GEOG/GEOL 4093
Remote Sensing of the Environment
Lecture 9
Outline of todays lecture
Review
Imaging Systems- Passive Sensors
Whiskbroom vs. Pushbroom
Multi-spectral remote sensing: Landsat (MSS, TM, and ETM+)
Processes in color formation
Additive colors refer to the combination of light from multiple
sources at specific wavelengths
used in remote sensing, and on computer monitors, etc.
Aditive
Substractive
Landsat TM and Color Composites
Band 1
Band 2
Band 3
Band 4
Band 5
0.450-0.515 m
0.525-0.605 m
0.63-0.69 m
0.75-0.90 m
1.55-1.75 m
(Blue)
(Green)
(Red)
(Near-Infrared)
(Middle-Infrared)
Band 7
2.08-2.35 m
Band 6
10.40-12.50 m
(Middle-Infrared) (Thermal-Infrared)
Spectral Signature
Spectral Band: A spectral band in a digital image represents a narrow
slice of radiance in a given wavelength range. The brightness level in
a given spectral band is measured using a sensor that is responsive
only in that band or by placing a filter in front of a broad band sensor.
Resolution: Four types of resolutions in remote sensing:
(1) spatial: the smallest angular or linear separation between two
objects that can be resolved by the sensor (IFOV).
(2) Temporal: the repeat frequency of information gathered at a
specific point.
(3) spectral: the number and dimension of specific wavelength
intervals in the EM spectrum to which the instrument is sensitive.
(4) Radiometric: sensitivity of the sensor to different signal strengths.
Imaging Systems
Many electronic (as opposed to photographic) remote sensors acquire data
using scanning systems, which employ a sensor with a narrow field of view
(i.e. IFOV) that sweeps over the terrain to build up and produce a twodimensional image of the surface.
There are two main modes or methods of scanning employed to acquire
multispectral image data - across-track scanning, and along-track
scanning.
Imaging Systems: Whiskbroom Scanners
Across-track scanners scan
the Earth in a series of lines. The
lines are oriented perpendicular
to the direction of motion of the
sensor platform (i.e. across the
swath). Each line is scanned
from one side of the sensor to
the other, using a rotating
mirror.
Imaging Systems: Whiskbroom Scanners
The IFOV (C) of the sensor and the altitude of the platform
determine the ground resolution cell viewed (D), and thus the
spatial resolution. The angular field of view (E) is the sweep of the
mirror, measured in degrees, used to record a scan line, and
determines the width of the imaged swath (F).
Because the distance from the sensor to the target increases towards
the edges of the swath, the ground resolution cells also become larger
and introduce geometric distortions to the images.
Whiskbroom Scanners: Dwell Time
The amount of time a scanner has to collect
photons from a ground resolution cell:
(scan time per line)/(#cells per line)
depends on:
satellite speed
width of scan line
time per scan line
time per pixel
Dwell Time Example: Landsat TM
(down track pixel size / orbital velocity)
(cross-track line width / cross-track pixel size)
dwell time
=
[(30m / 7500 m/s)/(185000m / 30m)]
=6.5 x 10-7 seconds/pixel
This is a very short time per pixel
Imaging Systems: Pushbroom Scanners
Pushbroom scanners use a
linear array of detectors (A) located
at the focal plane of the image (B)
formed by lens systems (C), which
are "pushed" along in the flight
track direction (i.e. along track).
Each individual detector measures
the energy for a single ground
resolution cell (D) and thus the size
and IFOV of the detectors
determines the spatial resolution of
the system.
