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DESDynI TIME
Es+ma+on of Forest Biomass Change from Fusion of Radar and Lidar Measurements
Sassan Saatchi (Jet Propulsion Laboratory/UCLA) Ralph Dubayah (University of Maryland) David Clark (University of Missouri )
Robin Chazdon (University of ConnecCcut) David Hollinger (USDA Forest Service)
Other contributors: Hank Shugart (University of Virginia)
Michael Lefsky (Colorado State University) ScoJ Hensley (JPL)
Maxim Neumann (JPL)
DESDynI
ECOSYSTEM STRUCTURE Baseline Requirements
The DESDynI Mission shall map aboveground woody biomass within the greater of 20 Mg/ha or 20% (errors not to exceed 50 Mg/ha), at a spaMal resoluMon of 250 m globally and 100 m for areas of low biomass annually ( < 100 Mg/ha).
The DESDynI Mission shall map global areas of disturbance at 100 resoluMon annually and measure subsequent regrowth to an accuracy of 4 Mg/ha/yr* at 100 (1-‐ha) resoluMon.
Measurement requirements for SAR and Lidar Fusion are:
Lidar: 5 beams on sun-‐synchronous orbit with at least 50 shots within a 600 m grid at the equator at the end of 5 years.
Radar: Polarimetric (linear polarizaMons) L-‐band SAR 25-‐35 degrees incidence angle with 100m resoluMon (>100 looks) Two seasons of polarimetric coverage for annual biomass maps
Monthly global imaging capability at dual-‐pol (linear polarizaMon) for mapping disturbance and biomass change
Mission Life+me: 5 years
DESDynI
DESDynl Mission ObjecMves
Inventory
Disturbance
DeforestaMon
Recovery
Logging
Aboveground Biomass from Fusion Of Lidar and Radar
Mapping Deforesta+on and Disturbance
Mapping Degrada+on (logging, infesta+on)
Forest Recovery
DESDynI
Depending on antecedent history, a forest with the biomass level associated with a mature forest, could be storing carbon, losing carbon or staying the same.
This means that a single biomass “snapshot” does not completely reveal forest carbon dynamics.
Changes of Forest Biomass
DESDynI
Large and Small Scale Dynamics are Different
and Influenced by Structure
Small-Scale Dynamics
Large-Scale Dynamics
≠
Scale of Forest Biomass
DESDynI
2005 storm killed between 300,000 and 500,000 trees in the area of Manaus which is equivalent to 30 percent of the annual deforesta+on in that same year for the Manaus region, which experiences rela+vely low rates of deforesta+on.
+mber losses from Hurricane Katrina alone amount to roughly 4.2 billion cubic feet of +mber (15-‐19 billion board feet), spread over 5 million acres of light to heavily damaged forest land in Mississippi, Alabama, and Louisiana.
2005 Storm in Amazon Killed ½ Million Trees (Negron-‐Juarez et al., 2010)
2005 Katrina Hurricane Forest impact was equivalent to 25% of annual forest Sequestra+on (chambers et al., 2007)
Forest Disturbance
DESDynI
Lucas et al. 2002
Forest Recovery Process
DESDynI
Statement of Problem
1. DESDynl Es+ma+on of Annual Deforesta+on (Radar)
2. DESDynl Es+ma+on of disturbance (Fire, Storms, etc.) (Radar)
3. DESDynl Es+ma+on of Forest Degrada+on (Radar)
4. DESDynl Es+ma+on of Forest biomass loss (Radar/Lidar)
5. DESDynl Es+ma+on of Forest biomass recovery (Radar/Lidar)
( accuracy/precision, resolu1on, temporal coverage)
DESDynI
Old Growth Height 1997
DESDynI
Old Growth Height 2006
DESDynI
Changes in Forest Height
Height difference: h(2006)-‐h(1997)
Mean: 1.18 m Stdev: 8.1 m
DESDynI
Secondary Forest Height 1997
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Secondary Forest Height 2006
Mean:4.84 m Stdev: 6.2 m
DESDynI
Growth Dynamics From Lidar
• Sampling lidar can be used to observe dynamics
– Not efficient for forest loss mapping (compared to radar or TM)
– Can directly measure growth/loss in canopy at footprint or grid scale • Orbital cross-‐overs could provide millions of direct observaMons
Amplitude
ElevaM
on
1998
2005
DESDynI
La Selva Forest Dynamics (2005-‐1998)
Biomass Change [Mg/ha] 0.5 ha Old Growth Plots
Field Es+mate
r2 = 0.79
1:1 line
DESDynI
16
SAR Measurement of Disturbance
• Annual forest disturbance, deforestation, degradation, fragmentation are mapped at 100 m resolution
a) Disturbance: -‐ 12.5 dB b) Disturbance: -‐ 5 dB
d) Disturbance: -‐ 1.0 dB c) Disturbance: -‐ 2.5 dB
Maximum Likelihood ClassificaMon
90% classificaMon accuracy
€
σ dist0 ≅ 0.78σ ref
0
At 100 m resolu+on (~100 looks) forest degrada+on of 1.0 dB change can be classified at 90% accuracy by LHV channel only.
