mapping of above-ground forest biomass with satellite synthetic
TRANSCRIPT
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Lars Ulander Swedish Defence Research Agency (FOI) & Chalmers University of Technology
Mapping of above-ground forest biomass with satellite synthetic-aperture radar (SAR)
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Biomass - A candidate Earth Explorer
• ESA has six Earth Explorers launched or under development in the Living Earth Program • Launched: Cryosat-2, GOCE, SMOS • Under development: Swarm, ADM-Aeolus, Earthcare
• 7th Earth Explorer • 3 candidates completed phase A: Biomass, CoreH2O, Premiere • Biomass was recently recommended by ESAC • Final mission selection with be in May 2013. • Launch currently planned for 2019
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Forest biomass Forest height Disturbances
Biomass will map global forest biomass and height
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The role of biomass in the global carbon cycle
Global Carbon Project, 2012
Biomass will improve understanding and reduce uncertainties of the carbon fluxes due to land-use change and the land sink
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Mapping forest biomass requires a radar sensor with long wavelength: 1. to penetrate the canopy in all forest
biomes
2. to interact with woody vegetation elements
3. so that forest height can be estimated with a single satellite
This implies a synthetic-aperture radar (SAR) at P-band, wavelength ~70 cm, the longest possible and first of its kind in space
How can biomass be measured from space?
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Space Object Tracking Radar P-band constraints
Land use change
Land use change
Land use change
reforestation
fire & climate warming
drought
pests regrowth
Reducing Emissions from Deforestation & Degradation (REDD)
Global Forest Observations Initiative
Large biomass uncertainty
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PolSAR (SAR Polarimetry)
x
y
z
o
PolInSAR (Polarimetric SAR Interferometry)
x
y
z
o
TomoSAR (SAR Tomography)
x
y
z
o
P-band SAR can deliver 3 types of information for biomass
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Minimum Mean Square (MMSE)
Estimate
Biomass Estimation from
Intensity
PolSAR Covariance
Matrix
PolInSAR Covariance
Matrix
Biomass Map &
Error Map
TomoSAR results DEM
In situ data
Allometric Biomass
Estimation
Biomass Estimate 2
Biomass Estimate 1
Ion
osp
he
re C
orr
ec
tio
n
Forest Height Estimation
Baseline biomass estimate from PolSAR & PolinSAR
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La Selva, Costa Rica
Maine
Colombia
Landes Alaska
Paracou F.Guiana
Remningstorp Krycklan
Kalimantan
Major recent ESA campaigns: 1. Kalimantan 2004 (Indrex) 2. Remningstorp 2007 (BioSAR 1), 2010 (BioSAR 3) 3. Krycklan 2008 (BioSAR 2) 4. F. Guiana 2009 (TropiSAR), 2011-13 (TropiScat)
ESA campaigns non-ESA campaigns
Campaigns to develop retrieval methods and assess performance
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Remningstorp forest (Sweden)
March
April May
March 2007 April 2007 May 2007
Bac
ksca
tter
Because the disturbing effects differ among polarisations, all polarisations and a DEM are used to account for environmental and topographic effects.
Soil moisture and topography affect radar-biomass relationship
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Blue - from airborne lidar map, std. error = 25 ton/ha Black - from 80 m x 80 m in situ plots, std. error = few % Training on stratified subset of Krycklan data. Performance assessed on data from Remningstorp.
Remningstorp 70 MHz data: varying environmental conditions over 3 months
Sweden
Finland
Norway
Denmark
Remningstorp
N
N
N
N
HV only HV, HH & VV HV, HH, VV & DEM
RMSE: 84% RMSE: 38% RMSE: 24%
Polarisation & ground slope radically improves accuracy
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Radar RMSE ~ 20 t/ha (based on 6 reference plots).
Biomass changes can be measured with improved accuracy
Lidar RMSE is comparable (slightly worse).
Change in biomass from spring 2007 to autumn 2010 at Remningstorp, Sweden
A 20 ton/ha change can be measured over a 4-year period.
-240 -160 -80 0 40 80 120 Change in biomass [ton/ha]
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Height (m)
Remningstorp, Sweden
PolInSAR Lidar
r2=0.65 RMSE=4m
Height maps
Boreal height mapping using P-band PolInSAR
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0
20
40
60
0
20
40
60
Normalised backscatter intensity
1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0
Forest
HV
HH
Marshland River
Tomographic transects
TomoSAR: 1. Provides a 3D reconstruction of forest backscatter. 2. Allows an interpretation of scattering processes 3. Gives guidance to the PolSAR and PolInSAR retrieval algorithms.
Hei
ght (
m)
Hei
ght (
m)
HH SAR image Paracou,
French Guiana
(6 MHz bandwidth P-band data)
What about SAR tomography? It provides basic information to improve biomass retrieval algorithms
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Forest biomass
Above-ground biomass (tons / hectare)
Upper canopy height (meter)
Areas of forest clearing (hectare)
• 200 m resolution • 1 map every 6 months for 4
years • global coverage of forested
areas • accuracy of 20%, or 10 t ha–1
for biomass < 50 t ha–1
• 50 m resolution • 1 map every 6 months for
4 years • global coverage of forested
areas • 90% classification
accuracy
• 200 m resolution • 1 map every 6 months for
4 years • global coverage of
forested areas • accuracy of 20-30%
Forest height Disturbances
Biomass product requirements
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Biomass - A candidate Earth Explorer
• After the User Consultation Meeting in Graz on 5-6 April 2013, the mission candidate Biomass was recommended by ESAC to become ESA’s 7th Earth Explorer
• Final decision will be taken by PBEO in May 2013
• Launch currently planned for 2019