The residents of Puerto Rico were still coping with the aftermath of Hurricane Irma, when Hurricane Maria ripped across the island on September 20-21, 2017. Maria was a strong Category 4 storm when it made landfall, but just how strong its winds were is unclear. There are no land-based records of Maria’s maximum sustained winds because the storm damaged most of Puerto Rico’s wind sensors and destroyed the island’s weather radar system. Maria also took out most of the island’s electric power grid and telecommunications network, destroyed homes and businesses, and blocked roads with downed trees and flooding. Thus, there was little doubt that emergency managers and first responders would face significant challenges when they arrived on the island.
In the wake of such extreme weather, knowing where and how long electrical power has been out is vital information for emergency managers tasked with deciding where to send first responders, repair crews, and much-needed supplies. So, in the days and weeks after the storm, NASA scientists worked around the clock to make sure disaster response agencies such as FEMA and the National Guard received timely, high-quality satellite imagery and maps showing the precise locations of Puerto Rico’s power outages.
That high-quality satellite imagery was made possible by NASA’s Black Marble at Sensor Radiance (aka: Black Marble) dataset. This product capitalizes on the sensitivity of the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument’s Day/Night Band (DNB) to detect city lights, lightning, fires, gas flares, fishing fleets, and other anthropogenic light sources under varying conditions of illumination around the globe. The VIIRS instrument sits aboard the joint NASA-NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites. Suomi NPP and NOAA-20 observe nearly every location on Earth at roughly 1:30 pm and 1:30 am (local time) each day, as they image the planet in vertical 2,000-mile swaths from the North to the South poles.
Although the Black Marble dataset provides images of nighttime lights and other sources of light in greater detail than traditional nighttime imagery (such as the DNB, Enhanced Near Constant Contrast) it isn’t perfect. Because the VIIRS instrument’s DNB channel is sensitive to light from the moon, it can be difficult to discern the presence of clouds in instances where the moonlight isn’t bright enough to highlight them. Detecting the presence of clouds is important, as cloud cover can block or diminish sources of light on the ground, making it harder for analysts to determine whether missing lights are the result of a power outage.
To address this problem, scientists at the U.S. Naval Research Laboratory combined DNB and longwave infrared data to create DNB imagery in which clouds were easier to detect. The product was later adapted by NASA’s Short-term Prediction Research and Transition (SPoRT) Center at NASA's Marshall Space Flight Center for use with NOAA’s National Weather Service partners to demonstrate how DNB and infrared imagery could be used in concert. (Some of those applications continue today and have been further extended by NOAA with products like the GOES-R GeoColor, which combines geostationary imagery with nighttime lights as a base layer during nighttime imagery.) The SPoRT product, known as the Black Marble Nighttime Blue/Yellow Composite (DNB), joins NASA’s Black Marble daily at-sensor top-of-atmosphere nighttime radiance product with traditional infrared imaging provided by other bands of the VIIRS sensor to produce imagery that shows nighttime city lights in shades of yellow with clouds presented in shades of blue when no moon is present. Clouds appear yellow or white when the moon is at its brightest.
“This red, green, blue composite, when combined with training, makes it easier for the user to more readily identify clouds blocking the lights,” said Lori Schultz, a researcher in Earth Science and Remote Sensing with the Applied Sciences Team at Marshall. “This is particularly important with thin cloud cover, where lights may be visible through the clouds, yet may be more diffuse or less intense.”
According to Dr. Andrew Molthan, Deputy Branch Chief of Earth Science at Marshall, the Blue-Yellow Composite product complements the suite of existing DNB products.
“[This product] fills a gap by providing a clean, consistent depiction of the DNB radiance data across a range of moonlight conditions while providing the infrared cloud imagery for interpretation and context,” he said. “Severe weather events often disrupt power over an area for a substantial amount of time. By knowing with confidence what pre-event conditions looked like, one can then look at post-event conditions and visually compare, or offline acquire the VIIRS Black Marble data through NASA, and derive more quantitative and objective differences.”
The Blue-Yellow Composite product will be especially beneficial to members of the Emergency Management Community.
“The daily global product allows the emergency management community to observe changes in nighttime lights that may be due to power outages caused by disasters,” said Jeremy Kirkendall, Emergency Management Specialist at NASA's Goddard Space Flight Center. “It also makes it faster and easier for emergency managers to identify remote communities that may have been impacted by disasters before they can reach those communities to evaluate them in person.”
Members of the emergency management community have already used the Blue-Yellow Composite product to monitor the impact of Hurricanes Michael, Florence, and Dorian, and the January 2020 earthquake in Puerto Rico. The coming 2021 Hurricane Season will provide another opportunity.
“The fact that the product had to be made manually in the past limited its availability, since staff were not always available to generate the imagery,” said Kirkendall. “Now that it’s been automated, we can check the near real-time (NRT) product at any time there is a disaster to see if there is a noticeable difference in the nighttime lights.”
The NRT Blue-Yellow Composite product is distributed by NASA’s Land, Atmosphere NRT Capability for EOS (LANCE), and users can access it in NASA Worldview. LANCE is part of NASA’s Earth Observing System Data and Information System (EOSDIS), and distributes NRT data products from almost a dozen satellite-borne instruments. In addition, the product is available through the ArcGIS online platform as a REST endpoint, which allows emergency managers to easily ingest it into the web applications, dashboards, and maps they’re using to monitor conditions, increasing how quickly situations on the ground can be assessed.
The underlying Black Marble dataset is available from NASA’s Level 1 and Atmosphere Archive and Distribution System Distributed Active Archive Center (LAADS DAAC).
“For NASA’s applications, we adapted the SPoRT product for Worldview so that the broader user community would be able to use it, either to see change in their local area over time or to use the product in disaster-response scenarios to ascertain whether missing light is the result of damaged infrastructure or cloud cover,” Molthan said.
There are efforts underway to develop additional, more refined DNB products as well.
“The imagery available online is from the NRT/reduced latency products of VIIRS. With additional delay, comes a more refined product — Lunar Bi-directional Reflectance Distribution Function (BRDF)-corrected — that removes changes in light associated with moonlight illumination, making it better for performing quantitative differencing and mapping short to long-term changes in night light emissions,” Molthan said. “We would like to use some of this Worldview imagery for quick-look assessments of post-disaster conditions while continuing to develop more rigorous and quantitative approaches using the refined, BRDF-corrected day night band radiance.”
While these more refined products remain in development, users will find that the Blue-Yellow Composite’s combination DNB radiance and infrared data vastly improves their ability to determine whether changes in light are attributed to power outages or dense cloud cover as compared to earlier DNB products.
“Although it is impossible to make a definitive determination of the amount of loss of light from this RGB, this product, when used with other information sources, can certainly improve the overall awareness of the possible extent of the damage caused by the hazard,” said Schultz.
For More Information:
Users can access the Blue-Yellow Composite product in NASA Worldview.
The Black Marble dataset is available in near-real time from NASA’s Land, Atmosphere near real-time Capability for EOS and as a standard product from LAADS DAAC. The LAADS DAAC manages, archives, and distributes the data, tools, and resources in NASA’s EOSDIS collection that pertain to Moderate Resolution Imaging Spectroradiometer (MODIS) and VIIRS Level 1 data (geolocation, L1A, and radiance L1B) and Atmosphere (Level 2 and 3) data products.
To learn more about nighttime lights imagery, see NASA Earthdata's Nighttime Lights Backgrounder, which provides information about how these data are collected, examples of how these data are used, and direct links to nighttime lights datasets.