Change detection at the recently erupted Te Maari crater, Tongariro, from stereo aerial photographs Strong, D.T., Jones, K.E., Ashraf, S. and Lee, J.
Outline Geographic context Setting and eruption Science and hazard questions Methods Imagery and software Block triangulation Orthorectification Digital Stereo Models Change detection Results Block triangulation Orthorectification DSM creation Change detection Comparison of DTMs Summary Geological mapping from stereo photos RS capability at GNS Science
Tongariro National Park Auckland New Zealand s oldest national park Three volcanoes: Tongariro Ngauruhoe Ruapheu Wellington Christchurch Dunedin
Tongariro National Park Topography Geology
Te Maari crater, Mount Tongariro Eruptions at Te Maari in Aug and Nov 2012 A new fissure was produced Continuous emissions of steam and volcanic gas expected to continue for years Map showing Te Maari eruption phenomena ()
Te Maari crater, Mount Tongariro Significant hazard to life Tongariro Alpine Crossing, other recreation activities Further eruptions are possible Potential hazards lava & debris flows, ash & debris falls from violent eruptions Map showing Te Maari eruption phenomena ()
Background, low-level steam emission All photographs: / EQC
The eruption recorded in a nearby seismograph drum
Eruption time lapse video Geonet
Steam from the new fissure and Te Maari crater ~400 year old lava flow All photographs: / EQC
Damage to Ketetahi Hut, Tongariro Crossing
Science & hazard What questions are the geologists asking? What is the volume of the debris erupted? Where is the new fissure located? How long & wide is the new fissure? Remote sensing provides access to high hazard areas Te Maari crater area is still largely inaccessible to volcanologists
Can we detect geomorphic change at the crater? What features can we see with the eye? Lava flow, crater rim, fluvial channel Part of the Tongariro Crossing track 2010 aerial photograph mosaic 2012 aerial photograph mosaic
Can we detect changes in elevation at the crater? What features can we see with the eye? Lava flow, crater rim, fluvial channel New fissure, new debris flow Can we quantify these? Before and after aerial photographs Build digital surface models (DSMs) Extract changes in elevation Map changes in geomorphological features
Images and software Digital aerial photographs from NZ Aerial Mapping 2010 (pre-eruption) 2012 (post-eruption) same solar incidence November some cloud cover, steam from vents in 2012 Leica Photogrammetry Suite (LPS) ERDAS Imagine 2013 ArcGIS 10.0
2010 digital aerial photo orthomosaic
2012 digital aerial photo orthomosaic
Methods 1) Block triangulation (LPS) 2) Image orthorectification (LPS) orthomosaics for 2010 and 2012 (ERDAS 2013) 3) Digital Surface Models (DSMs) (LPS) 4) Extract elevation changes between DSMs (ArcGIS)
Block triangulation Digital aerial photos Camera calibration reports from NZAM Block area ~ 20 km 2 2010 2012 Image acquisition date 17/11/2010 27/11/2012 Sensor UltraCamXp UltraCamX Image size (megapixel/image) 195.7 135.9 Ground pixel size (m) 0.40 0.50 Av. flying altitude (m) 7238 7408
Block triangulation Automatic tie point generator Collected GCPs on-screen horizontal reference = existing orthomosaic of aerial photos vertical reference = 8 m DEM (Geographx) 2010 2012 No. of images 4 4 No. of tie points 44 66 No. of ground control points 11 11 Triangulation RMSE (pixels) 0.3402 0.2944 Control point RMSE X,Y,Z (m) 2.15, 2.98, 2.63 1.72, 2.56, 2.21
Generating DSMs eate (enhanced Automatic Terrain Extraction) AOI to mask the crater lake Seed source = mass points from block file default seed source (globaldem) up to 20 m error Our parameters: cell size 0.5 m correlation window 5, search window 25 moderate smoothing low contrast setting (best for mountainous terrain)
Results: orthomosaics & DSMs 2010 orthomosaic & DSM
Results: orthomosaics & DSMs 2012 orthomosaic & DSM
Results: change detection red = erosion/subsidence; green = deposition; yellow = no change in surface elevation > 4 m of vertical change (erosion or deposition) Deposition Erosion
Change in elevation along four profiles
Change detection: Profile A A B B Deposition in and along channel up to 26 m A C Deposition Erosion C D D
Change detection: Profile B A B B Deposition in and along channel up to 23 m A C Deposition Erosion C D D
Change detection: Profile C A B B Accumulation across debris flow path Erosion of surface Deposition Erosion A C C D D
Change detection: Profile D A B B Up to 46 m of erosion A C Deposition Erosion C D D
Old vs new DTMs for geological mapping Let s look at the crater rim
Old vs new DTMs for geological mapping New 0.5 m 2010 DTM Old 8 m DTM
Old vs new DTMs for geological mapping Exposed lava sheets around crater rim New 0.5 m 2010 DTM Old 8 m DTM
Summary of Te Maari crater work Comparison of DSMs shows clearly defined changes in surface elevation Maximum debris accumulation ~26 m thick Maximum erosion ~46 m 2012 eruptions drove geomorphic change a new fissure opened up erosion of existing surface & deposition of debris Methods and materials used here are suited to high resolution geomorphic mapping
Big picture: DTM of Tongariro National Park Geological Map of Tongariro National Park (Townsend, Leonard and others, in prep) 3D (stereo) feature collection will be used to map some components of the geology & geomorphology >300 aerial photographs 2010 and 2012 ~50 km 2 area Highly diverse, mountainous terrain maximum elevation approximately 2,800 m ASL slopes reach >70 degrees, crater walls are nearvertical
1:50,000 map Digitised at various scales as high as 1:2,500
Applying our remote sensing capability Salman Ashraf Hazard response earthquakes, landslides, volcanic eruptions, flooding, coastal erosion, tsunami Geological mapping DTM and orthomosaic generation 3D (stereo) feature collection 3D geology modelling (Leapfrog Geothermal) Resource mapping Groundwater InSAR (Ian Hamling) Julie Lee Katie Jones Delia Strong Ian Hamling