REMOTE SENSING EXAM 1: STUDY GUIDE

Electromagnetic Spectrum Everything with heat (>0 K) with heat (>0 K) emits Electromagnetic Radiation (EMR)

• EMR is a combination of electrical and magnetic waves

– Waveform

• Sinusoidal

• Speed of light “c” (c=3X108

m/sec)

c= λ(lambda)v

• v= frequency (# waves per unit time)

• (λ)= wavelength

Regions of the Electromagetic Spectrum (EMS)

Radiation Laws

• Isaac Newton, Max Plank, Albert Einstein studied (EMR).

• Plank found that EMR emitted and absorbed as found that EMR emitted and absorbed as

discrete bundles of energy called ‘photons’ or ‘quanta’.

– The size of each unit is proportional to frequency

– And is a measure of the energy at that frequency

– Everything > 0 K emits energy

• Energy is subsequently re-emitted emitted at longer wavelength at longer wavelength

Q (radiant energy, J) = h * v h = constant v = frequency (waves per sec.)

f( temperature, material properties)

Stefan-Boltzmann law The energy radiated by a blackbody radiator per second per energy radiated by a blackbody

radiator per second per unit area is proportional to the fourth power of the absolute temperature.

(1) M= σT4

(a) M = total radiance in Watts/cm2

(b) σ = SB constant (5.699 x 10-8

* Wm-2

* K-4

)

(c) T = temperature in K

(i) note the importance of 4th

power

(d) Total energy emitted rises v rapidly as T rise

Wien’s Displacement Law

Distribution of this energy not uniform over the EMS of this energy not uniform over the EMS

shift toward shorter wavelength with increasing T. Peak of the curve is called the dominant

wavelength mathematically...

States that as a bodies T rises, more energy given

per unit area per unit area.

Example - Earth’s ambient T = 300 K (27°C, 80°F) Lambda(λ) = 2898 / 300 = 9.7µ

Lambda (λ) = A/T

- Lambda(λ) = wavelength of maximum emitance

- A = 2898 m * K

- T = temperature

Energy Interactions with the atmosphere – “SCATTERING”

Rayeigh Scattering

– Particles << Wavelength (λ)

– Greatest at high altitude

– Primarily caused by ‘Oxygen’ & ‘Nitrogen’

– Scattering inversely proportional to 4th power of λ

• shorter waveleng y gths scattered much more readily

• blue scattered 4x's more than green

• 16x's more than Red

• Green scattered 4x more than red etc.

– Blue sky & Red sunsets

– Significant in clear skies

• Causes haze, reduces contrast and sharpness

Mie Scattering

– Particles >= Wavelength

– Lot of scattering in visible portion

• Tends to affect longer (λ) than Rayleigh

• Water vapor, dust, ash, smoke

• More complex than Rayleigh

• Significant in overcast skies

• Greatest in lower in lower atmosphere (0-5 km.)

Nonselective Scattering

– Particles >> wavelength

– Water droplets, Ice, Fog, Haze

• not wavelength dependent wavelength dependent

• we see grayish haze

– “nonselective” WRT (λ)

• effects all equally

Effects of Scattering

– light in shadows

– reduction of contrast

– colors different

• wavelengths removed with increased distance

Remediation

– filters

• remove blue portions & UV

Absorption (Energy interactions with the atmosphere) • Wavelength selective

• Bands

– Transmission bands

• Atmospheric Windows

– Absorption Bands

• Specific wavelengths are blocked by specific gasses

• H20, CO2, & O3 mostly

Refraction (Energy interactions with the atmosphere)

-Different densities

-Glass lenses bend light

-Atmosphere does too

-Changes density from earth to space

-Also changes, with variations in T, humidity

-Example:Why the sun seems to stay on horizon long time, then disappear quickly.

-As light passes into denser medium it is bent toward it

ENERGY-MATTER INTERACTION

Energy can be;

(1) Transmitted (2) Reflected

(3) Absorbed by matter as f (λ)

EI (λ ) = ET (λ ) + ER (λ ) + EA (λ)

EI = incident radiant energy

ER = energy reflected

ET = energy transmitted

EA = energy absorbed

REFLECTION What we observe is what is reflected (visible spectrum)

– divided into 3 segments, called “Additive Primaries” Red, Green, Blue

– No addition of 2 colors can make these

– Additions of primaries make other colors

– Equal proportions of each make white light

• Specular – (like a mirror) 100% of energy reflects off at an opposite angle.

• Diffuse – energy reflects off equally in all directions (Lambertian Reflector)

–Which happens is f (wavelength, surface roughness)

• Thus, at one (λ ) may be specular & at another (λ ) may be diffuse

• Combination of above (Near-Perfect Specular & Near-Perfect Diffuse)

– Most common

EMR – SURFACE INTERACTION

Spectral Reflectance

-Expressed as a percentage

-Average admittance of incident

radiation reflected by an object. -admittance reflected / admittance in * 100 = percentage

Spectral Signatures

-"Fingerprint”

-Be careful in using this

-time of year (temporal effects)

-mixtures (spatial effects)

DATA ACQUISITION

• Detection

• Record

– Photo – both detecting & recording medium

– Digital – separate recording & detecting medium

• Interpret

– Visual

• Qualitative

• Experience important

• Spatial patterns easier for human brain to discern

– Digital

• Quantitative

• Spectral patterns easier to identify using computer

DIGITAL NUMBERS (DN)

4 TYPES of RESOLUTION

• Spatial

–Area covered / detected, Usually by a single pixel or film emulsion)

• Spectral

– The region of the EMS data / imagery collected

• Temporal

– Days/times imagery acquired (Landsat, flown once every 16 days!)

