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Spatial Data > Post Midterm 2 > Flashcards

Post Midterm 2 Flashcards

0
Q

What is remote sensing?

A

The use of emr to collect information at a distance

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1
Q

Explain parallax

What kind of image is produced?

A

Parallax is an effect achieved by viewing with two lines of sight. It gives a 3d effect by combining both images

Results in a stereoscopic image

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2
Q

What does signature refer to?

A

The wavelength reflected by an object

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3
Q

What is the difference between passive and active sensing?

A

Passive sensing uses visible light while active sensing uses synthesized wavelengths in pulses to detect objects

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4
Q

What does planimetric shift refer to?

A

When elevated objects appear to be leaning away from the Center of the photo
A.k.a. Radial displacement
-the closer to the ground, the more distortion
-can measure height of objects using ratio’s

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5
Q

What is the difference between controlled and uncontrolled images?

A

Controlled image is precise
-real world scale

Uncontrolled image is not fixed with real points

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6
Q

What is an orthophoto?

What are its pros and cons in forestry applications?

A

Controlled image of combined air photos that are precise and to scale.

Cons- cannot calculate heights or see in stereo
Pros- can gain information like texture, color and branch arrangement

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7
Q

What percent overlap is required for stereo paired photos?

A

60%

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8
Q

What is drift ?

A

When planes veer off the desired flight line when taking air photos

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9
Q

What is CRAB?

A

When planes are not oriented parallel to the flight path due to wind interference. Creates an issue when attempting to overlap photos for a stereoscopic view.

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10
Q

What is TILT?

A

When the plane is not level at the time of an air photo the error is called tilt and results in un-uniform scale

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11
Q

What is the nadir?

A

The point directly below a camera or sensor

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12
Q

What is the principal point?

A

The location on the ground at which an aerial camera is pointed

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13
Q

What is the fiducial mark?

A

Marks on an aerial photo used to locate the principal point

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14
Q

What are the seven factors in aerial interpretation

A 
Size 
Shape 
Shadow
Tone
Texture
Pattern
Convergence of evidence
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15
Q

What is an absolute size measurement compared to a relative size measurement?

A

Absolute- surface area measurement

Relative- size of unknown in relation to known

  • camper vs car
  • apt vs houses etc
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16
Q

What can shape reveal in an air photo?

A

Tree specimens and landforms

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17
Q

What can be gathered from tone/color in an air photo?

A

Moisture variation
Age of slash
Conifer vs hardwood
Land or water

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18
Q

What can be revealed by patterns in air photos?

A

Spatial arrangement
Harvest pattern
Riparian retention
Dendritic patterns

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19
Q

What applications do air photos have?

A

Forestry

  • cover maps
  • damage appraisal
  • timber volume estimate
  • habitat management

Geology - drainage patterns reveal geology present

Soils- soil classification based on bedrock and surface geology

20
Q

What are the 3 segments of a Global Positioning System?

Briefly describe each

A 
Space
-24 sv's
-need 4 for accurate data
-high orbit
-2 orbits/day
-solar powered
Ground 
-5 stations
-monitor sv's
-sync clock and send ephemeris (precise position) data
User
-GPS units
-quality depends on price
21
Q

How many sattelites does the receiver need data from to provide an accurate location?

A

3 sv’s give 2 possible locations but only one is on the earths surface

For truly good reception you need 4 satellites

  • The 4th satellite is needed for adjustment of clock
  • Gps cant have atomic clock due to high cost
22
Q

How do receivers detect the distance to sattelites?

A
  • each SV has its own unique code
  • The receiver has all codes
  • Receiver plays same code as satellite and records the time delay
  • time delay x speed of light = distance
  • distance = radius of sphere
23
Q

what is the speed of light?

A

300 000 000 m/s

300 000 km/s

24
Q

explain how an atomic clock works

A

Atomic clocks contain quartz which oscilates when jolted with electricity like regular clocks but the quartz is constantly bombarded by cesium atoms. A detector senses whether or not the cesium is passing through the quartz. If cesium fails to pass through quartz it means that its oscillations are decaying and the sensor instantaneously signals the re-electrification of the quartz to maintain its accuracy.

25
Q

how accurate is an atomic clock?

A

loses less than 1 second over 150 billion years

-provides 1-3 ft error

26
Q

What are some common sources of error in GPS data that result in reduction of accuracy?

A

Clock error 1-2m

Ephemeris
- (wobble of satellite causes small errors in the detection of the satellites actual position which translates to and error of 2-3m)

Receiver error
- (0.5 m depending on quality of receiver)

Ionosphere
- layer of earths atmosphere outside troposphere. Signals deteriorate as they pass this barrier due to refraction, giving an error of up to 5m.

