Topic 14

Question 1

two types of advanced terrain analysis

Answer 1

viewshed analysis

watershed analysis

Question 2

viewsheds

Answer 2

maps that communicate the property of intervisibility

map of all the locations that can be seen directly from some observation point

may or may not recognize the role of obstacles like buildings or rocks

Question 3

intervisibility

Answer 3

the ability to obtain clear line of sight between two points

Question 4

4 major themes of watershed

Answer 4

surface flow

flow accumuation

stream networks

watershed delineation

Question 5

how is the useability of a model controlled

Answer 5

controlled by the quality of the elevation model

Question 6

uses for viewshed

Answer 6

cell towers, urban development, millitary

Question 7

intervsibility and viewsheds

Answer 7

related techniques

intervisbility refers to discrete features

viewsheds can be applied to continuous surfaces

Question 8

3 types of line of sight operations

Answer 8

basis for viewshed analysis

a sigjtline is a computation for one pair of locations, identified by a viewpoint target or observer target coordinates

point targets, line targets, polygon targets

Question 9

line of sight operations: viewshed

Answer 9

aggregate all the possible visible points from a location

bigger the pixel, the worse the accuracy of high point in elevation

Question 10

elevation target

Answer 10

entered directly with coordinate or interpolated from terrain model

eg tree heights

Question 11

height of observer

Answer 11

typically not useful at ground level (eg require height of camera, height of tower)

Question 12

constraints on view angle

Answer 12

imposed by viewing through a window or telescope

Question 13

maximum view of distance

Answer 13

limits the radius of possible visibility

Question 14

earths curvature

Answer 14

may be necessary to consider for very large viewsheds

Question 15

viewshed accuracy

Answer 15

sensitive to the quality of the DEM and quality of environment modelling

low precision data over-estimates visibility

Question 16

irradiance mapping

Answer 16

related to intervsibility where teh goal is to compute the amount of solar energy falling on a surface

Question 17

what is a watershed

Answer 17

an upslope area constrained by topographic divides that drain water to a common outlet

can be subdivided into sub-basins

Question 18

outlet

Answer 18

often called a drainage basin

pour points

Question 19

what is watershed analysis

Answer 19

automated terrain analysis that estimates any of the follow hydrological features

watershed boundaries (basins)
surface flow direction and accumulation

location of streams or stream networks

Question 20

how are watersheds perfomed

Answer 20

generally perfomed using raster DEM (not TIN)

Question 21

flow direction

Answer 21

modelling hydrologic flow is dependent in how water moves downhill

Question 22

basic approaches in hydrology tools

Answer 22

flow direction and DEM filling

flow accumulation and stream channel identification

stream network estimation

watershed delineation

Question 23

flow direction

Answer 23

modelling flow is dependent on understanding surface constraints

what the pixel does to the flow

helps visualize stream networks

identifies flow accumulation

Question 24

sinks

Answer 24

spurious depressions in the DEM that trap flow

Question 25

peaks

Answer 25

spurious high elevation cells that will divert flow

Question 26

what is a fill operation

Answer 26

used to correte the errors from sinks and peaks

Question 27

flow accumulationstream channels

Answer 27

basis for indentifying streams each cell in a flow raster gives information on the water being contributed to the stream

Question 28

whst is stream channel

Answer 28

defined as cells exceeding a threshold amount of accumulation channel initiation threshold

Question 29

stream network identification two types

Answer 29

streams ordered by values stored in the dataset stream junction points stream segments (links)

Question 30

junction points

Answer 30

points coded in a separate raster layer points of confluence

Question 31

stream links

Answer 31

used to identify individual segments and are coded with unique IDS for derivative products

Question 32

stream order rasters

Answer 32

derivative layer tha are estimated from stream junctions and links stream order values are stored in a new raster dataset

Question 33

watershed delineation

Answer 33

outlet or pour point (location of interest) trace backwards in flow accumulation intil cells hit a value of 1 major stream junctions are commonly identified pour points

Question 34

are watersheds outputs accurate

Answer 34

usually outputs are not very accurate when comparing results to ground based data so treat the model as a rough estimate