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Mapping Fire Scars in Global Boreal Forests Using Imaging Radar Data

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Mapping Fire Scars in Global Boreal Forests Using Imaging Radar Data ... Fire scar mapping in deciduous forests. Fire scar mapping in chaparral. ... – PowerPoint PPT presentation

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Title: Mapping Fire Scars in Global Boreal Forests Using Imaging Radar Data


1
Mapping Fire Scars in Global Boreal Forests Using
Imaging Radar Data
  • Written By L.L. Bourgeau-Chavez, E.S. Kasischke,
    S. Brunzell, J.P. Mudd, and M. Tukman
  • Reviewed By Daniel C. Dunning

2
Overview
  • Fire scars are mappable due to ecological changes
    that occur post burn including increased soil
    moisture.
  • High soil moisture causes an enhanced backscatter
    signal to be received from burned forests.
  • Regional ecological differences can affect post
    fire changes thus impacting appearance of scars
    in C-band SAR imagery.
  • C-band European Remote Sensing Satellite (ERS)
    and Radarsat SAR data was used in this study to
    detect, map, and monitor boreal forests globally.
  • Study sites include four areas in Canada and an
    area in central Russia.

3
Overview Continued
  • Fire boundaries were mapped from ERS SAR data
    without prior knowledge of fire scar locations.
  • Maps were validated utilizing fire service
    records and ground-truthing.
  • C-band SAR data has a high potential for
    detecting and mapping fire scars globally.

4
Review
  • SAR Synthetic Aperture Radar
  • Uses a 1-2 meter fixed length antenna and
    synthesizes a much larger antenna that can be
    hundreds of meters in length and has improved
    resolving power which achieves very fine
    resolution from great distances.
  • C-band Radar Wavelength of 5.6 cm
  • Experiences some surface scattering and volume
    scattering in the heart of a tree stand, does not
    reach the ground if trees are present. Also has
    the ability to penetrate clouds.

5
Introduction
  • Mapping and monitoring fire scars is important
    for resource and land management.
  • ERS SAR images of Alaska fire scars were 3-6 dB
    brighter that adjacent unburned forests.
  • Burned areas were determined to be detectable due
    to ecological changes occurring post burn.
  • Changes included removal of tree canopy, exposure
    of rough surfaces, and increased ground moisture.
  • Research revealed phenomenon only occurred when
    burned areas were wet such as early spring, early
    autumn, or after rain events.
  • The enhanced brightness allowed fire scars to be
    detected with moderate precision.

6
Introduction Continued
  • Increased ground moisture is due to reduced
    surface albedo and the melting of the permafrost
    layer as well as reduced evapotranspiration.
  • Study was conducted using C-band SAR imagery
    collected over four Canadian boreal regions and
    an area in central Russia.

7
Objectives
  • Goal of study was to develop technique for
    mapping and monitoring fire-disturbed boreal
    forests on a global basis with the following
    objectives
  • Determine if fire scars can be detected and
    mapped in varying ecological conditions using
    C-band SAR data
  • Determine if mapping fire scars with SAR imagery
    alone is feasible and
  • Identify any geophysical, ecological, or temporal
    conditions which may affect fire scar detection
    and area estimation in ecologically different
    boreal regions.

8
Background on Fire Mapping with SAR
  • Benefit of using C-band SAR for fire scar mapping
    is its ability to penetrate ground cover.
  • ERS SAR sensor is a C-band, 5.6 cm wavelength
    imaging radar with vertical transmit and receive
    polarization (C-VV). It has a resolution of 30 m
    and a footprint of 100 km by 100 km. ERS-1 was
    launched in 1991 and ERS-2 (still in operation)
    was launched in1995.
  • Radarsat launched in 1995, and is also a C-band
    system. It also has a resolution of 30 m and a
    footprint of 100 km by 100 km.
  • Research indicates that SAR C-band data has the
    potential to be used in conjunction with Landsat
    TM data for high accuracy fire scar mapping and
    monitoring.
  • Image on following slide indicates a before and
    after of a fire occurring in Alaska. Imagery
    indicates that both Radarsat and Landsat can be
    used to map burn extent, but cloud obscurity is a
    problem with the Landsat TM imagery.

9
Radarsat VS Landsat
Clouds
10
Ecology of Canada Study Areas
  • The North American boreal forest extends from New
    Foundland to Alaska with the northern limit
    ranging from 68 N Latitude in the Brooks Range
    in Alaska to 58 N Latitude at the western edge
    of Hudson Bay. The southern limit is less
    distinct and is dependant on precipitation and
    soil moisture.
  • Climate ranges from dry with extreme annual
    temperature variations in the west to relatively
    warmer, wetter, maritime climate of eastern
    Canada.
  • Fire is more frequent in the drier regions of
    western Canada and Alaska than in the eastern
    regions. Variations in fire frequency are tied
    to variations in climate.

11
Study Areas
  • To determine if fire scars can be detected and
    mapped in ecologically varying boreal ecozones of
    Canada three ERS study areas were chosen to
    capture the west to east differences.
  • The study areas selected were the Northwest
    Territories, Ontario, and Quebec.
  • To capture ecological variation in the
    north-south direction, a sequence of three to
    eight adjacent north-south images were obtained
    from each study swath.

12
Study Areas
13
Climate and Fire Data
14
Fire Scar Detection and Mapping in Canada
  • Procedure
  • SAR data acquisition
  • Visual evaluation and rating of data
  • Selection of best rated images to be
    georeferenced and mosaicked and
  • Digitization of potential fire scar boundaries.

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19
Results of Fire Scar Analysis
20
Results of Fire Scar Analysis
21
Results of Fire Scar Analysis
22
Results of Fire Scar Analysis
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29
Discussion and Conclusions
  • Fire scars are mappable in in boreal ecosystems
    using C-band SAR imagery.
  • For Ontario and NWT study sites, fire detection
    is feasible with SAR. For NWT, SAR data
    indicates more area burned than was mapped by
    CFS.
  • Data availability for Quebec was limited and
    analysis inconclusive. Further evaluation of SAR
    data collected over Quebec is necessary for any
    conclusions to be drawn.
  • Seasonal variations in fire scar visibility occur
    globally, with the best viewing season being
    either spring or autumn.
  • Major problem distinguishing fires form wetlands.
  • For boreal regions in Russia the SAR data was
    limited to only two years over a geographic
    region, and the areas were not well mapped by
    fire service agencies.
  • Manual interpretation was used for this study,
    but technology exists to automate the process.
  • An improved method for fire scar mapping and
    monitoring might use a combination of SAR and
    multi-spectral data.

30
Potential Applications
  • Fire scar mapping in deciduous forests.
  • Fire scar mapping in chaparral.
  • Fire scar mapping in grasslands.
  • Forest reduction in Amazon rainforests.
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