IGARSS 2011 Ulander Biomass retrieval.ppt
-
Upload
grssieee -
Category
Technology
-
view
387 -
download
2
Transcript of IGARSS 2011 Ulander Biomass retrieval.ppt
![Page 1: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/1.jpg)
Biomass retrieval algorithm based on P-band BioSAR experiments of boreal forest
Lars Ulander1,2, Gustaf Sandberg2, Maciej Soja2
1Swedish Defence Research Agency (FOI), Sweden2Chalmers University of Technology, Göteborg, Sweden
![Page 2: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/2.jpg)
Outline
• Background
• Test sites and data collections
• Temporal stability of backscatter
• Backscatter vs biomass
• Regression modeling
• Validation
![Page 3: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/3.jpg)
Background
• BIOMASS is a P-band polarimetric SAR mission
• Frequency band 432-438 MHz
• Repeat pass PolInSAR and - during initial orbit - tomography
• BIOMASS is in phase A for ESA:s 7th Earth Explorer
• Three candidate missions are competing
• The other candidates are CoreH20 and Premiere
• Final selection of mission with be in 2013
• This presentation reports on development & evaluation of biomass estimation algorithms for BIOMASS
![Page 4: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/4.jpg)
P-band SAR experiments over boreal forest
• ESA has funded multiple SAR campaigns in support of satellite P-band SAR BIOMASS candidate mission
• BioSAR-1 (2007), Remningstorp
• 3 dates (Mar, Apr, May), 2 headings
• Stand-level biomass < 290 ton/ha
• Flat topography
• BioSAR-2 (2008), Krycklan
• 1 date (oct), 4 headings
• Stand-level biomass < 180 tons/ha
• Hilly topography
Sweden
Finland
Norway
Denmark
Remningstorp
30°E
20°E
20°E
10°E
10°E0°
70°N70°N
65°N65°N
60°N60°N
55°N 55°N
Remningstorp
Krycklan
![Page 5: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/5.jpg)
BioSAR-1: Remningstorp, southern Sweden
E-SAR coverage Species
Spruce
Pine
Birch
Biomass range: 10-290 tons/haLow topography: 120–145 m asl
In situ and lidar data
![Page 6: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/6.jpg)
BioSAR-2: Krycklan, northern Sweden
Biomass range: 20-180 tons/ha; Hilly topography: 135–350 m asl
SAR images (blue); forest stands (red) Species
Spruce
Pine
MIxed
![Page 7: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/7.jpg)
BioSAR-1: Short-term backscatter stability
Each data point corresponds to a forest stand and is defined by o [dB] backscatter from 2 tracks on 1 day
Max diff is 0.6 dB, which is similar to the radiometric stability.
![Page 8: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/8.jpg)
BioSAR-1: Long-term backscatter stability
Mar vs May
HH VV
Apr vs May
HV HH VV
HV HH VV
Mar vs May
Apr vs May
Mar vs May
Apr vs May
Observed backscatter reduction most likely due to decreasing moisture
![Page 9: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/9.jpg)
BioSAR-1/-2: PHV backscatter vs Biomass Data from all stands, tracks, test sites
• Re = Remningstorp• Kr = Krycklan• In general,
backscatter spread is due to:– Moisture variations– Ground topography– Forest Structure
Site Date Heading
![Page 10: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/10.jpg)
…and the same for HH and VV
Site Date Heading
![Page 11: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/11.jpg)
General observations
• HV and HH shows good sensitivity to biomass across the entire range of biomass (10-290 tons/ha)
• HH gives largest dynamic range but also largest spread
• VV shows little dependency on biomass
• Krycklan results are, in general, a few dB lower than Remningstorp
• Observed backscatter variability implies that algorithm based only on single polarisation will perform poorly.
• Need for both multi-pol and topographic corrections
![Page 12: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/12.jpg)
BioSAR-1/-2: Polarisation ratio
• Potential to correct for soil moisture effects, since dependent on dielectric constant for a slightly rough surface.
• Surface backscatter dominates for low biomass (VV > HH)
• Sensitivity to biomass but large spread for low biomass
![Page 13: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/13.jpg)
Algorithm development and evaluation
• Six regression models developed and evaluated
• Algorithm test designed to be challenging, i.e.
