A1262196909tbIZl

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Remote Sensing
John Wilkin
jwilkin_at_rutgers.eduIMCS Building Room
214C732-932-6555 ext 251
Active microwave systems (4) Coastal HF Radar
Dunes of sand and seaweed, Bahamashttp//www.envi
ronmentalgraffiti.com/ecology/30-most-incredible-a
bstract-satellite-images-of-earth/1324
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• Scatterometers
• satellite borne
• ocean surface vectors winds
• Incorporated into ECMWF meteorological analysis
• Synthetic Aperture Radar (SAR)
• satellite and aircraft
• high spatial resolution (tens of meters)
• image ocean surface wave field and, by inference,
  processes that modulate the surface waves
• CODAR (Coastal Ocean Dynamics Application Radar)
• land-based HF radar system
• ocean surface currents and waves
• All these systems exploit the resonant Bragg
  scattering of centimeter to decameter wavelength
  microwave radiation from ocean surface roughness
  due to short waves.

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Quikscat scatterometer frequency is 13.4 GHz 2
cm wavelength HF Radar is 3 50 MHz 100 m to
6 m
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CODAR
http//www.codaros.com

• High-frequency (HF) radio in the band 3-50 MHz
  has wavelengths6 m to 100 m
• The ocean surface is rough surface, with water
  waves of many different periods
• Bragg scattering occurs for narrow band of
  wavelengths depending on CODAR frequency
• 25 MHz transmission -gt 12m EM wave -gt 6 m
  ocean wave12 MHz transmission -gt 25m EM wave -gt
  12.5 m ocean wave 5 MHz transmission -gt 60m EM
  wave -gt 30 m ocean wave
• Radar return is greatest for waves traveling
  directly toward or away from the antenna
• Therefore we know wave direction and wavelength

http//www.encora.eu/coastalwiki/Use_of_ground_bas
ed_radar_in_hydrography
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• From surface gravity wave dispersion theory we
  know the wave period and hence wave speed
• The phase speed C of these resonant ocean waves
  is given by the dispersion relationship
• Where g is the acceleration due to gravity, ? is
  the ocean wave length, and h is the water depth.
• Wave speed creates a Doppler frequency shift in
  the radar return

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• From surface gravity wave dispersion theory we
  know the wave period and hence wave speed
• Wave speed creates a Doppler frequency shift in
  the radar return
• In the absence of ocean currents, the Doppler
  frequency shift would always arrive at a known
  position in the frequency spectrum
• Observed Doppler-frequency shift includes the
  theoretical speed of the speed of the wave PLUS
  the influence of the underlying ocean current on
  the wave velocity in a radial path (away from or
  towards the radar)
• Once the known, theoretical wave speed is
  subtracted from the Doppler information, a radial
  velocity component of surface current
  is determined.
• The effective depth of the ocean current
  influence on these waves depends upon the wave
  period and wave length. The current influencing
  the Bragg waves falls within the upper meter of
  the water column.
• By looking at the same patch of water using
  radars located at two or more different viewing
  angles, the total surface current velocity vector
  can be resolved

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• A SeaSonde HF radar unit has onetransmitting
  antenna and one receiving antenna
• The transmitting antenna is omni-directional- it
  radiates a signal in all directions
• The receive antenna unit consists of three
  colocated antennas, oriented with respect to each
  other on the x, y, and z-axes (like the sensors
  on a pitch and roll buoy). It is able to receive
  and separate returning signals in all 360 degrees
• For mapping currents, the radar needs to
  determine three pieces of information
• bearing of the scattering source (the target)
• range of the target
• speed of the target

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• A SeaSonde HF radar unit has onetransmitting
  antenna and one receiving antenna
• The transmitting antenna is omni-directional- it
  radiates a signal in all directions
• The receive unit consists of three co-located
  antennas, oriented with respect to each other on
  the x, y, and z-axes (like the sensors on a pitch
  and roll buoy). It is able to receive and
  separate returning signals in all 360 degrees
• For mapping currents, the radar needs to
  determine three pieces of information
• bearing of the scattering source (the target)
• range of the target
• speed of the target

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• The first determination is Range to target.
• The SeaSonde modulates the transmitted signal
  with a swept-frequency signal and demodulates
  this in the receiver
• the time delay is converted to a large-scale
  frequency shift in the echo signal
• Therefore, the first digital spectral analysis
  of the signal extracts the range (distance) to
  the sea-surface scatterers, and sorts it into
  range bins (typically 5 km)
• the frequency shift of transmitted minus
  received signal contains time lag and range
  information

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The frequency shift of transmitted minus received
signal contains time lag and range information
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• The second determination is Speed of the target.
• the signal is processed for 4 minutes to
  produce an average spectrum from which the
  Doppler shift is calculated
• this gives speed accuracy of 4 cm/s
• The third determination is Bearing of target
• the receive antenna has 2 directional loop
  antennas and 1 omni-directional whip antenna
• the loop antenna patterns receive power
  differently from the same incoming direction
• processing the signal difference from the 2 loop
  antennas, normalized by the omni-directional
  antenna, performs the direction finding

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Beam forming approach for direction
determination phased array antennas
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http//marine.rutgers.edu/cool/codar.html
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Spatial Maps 10/16/2002 0700 GMT
1002 mb
Contour resolution 1 mb
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10/16/2002 1500 GMT
991 mb
Contour resolution 1 mb
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10/16/2002 1800 GMT
989 mb
Contour resolution 1 mb
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10/17/2002 0000 GMT
992 mb
Contour resolution 1 mb
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http//www.bml.ucdavis.edu/boon/scur.html
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Georges, T.M., and J.A. Harlanhttp//ieeexplore.i
eee.org/stamp/stamp.jsp?arnumber00569128
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Akpatok Island, Canada
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Lake Carnegie is an ephemeral lake in Western
Australia. It fills with water only during
periods of significant rainfall. In dry years, it
is reduced to a muddy marsh
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Bolivia deforestation. Fanning out from the large
blocks of land cleared by ranchers and loggers
radiate arrangements of fields and farms, the
remaining healthy vegetation appearing in bright
red.
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Lena River, Russia