Mapping Scotland with PALSAR: An Assessment of the Importance of L-Band Polarimetry

Transcription

1 Mapping Scotland with PALSAR: An Assessment of the Importance of L-Band Polarimetry Shane R. Cloude, AEL Consultants,Scotland, UK aelc@mac.com Web : Iain H Woodhouse (2), Karin Viergever (2) School of Geosciences (Geography), University of Edinburgh, EH8 9XP,SCOTLAND, UK Juan C.Suárez (3), Forest Research, Roslin, EH25 9SY, SCOTLAND, UK 1

2 Outline Quad vs Dual pol modes: Do we need quadpol for forestry? PLR vs. FBD modes : New test statistic* ALOS-PALSAR Case Study: - Mapping Scotland with PALSAR: - Scotland Data Acquisitions 3 main application areas - Urban Polarimetry - Surface Roughness Mapping - Forestry - Biomass from Polarimetry - Forest Height Estimation from POLInSAR Conclusions Dual versus Quadpol: A New Test Statistic for Radar Polarimetry, S. R. Cloude, submitted to ESA POLInSAR

3 Mapping Scotland with PALSAR: Coverage of PLR21.5 Mode 28/10/08 3

4 Objective : Determine if Quadpol adds any new information beyond Dualpol for forestry applications Methodology employed: 1) Entropy/Alpha approach (1) 2) Leads to simple decision for quad vs. dualpol information HSV Colour Coding Scheme for Polarimetry 3) Is pixel P significantly away from boundary? 4) Expressed as a probability 0 = no, 1 = yes P 4

5 ALOS-PALSAR PLR data: Fife, Scotland 5

6 Scotland Full Country Quadpol Data Set 48 (96) scenes, level 1.1. JAXA SLC product form PLR21.5 mode PLR mode coverage = 2 consecutive cycles (46 days) biannually, March-May, starting 2007 Data sets collected between 18/04/07 and 29/05/07 JAXA 1.1 product is slant range/azimuth (no geocoding) Resolution (single look) 11m x 5m (range x azimuth) then multi-look processed to 100m x 100m (100 looks) Swath size 12km x 70km Angle of Incidence degrees across swath Approximate single look ground range resolution/swath : 30m/30km Narrow swath leaves gaps between passes for regions < N60 o 6

7 Full Scotland Data Set (results imported into Google Earth) 1) Basic Coverage map (lat/long of scene edges) 2) Entropy/Alpha HSV image of whole country 3) Quad/Dual Hypothesis test Shown as probability that hypothesis is true (0.8 = black 1 = white) 4) Example derived products from radar polarimetry a) Urban Polarimetry: Dielectric Constant of Buildings b) Surface Roughness from X-Bragg model c) Forestry : 1) Maximum Ratio of surface-to-volume scattering µ 2) Forest biomass using water cloud model (WCM) inversion of 1) 3) Forest Height Estimation from POLInSAR 7

8 Coverage Map of Scotland 8

9 Η/α image of Scotland 9

10 Symmetry Statistic for Scotland 10

11 Application 1: Urban Polarimetry Dundee Edinburgh Colour is an indicator of the dielectric constant of building material Glasgow Aberdeen 11

12 Application 2 : Surface Roughness Estimation Agricultural Area Open Moorland 12

13 Application 3 : Forestry Products 1) Above-Ground-Biomass estimation (when quadpol hypothesis is null) Only 2 parameters a backscatter RCS and a ratio or a) using HV backscatter with regression parameters from test sites b) Using ratios to invert the water cloud model e.g. µ is related to biomass by relations like R = σ surf o ( θ) B = 0.6 β log(1+ R µ ) Need 2 parameters β σ o veg 2) Tree height estimation from POLInSAR..have full repeat pass grid over Scotland 46 day repeat 13

14 Surface-to-volume ratio vs. biomass Assumes biomass always increases when µ decreases not always true need quadpol data to mask regions where this model applies.. 14

15 µ-max Map of Scotland (db) 15

16 Biomass Map of Scotland (t/ha) 16

17 Support Data I: Digital Woodland Map to produce a digital map showing the location and extent of woodland >0.5 ha across GB. to provide the total woodland area, plus data on forest types, tree species, age class, etc. to assist in providing Private Sector timber production forecasts to assist with decisions on land use planning and expansion of woodlands to assist in the monitoring the sustainability of Britain s woodlands 17

18 Support Data II : Hi-Res Lidar Data Estimations of Individual Tree Height ALS survey 2007 Parameter Sensor Laser frequency Flying altitude pulse Beam divergence Scanning angle Sampling intensity Position accuracy Elevation accuracy Performance Optech ALTM ,000 Hz 1000 m 10 cm 10 degrees returns per m 2 X,Y < 40 cm Z < 9-15 cm 18

19 POLInSAR Height Retrieval using ALOS Glen Affric Baseline ALOS-PALSAR PLR21.5 mode : Baseline vs. K z 19

20 POLInSARTest Site : Glen Affric Estimation of µ max from PLR21.5 data γ γ v + µ max 1+ µ max µ = -2dB 20

21 Expected POLInSAR Coherence and Phase Performance 21

22 Interferometric Coherence: Forested Areas Dominated by temporal decorrelation from 46 day repeat 22

23 Conclusions and Discussion FBD vs PLR Mode Assessment Have derived a new test for Quad vs. Dual polarimetry: The test can be applied to arbitrary sensors, but for ALOS-PALSAR we found the following main points: Forest cover in Scotland at ALOS resolutions fails the quadpol hypothesis test FBD mode is sufficient for forested areas (2 parameter description) However many non-forest regions pass the test and so quad-pol is useful for non-forest applications (surfaces and urban areas) Also, some forest types (savannna in particular) do pass the quadpol test and here there are > 2 parameters to describe forest scattering Polarimetry for POLInSAR assessment Established a methodology for using quadpol data to assess POLInSAR Confirms good potential for L band single pass height retrieval.. But temporal decorrelation dominates 46 day repeat ALOS-PALSAR. 23

24 Savanna : Injune QA, Australia..an example where PLR provides more information than FBD for forestry HSV Image Quapol test statistic 24