26 september 1997 atlas band 4 (0.63-0.69 µm)
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ATLAS digital image of the UW-Madison
Arboretum
26 September 1997
ATLAS band 4(0.63-0.69 µm)
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14433
Pixel A:Pixel B:
ATLAS digital image of the UW-Madison
Arboretum
26 September 1997
ATLAS band 4(0.63-0.69 µm)
Band 1
Band 2
Band 3
Band 4
Band 5
…
47
19
103
62
39
… …
DNs for a single pixel:
Wavelength bands:
Multi-Band Digital Images
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Band 6 (0.76-0.90 µm) Band 4 (0.63-0.69 µm) Band 2 (0.52-0.60 µm)
Band 6 (0.76-0.90 µm) Band 4 (0.63-0.69 µm) Band 2 (0.52-0.60 µm)
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ATLAS image ofthe UW-Madison
Arboretum
26 September 1997
ATLAS band 6(0.76-0.90 µm; NIR)
displayed in red
ATLAS band 4(0.63-0.69 µm; red)displayed in green
ATLAS band 2(0.52-0.60 µm; green)
displayed in blue
ATLAS digital image of the UW-Madison
Arboretum
26 September 1997
Color composite ofbands 6,4,2 (R,G,B)
095 127 157 144 106 082
056 044 042 033 050 049
B1 B2 B3 B4 B5 B6ATLAS Band #
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Reference Data
1. Aid in the analysis and interpretation of remotely sensed data (e.g., field check on rock type).
2. Calibrate a sensor (e.g., surface temperature measurements made during thermal scanner mission).
3. Verify information extracted from remote sensing data (e.g., checking automated land cover classification vs. existing land cover map or GIS data layer).
Uses of Reference Data
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Visual verification in the field• crop type/condition• land use• tree species
Sample collection/measurement• water quality samples (e.g., suspended solids, turbidity)• crop yield• timber volume• temperature measurement• radiometer readings to measure reflectance
Examples of Reference Data
Information interpreted from airphotos or aerial observation• timber blowdown• natural disasters
Information resident in a GIS• wetland boundaries• ownership boundaries• well locations
Examples of Reference Data
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Cost
Timeliness• time stable - e.g., rock type• time critical - e.g., water quality measurement
Data quality• accuracy required• statistical representation
Geographic position of data (often with GPS)
Considerations for Collection of Reference Data
Simultaneous measurement of upwelling and downwelling radiation
Field Spectroradiometer Example
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0.0
1.0
2.0
3.0
4.0
5.0
400 500 600 700 800 900
Wavelength (nm)
Ref
lect
ance
(%)
Lost Lake
Crystal Lake
Trout Bog
Field Spectroradiometer Example
Bidirectional Reflectance
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solar azimuth
The amount of energy that is reflected from an object depends on the position of the source of illumination (the sun) and on the position of the sensor.
The overall pattern of reflectance at all possible combinations of illumination angle and viewing angle is referred to as the Bidirectional Reflectance Distribution Function (BRDF).
An object’s BRDF depends on the wavelength of illumination.
Bidirectional Reflectance
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ATLAS
Bands 6, 4, 2(NIR, red, green)
Chequamegon NFPrice Co, WisconsinSeptember 10, 1998
nadir line
scan lines
solar azimuth
The Global Positioning System (GPS)
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• Developed by the US Department of Defense (Russian counterpart called GLONASS; European system in development).
• A group of 24 satellites (4 in 6 different orbit planes).
• About 20,200 km above the earth’s surface.
• Satellites each weigh 860 kg (about 1 ton), are 8.7 m wide, travel at 3.87 km/sec (8653 mph), in circular orbits inclined about 55° from poles, revolve around earth once every 12 hours.
The Global Positioning System (GPS)
• With GPS receiving instruments, the user’s position on the earth’s surface can be determined through the use of triangulation.
• Distance from each satellite determined by measuring travel time of signal from satellite to receiver.
The Global Positioning System (GPS)
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A fourth distance measurement would go through one of these two points, but in actual practice a fourth measurement may not be needed because one of the two points will be unreasonable (i.e., thousands of kilometers away from earth). However, most systems use a minimum of four distance measurements.
Field surveys in support of remote sensing and GIS activities
Aircraft (navigate flight lines)
Location of trucks and ships/boats
Farming - use GPS positioning to vary fertilizer rates within individual fields (because of different soil conditions)
Uses of GPS: Examples
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1. Single unit measurement
2. Simultaneous measurements at a base station(known position) and one or more rovers. Data from base station and rovers then later brought together for computer post-processing (Differential GPS).
3. Like (2), only a radio link is set up between the base station and the rovers. A correction signal is instantaneously broadcast by the base station to correct the rover’s position (Real-Time Differential GPS).
Types of GPS Measurement
•Satellite clock errors
•Satellite ephemeris errors (position errors)
•Atmospheric conditions
•Multipath errors
•Receiver errors
•Selective availability [eliminated May 1, 2000]
(errors deliberately introduced)
•Vertical positioning error usually 2x horizontal error
GPS Errors
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30 m resolution
10 m resolution
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4 m resolution
1 m resolution
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1 m resolution
0.6 m resolution
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0.2 m resolution
Geographic Information Systemsand Remote Sensing
Relationship Between GIS and Remote Sensing
• Digital remote sensing data used as layers in a GIS• Layers in a GIS help analyze remote sensing data
Geographic Information System (GIS):
• Computer-based system for collection, storage, analysis, and display of information about features that are referenced by geographic location.• Data types: locations and attributes of features.