Remote Sensing Microwave Remote Sensing

1
Remote SensingMicrowave Remote Sensing
2
1. Passive Microwave Sensors

• Microwave emission is related to temperature and
  emissivity
• Microwave radiometers are sensitive to
• l 0.1mm - 30cm
• The interpretation requires knowledge of the
  system, the atmosphere, and the thermal property
  of the objects

3
2. Active Microwave Sensors - Radars

• RADAR RAdio Detection And Ranging

4
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

5
2. Active Microwave Sensors - Radars

• Antenna array transmits a narrow beam of
  microwave energy
• Recorder records and displays the signal as an
  image

6
(No Transcript)
7
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

8
(No Transcript)
9
3. Side-Looking Airborne Radar (SLAR)

• The "all weather" capability
• - the l 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

10
3. Side-Looking Airborne Radar (SLAR)

• Spatial resolution
• - spatial scale at 1100,000, between Landsat
  and air photo
• - spectral information different from other
  sensor systems

11
4. Geometry of the Radar Image

• Radar shadow
• Radar layover
• Radar foreshortening

12
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

13
4. Geometry of the Radar Image
14
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

15
(No Transcript)
16
4. Geometry of the Radar Image

• Geometric errors
• - because radars collect information in slant
  range distance
• Radar layover
• Radar foreshortening

17
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        

18
Radar Layover
19
Radar Layover
20
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
•  

21
Radar Foreshortening
22
(No Transcript)
23
5. Resolutions

• Slant range resolution
• Ground range resolution
• Azimuthal resolution

24
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

25
(No Transcript)
26
(No Transcript)
27
Range Resolutions (along track)

• Slant-range resolution (Sr) is consistent
• - equal to half the transmitted pulse length
  PL/2
• Ground-range resolution (Rr) changes with
  distance from the aircraft        
• - inversely related to the cosine of depression
  angle
• Rr slant range resolution/cosqd,
• qd - depression angle

28
Range Resolutions
29
Azimuth Resolution (cross track)

• is determined by the angular beam width b and
  slant range Sr
• - while beam width b is inversely related to
  antenna length AL
•   Ra Sr b, b l/AL, l-pulse wavelength
• - near range portion has finer resolution than
  the far range

30
(No Transcript)
31
(No Transcript)
32
Readings

• Chapter 8