Saturday, 10 March 2012

Visualization: From Energy to Image


False color, or representative color, is used to help scientists visualize data from wavelengths beyond the visible spectrum. Scientific instruments onboard NASA spacecraft sense regions within the electromagnetic spectrum—spectral bands. The instruments direct the electromagnetic energy onto a detector, where individual photons yield electrons related to the amount of incoming energy. The energy is now in the form of "data," which can be transmitted to Earth and processed into images.


Digital cameras operate similarly to some scientific instruments. A sensor in the camera captures the brightness of red, green, and blue light and records these brightness values as numbers. The three sets of data are then combined in the red, green, and blue channels of a computer monitor to create a color image.
Three small grayscale images showing each channel of a digital photo of a hot air balloon. The blue channel shows a light gray area along the blue strip of the balloon. The composite shows a full color image with bright yellow, blue, orange and red stripes.


Instruments onboard satellites can also capture visible light data to create natural color, or true color, satellite images. Data from visible light bands are composited in their respective red, green, and blue channels on screen. The image simulates a color image that our eyes would see from the vantage point of the spacecraft.
Three small grayscale images showing each channel of an image of Saturn. The forth image shows a full color image of Saturn with light browns and warm grays.
Credit: NASA and The Hubble Heritage Team


Sensors can also record brightness values in regions beyond visible light. This Hubble image of Saturn was taken at longer infrared wavelengths and composited in the red, green, and blue channels respectively. The resulting false-color composite image reveals compositional variations and patterns that would otherwise be invisible.
Three small grayscale images showing each channel of an image of Saturn in false color. The forth image show Saturn with brilliant colors of purple, blue, green and orange.
false-color infrared image from the Thermal Emission Imaging System (THEMIS) camera onboard the Mars Odyssey spacecraft
Martian Soil
This false-color infrared image from the Thermal Emission Imaging System (THEMIS) camera onboard the Mars Odyssey spacecraft reveals the differences in the mineralogy, chemical composition, and structure of the Martian surface. Large deposits of the mineral olivine appear in this image as magenta to purple-blue.


This composite image of the spiral galaxy Messier 101 combines views from Spitzer, Hubble, and Chandra space telescopes. The red color shows Spitzer's view in infrared light. It highlights the heat emitted by dust lanes in the galaxy where stars can form. The yellow color is Hubble's view in visible light. Most of this light comes from stars, and they trace the same spiral structure as the dust lanes. The blue color shows Chandra's view in x-ray light. Sources of x-rays include million-degree gas, exploded stars, and material colliding around black holes.
The three small images used for the composite show a galaxy in red, yellow, and blue. The composite shows all three colors together revealing a multi-colored galaxy.
Credit: NASA, ESA, CXC, JPL, Caltech and STScI
Such composite images allow astronomers to compare how features are seen in multiple wavelengths. It's like "seeing" with a camera, night-vision goggles, and x-ray vision all at once.


Often a data set, such as elevation or temperature data, is best represented as a range of values. To help scientists visualize the data, the values are mapped to a color scale. The color code is arbitrary and thus can be chosen according to how the data can best be visualized. The sea surface temperature map below uses a scale from dark blue for cold temperatures to red for warm temperatures.
An image of the Earth with red color around the equator representing ocean temperatures of 30 degrees centigrade. The colors get cooler, from yellow to green to blue, the closer the ocean is to the poles.
Credit: NASA/Goddard Space Flight Center
Evaporation at the ocean's surface leaves minerals and salts behind. For this and other reasons, the salinity of the ocean varies from place to place. This map shows the long-term averages of sea surface salinity using practical salinity units—units used to describe the concentration of dissolved salts in water. The white regions have the highest salinity and the dark regions have the lowest.
An image of the Earth with the ocean colored a variety of shades from white to dark blue. The white indicates high levels of salinity and are prevalent in the Atlantic Ocean, Mediterranean Sea and bodies of water around the Middle East.
Credit: NASA/Goddard Space Flight Center