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, Authors: Tore Guneriussen and Harold Johnsen Presented by: Joey Boggess Date: December 1, 2004

What is SAR? Synthetic Aperture Radar (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 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. SAR instruments can penetrate through clouds, haze, smoke, and vegetation. Airborne and Earth Resource Satellite (ERS) Airborne and Earth Resource Satellite (ERS)

Airborne Remote Sensing

Satellite Remote Sensing

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

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

ASAR Modes Image Mode Image Mode Alternating Polarization Mode

ASAR Modes (Continued) Global Monitoring Mode Global Monitoring Mode Wave Mode

ASAR Modes (Continued) Wide Swath Mode

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

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

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. 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.

Study Area Norwegian part of the snow and ice experiment within the European Multi- sensor Airborne Campaign (EMAC’95) acquired in the Kongsfjellet area Norwegian part of the snow and ice experiment within the European Multi- sensor Airborne Campaign (EMAC’95) acquired in the Kongsfjellet area

Data Data stemmed from the combination of three remote sensing and in situ campaigns that were conducted in Data stemmed from the combination of three remote sensing and in situ campaigns that were conducted in 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 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.

European Multi-Sensor Airborne Campaign (EMAC’95) 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. 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.

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

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. σ σo (θ) = σoss (θ) + ψ (θ)2 [σosv(θ’) + σosg (θ’)L -2 (θ’)]

The Problem of Backscattering

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

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

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. 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. 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.

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. 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.

Conclusion The conclusion was drawn that the best separation between wet snow and the ground was found using the C-band data. 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. 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.

References _asar/asar_modes_ge.htm _asar/asar_modes_ge.htm

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