N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 1 Nicolas Ackermann Supervisor: Prof. Christiane Schmullius Co-supervisors: Dr. Christian Thiel, Dr. Maurice Borgeaud Prague, the 3rd June 2011 Investigations of ALOS PALSAR backscatter intensity and interferometric coherence over Germany’s low mountain range forested areas EARSeL SIG Forestry workshop ENVILAND2 is sponsored by the Space Agency of the German Aerospace Center with federal funds of the German Federal Ministry of Economics and Technology on the basis of legislation by the German Parliament grant no. 50 EE EE 0847

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 2  Introduction  Test site & available data  Pre-processing & preliminary investigations  Analysis of the data  Conclusions Presentation outline

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 3  Context:  The monitoring of forested areas represents a great challenge in the context of the actual Global Warming.  The launch of ALOS PALSAR spaceborne system in January 2006 has been pioneer of new capabilities for the retrieval of forest biophysical parameters.  Objectives:  Investigate the ALOS PALSAR backscattter intensity and interferometric coherence.  Underline the scattering and decorrelation mechanisms occuring in the temperate forest.  Provide some new scientific knowledge for future researches. Introduction

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 4 Test site & available data

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 5 Test site  Thuringian Forest (Germany)  Surface: 110 km x 50 km  Terrain variations  Tree species composition Scots pines Norway Spruce European Beech  Weather conditions cool and rainy frequently clouded  Peculiarities logging for forest exploitation Kyrill storm (February 2007)

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 6 Test site Topography

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 7 Test site Forest understory

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 8 SAR data ALOS PALSAR (L-Band, 46 days) TerraSAR-X (X-Band, 11 days) Cosmo-SkyMed (X-Band, 1 day) Optical data RapidEye Kompsat-2 Ancillary data DEM: SRTM 25[m], LaserDEM 5[m] Laser points (2004), Orthophotos (2008) HyMap (2008,2009) Forest inventory ( ) Photos with GPS coord. (2009) Weather data Field work Available Data (state May 2011)

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 9 Sensor Radar- Frequency BeamPolarisation Incident angle # Scenes available PALSARL-BandFBDHH, HV34°60 PALSARL-BandFBSHH34°51 PALSARL-BandPLRHH/HV, VV/VH21°13 ALOS PALSAR data 124 scenes Summer acquisitions Winter acquisitions PLR FBS FBD

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 10 Pre-processing & preliminary investigations

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 11 Topographic normalisation PALSAR PLR 21° R-HH, G-HV, B-HH Asc. 12apr09 Non normalised LiDAR DEM shaded relief High geometrical distorsions by steep incident angle. PALSAR FBD 34° R-HH, G-HV, B-HH Asc. 10jun10 Non normalised

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 12 Local incident angle Ground scattering area Topographic normalisation  Correction main components (Castel et al., 2001)

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 13  Optical crown depth (Castel et al., 2001) Volume scattering: a) Tilted surface facing the radar, b) flat surface, tilted surface opposite to the radar (Castel, 2001) Topographic normalisation

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 14 Sensor orientation : 350° Sensor azimuth angle : +90° 0° PALSAR 34° HV Asc. 06may08 Normalised PALSAR 34° HV Asc. 06may08 Non normalised Gamma nought [dB] Aspect [°] Slopes oriented in Radar flight direction High intensity for steep slopes facing radar. Topographic normalisation

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 15 Topographic normalisation PALSAR 34° HV Asc. 06may08 Normalised Gamma nought [dB] Slopes away from the radar Slopes facing the radar Aspect [°] Overcorrection? Crown optical depth? Other effects?

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 16 Topographic normalisation PALSAR 34° HV Asc. 06may08 Normalised PALSAR 34° HV Asc. 06may08 Normalised + Normalised with n coefficient Gamma nought [dB] Aspect [°]

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 17 Analysis of the data

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 18 Precipitation [mm] Temp [°] Wind [m/s] Series of PALSAR FBD, FBS, 34.6°, HH, Asc. Acquisition date Gamma nought [dB] frozen Snow + high Water equivalent frozen Weather - PALSAR intensity Temperature approaching 0 [°C] implies a decrease of the backscatter intensity

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 19 Weather - PALSAR coherence Precipitation map PALSAR Coherence HH 23jul09_X_ 07sept09 A precipitation event highly affects the degree of coherence

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 20 Urban Layover Precipitation [mm] Coherence Azimuth Weather - PALSAR coherence PALSAR FBD, 34.4°, HH, Asc.