Imaging Systems: Pushbroom Scanners
Dwell Time Example: Pushbroom Scanner
(down track pixel size / orbital velocity)
(cross-track line width / cross-track pixel size)
denominator = 1.0
dwell time is longer than that of whiskbroom
but different response sensitivities in each detector can cause
striping in the image
Whiskbroom vs. Pushbroom
Wide swath width
Narrow swath width
Complex mechanical system
Simple mechanical system
Simple optical system
Complex optical system
Filters and sensors
Dispersion grating and CCDs
Shorter dwell time
Longer dwell time
Pixel distortion
Less pixel distortion
Whiskbroom vs. Pushbroom
Whiskbroom
Landsat Multispectral Scanner (MSS)
Landsat Thematic Mapper (TM)
Pushbroom
Visible (HRV) . SPOT 4 and 5 (HRVIR)
and Vegetation sensors
Landsat 7 Enhancement Thematic
Mapper (ETM+)
NOAA Advance Very High Resolution
Indian Remote Sensing System (IRS)
Terra Advance Spacebone Thermal
Emission and Reflection Radiometer
Radiometer (AVHRR)
(ASTER)
Geostationary Operational
Environmental Satellite (GOES)
SPOT S 1,2, and 3 High Resolution
Terra Multiangle Imaging
Spectroradiometer (MISR)
IKONOS , QuickBird
Selected Remote Sensing System and Their characteristics
Adapted from Jensen, 2007
Multi-spectral remote sensing: Landsat
(MSS, TM, and ETM+)
Sun-synchronous near polar orbits
Inclination 99 and 98.2
919 km altitude (landsat 1, 2, 3), 705 km for the others
Orbits the earth every 103 minutes (landsat 1, 2, 3)
Cross latitude at approximately the same local time (equator
9:30 to 10:00 am)
Multi-spectral remote sensing: Landsat (MSS, TM, and ETM+)
Landsat 1: 19721978
Landsat 2: 19751982
Landsat 3: 19781983
Landsat 4: 19822001
Landsat 5: 1984
Landsat 6: failed launch, 1993
Landsat 7: 1999
LDCM: Scheduled to launch in December 2012
Landsat-1 to 3
Landsat-4 and 5
Landsat-6 and 7.
Landsats sensors
carried combinations of 5 types of sensors:
Return Beam Vidicon (RBV) camera systems
Imaged entire ground scene instantaneously
Improved cartographic fidelity
Only flew on Landsats 1-3
Multispectral Scanner (MSS) systems
Thematic Mapper (TM)
Enhanced Thematic Mapper (ETM)
Enhanced Thematic Mapper Plus (ETM+)
Landsat Ground Receiving Station
http://landsat.usgs.gov/about_ground_stations.php
Landsat 4 & 5 coverage
Augmented by Tracking and Data Relay Satellite System (TDRS)
- Geosynchronous
Multi-spectral Scanner (MSS)
IFOV at nadir
79 x 79 m for bands 4 to 7
240 x 240 m for band 8
Quantization levels
6 bit (values from 0 to 63) in 1970s
8 bit (values from 0 to 255) in 1980s
Earth coverage
18 days Landsat 1,2,3
16 days Landsat 4,5
Altitude
919 km
Swath width
185 km
Inclination
99
Multi-spectral Scanner (MSS)
MSS Scanning Geometry
Multi-spectral Scanner (MSS)
Landsat 4 and 5 Thematic Mapper (TM)
IFOV at nadir
30 x 30 m for bands 1through 5, 7
120 x 120 m for band 6
Quantization levels
8 bit (values from 0 to 255)
Earth coverage
16 days Landsat 4,5
Altitude
705 km
Swath width
185 km
Inclination
98.2
Landsat 4 and 5 Thematic Mapper (TM)
Landsat 4 and 5 Thematic Mapper (TM)
Enhanced Thematic Mapper Plus (ETM+)
IFOV at nadir
30 x 30 m for bands 1through 5, 7
60 x 60 m for band 6
15 x 15 m for band 8 (panchromatic)
Quantization levels
8 bit (values from 0 to 255)
Revisit
16 days
Altitude
705 km
Swath width
185 km
Inclination
98.2
Enhanced Thematic Mapper Plus (ETM+)
Spatial and Spectral Resolution of Landsat
Multi-spectral Scanner (MSS), Thematic Mapper (TM),
and Enhanced Thematic Mapper Plus (ETM+)
Multi-spectral Scanner (MSS), Thematic Mapper (TM),
and Enhanced Thematic Mapper Plus (ETM+)
Jensen, 2007
Landsat Path and Row
Orbit paths are numbered westward, with path 001 passing through Eastern
Greenland and South America
Image rows are numbered southward beginning at 80 deg. N. Latitude, and with
row 60 being closest to the equator
Landsat Path and Row
http://www.idwr.idaho.gov/GeographicInfo/gisdata/remote_sensing.htm
Landsat Path and Row
http://glovis.usgs.gov/
Landsat Data Availability
All data available through EROS Data Center (EDC); partnership
w/USGS
Prices Prior to 2009:
ETM+
~$600/scene ($250 each additional scene)
TM
~$400/scene ($200 each additional scene)
MSS
~$200/scene ($100 each additional scene)
Since 2009, global data sets have been made available free of
charge from Landsats 4, 5, and 7, TM.
Mount St. Helens
The 1973
http://eros.usgs.gov/
Mount St. Helens
The 1983
http://eros.usgs.gov/
Mount St. Helens
The 1988
http://eros.usgs.gov/
Mount St. Helens
The 1992
http://eros.usgs.gov/
Mount St. Helens: Thirty Years Later
NASA Goddard space flight center
