1. Remote Sensing Part 1

2. Lecture Overview Introduction to electromagnetic waves
What is remote sensing?
Introduction to satellite imagery
5 resolutions of satellite imagery
Image display

3. Energy and Electromagnetic Waves
Processes that produce or release energy emit electromagnetic waves
Electromagnetic waves can also come from objects that release energy previously absorbed from elsewhere
For Example:
The sun is emitting heat, light, and many other types of electromagnetic waves that are produced through the process of fusion
You are also emitting electromagnetic waves right now as your body metabolizes calories and emits heat (infrared energy)
So, if we could see infrared light, you would appear brighter than the wall
Can you think of an example for emitting energy that was previously absorbed?

4. Electromagnetic Waves
Examples of electromagnetic waves:
Radio waves
Infrared waves
Red light
Green light
Blue Light
Ultraviolet rays
X rays
Gamma rays

5. Electromagnetic Waves
Wavelength ()
f = frequency: The number of waves passing through a point within a unit time (usually expressed per second)
EMR energy moves at the speed of light (c): c = f 
Energy () carried by a photon:  = h f [h=Planck constant (6.62610-34 Joules*seconds)]
The shorter the wavelength, the higher the frequency, and the more energy a photon carries.
For example, ultraviolet rays are shorter than visible light so they have more energy and are more dangerous (sunburns)
C stays constant (in a vacuum) so if the frequency (i.e., energy goes up) what must happen to the wavelength?

6. One micrometer (μm) = one millionth (10-6) of a meter
ers)
One micrometer (μm) = one millionth (10-6) of a meter

7. You may also see wavelength in nanometers:
One nanometer (nm) = one billionth (10-9) of a meter

8. What makes objects a certain color?
The color of an object is determined by how much energy it reflects from each wavelength in the visible light portion of the EM spectrum.
Objects reflect some wavelengths
Objects absorb some wavelengths
Objects don’t interact with some wavelengths (i.e., the waves pass through the objects largely unaffected)
Examples
White objects reflect all wavelengths of light
Black objects absorb all wavelengths of light
Blue objects reflect blue light and absorb red and green light
Why is vegetation green?

9. Spectral Signatures
Note red edge
As with color, different objects reflect different amounts of energy at other wavelengths

10. Remote Sensing
Remote sensors are devices that sense energy from a remote location (i.e., a device not in physical contact with what it is sensing)
Remote sensing is the science of acquiring, processing and interpreting information/data collected by remote sensors
The most common application of remote sensing is classification
Differentiating land cover classes (e.g., water, pavement, vegetation)
Differentiating subtleties within classes (e.g., tree species)

11. Remote Sensing
Passive - detect emitted/reflected energy from other sources (e.g., the sun)
Satellite sensors
Air photos
Cameras
Video recorders
Active – emit energy and detect reflections
Sonar
Radar
Lidar

12. Satellite Imagery
Digital data is obtained by sensors on satellite platforms.

13. Imagery Resolutions Spatial resolution Temporal resolution
Spectral resolution
Radiometric Resolution
View angle resolution

14. Spatial Resolution
The area on ground represented by each pixel (i.e., raster cell size)
There is a tradeoff between the image footprint (area captured by a single image) and spatial resolution
Some sensors have different spatial resolutions for different bands
Examples
Advanced Very High Resolution Radiometer (AVHRR) ~ 1 km
Landsat Multispectral Scanner (MSS) – 79 m
Landsat Thematic Mapper (TM) – 30 m
IKONOS – 1 m panchromatic /4 m multispectral

15. Temporal Resolution
How often a satellite can obtain imagery of a particular area
For a fixed sensor (can only point straight down) this depends on:
1) The number of days between overhead passes at the same location
2) The swath width of the sensor (i.e. the footprint of the images produced)
Temporal resolution is higher for sensors that can move/tilt (side-to-side), but views from angles introduce distortion
Examples
Landsat - 16 days
AVHRR - daily
IKONOS - 1 to 3 days (sensor can tilt)

16. Spectral Resolution
The specific wavelength intervals in the electromagnetic spectrum captured by each sensor
Determined by the number, spacing and width of sampled wavelength bands
Higher resolution results in more precision in representation of spectral signatures
Hyperspectral imagery has very high spectral resolution (e.g., Aviris data has 220 bands)
This makes a very detailed spectral signature, but the data are somewhat rare, expensive, and cumbersome to use

17. Radiometric Resolution
The number of possible data values reported by the sensor (i.e., how sensitive the sensor is to changes in brightness of objects that it views)
Range is expressed as a power (2n )
8-bit resolution has 28 values, or 256 values Range is 0-255
11-bit resolution has 211 values, or 2048 values Range is
The value in each pixel is called the
Digital Number (DN)
Brightness Value (BV)

