Mapping of above-ground forest biomass with satellite synthetic-aperture radar (SAR)

Transcription

1 Mapping of above-ground forest biomass with satellite synthetic-aperture radar (SAR) Lars Ulander Swedish Defence Research Agency (FOI) & Chalmers University of Technology

2 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 Launch currently planned for

3 Biomass will map global forest biomass and height Forest biomass Forest height Disturbances

4 The role of biomass in the global carbon cycle Biomass will improve understanding and reduce uncertainties of the carbon fluxes due to land-use change and the land sink Global Carbon Project, 2012

5 How can biomass be measured from space? 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

6 Space Object Tracking Radar P-band constraints pests regrowth fire & climate warming reforestation Reducing Emissions from Deforestation & Degradation (REDD) drought Land use change Land use change Land use change Global Forest Observations Initiative Large biomass uncertainty

7 P-band SAR can deliver 3 types of information for biomass PolSAR (SAR Polarimetry) PolInSAR (Polarimetric SAR Interferometry) TomoSAR (SAR Tomography) z x z x z x o o o y y y

8 Baseline biomass estimate from PolSAR & PolinSAR PolSAR Covariance Matrix PolInSAR Covariance Matrix Ionosphere Correction Biomass Estimation from Intensity TomoSAR results DEM In situ data Forest Height Estimation Allometric Biomass Estimation Biomass Estimate 1 Biomass Estimate 2 Minimum Mean Square (MMSE) Estimate Biomass Map & Error Map

9 Campaigns to develop retrieval methods and assess performance Alaska Maine Krycklan Remningstorp Landes La Selva, Costa Rica Colombia Paracou F.Guiana 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), (TropiScat) ESA campaigns non-esa campaigns

10 Soil moisture and topography affect radar-biomass relationship Remningstorp forest (Sweden) March April May Backscatter March 2007 April 2007 May 2007 Because the disturbing effects differ among polarisations, all polarisations and a DEM are used to account for environmental and topographic effects.

11 Polarisation & ground slope radically improves accuracy Remningstorp 70 MHz data: varying environmental conditions over 3 months HV only HV, HH & VV HV, HH, VV & DEM RMSE: 84% RMSE: 38% RMSE: 24% Blue - from airborne lidar map, std. error = 25 ton/ha Black - from 80 m x 80 m in situ plots, std. error = few % N N Finland Training on stratified subset of Krycklan data. Performance assessed on data from Remningstorp. N N Norway Sweden Remningstorp Denmark

12 Biomass changes can be measured with improved accuracy Change in biomass from spring 2007 to autumn 2010 at Remningstorp, Sweden Change in biomass [ton/ha] Radar RMSE ~ 20 t/ha (based on 6 reference plots). Lidar RMSE is comparable (slightly worse). A 20 ton/ha change can be measured over a 4-year period.

13 Boreal height mapping using P-band PolInSAR Remningstorp, Sweden Height maps r 2 =0.65 RMSE=4m PolInSAR Lidar Height (m)

14 What about SAR tomography? It provides basic information to improve biomass retrieval algorithms HH SAR image Tomographic transects (6 MHz bandwidth P-band data) Height (m) Height (m) HV HH Forest Marshland River 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. Paracou, French Guiana Normalised backscatter intensity

15 Biomass product requirements Forest biomass Forest height Disturbances Above-ground biomass (tons / 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 Upper canopy height (meter) 200 m resolution 1 map every 6 months for 4 years global coverage of forested areas accuracy of 20-30% Areas of forest clearing (hectare) 50 m resolution 1 map every 6 months for 4 years global coverage of forested areas 90% classification accuracy

16 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 7 th Earth Explorer Final decision will be taken by PBEO in May 2013 Launch currently planned for