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 21 Stem Volume - PALSAR intensity Investigations 1. Topography 2. Weather 3. Understorey 4. Forest inventory Stem volume [m 3 /ha] Gamma nought [dB] PALSAR 34° HV Asc. 10jun10 r 2 = 0.11 Weak negative correlation between PALSAR HV and stem volume

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 22 r 2 = 0.29 r 2 = 0.31 Stem Volume - PALSAR intensity Stem volume [m 3 /ha] Gamma nought [dB] Stem volume [m 3 /ha] PALSAR 34° HV Asc. 10jun10 Non normalised PALSAR 34° HV Asc. 10jun10 Normalised Daily Precip: 1.9 [mm] Hourly Precip: 0 [mm] Daily Precip: 1.9 [mm] Hourly Precip: 0 [mm] Slopes < 4° !

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 23 Stem Volume - PALSAR intensity Legend Red: Forest stands Blue: Field observations Yellow: Stem volume [m 3 /ha] Orthophoto A. Grass, No forest B. Young, dense C. Young, sparse D. Mature, dense E. Mature, sparse A. B. E. D. Forest typology Low stem volume High stem volume

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 24 Stem Volume - PALSAR intensity Observed values CoherencePALSAR HH PALSAR HVOrthophoto

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 25 CoherencePALSAR HH PALSAR HVOrthophoto Stem Volume - PALSAR intensity

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 26 Stem Volume - PALSAR intensity Stem volume [m 3 /ha] Scattering intensity PALSAR PLR, 21° Asc., 12apr09 r 2 Vol =0.008 r 2 Surf =0.09 r 2 Dbl =0.000 r 2 Vol =0.009 r 2 Surf =0.08 r 2 Dbl =0.005 Stem volume [m 3 /ha] PALSAR PLR, 21° Asc., 12apr09 Freeman DecompositionVan Zyl Decomposition Surface scattering seems to be the dominant scattering mechanism.

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 27  Coherence  The degree of coherence can be related to several factors, each expressing a specific source of decorrelation. Interferometric coherence The temporal decorrelation is related to the stability of the objects between the two acquisitions. The volume decorrelation is related to objects presenting a vertical extension. This factor is spatial baseline dependent.

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 28 ALOS PALSAR coherence A. B. C. PALSAR HH, 7sep oct09 intermediate coherence low coherence high coherence A.Forests: B. Crops: C. Urban:

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 29 ALOS PALSAR coherence Stem Volume [m 3 /ha] Interferometric Coherence R 2 S =0.19 R 2 B =0.038 R 2 P =0.044 R 2 S =0.10 R 2 B =0.009 R 2 P =0.009 R 2 S =0.22 R 2 B =0.012 R 2 P =0.06 R 2 S =0.35 R 2 B =0.12 R 2 P =0.08 R 2 S =0.36 R 2 B =0.15 R 2 P =0.088 R 2 B =0.002 R 2 S =0.29 Spatial baseline Precipitation: 23jul09: 28.6mm 07sept09: 3.9mm Legend Blue: Spruce (S) Yellow: Beech(B) Red: Pine(P) Increase of correlation with higher perpendicular baseline. Stem volume [m 3 /ha]

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 30 SANTORO et al., 2000; SANTORO, et al., 2002b Coherence „Stack“ Select and „fit“ Model Scatterplot + model Inverse model and retrieve Stem volume Estimated Growing stock Volume Compute RMSE and weights Weights Compute Growing Stock volume map Multitemporal GSV map 1., Forest inventory ALOS PALSAR coherence