18. View Angle Resolution
The number of angles at which the ground objects are recorded by the sensor
It can be useful to view objects from multiple angles for stereoscopic analyses
Some features reflect light differently in different directions
Isotropic vs. anisotropic reflectance
Example
The Multi-angle Imaging SpectroRadiometer (MISR) sensor has 9 view angles

19. Resolution Caveats
Some remote sensing initiatives have multiple satellites/sensors, with later versions featuring improvements (i.e., better resolutions)
E.g., Landsat MSS, TM, ETM+
Some satellites have more than one sensor on them, so resolutions are associated with the sensors and not satellites
E.g., Earth Observing System (EOS) – 2 satellites that each contain MODIS, ASTER, etc. sensors

20. Landsat Thematic Mapper (TM)
Resolution Example
Landsat Thematic Mapper (TM)
Spatial Resolution = 30 meters
Greenville, NC

21. Landsat TM Spectral Resolution
Wavelength (in micrometers)
Description
Blue-green Green Red Near-IR Mid-IR Thermal Mid-IR

22. Spectral Signatures Complete Signature Landsat TM Signature
Note the overall loss of detail
This is the case for hyperspectral imagery
* TM bands 5, 6, & 7 aren’t on this graph

23. Spectral Regions – Landsat TM
BAND 1 (Visible Blue)
PANCHROMATIC
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
WAVE IR
LONGWAVE IR
0.4
0.5
0.6
0.7
1.1
3.0
5.0
14.0 mm
Blue Visible - Used for bathymetry - water penetration to about 50m in clear water. Necessary for a true color image
Illuminates Materials in Shadows
Water Penetration for Bathymetry
Soil / Vegetation Differentiation
Deciduous / Coniferous Differentiation

24. Band 1
Band 1 is used with bands 2 and 3 to construct true color composites to assess a variety of features.

25. Spectral Regions – Landsat TM
BAND 2 (Visible Green) mm
Water Penetration for Bathymetry
Clear and Turbid Water Contrast
Discrimination of Oil on Water
Green Reflectance Peak of
Healthy Vegetation
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
LONGWAVE IR
14.0
5.0
3.0
1.1
0.7
0.6
0.5
0.4
PANCHROMATIC
Green Visible - Peak chlorophyll reflectance band, used for vegetation analysis. Also bathymetry - water penetration to about 40m.

26. Band 2
Band 2 is used with bands 1 and 3 to construct a true composite and bands 3, 4, and 7 to construct near and shortwave infrared composites to assess a variety of features.

27. Spectral Regions – Landsat TM
BAND 3 (Visible Red) mm
Vegetation Differentiation
Chlorophyll Absorption
Limited Water Penetration for
Bathymetry
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
LONGWAVE IR
14.0
5.0
3.0
1.1
0.7
0.6
0.5
0.4
PANCHROMATIC
Red Visible - Provides added value information to vegetation analysis.

28. Band 3
Band 3 is used with bands 1 and 2 to construct true color composites and bands 4 and 2 to construct near infrared composites to assess a variety of features.

29. Spectral Regions – Landsat TM
BAND 4 (Near Infrared)
Vegetation Analysis
Shoreline Mapping
Landcover Discrimination mm
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
LONGWAVE IR
14.0
5.0
3.0
1.1
0.7
0.6
0.5
0.4
PANCHROMATIC
Near Infrared - This is the primary band used to assess vegetation. Analysts can also assess camouflage detection and land water delineation using band 4.

30. Band 4
Band 4 is used with bands 3, 5, 7 and 2 to construct near and shortwave infrared composites to assess a variety of features.

31. Spectral Regions – Landsat TM
BAND 5 (Short-wave Infrared)
1.55 – 1.75mm
Fire Mapping
Discrimination of Oil on Water
Moisture Content of Soil and
Vegetation
Snow / Cloud Differentiation
Vegetation Analysis
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
LONGWAVE IR
14.0
5.0
3.0
1.1
0.7
0.6
0.5
0.4
PANCHROMATIC
Short-wave Infrared - Camouflage detection, change detection, vegetation analysis.

32. Band 5
Band 5 is used extensively with bands 3, 4, 6, and 7 to construct shortwave and longwave infrared composites to assess a variety of features.

