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RS EducationPart 3


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Microwave

Remote Sensing


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Introduction

Microwave portion of the spectrum coversfrom 1cm to 1m wavelength

Microwave sensing encompasses bothactive and passive


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Introduction

passive Microwave

- Passive microwave sensing is similar in concept to thermal remote sensing

- All objects emit microwave energy of some magnitude, but in very small amounts

- The emitted energy is related to the temperature and moisture properties of theemitting object or surface

- Passive microwave sensors are typically radiometers or scanners by this difference thatantenna is used to detect and record the microwave energy.

-The microwave energy recorded by a passive sensor can be emitted by:

(1) atmosphere

(2) reflected from the surface(3) emitted from the surface or

(4) transmitted from the subsurface

- Because of the long wavelengths, the available energy is quite small

cause low spatial resolution


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Introduction

passive Microwave applications

- Meteorological applications:

- measure atmospheric profiles

- determine water and ozone content in the atmosphere

- Hydrological applications:

- measure soil moisture

- Oceanographic applications:

- mapping sea ice, currents, and surface winds

- detection of pollutants, such as oil slicks


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Introduction

Active Microwave

- non-imaging

- altimeters

- Transmit short microwave pulses

- look straight down at nadir below the platform

- measure height or elevation (if the altitude of the platform is accurately known)

- Scatterometers

- precise quantitative measurements of the amount of energy backscattered from targets

- Ground-based scatterometers are used extensively to accurately measure the backscatterfrom various targets in order to characterize different materials and surface types

- Imaging

- RADAR (RAdio Detection And Ranging)


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Why Microwave Remote Sensing?!!active and passive

All-weather imaging capability (because of their Long Wavelength)

Day/night data acquisition (because of their Active mode)

Sensitivity to geometric shape, surface roughness, and moisture

content

Partial penetration through soil, snow and vegetation


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Radar History

Canada's SURSAT (Surveillance Satellite) project from 1977 to 1979 led toCanada participation in the (U.S.) SEASAT radar satellite, the first operationalcivilian radar satellite

The Convair-580 airborne radar program, carried out by the Canada Centrefor Remote Sensing following the SURSAT program, in conjunction with radar

research programs of other agencies such as NASA and the European SpaceAgency (ESA), led to the conclusion that spaceborne remote sensing wasfeasible

ESA's ERS-1 in 1991, spaceborne radar research intensified

major launches of Japan's J-ERS satellite in 1992

ERS-2 in 1995

Canada's advanced RADARSAT satellite in 1995

Envisat in 2002 by ESA


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Radar Basics

A radar is essentially a ranging or distance measuring device.

consists of

- a transmitter

- a receiver

- an antenna

-an electronics system

generation of successive short bursts (or pulses of microwave (A)at regular intervals which are focused by the antenna into a beam(B).

The radar beam illuminates the surface obliquely at a right angleto the motion of the platform.

The antenna receives a portion of the transmitted energyreflected (or backscattered) from various objects within theilluminated beam (C).


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Radar Basics

location and distance measure by Time delay between the transmission of a pulse

and the reception of the backscattered "echo" from different targets

By motion of platform forward, recording and processing of the backscatteredsignals builds up a two-dimensional image of the surface.


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Radar Basics

Microwave bands given code letters during World War II, and remain to this day:

- Ka, K, and Ku bands: very short wavelengths used in early airborne radarsystems but uncommon today.

- X-band: used extensively on airborne systems for military reconnaissanceand terrain mapping.

- C-band: common on many airborne research systems (CCRS Convair-580and NASA AirSAR) and spaceborne systems (including ERS-1 and 2and RADARSAT).

- S-band: used on board the Russian ALMAZ satellite- L-band: used onboard American SEASAT

and Japanese JERS-1 satellites and NASAairborne system

- P-band: longest radar wavelengths, used onNASA experimental airborne research system


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Radar Basics

A C-band Radar image

An L-band Radar image

Radar Images from same agricultural field


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Radar Basics

PolarizationThe shape and the locus of the tip of the Electric field vector in the planeorthogonal to the direction of propagation at a given point in space as afunction of time

Horizontal Polarization

Vertical Polarization

HH - for horizontal transmit and horizontal receive

VV - for vertical transmit and vertical receive

HV - for horizontal transmit and vertical receive

VH - for vertical transmit and horizontal receive.

Like-polarized

Cross-polarized


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Radar Basics

Polarization

Both wavelength and polarization affect how a radar "sees" thesurface.

radar imagery collected using different polarization and wavelength

combinations may provide different and complementary informationabout the targets on the surface.


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Radar Basics


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Viewing Geometry and Spatial Resolution

flight direction (A)

nadir (B)

The microwave beam is transmitted obliquely atright angles to the direction of flight

swath (C)

Range (D)

the across-track dimension perpendicular tothe flight direction

azimuth (E)

along-track dimension parallel to the flightdirection.

This side-looking viewing geometry is typical of

imaging radar systems (airborne or spaceborne)


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Viewing Geometry and Spatial Resolution

range or across-track resolution

azimuth or along-track resolution

RAR (Real Aperture Radar)

SAR (Synthetic Aperture Radar)


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Radar Image Distortions Slant Range

Slant Range Image

Ground Range Image

Top: a radar image in slant-range

the fields and the road in the nearrange on the left side of the imageare compressed

Bottom: the same image in ground-range

the features in their proper geometric

shape


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Radar Image Distortions Foreshortening


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Radar Image Distortions Layover


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Radar Image Distortions Shadow


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Target Interaction and Image Appearance

Geometric Roughness

Smooth Surfaces (A)

Rough Surfaces (B)

Local Incidence Angle

look direction or aspect angle

dielectric constant


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Corner reflectors

cities,

Volume Scattering


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Radar Image Properties Speckle

speckle is the "salt& pepper" noise on

a radar image; it is a

function of thecoherent nature of

radar waves

causing randombright and dark

areas in the scene


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Radar Image Properties Speckle


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Radar Image application

Radar images have many applications which we will speak more about themlater, but the most well-known of them are:

Structural mapping

DEM Generation

Displacement measurement

oil spill detection

Soil moisture


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