topographic landsat maps lecture
TRANSCRIPT
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8/8/2019 Topographic Landsat Maps Lecture
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Topographic Maps, AerialPhotos and Satellite
Images(Or things that are really
useful whether you’re intogeology or not!)
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The Basics: What is atopographic map?
• A 2-D model of 3-D landscape
• Relief – difference in elevation (i.e.valleys, peaks, coastlines, etc)
– Contour lines – represent elevations
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Latitude
• “Latitude is fat-itude”
• Measured in degrees
•
From 0° to 90°N or 90°S– What do those represent?
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Longitude
• Also measure in degrees
• Degrees east or west of the primemeridian
– Runs from N to S through Greenwich,UK
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Breaking down degrees…..
• 1 degree 60 min (‘) 60 sec (“)
• Quadrangle – Section of earthbounded by latitude and longitude
• 15 minute quadrangle
• 7.5 minute quadrangle
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North
450mi from TrueNorth
–Declination Difference in
degrees
True north based ongeography
Magnetic North shifts on the
’earth s magnetic
field due to( )metallic iron core
What does this mean for map accuracy?
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Symbols
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Digital Terrain Models
-Constant altitude flight-Overlapping radar pulses- –Similar elevation similar color
Why do you have to be above?
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Making the map from aerialview
• Eliminate angular distortion
• Ground truth – check elevations onthe ground!
– How would you do this?
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• Contour lines connect all points thathave the same elevation above sealevel
• Index contours – elevations printed
• Contour interval – specified on mapas the regular change betweenelevations
• Fig. 9.3 – What’s the contour
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RULES! (And guidelines…)
• Contour lines NEVER cross? (Thinkabout why….)
• Contour lines ALWAYS close to form acircle (unless you are going off themap)
• The tip of a V-shaped notched
ALWAYS points uphill
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Contour Lines (Fig 9.6)•
Can estimate elevation between twopoints
• Even-spaced contours of different
elevations tell us something aboutslope!
• Line can show steep vs. gentle slope
•
Depression contours – closed circlewith hachure marks on the downhillside
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Reading contour lines
• Fig 9.7
• What is the elevation of the middlehill?
• What cardinal direction is downhill onthe valley river?
• What is the easiest route up to theridge point?
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Benchmark
• i.e. BM 463 – Permanent marker withknown elevation
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Scales of Maps and Models
• Ratio scale
• 1:50, 1:24,000, etc (Always sameunits)
• Think of zooming in and out!
• Convert!
– 1:24,000 – 1in is 24,000in
– 24,000in is 2000ft
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GPS• 28 satellites,
• 12-hour orbit
• Uses foursatellites
and a receiverto triangulate
• Usually anaccuracy of
10-15m• Idea is 4 sats
are 15° abovethe horizonanywhere at
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UTM – Universal TransverseMercator System
• Rectangular grid in meters
• 60 N-S zones – Zone 01 to Zone 60
•
Easting – measured in meters E of Wedge
• Northing – distance from equator inmeters
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Today’s Lab…..
• Complete the questions aboutvarious topo quadrangles
• Draw your own topo map
– PART I
– PART II