Remote Sensing Chapter 3

Front 1

thermal infrared radiation

Back 1

radiation in infrared wavelengths

- longer than NIR and middle IR

all objects emit electromagnetic energy

-emitted radiation vs reflected radiation

Front 2

kinetic heat

Back 2

internal heat or true heat

the energy of particles of matter in random motion

- true kinetic temperature - (concentration of heat) measured using a thermometer

Front 3

radiant energy

Back 3

all objects internal kinetic heat is converted to radiant energy --> external or apparent energy

Front 4

radiant flux

Back 4

the radiation exiting an object

Front 5

radiant temperature

Back 5

the concentration of the amount of radiant flux

- there is usually a high positive correlation between the kinetic temperature and the amount of radiant flux emitted from the object

Front 6

blackbody

Back 6

a theoretical construct

-absorbs all radiation that falls on it

-radiates energy at maximum possible rate per unit area at each wavelength for a given temperature

sun approximates a black body at 600K

earth ---- at 300K

REAL WORLD OBJECTS ARE NOT BLACK BODIES

Front 7

emissivity

Back 7

Emissivity=amount of energy emitted by real object/amount of energy emitted by a black body at the same temperature

if an object is acting like a blackbody,

emissivity = 1

emissivity cannot be more than 1

emissivity values are between 0 and 1

real world objects usually selective radiator

Front 8

graybody

Back 8

a real world object that has same emissivity at all wavelengths

Front 9

water - emissivity

Back 9

a graybody with high emissivity

Front 10

emissivity & kinetic temp.

Back 10

two objects could have the same true kinetic temperature but different apparent (radiant) temperature if emissivity is different for the two objects

Front 11

factors that influence emissivity

Back 11

color --> darker colored objects usually have higher emissivity

surface roughness ---> objects with high surface roughness have high emissivity

moisture content --> high moisture content means high emissivity

emissivity is wavelength dependent

Front 12

kirchoff's radiation law

Back 12

at a given wavelength, spectral emissivity of an object equals the spectral absorptance

good absorbers are good emitters

poor absorbers are poor emitters

highly reflective objects usually are poor emitters

water

- is a poor reflector

- is a good emitter

- emissivity close to 1

sheet metal roof

- reflects well

- emits poorly

- emissivity much less than one

Front 13

thermal conductivity

Back 13

the rate that heat passes through a material

Front 14

thermal capacity

Back 14

ability of the material to store heat

---> water has a high thermal capacity (takes a long time to change its temperature)

Front 15

thermal inertia

Back 15

a measurement of the thermal response of a material to temperature changes

Front 16

digital whisk broom scanner

Back 16

instantaneous field of view (IFOV)

area on ground sensed at a given time by the sensor (one pixel)

IFOV is smaller when aircraft is close to ground

area of a pixel on the edges of the images is larger than the center of the image ---> makes objects on the edges of the image appear smaller than objects in the middle

Front 17

passive remote sensing

Back 17

records energy that is reflected or emitted from the surface

Front 18

active remote sensing

Back 18

create their own electromagnetic energy that is reflected from the terrain

Front 19

radar remote sensing

Back 19

radio detection and ranging

microwave energy can penetrate some things that are opaque to visible/IR light: clouds

Front 20

side-looking airborne radar (SLAR)

Back 20

instrument points of an angle to the side of the airplane

Front 21

radar geometry

Back 21

range direction or look direction ---> at right angles to flight line

depression angle: angle between horizontal and the line of sight

look angle: angle between straight down and line of sight

Front 22

look direction

Back 22

look direction will influence how bright objects are:

objects that trend perpendicular to the look direction will appear brighter than objects that are parallel to it

Front 23

slant-range and ground-range geometry

Back 23

on the near range of the slant range image, objects look smaller than they look in the far range

Front 24

spatial resolution of a radar image - range resolution

Back 24

resolution in range direction

- range resolution is directly dependent on pulse length --> shorter pulses lead to higher resolution

range resolution is better in the near range than in the far range

Front 25

azimuth resolution

Back 25

the longer the antenna length, the higher the azimuth resolution

other factors:

