Using SAR Intensity and Coherence to Detect A Moorland Wildfire Scar

Gail Millin-Chalabi, Julia McMorrow & Clive AgnewSchool of Environment & Development

Presentation Structure• Fire

– Fires & Moorlands– UK Wildfires (news clip)– Fire Scar Detection

• Research question & objectives (pilot study)• Methodology

– Why SAR?– Study Site– SAR pre-processing chain

• Results– Intensity– Coherence

• Conclusion & Future Work

Why Fire is Important in Moorlands?

Destroy vegetation

Fuel load, adaptation

Climate Wildlife

Vegetation

Soil

Humans

CO2 emissions Remove habitatAdaptation

Managed burns Arson

Degradation

ErosionRate of re vegetation

UK Wildfires

Source: BBC News, 4 May 2011http://www.bbc.co.uk/news/uk-13277476

UK Fire Scar Detection

Source: http://effis.jrc.ec.europa.eu/

Research Question (Pilot Study)

How well can the C-band SAR intensity and coherence signal detect a fire scar within a degraded UK moorland

environment?

Objectives• Determine the ability of SAR intensity and InSAR

coherence to detect the fire scar over time in a moorland environment

• Analyse qualitatively how scene variables such as precipitation and CORINE land cover classes affect the SAR intensity and coherence signal, both inside and outside the fire scar

Why SAR?

• See through cloud and smoke

• Active sensor: acquire images day and night

• Good temporal resolution of data

• SAR very sensitive to moisture content ideal for mapping fire scars

Source: Landmap Radar Imaging Coursehttp://landmap.mimas.ac.uk

SAR Interaction

Source: Landmap Radar Imaging Coursehttp://landmap.mimas.ac.uk

Study AreaLongdendale

· Nearest Neighbour resampling method· One image used as the input reference file, the other image is coregistered to this.

ENVI Band Math using the formula 10*alog10(b1)

Degraded to 100m using a Nearest Neighbour resampling method in ENVI.

5 backscatter sample points for each land cover class was extracted from the radar data.

· Equivalent looks variable set to -1 threshold for speckle filtering is calc by the software – 0.5227/sqrt

· Multitemporal DeGrandi Filter used· 25m DEM· No GCP (however a sub-pixel accuracy can still be achieved when DORIS data has been used)· Generated Sigma Nought values

· Calculate Ground Range GR (m) = Rg ÷ sin IA· Calculate number of Azimuth Looks = GR ÷ Az

1. Basic Import for ASAR or ERS-2

Single Look Complex (slc)

Intensity Image (pwr)3.A Amplitude Coregistration

Resampled & resized images (rsp)

Filtered image(fil)

5. Geocoding Radiometric Calibration

Geocoded 25m images (geo)

Level 1 SLC from ESA

4. Multi-temporal Despeckling

2. Focusing and Multilooking

6. Geocoded images to dB

100m GreyscaleGeocoded SAR image

Process Outputs/Inputs

Processes

Final Product

Key

3. Amplitude Coregistration

Intensity & Precipitation time series

Pre-fire

Post-fire

Intensity & Land Cover Results

InSAR Pairs – Coherence Analysis

ERS-2 InSAR Pairs Orbit/ Track Baseline (m) DescriptionPair 108/02/2003 / 15/03/2003

40801 & 41302366

134 Pre-fire

Pair 215/03/2003 / 19/04/2003

41302 & 41803349

349 Pre & immediately post-fire

Pair 319/04/2003 / 24/05/2003

41803 & 42304366

147 Post-fire

Pair 424/05/2003 / 28/06/2003

42304 & 42805366

654 Post-fire

Coherence Results

Summary & Conclusion

• Precipitation & land cover are key variables for understanding the SAR intensity and coherence– Within the fire scar peat bog gave highest intensity return– Rainfall just prior to image acquisition increased intensity values

for all land cover classes inside the fire scar

• Image results are sensitive to:– Filtering algorithm applied > recommend Degrandi multitemporal– Initial baseline of InSAR pairs > temporal decorrelation

• A large fire scar in a degraded moorland environment can be detected using SAR intensity. InSAR coherence needs to be further explored.

Future Work

• Investigate fire scars of different sizes, severity, land cover & precipitation conditions

• Analyse the affect of radar polarisation and frequency on fire scar detection– X band & L band data– Cross polarised and co-polarised data

• Applying classification method for fire scar mapping• Explore Kinder 2008 & Wainstalls 2011 case studies

– GPS boundary collected this summer– Kinder boundary obtained from MFF

Acknowledgements

Access to fire log and fire scar GPS dataPDNP Fire Operations Group

Access to ERS-2, ALOS PALSAR & ASAR data as part ofCategory 1 Project 2999

School of Environment & Development for funding to support this researchMimas & Landmap for funding, time & resources to support this research

ReferencesKEELEY, J. (2009) Fire intensity, fire severity and burn severity: a brief review and suggestedusage. International Journal of Wildland Fire, 18, 116-126. LENTILE, L. B et al., (2006) Remote sensing techniques to assess active fire characteristics andpost-fire effects. International Journal of Wildland Fire, 15, 319-345.

Martin Evans & Juan Yang at SED for Upper North Grain weather data

Thank you for Listening

Images for Intensity Analysis

SAR Data/Mode/Swath

Acquisition Date/Time

dd/mm/yyyy

Time relative to

fire (JD Julian

day)

Incidence Angle

(IA)

Az pixel spacing

(m)

Rg pixel spacing

(m)

GroundRange

(GR) (m)

Pass Type

ERS-2 08/02/2003 11:01

-69 days (39 JD)

23.23º 3.97 7.90 20.26 Desc-ending

ERS-2 15/03/2003 11:01

-34 days(74 JD)

23.23º 3.97 7.90 20.26 Desc-ending

ASAR IM I2

22/03/2003 21:37

-27 days(81 JD)

22.82º 4.04 7.80 20.00 Asc-ending

ASAR AP I2 HHVV

03/04/2003 10:36

-15 days(93 JD)

22.76º 4.04 7.80 20.00 Desc-ending

ERS-2 24/05/2003 11:01

+36 days(144 JD)

23.21º 3.97 7.90 20.26 Desc-ending

ERS-2 28/06/2003 11:01

+71 days(179 JD)

23.28º 3.97 7.90 19.75 Desc-ending