• Training using data from Krycklan (single date)
• Validation using all data from Remningstorp (three dates)
• All algorithms use a logarithmic transform of the biomass (W = above-ground dry biomass) to stabilise the variance
![Page 14: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/14.jpg)
Six regression models tested
HV only, one-parameter model
HV + polarization ratio, 3 parameters
Model from Saatchi et al (TGRS 2007). Multiple polarisations, 7 parameters
Model from Saatchi et al (TGRS 2007). Multiple polarisations, 14 parameters. Requires separate crown and stem biomass; includes slope corrections.
HV + polarization ratio, 6 parameters.Includes slope correction.
HV only, two-parameter model
NB. Backscatter in dB
Recently proposed models:
![Page 15: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/15.jpg)
Algorithm development and evaluation
• Models trained on 29 in-situ stands from Krycklan October 2008
• Model validation using data from Remningstorp 2007
• The validation results have been separated into different dates (Apr-May) and different test site data in Remningstorp, i.e.
• plot-level biomass where all individual trees within 80 m x 80 m have been measured and biomass error is a few percent
• stand-level biomass from helicopter lidar and field measurement with an error of 25 tons/ha
![Page 16: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/16.jpg)
Residuals after model training; Krycklan data
Test site data Date Heading
Alg 1 RMSE (t/ha)
Alg 2 RMSE (t/ha)
Alg 3 RMSE (t/ha)
Alg 4 RMSE (t/ha)
Alg 5 RMSE (t/ha)
Alg 6 RMSE (t/ha)
Stands Oct 2008 43° 36.3 36.5 21.9 30.0 30.2 23.6
Stands Oct 2008 134° 34.3 33.7 22.9 29.1 25.9 23.1
Stands Oct 2008 314° 34.8 34.0 25.4 27.4 30.7 27.4
Stands Oct 2008 358° 40.1 40.0 29.5 33.5 37.8 36.1
Training on all data and residuals separated for different headings. Algorithm 3 has smallest residuals, but all algorithms perform similar.
![Page 17: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/17.jpg)
Independent validation; Remningstorp data
Test site data Date Heading
Alg 1 RMSE (t/ha)
Alg 2 RMSE (t/ha)
Alg 3 RMSE (t/ha)
Alg 4 RMSE (t/ha)
Alg 5 RMSE (t/ha)
Alg 6 RMSE (t/ha)
Stands Mar 2007 179/200° 161.8 102.5 99.2 103.5 58.6 33.2
Stands Apr 2007 179/200° 116.3 74.4 90.4 96.4 45.8 29.2
Stands May 2007 179/200° 95.3 62.7 76.2 81.6 48.3 31.2
Plots 80x80 Mar 2007 179/200° 235.4 127.1 163.0 165.0 73.6 35.1
Plots 80x80 Apr 2007 179/200° 164.1 86.4 149.2 154.1 62.5 38.1
Plots 80x80 May 2007 179/200° 120.2 64.8 126.4 129.4 62.3 42.4
Algorithm 6 (HV, pol-ratio, topo-corr) significantly better than the others
![Page 18: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/18.jpg)
Biomass retrieval performance
Algorithm 5 Algorithm 6
Algorithms trained with all data from Krycklan and evaluated with data from Remningstorp.Validation results from Remningstorp are shown in the plots above.
T = standsV = plots 80 m x 80 m
![Page 19: IGARSS 2011 Ulander Biomass retrieval.ppt](https://reader036.fdocuments.in/reader036/viewer/2022081401/5565ab55d8b42a4c6f8b48d4/html5/thumbnails/19.jpg)
Conclusions
• Single-pol P-band backscatter shows significant variability when data from different test sites, headings and dates are pooled
• Six different regression models have been trained and validated on BioSAR-1/2 data over boreal forests in Sweden
• Results show that multiple polarisations and topographic corrections significantly improve biomass retrieval
• Algorithm 5 and 6 perform significantly better
• Algorithm 6 includes HV, polarisation ratio and topographic corrections and gave the best results (RMSE 30-40 tons/ha)
• Algorithm 5 includes HV and polarisation ratio and gave the second best results (RMSE 50-70 tons/ha)
• The study shows importance of including polarisation ratio and topographic corrections besides HV-pol