1. This week’s earth observatory: false colour image

2. DIGITAL DATA and DISPLAY
Satellite data capture and transmission
Onboard scanners capture the energy
reflected by band (wavelength) for each
pixel (picture element)
by row and column (captured row by row)
… as seen in
Data are recorded in a continuous swath and then cut into scenes several thousand pixels in both x and y. see:
Landsat 1

3. Data transmission and storage
These data are stored and transmitted to ground receiving stations. The main ones in Canada are in Prince Albert, SK and Gatineau, QC. Many global stations were built by MacDonald-Dettwiler Associates (MDA) in Vancouver.
Data were previously stored in BIL (Band InterLeaved) and BSQ (Band Sequential) formats on reel tapes.The most common format now is as GEOTIF on CD or now online, which can be imported into DIPS or GIS software (or graphics software).

4. Canada’s ground receiving stations Prince Albert and Gatineau

5. Data characteristics: resolution a. Spatial resolution (pixel size)
Spatial resolution is the size of the pixels. This is determined by the sensor design, satellite altitude, and available energy.
Remote sensing data generally varies from ~1 metre to 10km
Google Earth:
Landsat (30m) and air photo or high-res imagery (1m)
Very high res: m
High resolution: 5-50m
Medium res: m
Low res: km +

6. Mixed pixels One pixel = one value per layer
Remote sensing data and raster GIS data give the impression that a pixel has one uniform value across its width. This may be true for a small pixel or a homogenous cover, such as a large lake, or field, but often we need to know the nature of geographic data and understand that what we are seeing is an average value for a variable forest or a mixture of different surface covers. Landsat example: Bowron Lakes

7. b. Spectral resolution
defines the spectral resolution of the system. A small width equals a finer resolution. The width of each portion of the EM spectrum captured by a scanner

8. c. Radiometric resolution
Scanner input (amount of reflectance) is converted from a continuous radiance value (watts per sq metre) into a discrete value known as the digital number (DN).
These are integer numbers .. commonly 8-bit (256 values) for easier handling and smaller overall file size: one value per pixel per band.
Each value ranges from 0 (no reflection) to 255 (for 8 bit data).
They can be converted back to radiance in real numbers if required.

9. d. Temporal resolution
This is the time between successive images of the same area
can vary from multiple images per day to one every several weeks
Weather satellites: multiples per day
Landsat: ~ 2 weeks (subject to cloud cover, and overlap).
Download availability has greatly expanded since copyright was lifted on Landsat data in 1999

10. 2. Data display
early PCs had less e.g. 2 bit = 4 colours (1982) and 8 bit display (1990)
Modern computer screens display 24 bit colour - 8 bits each (256 shades) in red, green and blue for a realistic image (right)
e.g. Black = 0,0,0; white = 255,255,255; gray = 128,128,128; red = 0,0,255)
Interactive color wheel:

11. a. Histogram Stretching
Most data are acquired in 8 bit values (0-255), but the data rarely fill the range, so the screen image lacks contrast – see next slide
Stretching is the manipulation of display colours to fit the DN ranges:
A histogram plots the Digital Numbers (DN) e.g , on the x-axis against the frequency of values with those DNs.
Histograms can be used to analyse the distribution of the data values, - minimum, maximum and spread
Stretches include:  None, Linear, Equal, Root, Special     : Stretches
(see next next slide)

12. Digital Image Processing: Image Enhancement
des.memphis.edu/esra/Teaching/Geog6515/Newlectures/lecture13_rs2.ppt

14. b. Bands, Channels, and RGB Guns
Bands        scanned by the sensor (limited by the data captured)
e.g. 1-7 for Landsat TM, 36 for ASTER
Channels    data layers (including bands) stored in a database: no limit
RGB        the three colour display guns (Red, Green, Blue)
A monitor has 3 guns (RGB), so only 3 bands can be displayed at once

15. Display Modes A: Colour composites
Three different channels compose a RGB colour composite: any three channels can be selected.
Selecting TM band 1 in Blue, 2 in Green and 3 in Red displays a 'normal colour' composite.
A combination is similar to false colour film.
A composition gives a higher contrast image as it incorporates 3 bands from different portions of the EM spectrum.
Landsat compositor:

16. Single band displays B. Grayscale C: Pseudocolour
B. The same one band or channel in all three guns creates a grayscale image: this is useful for examining the characteristics of features in a single wavelength region e.g. vegetation in the Near IR
C. One channel can also be displayed in pseudocolour (PC) - selected colour schemes: not useful for single bands, except for the thermal. 
A density slice: certain DNs are classed or thresholded

17. Satellite imagery versus aerial photography
Most satellite imagery is digital and multispectral (its all digital now)
More aerial photography is analogue and often panchromatic
But, some satellites carry photographic systems, and there are airborne digital systems.
Astronaut photography:
Terrasaurus, Williams Lake:

18. Satellite imagery versus aerial photography
aerial photographs
Greater Areal Extent
Higher Resolution (?) 
Digital data
Analogue photos (?)
Repetitive Coverage 
Lower cost of 'launch'
Regular Distortion 
3D Stereo Effect
Greater Wavelength Range
Higher understanding
Analysis / GIS
Easier interpretation

19. Part-time work 1. Caribou Brewmasters: 15-20 hours/week 2
Part-time work 1. Caribou Brewmasters: hours/week Cranbrook Hill Greenway webmaster – volunteer