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 31 -Similarly to spatial averaging, the multitemporal combination act as a filter and decreases the noise. -RMSEi>200 [m 3 /ha] is very high, in particular due to the high dispersion of the coherence. -The methodology should be tested for each species separately and by inversing testing and training stands. -Water and urban can be recognized, with respectively low (dark green) and high (gray) coherence Multitemporal coherence biomass map RMSE>200 [m 3 /ha] Preliminary results! ALOS PALSAR coherence

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 32 Conclusions and outlook

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 33 Conclusions and outlook  Different investigations of the ALOS PALSAR backscattter intensity and interferometric coherence have been conducted.  Conclusions and open issues  The topography influence is not fully understood.  Weather conditions and particularly precipitations and temperature affect the backscatter intensity and interferometric coherence.  Interferometric coherence in L-band with 46 day temporal baseline shows a potential for estimating forest biomass.  Future work  Further investigations for the topographic normalisation  Explaination of the weak negative correlation between PALSAR and stem volume  Derivation of indices and ratios between X-band and L-band  Combination/Fusion with optical data

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 34 I would like to thank DLR, ESA, ASI and RESA for the distribution of the data ENVILAND2 is sponsored by the Space Agency of the German Aerospace Center with federal funds of the German Federal Ministry of Economics and Technology on the basis of legislation by the German Parliament grant no. 50 EE EE 0847 Acknowledgements

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 35 Thuringia Forest – July 2010 Thank you for your attention ! Questions ?

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 36  Weather data  DWD: Deutsche Wetter Dienst  Acquisition period:  Parameters: Precipitation, Snowdepth, Water-equivalent, Wind, Temperature, Sunshine duration, relative Humidity  Pre-processing  Collaboration with FSU geoinformatic institute  JAMS (Jena Adaptable Modelling System) Software  2 temporal scales : daily / hourly Weather data [.xml ] Daily output generation Hourly Regionalised [.txt ] Daily [ raster ] Hourly Input conversion Daily input conversion Hourly Regionalisation Daily Selected [.dat ] Hourly Selected [.dat ] Daily Regionalisation Daily Regionalised [.txt ] Hourly output generation Hourly [ raster ] JAMS Software 90m Station 1 Station 2 Station 5 Station 3 Station 4 Weather data

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 37  Weather parameters outputs  Raster data  90m spatial resolution  Excel table  Describe mean weather values of the overlapping selected forest stands and satellite data Temperature [°C] Precipitations [mm] High: 36 0 Table weather data (simplified version) SensorAcquisition-date Daily (4 days meteorological conditions) Hourly (4 hours meteorological conditions) Beam T°air_mean [°C] T°air_mi n [°C] T°air_max [°C] Precipitation [mm] Humidity [%] Sunshine [hrs] Wind speed [m/s) T°air_mean [°C] Precipitation [mm] Humidity [%] Wind speed [m/s} TSX06/08/ :09:13spot_ TSX31/10/ :25:57spot_ …………………………………… TSX31/08/ :34:23stripNear_ Weather data Daily: 4 daysHourly: 4 hours Example Daily: 31mar apr08 High: 10 0

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 38 K-Nearest Neighbor (K-NN) Non parametric (data-based) Reference data: Forest inventory Assumption: stands with similar forest properties have also similar spectral characteristics Ponderation computed with the Euclidian or Mahalanobis Distance Lehtonen et al K-NN GSV retrieval

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 39 1 Scene 8 Scene RMSE [m 3 /ha] – FBD HV K Distance 50% stands Entire stands PALSAR, FBD, HV 25m -Leave-One Out Cross- Validation (LOOCV) at stand level. -RMSE decreases until reaching a specific K distance. -Best results with “Entire stands” und “8 scenes” (Multitemporal) Tree species Blue: Spruce Green: Beech Red: Pine K-NN GSV retrieval – PALSAR intensity Preliminary results!

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 40 PALSAR HV K-Nearest Neighbor (KNN) K-NN GSV retrieval – PALSAR intensity Preliminary results! Reference Growing Stock Volume (GSV)

N. Ackermann ALOS PALSAR – Backscatter intensity – Interferometric coherence – Forest – Biomass 41 Reference Growing Stock Volume (GSV) PALSAR HV K-Nearest Neighbor (KNN) Preliminary results! K-NN GSV retrieval – PALSAR intensity