Multipath
-objects blocking or reflecting signal

PDOP
Position dilution of precision
-refers to angle of satellite to receiver. Less than 25 degrees is considered poor data and will result in error.

S/A
Selective availability - how many satellites are available? Need 4

27
Q

What’s PDOP?

A

Position dilution of precision

  • refers to angle of satellite to receiver
  • above 25 degrees gives accurate data
28
Q

How are errors corrected so that we can achieve accurate data for applications?

A

Differential correction

  • refers to the additional use of a stationary unit with the roving unit
  • the error correction for the stationary unit gets applied to the roving unit using the same satellites and time of day.
  • can be done post survey or in real time
29
Q

What does GNSS refer to?

A

Global navigation satellite systems

30
Q

What systems are combined under GNSS?

A

NAVSTAR GPS - USA
GLONASS - RUSSIA
GALILEO - EU
Beidou - CHINA

31
Q

How can accuracy of GPS unit be increased?

A

Use an antennae on your unit

Employ the use of a stationary unit for differential correction

Wait at waypoints for at least 45 seconds and 3-5 minutes at significant points like poc, tie points, etc

32
Q

What does SOP refer to?

A

Standard operating procedures

33
Q

What does the elevation mask refer to?

A

Elevation mask refers to the area of acceptance of a receiver for good data. The pdop error will be too high if SV is lower than 15 degrees due to troposphere refraction

34
Q

What are some things that block or cause obstacles for GPS reception?

A

Moisture in the canopy, topography, position on slope, wood, equipment, cracked cables and moisture damage to electronics

35
Q

What are some good habits for collection of GPS data?

A

Take one or more files per day to avoid major data losses

Do not open existing file the next day

Sync data often

36
Q

What standards does GPS data have to meet to be used in forestry?

A

MFLNRO Standards

  • specific accuracy levels
  • differential correction is mandatory
37
Q

What are some other forestry apps for GPS?

A

Machine mounted

Aerial fertilizer application

Liar calibration

Georeferenced PDFs on iPads

38
Q

What is LIDAR?

A

Active remote sensor that measures scattered light to find range and other info

39
Q

What are some benefits of LIDAR over GPS ?

A

Lidar can fly at night
Data is not nearly as sensitive to error as orthophoto’s
Lidar can fly in overcast weather

40
Q

What are the three modes of deployment of LIDAR

A

Ground
Air ( fixed or rotary wing) drones
Space

41
Q

What would be a normal pulse rate for modern LIDAR?

A

500,000 pulses per second

42
Q

How does LIDAR Measure distance?

A

Precisely measures time for signal to be reflected back to sensor and multiplies by speed of light since the signal it sends is still a form of light and travels at the speed of light.

Uses GPS and Inertial measuring unit for location

43
Q

What are some obvious benefits of using LIDAR technology in forestry?

A

Gives a 3d canopy model (dsm) as well as a ground model (dtm)

Can accurately determine forest inventory before anyone sets foot in an area

Can accurately determine topography for road construction and cut block planning without the need for foresters to do reconnaissance

Basically this stuff is very useful technology and has set the standard for accuracy and the amount of information that can be gained from the use of its data.

44
Q

What is the standard industry reference for collected LIDAR data?

How many of these units are needed for accurate data in bc? In the interior?

A

Pulses per metre squared is the standard industry reference for LIDAR data

8-10 pulses per meters squared are needed in bc forests due to high wood density

Less needed in interior due to more widely spaced trees

45
Q

How does LIDAR get its data?

A

Sends out synthetic pulses. The pulses are reflected by whatever they hit, and can generate multiple returns as only portions of them are reflected from different levels of the canopy until they hit solid ground. The sensor detects the returning pulses and generates a 3d model of the surface.

46
Q

List some products and applications of LIDAR as stated in steves lecture

A

DEM digital elevation model

Catchment areas of water sheds

Very detailed stream positions

Flow models

Hillside wetness index

Canopy height model

Can detect wetted perimeter of streams accurately

Can detect net volumes to 2-4% accurate

47
Q

What’s a dsm? Dtm?

A

DSM is a digital surface model which would show the surface of whatever it was recording data from

DTM is a digital topographic model where the LIDAR data has been manipulated to only show the surface of the earth that was under the canopy.

The beauty of LIDAR is that a forester can view both maps simultaneously

Spatial Data (3 decks)

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