Monitoraggio Geodetico e Telerilevamento 3 Radar Imaging Carla Braitenberg Dip. Matematica e Geoscienze Universita’ di Trieste Tel Tel. Assistente Dr. Nagy:

Radar image compared to multispectral image for geological applications Radar image is single frequency Gives relief, roughness moisture Represents ground reflectivity at 1 to 100cm in the microwave range Penetrates clouds, fog and rain. Therefore continuous observation Active system- retrieves images also during night

Part of the Spectrum used for Radar Radarsat Geology Handbook

Properties of Radar image Black and white picture Consists of ratio of Microwave energy reflected from surface to transmitted energy Transmitted energy due to backscatter of illuminated surface Backscatter depends on local topography and cm- scale roughness, dielectric properties, moisture Low backscatter: dark image Usage: geology, agriculture, landcover mapping, land movement, Landslides, coseismic movement, land subsidence

Radar pulse emission and record

Characteristics of radar data Radar sensor measures time delay between transmission and reception of radar pulse Time delay is inherent to sideway look Later arrival from more distant locations. Therefore reflectance in time is mapped to different locations To be considered: topography can distort images: high topography is displaced towards look direction

Image Radiometry Images are monochromatic Relative brightness of pixel related to radar reflectivity of ground target it portrays Low reflectivity is dark, high reflectivity is bright A shadow zone will be dark

Backscatter energy depends on terrain

Sensor facing slope is brigher than the slope to the back of it. Results in enhancement of structures

Look direction effects on lineaments Aligned lineaments have reduced backscatter Linear geologic features oriented normal or oblique to look direction are enhanced by highlights and shadows If lineaments are in suppression zone, choose image from opposite orbital direction (e.g. Descending in this case). In general acsending and descending passes allows complete detection of lineaments.

Tectonic signatures Strike and dip: River drainage networks and erosion patterns are signs of faulting Scarp slopes: Scarp slopes perpendicular to bedding are characterized by parallel topographic lineaments. These are due to rocks of different resistivities. Appear as light and dark bands

Sentinel1 Radar image over Vittorio Venento Pedemountain area.

Sentinel1 Radar image on map Vittorio Venento Pedemountain area.

Lithologic interpretation To be distinguihsed: exposed bedrock, layers of vegetation, overburden Dominant parameter fo rock: surface texture Different rock types are distinguishable due to contrasting backscatter

Volcanic environments Volcanic environments have topography which is highlighted by side-look configuration Surface texture controls appearance of strata Affected by age and texture of lava flows, soil moisture, absence or presence of snow

Tectonic applications of radar Lineaments, joints, shear zones, changes in relief Quaternary mapping Minerals and Hydrocarbon exploration Geologic hazard estimation Lineaments should be non-parallel to look direction Origin: anthropogenic, geomorphological, structural

Forested and Tropical Environments Overburden is present on most terrains. In many cases radar signal does not penetrate the overburden (soil, vegetation) Lithological information can be obtained from erosional patterns and structures In tropical regions the radar image maps the treetops surface The local and regional geomorphology is reflected in the tree top surface Geologist extracts: small scale geologic structures, erosional patterns, topographic features

Basic Principles on Radar imaging usage for geologic mapping 1 Geologic structure mapping: characteristic forms of geologic structures if located near surface, may be manifested in topography. Radar side-looking configuration highlights relief Shallow incidence angles are ideal through shadowing. In high relief intermediate angles may be more suitable Look direction should be considered in relation to orientation of geological structures

Basic Principles on Radar imaging usage for geologic mapping 2 Lineament identification: Lineaments, as folds and faults may be manifested as topographic relief. Shallow ncidence angle ideal for subtle relief Look direction perpendicular to direction of lineaments enhances detectability. Acquisition of ascending and descending passes maximizes lineaments to be identified

Basic Principles on Radar imaging usage for geologic mapping 3 Seismic zone identification: seismic zones have presence of faults which may be manifested topographically Side looking configuration highlights this topography Ascending and descending passes maximize identification of lineaments

Basic Principles on Radar imaging usage for geologic mapping 4 Surficial bedrock geological mapping: depending on physical weathering, surficial bedrock may have fractures and fragment sizes These depend on rock fabric, texture, mineral composition This results in a unique backscatter to the rock type Main parameter to characterize bedrock unit is surface roughness. Shallow incidence angles maximize contrast in backscatter due to variance of roughness Better acquire data when moisture level is low, so backscatter is correlated to roughness and not moisture content

Basic Principles on Radar imaging usage for geologic mapping 5 Sedimentology mapping: Unconsolidated sediments as those deposited by glaciers or fluvial systems are often manifested by topographic relief. Sediments have different grain sizes with different moisture holding capabilities Radar is sensitive to moisture and roughness-> contrasting backscatter between different sediments Consolidated sediments have unique erosional patterns, as karsting in carbonates

Basic Principles on Radar imaging usage for geologic mapping 5 cont. Incidence angle: for topographic relief and classification through surface roughness, shallow angles are preferred For moisture differences steep angles are better, as they maximize contrast in surface roughness Time: data should be acquired when vegetation is at minimum to not have vegetation dominate backscatter

Basic Principles on Radar imaging usage for geologic mapping 6 Landslides: landscape is changed through transportation of vegetation and soil. Affected areas have different soil roughness and may have changes in vegetation Backscatter variations may be present between affected and unaffected areas.

Basic Principles on Radar imaging usage for geologic mapping 7 Coastal erosion: smooth water is specular reflector-> low backscatter. Land: diffuse backscatter. Change in backscatter over time allows assessment of coastal erosion Shallow incidence angle creates greatest contrast between water and land.