• Radiometric

– # of Bits of the data

Spatial Resolution Multi-Stage RS

Radiometric Resolution Data according to # of Bits

Ideal Remote Sensing System (Nowhere near it, or is it Possible)

• Uniform energy source

• Noninterfering atmosphere

• Unique energy-matter interactions

• Supersensor

• Real-time data handling system

• Multiple data user

Global Positioning Systems

Noise – second recalculations

Bias – governmental error on purpose

Blunder – human error

Elements of Photographic Systems

Advantages

– Improved vantage point

– Capability to stop action

– Permanent recording

– Broadened spectral sensitivity (compared to our eyes)

– Increased spectral resolution & geometric fidelity

Disadvantages

– Restricted to 0.3-0.9um range

– Restricted by weather/lighting conditions

– Non-digital format

Photo products available

• Black & White Panchromatic Black & White Infrared

– Panchromatic

– Black & White infrared

• Color

– Color

– Color IR

• Positives

– Transparencies

• Negatives

Factors influencing exposure

• Scene brightness

• Diameter of lens opening (aperture)

– f-stop – ratio of focal length to aperture diameter

• Each f-stop in succession allows 2x’s less light in (left-to-right below)

– 1.4, 2, 2.8, 4, 5.6, 8, 11, 16…

• Doubling the f-stop results in 4x’s the light

• Exposure time

– Again, each increment allows 2x’s more /less light in

• 1/1000second, 1/500s, 1/250s, 1/125s, 1/60s, etc

• Focal length (Determines angular field of view)

Camera Types

Vertical frame

Oblique -High – see horizon

-Low – no horizon

Reconnaissance

Large format

Metric

Multi-lens

Strip

Panoramic

Panoramic Camera

Color Film Color IR Film

Color IR Color Matching

Blue isn’t recorded = Black

Green = Blue

Red = Green

Near IR = Red

Filters

Non-photographic systems

Digital cameras

– Uses CD’s - silicon chip that produces electrical charge

– CMOS – (Complementary Metal Oxide Semiconductor)

• Lower power consumption

• Direct analog-digital conversion

– Built-in

• Slightly poorer image quality (but improving)

Video (videography)

– Advantages

• Immediate viewing, low cost, can be digitally processed

– Disadvantages

• Resolution poor

• Limited spectral range

- Vidicon - whole scene at once

Image Interpretation

• Products, equipment determine how

• What to be done?

– Counting

– Delineation

• Classification System

• Minimum Mapping Unit (mmu)

• Once system and mmu decided, begin delineation between units

• Start with obvious (high contrast) and work toward more detail

– Photomorphic regions

• Fuzzy edge

-“Milar”

Land Land use/Land cover (LULC) mapping

• Land cover – the type of feature present on the surface of the earth.

– Forest, corn field, asphalt, etc

• Land use – the human activity or economic function associated with a specific parcel of land.

– Urban, agriculture, parking lot

• The land use class residential might have land cover categories of grass trees concrete and of

roofs.

• Ideally shown on separate maps, but not practical.

USGS Calcification System

– Developed in 1970’s

– 4 Different levels of detail

• For different remote sensing products

• And mmu’s

– Levels I & II

• For regional state national scales of mapping

• 5-100m+ spatial resolution

– Satellite data, small scale air photos

– Levels III & IV

• For very detailed mapping

• <5 spatial resolution

– Medium to large scale air photos & high resolution satellite

USGS National Gap Analysis Program (GAP)

– Provide consistent state, regional, & national level data; natural vegetation.

• Provides info about regions where species and communities are not adequately

represented in the existing network of lands subject to conservation practices.

• www.gap.uidaho.edu/gap

Multi-resolution Land Characteristics consortium (MRLC)

– Interagency (USGS, GAP, NAQWA, EPA, NOAA, etc)

– Develop a 30m res. TM & LULC Data set for entire US

• Centered on 1992 data

Elements of Image Interpretation

• Shape – general form, configuration outline of objects

• Size – in consideration of image scale

• Pattern – spatial arrangement (orchard, cemetary, etc)

• Tone & hue – brightness or color (spectral response)

• Texture – frequency of tonal change

• Shadows – shape or outline

• Site – topographic or geographic location

• Association – relation to other features

• Resolution – practical limits of interpretation

Image Interpretation Keys

• Selective key

– Photos of comparable objects of comparable objects (comparison)

• Elimination key

– Dichotomous key (True or false)

• Keys developed for developed for;

– Certain areas, certain cover types, certain time of year

– Keys cannot be used except for their original design