Remote Sensing Mid-term 2

Lidar

Operates in infrared range of EMS

Lidar stands for

Light Detection And Ranging

Lidar laser pulses are:

Shot form above ground

How Lidar works

Laser pulses shot from above ground

• Source sends laser pulses towards the target

• Records reflectance laser pulse

Lidar operates in the:

Infrared region of the EMS (some in blue-green regions)

Lidar deriving elevation

Based on time taken for laser pulse to travel to and from the target

Lidar derived surface models include:

Top of vegetation canopy buildings

• Lidar derived bare earth elevation must have all of those removed

• Needs human interactive processing

• Can deforest a forest to see bare earth

Ground based Lidar

Can survey for before and after natural disaster

Lidar wavelength

Infrared region (1000-1500 meters)

• Commonly used in many lidar scans

• Absorbed by water, not useful for hydrological studies

Lidar penetrating water:

Can penetrate but not very deep

Aerial Lidar

Used for mapping when heavy rain where water will pool

Used for inspecting bridges

Flood plains and where the water will flow/what houses will be affected by a flood

Satellite Lidar

Can be used to see volcano plumes

Very expensive

Lidar is an BLANK sensor

Active

Radar is a BLANK sensor

Active

Radar uses:

Microwave wavelengths

Radar stands for:

Radio Detection And Ranging

Radar applications:

Military

Air traffic control

Aircraft safety

Law enforcement

Ship monitoring

Space

Swath width =

Range

Radar low bands:

HF, VHF, UHF, and L band (3Mhz frequency)

Radar mid bands:

S, C band (2 GHz- 8 GHz frequency)

Radar high band:

X, Ku-, Ka- band (8 GHz- 40 GHz frequency)

Direction of flight=

Azimuth

Backscatter=

Reflectance

Angle of view=

Depression angle

Absorption=

Attenuation

Attenuation

As EM radiation passes through a medium its power reduces

What do atmosphere, rain, snow and hail cause

Caution attenuation of Radar signal

Longer distance=

More attenuation

Shorter wavelengths=

More attenuation

Side-looking Radar

Mounted active sensor on an aircraft/satellite that points in direction of flight path

Radar applications

Day or night use

Penetrate clouds

We know how much energy was sent out and can measure the amount the comes back

Used in archaeology

Radar disadvantages

Developed for and by military

Difficulties associated with interpretation radar images

Distortion of images

Ground penetrating Radar (GPR)

Signals sent to the ground

Reflectance recorded

Differences in reflected signal materials with different electrical properties

GPR

Used in locating

Limitations of GPR

Wet soil/clay

Radar signals frequency

Data interpretation

Often used with other tools

Data resolution

Resolution is an important factor for remote sensing applications

Radiometric resolution

Related to the values used for storing reflected EMR

Spatial resolution

Dimension of a single pixel in an image

Spatial resolution decides in:

The size of the smallest object on the ground that can be distinguished in the image

Spectral resolution

How we divide the EMR spectrum for measuring reflectance

Wide range of EMR=

Coarser resolution

Narrow range of EMR

Finer resolution

EMR range is denoted as band:

Blue band

Infrared band

Coarse spectral resolution:

Fewer spectral bands

Less information about reflection

Higher spectral resolution

More spectral bands

Detailed info about reflection

Temporal resolution

Referred as return or revisit time for satellites

How often a satellite collects data for the same place

Temporal resolution is influenced by:

Orbital characteristics

Swath width

Ability to point can cause change

B & W camera

Can’t separate colors

Only captures light reflecting

Color digital camera

3 bands

1 each for blue and green and red

Spatial data models

Represents, stores, and manipulate data associated with locations

Vector data model

3 common types

3 common types of vector data models

Points

• Trees, fire hydrants, streetlights, etc.

Lines

• Road, rivers, etc.

Polygons

• Property boundary

Raster data model

Grids and rows made of cells or pixels

Measured reflected light in each cell

• Avg. reflected light measured in each grid

GIS uses:

Grid or raster data

Remote sensing uses GRID or Raster data

Track of image pixels

Pixels are stored in an array of columns and rows

• Each pixel has a location (x,y) in the array

• Pixel position is described by image coordinates

Data storage

Different formats

All have a header and the image data

BSQ

Band sequential format

BSQ

By band

BIL

By line

Bands are interleaved by Line

BIP

By pixel

Bands are interleaved by Pixel

Nominal

• Distinguishes one entity for another

• Ex. house addresses, each number is a unique entity, only for name and identity sake

Ordinal

Values follow some order

• Below average

• Average

• Above average

Interval

Values have exact differences between them

Ratio

Values have exact differences between them and has an absolute zero

Cyclic

Data has direction

• Ex. Compass has direction, latitude and longitude

Nominal

Mode is a useful measure

Ordinal

Median and Mode are useful measures of central values

Interval

Mean, Standard deviation, Median & Mode can be computed

Ratio

Mean, Standard deviation, Median & Mode

Cyclic

Arithmetic operations are problematic

Thermal=

Emitted Infrared

Thermal Remote sensing

Thermal= Emitted Infrared

Also known as Far IR

No atmospheric scattering

Lots of absorption by atmospheric gases

Thermal remote sensing:

Incoming radiation from the sun is:

Absorbed and objects emits EMR

Thermal remote sensing is sensitive to:

differences in emissivity

Kinetic temperature

Caused by the vibration of molecules

Radiant temperature

Is the emitted energy of an object

Emissivity

Ratio of the energy emitted by an object to that of black body at the same temperature

Depends on wavelength

Reference books and websites publish emissivities of materials

Reflectance

Ratio of the reflected light in a wavelength over the incident light in the same wavelength

Expressed in %, by multiplying by 100

Earth surface features reflect different amount of light it also varies by wavelength

Reflectance=

Reflected light/Incident light

Interpreting Thermal Images

Often displayed as single-band

• Bright areas= relatively warmer places

• Dark area= relatively cooler places

Must know if the image is a negative or positive

Must know time of day image was acquired

TIMS

Thermal Infrared Multispectral Scanner

Complicating Factors for thermal imaging

Topography (amount of incoming radiation from sun)

Differences in emissivity of materials (in the image)

Cloud cover

Precipitation

Vegetation canopy geometry

Geothermal areas

Applications for thermal imaging

Agricultural water stress

Heat loss from urban area

Identifying and mapping materials based on their emissivities

Earthquake and volcanic activity prediction

Mapping moisture amounts

Ocean current mapping

Plumes of warm water from power plants, etc.

Atmospheric studies, weather forecasting, etc.

Spectroscopic Analysis

Study of how electromagnetic radiation is reflected, absorbed, emitted or scattered by surface material across narrow contiguous wavelength bands