Remote Sensing Microwave Remote Sensing

1. Passive Microwave Sensors ► Microwave emission is related to temperature and emissivity ► Microwave radiometers are sensitive to  = 0.1mm - 30cm ► The interpretation requires knowledge of the system, the atmosphere, and the thermal property of the objects

2. Active Microwave Sensors - Radars RADAR: RAdio Detection And Ranging

2. Active Microwave Sensors - Radars ► Transmitter: transmits repetitive pulse of microwave energy ► Receiver: receives the reflected signal through antenna and filters and amplifies the signal

2. Active Microwave Sensors - Radars ► Antenna array: transmits a narrow beam of microwave energy ► Recorder: records and displays the signal as an image

3. Side-Looking Airborne Radar (SLAR) ► Ranging - distance from the antenna to the features can be calculated by measuring the time delay between the time when a signal is transmitted to the time its echo is received ► Detecting frequency and polarization shifts - by comparing the transmitted signal of known properties to the received signal

3. Side-Looking Airborne Radar (SLAR) ► The "all weather" capability: - the used by SLAR is long enough to penetrate clouds and light rain, e.g. applications in tropical area - SLAR systems are independent from solar illumination, which makes night missions possible

3. Side-Looking Airborne Radar (SLAR) ► Spatial resolution - spatial scale at 1:100,000, between Landsat and air photo - spectral information different from other sensor systems

4. Geometry of the Radar Image ► Radar shadow ► Radar layover ► Radar foreshortening

4. Geometry of the Radar Image ► Depression angle ► Far, mid, and near-range portion of a radar image ► Radar shadow, more severe in the far range

4. Geometry of the Radar Image

► Slant range distance - direct distance from the antenna to an object on the ground measured by time delay ► Ground range distance - distance of correct scaling as we would measure on a map

4. Geometry of the Radar Image ► Geometric errors - because radars collect information in slant range distance ► Radar layover ► Radar foreshortening

4. Geometry of the Radar Image ► Radar layover - the top of a tall object appears closer to the antenna than its base - the antenna receives the echo of the top before the base - it is more severe in the near range - it is more severe in the near range

Radar Layover

4. Geometry of the Radar Image ► Radar foreshortening - with modest or high relief in the mid or far range portion - features maintain relative position but incorrect distance causing near range slope appear steeper and far range slope gentler

Radar Foreshortening

5. Resolutions ► Slant range resolution ► Ground range resolution ► Azimuthal resolution

5. Resolutions ► Two determinant parameters: pulse length and antenna beam width - the pulse length dictates the spatial resolution in the direction of energy propagation - the width of the antenna beam determines the resolution cell size in the flight direction

Range Resolutions (along track) ► Slant-range resolution (Sr) is consistent - equal to half the transmitted pulse length PL/2 - equal to half the transmitted pulse length PL/2 ► Ground-range resolution (Rr) changes with distance from the aircraft ► Ground-range resolution (Rr) changes with distance from the aircraft - inversely related to the cosine of depression angle Rr = slant range resolution/cos  d,  d - depression angle

Range Resolutions

Azimuth Resolution (cross track) ► is determined by the angular beam width  and slant range Sr - while beam width  is inversely related to antenna length AL R a = Sr · ,  = /AL, -pulse wavelength R a = Sr · ,  = /AL, -pulse wavelength - near range portion has finer resolution than the far range

Readings ► Chapter 8