GOES-16 and GOES-17, also known as GOES-East and GOES-West respectively, provide beautiful images of Earth. However, what you see on your TV, computer, and mobile device are digital representations of the data collected by those satellites, not actual photos or videos. How are these images created?
How satellites “see” the earth.
Use of satellite imagery camerasremote sensingGather information about the earth from above. GOES-R series satellites carry an instrument called the Advanced Baseline Imager (ABI) that measures energy at different wavelengths along the Earthelectromagnetic spectrum. The electromagnetic spectrum is the entire range of light that exists, from radio waves to gamma rays. Different objects absorb or reflect different wavelengths of light. ABI measures visible and infrared energy in 16 spectral bands or channels.
The Electromagnetic Spectrum. Photo credit: NASA
Rather than taking an instant snapshot of all of Earth's scenery beneath the satellite, ABI scans "swaths" of Earth with two scanning mirrors, one moving north-south and the other east-west. After each east-west scan is completed, the north-south scan mirror moves to a new position to begin a new east-west scan. Twenty-two of these scans create a full disk (the entire scene that ABI can see).
Each of ABI's 16 channels measures the amount of reflected or emitted energy in a specific wavelength of light along the electromagnetic spectrum to provide information about Earth's atmosphere, land or ocean. ABI's spectral bands include two visible channels, four near-infrared channels, and ten infrared channels. ABI's visible channels only see during the day, much like our own eyes because they only catch sunlight reflected off the Earth. In contrast, ABI's infrared channels detect energy that is not visible to the human eye. The infrared channels collect energy emitted by objects such as the earth's surface and clouds. ABI can detect infrared energy day and night. Think of ABI as night vision goggles that use image enhancement technology to see all available light. Each ABI channel is useful to indicate a specific characteristic, e.g. B. cloud type, water vapor in the atmosphere, ozone, carbon dioxide or ice or snow areas.
ABI measures the energy reflected and emitted by the earth.
ABI collects particles of light called photons. When photons hit ABI detectors, they create an electrical charge in the detector that is proportional to the amount of light incident on it. The ABI electronics read the value of the electrical charge and convert it into a digital signal. The ABI detectors are similar to those used in a smartphone or digital camera, but are much more sensitive as they have to detect very small signals from a long distance.
Translate satellite data
Information from ABI is converted into radio waves and transmitted to antennas on the ground. The information is then sent to computers at a satellite data processing center. This information is transmitted inbinary code, a numeric language that uses only two digits: 0 and 1, arranged in eight-digit strings understandable by computer software. A numerical value of the amount of light detected by each object is recorded digitally. The computer then translates the information into images.
Process for translating satellite data into images.
Satellite images, like television images, are made up of tiny squares called pixels (short for picture elements). Each pixel in satellite imagery represents the relative reflected or emitted light energy recorded for that part of the image. The binary code information transmitted by the satellite assigns a value to each segment of the electromagnetic spectrum. These numbers can be converted to grayscale (each pixel in an image represents just a quantity of light and consists entirely of grayscale) to produce a black and white pixelized image.
GOES-17 raw, uncalibrated image swaths of the entire disk from the "red" part of the electromagnetic spectrum on December 15, 2019.
Scientists can assign colors to the "bands" of ABI data based on what color of light they represent in the electromagnetic spectrum. To create a composite image from satellite data that makes sense to the human eye, we need to use colors from the visible part of the electromagnetic spectrum - red, green, and blue. These three primary colors can be combined in varying intensities to form all possible colors. The color red is assigned to the band representing red light and blue to the data band representing blue light. ABI does not have a true "green" band, so this information is simulated using a lookup table created with data from the Japan Meteorological Agency's Advanced Himawari Imager, which is very similar to ABI but includes a "green" channel.
GOES-16 Full Disk GeoColor image of October 16, 2019. GeoColor is an RGB that approximates what the human eye would see from space. Source: NOAA/CIRA
Combining data from multiple ABI channels provides even more information. Certain combinations of data from different channels allow us to highlight interesting features. When combined in a specific "recipe" they create a single image, with the colors combining to form all possible colors perceivable by the human eye. The result is a variety of red-green-blue orComposite "RGB" images, which can highlight atmospheric and surface features that are difficult or more time consuming to distinguish from single channel images. RGBs provide important information that gives forecasters situational awareness and helps them understand rapidly changing weather conditions. Geographical details such as country and state borders are often added to the images to help the viewer with orientation.
GOES-16 daily cloud phase discrimination RGB images (left) and 0.64 µm view channel images (right) from the same time on February 9, 2020. The daily cloud phase discrimination RGB uses the reflectance differences between surfaces and clouds in the visible and near-infrared channels and temperature variances between surfaces and clouds in the infrared to provide increased contrast between background surfaces and different cloud phases. In this example, snow cover, water clouds, and ice clouds all appear similar in the visible single-channel images, but are all easily identified in the multispectral RGB images.
"By analyzing composite RGB images, forecasters can diagnose atmospheric features and processes that aren't as readily apparent in the single-band images alone," explained NOAA physics scientist Bill Line. “Furthermore, a single RGB product can enable the interpretation of multiple phenomena that would otherwise require the use of multiple image channels or products. The RGB images therefore enable forecasters to produce more accurate and timely forecasts and alerts for the public," he said. "Some features that can be detected and tracked more efficiently using RGB imagery include convective initiation (the vertical transport of heat and moisture in the atmosphere, particularly by updrafts and downdrafts in an unstable atmosphere), volcanic ash plumes, dust turbulence , wildfire temperature trends, low cloud and fog, and snow cover.”
looping the images
A sequence of ABI images can be looped together to create an animation. Thanks to ABI's fast scanning capability, data for a specific area can be collected up to every 30 seconds. This gives forecasters the ability to see a weather event as it happens and track an area of developing storms in near real-time. Knowing how quickly storm clouds form can help meteorologists with their storm warnings and warnings. ABI also provides important data in the event of radar failures or in areas with poor radar coverage.
According to Stephanie Stevenson, meteorologist at the National Hurricane Center, “The atmosphere is a liquid, so animating satellite imagery helps to understand how the liquid moves and evolves. Forecasters can identify movement and cloud formations at different altitudes in the atmosphere to better predict where new storms may form or in which direction existing storms may be moving. The ability of rapid scan images offers the added benefit of features evolving on a finer time scale. Severe weather outbreaks can develop rapidly, and 30-second animated imagery can help extend lead times for forecasters.” Rapid scan imagery can also help pinpoint the center of tropical cyclones, particularly in weaker systems when the center of circulation is may be difficult to identify with less common images.
GOES-16 acquired this colorized infrared image of Hurricane Maria over Puerto Rico on September 20, 2017. This loop was created using Band 13, one of the new spectral bands offered by ABI. Band 13 is primarily used to monitor cloud and storm intensity. The dark red color, like that near the storm's eyewall, corresponds to areas of great intensity. Hurricane Maria knocked out radar on the island. With this critical technology disabled and a major hurricane approaching, forecasters used data from GOES-16 to track the storm in real time. Source: NOAA/CIRA
Not just a pretty picture
A lot goes on behind the scenes to create and deliver these colorful images, but these improvements result in more than just a pretty image. These vivid images convey complex environmental information from large satellite datasets to highlight the presence and evolution of key meteorological phenomena such as fog, dust, fire and smoke sources, snow/ice, volcanic ash clouds, cloud properties, air mass temperature and moisture properties. and more. Adding color, combining data from multiple ABI channels, and looping the images provide critical information so meteorologists can quickly identify the information they need to issue timely forecasts and alerts.