There is ocean of knowledge, but we know a drop of it...
Saturday, 10 March 2012
Visualization: From Energy to Image
HOW DO WE VISUALIZE LIGHT WE CAN'T SEE?
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.
NATURAL COLOR IMAGES
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.
Credit: NASA and The Hubble Heritage Team
FALSE COLOR IMAGES
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.
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.
DATA FROM MULTIPLE SENSORS
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.
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.
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.