33. Spectral Regions – Landsat TM
BAND 6 (Long-wave Infrared)
10.4 – 12.5 mm
Thermal Analysis
Vegetation Density
Urban Heat Islands
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
LONGWAVE IR
14.0
5.0
3.0
1.1
0.7
0.6
0.5
0.4
PANCHROMATIC
Long-wave Infrared - Thermal analysis.

34. Band 6
Landsat has the ability to sense EM radiation in the LWIR region using band 6. Unlike other TM bands, band 5 has a spatial resolution of 60 meters on Landsat 7(etm+) (120 meters on 4 & 5… TM)
It can be useful for geologic mapping, vegetation classification, vegetation stress detection, soil moisture content, fire management, thermal pollution, and ocean current studies.
Band 6 is used with bands 5 and 7 to construct infrared composites to assess a variety of features.
There is also a landsat TM panchromatic band with 15 m resolution
** The spatial resolution of Landsat TM band is ≠ that of the other bands

35. Spectral Regions – Landsat TM
BAND 7 (Mid-wave Infrared)
2.08 – 2.35 mm
Solar Reflectance From Metal Roofs
Smoke Penetration
Daytime Reflectance Mixed With
Emitted EM Radiation
Nighttime Emitted EM Radiation
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
LONGWAVE IR
14.0
5.0
3.0
1.1
0.7
0.6
0.5
0.4
PANCHROMATIC
Mid-wave Infrared.

36. Band 7
Band 7 is used extensively with bands 2, 4, 5, and 6 to construct shortwave and longwave infrared composites to assess a variety of features.

37. Landsat Bands Band 1 Band 2 Band 3
BLUE
GREEN
RED
NEAR IR
SHORT
WAVE IR
MID-
LONGWAVE IR
Review the differences in features between the bands.

38. Resolution Example AVHRR English Channel
Spatial Resolution: 1 km (swath width = 2700 km)
Temporal Resolution: daily
Spectral Resolution: 5 bands (1 visible, 1 NIR, 1 mid-IR, 2 thermal)
Radiometric Resolution: 8-bit (cells for each band)
View Angle Resolution: 1 view angle
English Channel

39. Resolution Example SPOT 5 Palm Springs, CA
Spatial Resolution: 20m, 10m, 2.5m (~ 60 km footprint)
Temporal Resolution: 1 day
Spectral Resolution: 5 bands (1 red, 1 green, 1 NIR, 1 mid-IR, 1 pan)
Radiometric Resolution: 8-bit (cells for each band)
View Angle Resolution: unlimited (movable sensor)
20 = mid-IR
10 = Red, Green, NIR
2.5 = Pan
Palm Springs, CA

40. Resolution Example IKONOS Sydney Olympic Park
Spatial Resolution: 4m, 1m (swath width ~ km
Temporal Resolution: 3-5 days (144 days for nadir)
Spectral Resolution: 5 bands (1 red, 1 green, 1 blue, 1 NIR, 1 pan)
Radiometric Resolution: 11-bit
View Angle Resolution: unlimited (movable sensor)
Sydney Olympic Park

41. Image Display Graphics display devices use three color guns
Red, Green, Blue
All colors can be formed from various combinations of these 3 colors (which is why they’re used in CRT computer/TV screens)
The brightness values (BV) to be displayed will often have an 8-bit range
0 to 255
In remote sensing, we assign one band to each color gun to give color to the image

42. Spectral Bands vs. Image Displayed
For digital data the spectral bands of the imagery can be displayed in any way
For example, red reflectance can be assigned to green light (on screen) or vice versa
Features we see on screen are usually ≠ what we would see with our eyes in terms of color
This is important because we can’t see in infrared etc., but we can still display this data by assigning it to a color that we can see

43. Image Display For a single band, the resultant color will be grayscale
All three colors display the same value, so the colors are shades of gray
Band 1
Band 1
Band 1
Red color gun
Green color gun
Blue color gun

44. Landsat Image Single Bands

45. Image Display
For a multi-band image, the resultant color will depend on which bands are assigned to which color guns
Red (3)
Green (2)
Blue (1)
True Color Composite
(321)
Red color gun
Green color gun
Blue color gun
Near Infrared (4)
Red (3)
Green (2)
False Color Composite
(432)
Red color gun
Green color gun
Blue color gun

46. Color composite image Color Composite Image Band A Band B Band C
Blue color gun
Green color gun
Red color gun

47. Landsat TM Composites
432
743
321
The order of the numbers indicates the color gun attributed to the bands red, green, and blue color guns.
The first number gets displayed using the red color gun and so on.
For example, in a 432 composite band 4 (NIR) reflectance gets displayed as red, band 3 (red) reflectance gets displayed as green, and band 2 (green) reflectance gets displayed as blue.