BioSAR 2010 – A SAR campaign in support to the BIOMASS mission

Lars Ulander, Anders GustavssonSwedish Defence Research Agency (FOI), Sweden

Pascale Dubois-Fernandez, Xavier DupuisOffice National d’Études et de Recherches Aérospatiales (ONERA), France

Johan Fransson, Johan Holmgren, Jörgen WallermanSwedish University of Agricultural Sciences (SLU), Sweden

Leif Eriksson, Gustaf Sandberg, Maciej SojaChalmers University of Technology, Göteborg, Sweden

BioSAR 2010: Background

• ESA has funded multiple SAR campaigns in support of the P-band BIOMASS satellite candidate mission

• Tropical rain forest

• 2009: TropiSAR in French Guiana

• Boreal forest

• 2007: BioSAR-1 in Sweden (Remningstorp)

• Demonstrated high temporal coherence over 2 months

• Developed soil moisture corrections using multiple dates

• 2008: BioSAR-2 in Sweden (Krycklan)

• Developed topographic corrections using multiple headings

• BioSAR 2010 in Sweden (Remningstorp) ← this presentation

BioSAR 2010: Objectives

• Ability of detecting, mapping and updated retrieval of changes in forest parameters (due to forest growth or disturbances such as thinning or clear-cuts)

• Cross-calibration between the ONERA SETHI airborne SAR system (used in 2010) and DLR E-SAR (2007)

• Robustness of biomass retrieval algorithms with respect to changes in forest conditions

• Long-term coherence of P-band over forested and other natural surfaces

Test Site at Remningstorp Estate, Sweden

Stand-level biomass: 0-370 tons/haGround topography: 110–150 m asl

1200 hectars divided into over 300 stands

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

Test site location

Remningstorp: Tree species

Photos of Norway spruce, Scots pine and birch stands

BioSAR 2010: Data collections

• Airborne SAR data using ONERAs SETHI system

• P-band (260-460 MHz) and L-band (1250-1400 MHz), full polarimetry

• 10 data acquisition tracks in one flight mission • 2 tracks from 2007 repeated to study long-term coherence (challenge!)

• Vertical offset for PolInSAR (horizontal offset used in 2007)

• 3 headings to study topographic corrections (2 headings used in 2007)

• Helicopter lidar data using TopEye MKIII

• Small footprint (< 0.2 m) and high pulse density (> 10 pulses/m2)

• In situ data

• Field notes, soil moisture and weather data during the flight

• Extensive forest field measurements after the flight

• Maps of clearings and thinnings between 2007 and 2010

Two calibration trihedrals

P + L, full polarimetry

SETHI SAR system

SAR flights by ONERA on 23 September

Geocoded SAR images (3 headings)

R=HH, G=HV, B=VV Geometric error < 2m

Helicopter lidar data collection

Lidar data in 2007 covered only central part

Lidar data in 2010covered the full extent of the test site

Lidar DSM 0.5 raster cell size

Field Inventory (200-m grid) by SLU

• 10 m radius plots

• Species and diameter for all trees (>40 mm dbh), height and age for a subsample

• Site variables (field layer, soil type, peat/mineral soil, lateral water movement, production capacity, ground structure)

• Accurate determination of plot center using post-processed dGPS

• Total 271 plots surveyed, 214 of these in forest > 50 mm mean dbh

Field Inventory (individual trees) by SLU

• Ten 80 m x 80 m square plots defined and measured in 2007

• All trees with dbh > 50 mm marked with number tags

• Accurate determination of position using post-processed dGPS

• Seven plots remained in 2010 after three were clear-cutted

• Species, dbh updated 2010-11

• Additional plots are being measured during summer 2011

Initial SAR imagery comparisonHH = redHV = greenVV = blue

Images geocoded to UTM 33 N

SETHI has higher (2x) bandwidth

E-SAR 2007 SETHI 2010

Initial SAR imagery comparisonHH = redHV = greenVV = blue

Clear-cutting easily delineated (red circles)

Thinning and growth result in subtle changes

E-SAR 2007 SETHI 2010

First analysis of mapping changes

Color-coded change images 2007 vs 2010

Red: Lower value in 2010

Cyan: Higher value in 2010

Gray: Unchanged value

Lidar: Biomass SAR: PHV-pol PHH-pol PVV-pol

thinning

clear cut

Conclusions

• All planned P/L SAR data acquisitions were collected

• 10 successful passes; 6 processed and calibrated

• Ground data collected according to plan

• Lidar data processed and biomass maps produced

• Processing of forest field data partly done

• First results

• Data are generally of very high quality

• Change maps from P-band SAR images (SETHI 2010 vs E-SAR 2007) delineate clear-cuts but also other forest features – to be further investigated.