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Relationships between PALSAR
backscattering data and forest above
ground biomass in Japan
○ Takeshi Motohka (Japan Aerospace Exploration Agency)
2011/07/28: IGARSS 2011, Vancouver, Canada.
Masanobu Shimada (Japan Aerospace Exploration Agency)
Osamu Isoguchi (Remote Sensing Technology Center of Japan)
Masae I. Ishihara (Japan Wildlife Research Center)
Satoshi N. Suzuki (Japan Wildlife Research Center)
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Outline
- Background
- Data
- In situ biomass data
- PALSAR yearly mosaic data
- Results
- Relationship between biomass and PALSAR data
- Mapping forest biomass
- Summary and future works
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BackgroundForest biomass is a key parameter to assess
Emission of greenhouse gasses (CO2, CH4, etc.)
Accumulated carbon in forests Biodiversity
A large-scale, time-series, globally consistent biomass monitoring is important for various projects such as REDD+.
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Biomass monitoring by PALSAR
- Microwave backscatter shows high correlation with forest tree biomass especially for longer wavelength (i.e. L-band, P-band, …).
- Spatial (10 – 100 m) and temporal (46 days) resolution meet the REDD+ or FCT methodologies.
- Well calibrated global datasets for 5 years (2006 ~ )
- ALOS mission was ended in 2011, but next ALOS-2 (PALSAR-2) will be launched in 2013.
Phased Array type L-band Synthetic Aperture Radar
PALSARPALSAR-2
ALOSALOS-2
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Lucas et al., 2011
Mitchard et al., 2009
Englhart et al., 2011
Many studies have revealed the relationships between forest biomass and PALSAR data at various regions and forest types.
AfricaAustralia
Indonesia
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Purpose of the study
• Target = Japan
• Investigating the relationships between PALSAR backscattering data and above ground biomass of Japanese forests
• Testing the retrieval of forest biomass using the obtained empirical relationships and PALSAR yearly mosaic data
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In situ Biomass Data
Website: http://www.biodic.go.jp/moni1000/
“Monitoring Site 1000” project by the Ministry of Environment of Japan (since 2003)
• Network of long-term research sites for biodiversity assessment
• 49 tree census sites
• Located at various forest types
• Only natural forests were selected in the study (not including artificial forests)
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Deciduous broadleaf forest(Tomakomai, Hokkaido)
Evergreen coniferous forest(Otanomousu-daira, Nagano)
Deciduous broadleaf forest(Chichibu, Saitama)
Evergreen broadleaf forest(Yona, Okinawa)
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Tree diameter of breast height [cm] (DBH)
Tree diameter of breast height [cm] (DBH)
Dry weight [kg]Dry weight [kg]
measured all trees in about 1 ha plotexcept for DBH < about 5 cm.
Allometric equationsfor each specie
Ʃ (dry weight) / stand-size
Biomass [t/ha]Biomass [t/ha]
Processing of tree census data
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Statistics of the forest stands (n=44)
Range Mean Median
Observation year 2005 - 2009 - 2007
Elevation (m) 40 - 1880 583 460
Annual mean temperature (degree) 2.5 - 21.9 10.5 9.4
Stand size (ha) 0.1 - 1.2 0.9 1.0
Tree density (number/ha) 493 - 3975 1304 1164
Mean DBH (cm) 8.7 - 26.8 16.9 17.3
Basal area (m2/ha) 13.0 - 78.2 44.8 44.0
Above ground biomass (t/ha) 46.7 - 467.9 270.7 270.7
DBH: Diameter at Breast Height
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PALSAR yearly mosaic
R: HH
G: HV
B: HH/HV
Year: 2007, 2009
Mode : Fine beam dual
(HH, HV)
Mosaicking period :
Jun. - Sep.
Pixel sampling : 10 m
Orbit: Ascending
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- Long-strip processing- Ortho-rectification- Slope-correction- Mosaicking
γ0 [dB] = 10 log 〈 DN2 〉 - 83
15 x 15 pixels averaging
Shimada & Otaki (2011); Shimada (2011) in “IEEE JSTAR special issue on Kyoto and Carbon Initiative”
Generation of PALSAR yearly mosaics
Converting DN to gamma naught
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xbay ln
Saturation level:
- dy/dx = 0.01… 91 [t/ha]
- dy/dx = 0.005… 182 [t/ha]
HV
RMSE: 0.703 [dB]
PALSAR γ0 vs. biomass
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Saturation level:
- dy/dx = 0.01… 68 [t/ha]
- dy/dx = 0.005… 136 [t/ha]
PALSAR γ0 vs. biomass xbay ln
RMSE: 1.053 [dB]
HH
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Red ●: After correction
Green +: Before correction
RMSE: 1.053 [dB] RMSE 0.703 [dB]
RMSE: 2.312 [dB] RMSE 2.073 [dB]
Effect of slope-correction
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HV
HH
Precipitation vs. PALSAR gamma naughtrainfall (over 10mm during 3 days before obs.)
RMSE:HH: 0.670 dB HV: 0.402 dB
Mean bias between rainy and non-rainy data:
HH: +0.177 dB HV: +0.044 dB
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Inversion of forest biomass
RMSE: 106.23 t/ha
%RMSE: 39.3 % (=RMSE/mean)
PALSAR HV γ0
(15 x 15 pix average)
Water, Lay-over, Shadowing mask
Urban area mask
Biomass map
b
aAGB
0
exp
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400 ~0 100 200 300
Above ground biomass (t/ha)
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400 ~0 100 200 300
Above ground biomass (t/ha)
Cropland
Cropland
Wetland
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1 km
(c) Google Earth
400 ~0 100 200 300
Above ground biomass (t/ha)
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Summary
• We examined the relationships between PALSAR backscattering data and forest biomass in Japan.
HV polarization was better to use (low RMSE and high saturation level).
Slope correction was very important to reduce the error especially in mountainous regions.
More data points were needed to investigate the difference among vegetation types. Airborne LiDAR can be good solution of this.
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Summary
• Simple inversion of forest biomass
Spatial pattern seems to be good.
Problems: accuracy and saturation
Possible solution:
• Additional SAR analysis (multi-temporal data, full-polarimetric data, etc…)
• Data fusion with ALOS/PRISM DSM and ALOS/AVNIR-2 (10-m res. VIS&NIR) data
• Data fusion with ICESAT/GLAS data
• More in-situ data points and more evaluation