- height above ground - lower heights ---> better resolution

wavelengths - lower wavelengths ---> higher resolution

Front 26

synthetic aperture radar (SAR)

Back 26

gives better azimuth resolution using antennas of practical length

synthetically simulates a long physical antenna

-using doppler effect

-frequency (wavelength) shift due to relative motion of two object

Front 27

radar relief displacement

Back 27

aerial photos --> tall objects lean away from principal point

radar ---> tall objects lean towards the radar antenna

Front 28

foreshortening and layover

foreshortening---> flight direction

Back 28

features in near range (greater depression angle) are more foreshortened than features in far range

higher objects are foreshortened more

layover

- most severe on near range side, in mountainous terrain (very tall objects)

top of object appears closer than the bottom of object (extreme foreshortening)

Front 29

radar speckle

Back 29

-grainy salt and pepper effect

-bright constructive and darker destructive interference waves interacting with each other

-can be processed to remove speckling but lose spatial resolution

Front 30

polarization

Back 30

unpolarized energy vibrates in all possible directions perpendicular to the direction of travel

-polarized energy vibrates only in a single plane

-vertically polarized (vibrating in vertical plane)

-horizontally polarized (vibrating in horizontal plane)

HV - horizontal send, vertical receive

VH - vertical send, horizontal receive

(cross-polarized)

Front 31

surface roughness

Back 31

is the object rough at the scale of the wavelength - centimeter cale

-surface is smooth (local relief 1/8 of wavelength) - energy reflects specularly

all of signal bounces away from the sensor--> no return --> dark

-intermediate surface roughness (between 1/8 & 1/2 of wavelength) - intermediate return --> some energy comes back to sensor

- rough surface (relief > 1/2 wavelength)

reflection is diffuse ---> some comes back to sensor ---> bright return

Front 32

corner reflectors

Back 32

specular reflection (smooth surface)

1. horizontal surface

2. vertical surface ---> signal returns in same direction it came from ---> nearly whole signal returns to sensor --> bright

Front 33

moisture content

Back 33

dielectric constant - a materials electrical characteristic

dry materials - 3 - 8

water - ~80

moist soils ---> bright

dry soils ---> dark

water bodies are usually dark (specular reflection)

Front 34

vegetation

Back 34

complex reflection

forest canopy often has medium reflection due to diffuse reflectance

longer wavelengths penetrate farther into the canopy

Front 35

vegetation polarization

Back 35

HH

VV

HV

VH

horizontal

vertical

HH or VV ---> return reflection results from a single reflection in the canopy

if energy is scattered multiple times it may become depolarized --> may be recorded in cross-polarized mode (HV or VH)

Front 36

urban features

Back 36

urban features are bright often due to corner reflection

cardinal effect - orientation of features relative to the radar will control whether this corner reflection occurs

Front 37

digital elevation models

four technologies:

Back 37

in-situ surveying

photogrammetry

radar (interferometric synthetic aperture radar - IFSAR)

LIDAR - light detection and ranging

Front 38

LIDAR

Back 38

light - laser

1040 nm (common)

instrument emits pulses of laser light - as many as 100,000 pulses/second

measures time (distance) from instrument to target and back

Front 39

instantaneous laser footprint

Back 39

circular area on ground of the laser pulse

Front 40

point spacing across track

Back 40

more points ---> higher resolution imagery

Front 41

determining the location of points

Back 41

time

- distance between instrument and target

GPS

measurement of antenna altitude

angle of scan

where instrument is, how it's tilted

Front 42

LIDAR returns

Back 42

multiple returns --> possible to get more than one reflection from a single pulse

first return ---> highest feature the pulse encountered

last return ---> lowest feature the pulse encountered

Front 43

LIDAR point cloud data

Back 43

Lidar data typicallu produce points with known

x,y location

z - elevation

intensity - strength of reflection

# of return - 1st, 2nd.... return

class - ground, vegetation

Front 44

LIDAR bare earth filtering

Back 44

ground or other --> determined by proprietary algorithms

only ground points are used in the creation of a digital elevation model

Front 45

LIDAR intensity

Back 45

how strong the reflection is