An Overview of Satellite Imagery

ARSET - AQ

Applied Remote SEnsing Training – Air Quality

A project of NASA Applied Sciences

Originally presented as part of:NASA ARSET- AQ On-line Short Course

Week 3 PresentationMay 23, 2012

Session 3 – Outline

1. What are true and false color images?2.What can we learn from images?3. A tour of useful image archives.4. Assignment #3

RGB Images

Red, Green and Bluecorrespond to the three color receptorsin the human eye.

These 3 colors are alsothe basis for all colordisplay technologiesfrom LCD sub-pixelsto television color “guns”.

Remote Sensing of Radiation

Earth-observing satellite remote sensing instruments typically make observations at many discrete wavelengths or wavelength bands.

36 wavelength bands covering the wavelength range 405 nm (blue) to 14.385 μm (infrared)

Terra

MODIS

MODIS Reflected Solar Bands

250 M

500 M

MODIS Thermal Bands

RGB Images and Remote Sensing Instruments

“True Color Image”To simulate what the human eye seeswe load the red, greenand blue satellite bandsinto the correspondingdisplay channels.

We can create an image by selecting any three bands and load them into the “Red”“Green” and “Blue” displaychannels.

R = 0.66 µmG = 0.55 µmB = 0.47 µm

0 = 36°

True Color Image

A MODIS “True Color Image”will use MODIS visible wavelength bands1-4-3

True Color Image from VIIRS

What can we learn from true color imagery?

(Possible) Identification of land, ocean and atmosphere features

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66

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What can we learn from true color imagery?

(Possible) Identification of land, ocean and atmosphere features

Dust over the Sahara

17 February 2008, Aqua Images courtesy of Yuval Ben-Ami

Plume’s area ~55,600 km2 = ~4.5 × area of Maryland

18 February 2008, Aqua

19 February 2008, Aqua

Geographic extent and transport of aerosols

Sahara dust Wildfire smoke

Urban-IndustrialPollution? Smoke from

Alaska wildfires

Feature Identification is more reliable when a clear source can be seen in the image.

ImagescourtesyofPhil Russell

The color of dust or smoke can tell us something about chemical properties.

Doing More with Satellite Imagery

In visible imagery water is dark because it absorbs most of the energy.

Clouds are white because most of the incoming energy is reflected

Pollution is hazy depending upon its absorptive properties

If we understand the physics of how particular wavelengths interact withobjects in the world we can create images to emphasize what we want to see

R = 1.6 µmG = 1.2 µmB = 2.1 µm

False Color Images

“False Color Image”To enhance particularfeatures we want to seein an image we loadbands into thered, green and bluedisplay channelswhich do not correspondto the visible red, green,and blue wavelengths.

Volcanic Ash

• R:0.645 um, G : 0.858um, B : 0.469 um (All channels equalized)

Volcanic Ash

• R:0.645 um, G : 0.858um, B : 11.03 um (All channels equalized, B channel also flipped)

Using False Color Images toIdentify aerosol types

Dust

Smoke

from Y. Kaufman

Both dust andsmoke interactwith the shorterwavelengthsreflecting lightback to the sensor.

Spectral optical properties of aerosol

Dust

Smoke

from Y. Kaufman

Dust particles interact with thelonger infraredwavelengthsbut not the smaller smoke particles which remain invisible.

Spectral optical properties of aerosol

Dust

Smoke

from Y. Kaufman

The distinctionof aerosol typesis madepossible by:

1.The wide spectral range of the MODIS sensor.

2.Understanding how light interacts with the particles, gases and surfaces it interacts with.

Visible (RGB=0.66m, 0.55m, 0.46m) SWIR (RGB=1.64m, 1.24m, 2.13m)

Spectral Images vs Color Maps

True Color Image False Color Image

AFRI=(0.86-2.1/2)/(0.86-2.1/2)NDVI=(0.86-0.66)/(0.86-0.66)

Color MapsValues are assigned colors according to the scale below each image.

Spectral information is used to detect chlorophyll. High values indicate more vegetation.

Landsat True and False Color Animation

http://landsat.gsfc.nasa.gov/education/resources/L7_sanfran_onionskin.mov

MODIS Rapid Response Sitehttp://earthdata.nasa.gov/data/near-real-time-data/rapid-response

MODIS-Atmos Sitehttp://modis-atmos.gsfc.nasa.gov/IMAGES/index.html

NASA’s Visible Earthhttp://visibleearth.nasa.gov

NASA’s Earth Observatoryhttp://earthobservatory.nasa.gov

NASA Earth Observations (NEO) http://neo.sci.gsfc.nasa.gov

MODIS Todayhttp://ge.ssec.wisc.edu/modis-today/

A Brief Tour of Some Useful Image Archives

MODIS Rapid Response Sitehttp://lance.nasa.gov/imagery/rapid-response

• MODIS only image archive which is easy to search.

• Quick posting of new MODIS images.

• Links to data used to generate MODIS images.

• Collections of images by region and by association with ground based instruments

NASA’s Visible Earthhttp://visibleearth.nasa.gov

• A tremendous archive of images and animations from and about many sensors.

• Search results can be too large to browse through unless many conditions are added to the search.

NASA’s Earth Observatoryhttp://earthobservatory.nasa.gov

• Site designed for outreach and education.

• Images and stories of Earth Science phenomena are linked.

• Subscriptions to newsletters to keep track of recent stories and Natural Hazards.

NASA Earth Observations (NEO)http://neo.sci.gsfc.nasa.gov

• Site designed for outreach and education.

• Can explore several remote sensing products with an easy to use interface.

• The ability to quickly produce high quality graphic images from the site.

• The ability to quickly create products that can be mapped onto Google Earth.

The site includes a searchablearchive of “Image of the Day”

Site #2NASA’s Earth Observatory

http://earthobservatory.nasa.gov/

NASA’s Earth Observatory is intended to be an educational site for the general public with an interest in Earth Science.

• Feature articles explaining Earth Science issues andphenomena

•The site includes a searchablearchive of “Image of the Day”

A simple search using “fires” “california”returns 63 pages of results.

You can use the drop down menu to choose a section of the site to search to reduce the number of results.

Site sections include:• Image of the day• Features• Natural Hazards• News• Blogs

You can browse the archive by broad topic categories

You can browse within a topic by subtopic

or by date.

Natural Hazards Section

http://earthobservatory.nasa.gov/Subscribe/

One very nice feature of this siteis the option to subscribe to any ofseveral e-mail news letters.

For example, if you wanted to keeptrack of the most recent news on volcanic eruptions, you would subscribe to the NaturalHazards Daily

Sample Update e-mail

from the Natural Hazard

mailing list

GLIDER Software

• GLIDER is a comprehensive tool for image analysis, classification and data mining.

• Explore the various aspects of GLIDER • More importantly, it’s free!• http://miningsolutions.itsc.uah.edu/glider/

Imagery Links

MODIS Rapid Response Sitehttp://earthdata.nasa.gov/data/near-real-time-data/rapid-response

NASA’s Visible Earthhttp://visibleearth.nasa.gov

NASA’s Earth Observatoryhttp://earthobservatory.nasa.gov

NASA Earth Observations (NEO)http://neo.sci.gsfc.nasa.gov

MODIS- Atmos (MODIS Atmosphere Product Reference Site)http://modis-atmos.gsfc.nasa.gov/IMAGES/index.html

•Tutorial on constructing RBG images.http://www.zamg.ac.at/eumetrain/CAL_Modules/CALRGB/rgb1_2.htm

•GLIDER Toolhttp://www.ssec.wisc.edu/hydra/