DOCUMENT OVERVIEW Title: Fully Polarimetric Airborne SAR and ERS SAR Observations of Snow: Implications For Selection of ENVISAT ASAR Modes Journal: International Journal of Remote Sensing, 2003, Vol. 24, No. 19, 3839-3854 Authors: Tore

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DOCUMENT OVERVIEWTitle Fully Polarimetric
Airborne SAR and ERS SAR Observations of Snow
Implications For Selection of ENVISAT ASAR
ModesJournal International Journal of Remote
Sensing, 2003, Vol. 24, No. 19,
3839-3854Authors Tore Guneriussen and Harold
Johnsen

• Presented by Joey Boggess
• Date December 1, 2004

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What is SAR?

• Synthetic Aperture Radar (SAR)
• SAR is a method of microwave remote sensing where
  the motion of the radar is used to improve the
  image resolution in the direction of the moving
  radar antenna.
• SAR instruments can penetrate through clouds,
  haze, smoke, and vegetation.
• Airborne and Earth Resource Satellite (ERS)

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Airborne Remote Sensing
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Satellite Remote Sensing
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What is Envisat?

• Envisat is the most powerful European Earth
  Observation satellite ever built. It has begun
  making the most complete sets of observations of
  the earths surface that any satellite has ever
  carried out. Envisat monitors
• The land
• Oceans
• Atmosphere
• Ice caps

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What Are ASAR Modes?

• Advanced Synthetic Aperture Radar (ASAR) are
  instruments on Envisat that enhances snow mapping
  capabilities.
• Modes are the different ways the remote sensor
  scans the earth.

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ASAR Modes

• Image Mode

• Alternating Polarization Mode

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ASAR Modes (Continued)

• Global Monitoring Mode

• Wave Mode

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ASAR Modes (Continued)

• Wide Swath Mode

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Purpose of Study

• The purpose of this study was to contribute to
  the growing understanding of the interaction
  between snow cover and microwaves.
• Answer the question
• Which band is more useful to the this type of
  experiment the C- or the L-band?

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Introduction

• The researchers used seven different ASAR image
  modes, which had incidence angles that ranged
  from 15 - 45, approximately the same variation
  as the Radarsat Standard beam mode data
  frequently used.

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Introduction (Continued)

• With the modes in place the researchers used
  their data and the theory of backscattering from
  snow cover to determine the optimum polarization
  and incidence angle combinations to successfully
  monitor the snow coverage of their point of
  interest.

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Study Area

• Norwegian part of the snow and ice experiment
  within the European Multi-sensor Airborne
  Campaign (EMAC95) acquired in the Kongsfjellet
  area

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Data

• Data stemmed from the combination of three remote
  sensing and in situ campaigns that were conducted
  in 1995.
• Fully polarimetric C- and L-band SAR data was
  gathered from the ElectroMagnetic Institute SAR
  (EMISAR), which is an airborne instrument
  operated by the Danish Center for Remote Sensing
  (DCR). The data gather from the DCR was attained
  in the months of March, May and July of 1995.

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European Multi-Sensor Airborne Campaign (EMAC95)

• One of the EMAC objectives was to encourage new
  experiments to help develop and test algorithms
  for snow parameters extraction based on existing
  and future spaceborne SAR systems (snow cover
  extent and snow water equivalent data) using
  combined airborne, spaceborne and ground data.

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C- and L-band HH, VV, and HV polarization

• C-band

• L-band

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Backscattering Theory

• The theory states that backscattering from a snow
  covered terrain depends on 1) sensor parameters
  which includes frequency, polarization and
  viewing geometry, and 2) snowpack and ground
  parameters which includes snow density, liquid
  water content, ice particle size and shape,
  surface roughness parameters, and stratification.
• so (?) soss (?) ? (?)2 sosv(?) sosg
  (?)L -2 (?)

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The Problem of Backscattering
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Backscattering

• Backscattering profiles, which clearly show the
  difference between the snow-covered areas with
  low backscatter and the snow-free ground with
  higher backscatter.

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Results

• First set of results focused on the
  backscattering angular dependency of snow and
  bare ground from ERS and EMISAR.
• The second set of results focused on the angular
  dependency of polarization features from snow and
  bare ground.

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First Set of Results

• The test results based on backscattering angular
  dependency of snow and bare ground from ERS and
  EMISAR showed that at high incidence angles the
  EMISAR backscattering corresponded to volume
  scattering, while at low local incidence angles
  the data corresponded more with surface
  scattering.
• By referring to the data the researchers assumed
  that the greatest distinction between the snow
  and bare ground was to be expected from SAR
  instruments with large incidence angles.

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Second Set of Results

• The researchers used their data to enhance the
  differences between VV and HH polarizations by
  increasing the incidence angles. The enhanced
  difference between VV and HH shown in the results
  were consistent with the theoretical results for
  the first-order solution of the radiative
  transfer equation for a randomly rough surface
  for which multiple scattering can be ignored.

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Conclusion

• The conclusion was drawn that the best separation
  between wet snow and the ground was found using
  the C-band data.
• The researchers also concluded that when the snow
  properties changed the C-band proved to be more
  affected than the L-band in the month when the
  snow cover was wettest, noting that a decrease in
  backscattering was observed for all the
  polarizations.

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References

• http//www.esa.int/export/esaEO/ESAXU0MBAMC_index_
  0.html
• http//www.westernsnowconference.org/
• http//www.informatics.org/gorilla/shuttle.html
• http//www.estec.esa.nl/vrwww/emac/Image/NokL_sw5.
  jpg
• http//www.caf.dlr.de/caf/satellitendaten/missione
  n/envisat/va_land/asar/_asar/asar_modes_ge.htm
• http//www.eurimage.com/products/radarsat.html
• http//folk.uio.no/kjetikj/fjellet/pics/v4rolig1.j
  pg
• http//esapub.esrin.esa.it/eoq/eoq53/gune53.htm
• www.maion.com/photography/

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The End