Daniel was a Category 1 storm and was observed by the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument carried aboard the Suomi National Polar-Orbiting Partnership (S-NPP), a polar orbiting satellite that provides continuity measurements for NASA and DOD instruments as a precursor to the Joint Polar Satellite System (JPSS). The VIIRS instrument is similar to MODIS in that it provides high resolution visible and infrared imagery. In this unique case, the VIIRS instrument includes a “near constant contrast” or day-night band that is capable of detecting moonlight in a manner similar to the way that current geostationary satellites provide visible imagery during the day. As with sun-lit visible imagery, a lot of detail is provided regarding cloud type and texture.
Below are a few examples of imagery from VIIRS for Hurricane Daniel. First, a traditional grayscale infrared image that has been enhanced to pick up areas of active convection in brighter white shades.
July 9th featured a moon phase slightly greater than a half moon, providing a substantial amount of visible light to be reflected off of the clouds associated with the storms and other features. Below is a gray scaled image similar to a day time visible image, except that the colors correspond to radiance associated with moonlight that is reflected back to the satellite from the clouds below.
The Naval Research Laboratory has used imagery from DoD satellites and other VIIRS imagery to produce a false color composite that combines the day night band’s moonlit imagery and infrared data to characterize both the texture and cloud type inferred from moonlight and the cloud top temperature inferred from the infrared data. This results in a color combination where low level clouds and city lights (when present) appear in yellow, while mid to high level clouds appear in shades of blue or white. Combined, these color characterizations can help to discriminate between various cloud types and portions of the storms’ structures.
SPoRT is working on methods that will incorporate these types of data sets within NWS decision support systems such as N-AWIPS, AWIPS, and AWIPS II. Although some of these systems cannot currently support the full color depth provided by the Google Earth examples above, techniques are available to provide these single and false color images to forecasters. Below is an example of Hurricane Daniel as could be viewed within the N-AWIPS system.