lava emplacement mapping with sar and optical satellite data · 2017-07-06 · • fogo continued...

Lava emplacement mapping with SAR and Optical satellite data

MultiTemp 2017 27 - 29 June 2017 Bruges - Belgium

• Beside using a small stack of TOPSAR images, we collected a series of optical images from Landsat8 and EO-1 missions

• “Innovative” methodology: multi-scale tiling of the change image to identify bimodal regions [previously applied for flood mapping purposes]

• The objective: mapping the temporal evolution of the lava field

Introduction • On April 3, 2014, the new Sentinel-1 mission was successfully launched and

it started its operational life. The onboard SAR instruments is capable to acquire images of the Earth surface with e new mode: the Terrain Observation with Progressive Scan (TOPS) SAR

• The first monitored natural events were the Mw 6.0 Napa (California, USA) earthquake and the Pico do Fogo (Cape Verde) volcano eruption: is the object of our study

From INSARP PROJECT website


The Pico do Fogo eruption • On 23rd of November, after almost 20 years from the

previous eruption, the volcano began its activity • The volcano discharged a big amount of lava in the

caldera • The village of Chã das Calderias was evacuated, saving

the population (about 1000 inhabitants) but the houses and the unique connection road were damaged by the lava flow

• Fogo continued erupting until February 8 2015, when the Observatório Vulcanológico de Cabo Verde stated the end of the eruption (Global Volcanism Program of Smithsonian Institution - volcano.si.edu)


The dataset • SAR: 9 Sentinel-1A images in TOPSAR mode, 5 ascending and 4 descending orbits • Multi-spectral data: Earth Observation 1 (EO1): 3 images from ALI - Advanced Land Imager -

sensor Landsat8: 3 scenes from OLI- Operational Land Imager & TIRS- Thermal

Infrared sensor


Approach for optical data • False colour representation + visual interpretation + change detection • Landsat8: Red= 2.2µm Green= 1.61µm Blue=0.65µm • ALI: Red= 2.2µm Green= 1.65µm Blue=0.66µm • this band combination (similar to natural colours) visually enhance some features:

Non-vegetated lava flows appear black and brown

Vegetated areas appear green Active lava flows appear red and yellow Plumes coloured in blue are related to

gases (SO2)


2014/11/24 2014/10/23 2014/12/16

2014/12/18 2014/12/24 2015/01/11


Optical Change Detection 1) pan-sharp of SWIR channel (2.2 µm) of

Landsat8 → from 30m to 15m resolution 2) change detection between October 23,

2014 and January 11, 2015

Different grey tones refer to different type of lava

Darker/Younger/Warmer in January

Lighter/Older/Colder in January


Lava Coverage from Optical


SAR: The Multi-scale Method • Lava extent extraction is performed by using an automatic algorithm • It is based on the statistics on areas selected by hierarchical tiling:

L0 L1 L2 L3


The Multi-scale Method • Fitting on the whole bimodal distribution • Iterative region growing (RG) algorithm to identify changes

• seeds are the pdf mode value of class of changes • at each iteration new threshold is tested for stopping RG • final threshold is the one that minises rmse between RG histograms

and pdf of change class

• Main advantage: the statistical-based change detection approach is independent from the different technical characteristics of the image scene such as spatial resolution or percentage of the changes extension

M. Chini, R. Hostache, L. Giustarini, P. Matgen, A Hierarchical Split-Based Approach (HSBA) for parametric thresholding of SAR images: flood inundation as a test case, IEEE Transactions on Geoscience and Remote Sensing (Under review).


Change Detection

Acquisition date Orbit

2014/11/03 Ascending





Acquisition date Orbit

2014/11/08 Descending 2014/12/02 Descending 2014/12/14 Descending 2014/12/26 Descending

Single master selection

• 4 change detection maps from ASC set • 2 change detection maps from DESC set


2014/11/27

2014/12/09

2014/12/14

2014/12/21

2014/12/26

2015/01/02

Lava Coverage from SAR


Areal Coverage Temporal Trend

On average the “effusion rate” is about: 0.08 km2/day from SAR 0.09 km2/day from Opt

SAR and optical data seem agree: very similar trend, although a bias between the two dataset is highlighted in the plot (about 2 km2 )


Bias & Roughness • SAR and Optical change detections and related polygons highlight

an area located approximately in the center the maps • Here deposited lava is not detected by SAR.


About roughness

Google Earth pictures reveal the similarity (and complexity) of the roughness in the mis-detected region.


Conclusions • Multi-sensor analysis of Fogo lava field emplacement during 2014

eruption • “Innovative” method, based on multi-scale tiling of SAR data • Estimated effusion rate of about 0.08-0.09 km2/day • Roughness before and after the eruption is a critical issue -> different

SAR bands? Future work • Better tuning of the algorithm for lava applications • Try to exploit X-band hi-res SAR


I‘m submerged by lava!

lava emplacement mapping with sar and optical satellite data · 2017-07-06 · • fogo continued...

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