€
class[N,µ] = 0.9 =1−Gamma[N −
N log(µ)−1+ µ
]
Gamma(N)µ = 0.78 : -1.04 dB
DESDynI
Requirement for PolarizaMon (Disturbance)
17
HH, HV, VV HH
HV VV
1. Single pol (HH) data will map disturbance with ~50% accuracy 2. Dual-‐pol data will be the Minimum requirement to map Disturbance with ~80% accuracy) 3. Quad-‐pol data will provide map Disturbance with > 90% accuracy
ResoluMon: 100 m Radar BW: 40 MHz
DESDynI
Global Biomass Change Requirements
Brown & Schroeder 1999
Average Production: ~5 Mg/ha/yr
2.5-3% of counties had wood production > 10 Mg/ha/yr
Hardwoods
Softwoods
Temperate & Boreal Forests
Average Biomass Production of forests after disturbance: ~4 Mg/ha/yr
Tropical Forests
DESDynI
SAR Measurement of Bioamss Recovery
Recovery Phase
Disturbance Even
Assump+ons for mapping forest recovery:
• Rate of RegeneraMon: 4 Mg/ha/yr Biomass EsMmaMon Accuracy: 20 Mg/ha ResoluMon: 100 m (> 100 looks) Aker 5 year SAR will measure 4Mg/ha/yr biomass change at 100 m ResoluMon • in US temperate forests about 50% of forests produce > 4 Mg/ha/yr.
• AssumpMon: radar looks achieved from azimuth and range averaging
• Aker 3 years, SAR will not meet the requirement of biomass change
• 3 year mission will only cover forests with > 7 Mg/ha/yr recovery. Over US forests, this is about 15% of forests.
DESDynI
Radar Forest DegradaMon Index
€
RFDI =HH −HVHH + HV
HV HH
HH: Dominated by volume & volume-‐surface Scajering HV: Dominated by volume scajering RFDI Sensi+vity to calibra+on is small RFDI Sensi+vity to topography and slope is small
ALOS La Selva Costa Rica
RFDI
DESDynI
RFDI to map disturbance, DeforestaMon, Intensive Logging
LHH LHV LHV Texture
DESDynI
RFDI over Slopes ALOS PALSAR Peru
ALOS PALSAR Peru
Forest Savanna
DESDynI
RFDI & Changes in Biomass
ALOS PALSAR Mosaic (Borneo) UAVSAR Howland Forest 100 m ResoluMon 80 MHz Bandwidth
DESDynI
Radar Forest DegradaMon Index For Forest Recovery EsMmates
€
p(I0
< I0 >) =
NNI0N −1
< I0 >N (N −1)!exp −
NI0< I0 >
⎧
⎨ ⎪
⎩ ⎪
⎫
⎬ ⎪
⎭ ⎪
where < I0 > is the mean intensity of a homogeneous region at time t0N is equivalent number of looksFor two independent measurements I0 = HH and I1 = HV , the difference and ratios will followthe integration of the joint probability over I0d = I0 − I1
p( d< I0 >
,< I1>) =
NN exp −NI0
< I0 >
⎧
⎨ ⎪
⎩ ⎪
⎫
⎬ ⎪
⎭ ⎪
(< I0 > + < I1>)N (N −1)!× (N −1+ j)
j!(N −1− j)!j = 0
j = N −1∑
r = I1/I0
p( r< I0 >
,< I1>) = (2N −1)!r NrN −1(r + r )2N (N −1)!N
where r =< I1> / < I0 >
RFDI =I0− I
1I0
+ I1
Change Detection will be performed between the ratio of RFDI for two dates.
RFDI =I0− I
1I0
+ I1 Delta (RFDI)*20
DESDynI
RFDI Base Forest Recovery ALOS June 2007
ALOS June 2010
DESDynI
RFDI Base Forest Recovery ALOS June 2007
ALOS June 2010
RFDI10-‐ RFDI07
DESDynI
For N lidar samples We have (N-‐1)! Δσ samples
25 m 100 m
DESDynI 28
L-‐band Measurement of Recovery
Radar & Lidar Fusion of Recovery
Baysian MLE Method
20% error in biomass change is detectable at 100-‐250 m resolu+on
€
N : Number of looksProb. of Error :PE =1/2 − f (x) + f (1/ x)
Lombardo and Oliver, 2001 Rignot & vanZyl 1995
DESDynI
SUMMARY
• Quad-‐Pol data is required to measure disturbance and recovery from L-‐band SAR data
• Increasing cross-‐points in Lidar will provide es+mates of biomass changes at the stand and ecosystem levels
• RFDI based on dual-‐pol data will provide the most consistent index to classify deforesta+on, degrada+on and recovery. However, more research is needed to assess its quan+ta+ve capability for measuring biomass loss and gain.
• Fusion of L-‐band polarimetry and Lidar has the poten+al of quan+fying stand scale patch scale changes in biomass.
• Use of repeat pass interferometry along with RFDI has the poten+al of mapping forest regrowth.