The hands-on will be based on a pre-produced QGIS project. Data layers are described in Venus data info
- Illustrate the particularities of Magellan SAR data and the basics of its interpretation.
- View examples of the different primary and secondary structures of Venus.
- Recognize the principal types of terrains and volcanic structures of Venus.
- Learn how to work with the VIRTIS data and how to interpret them in the 1 μm spectral region.
- View examples of mapping of high- and low-emissivity areas on Venus.
- Learn how to link high- and low- emissivity anomalies to main mineralogical surface composition based on the comparison with laboratory emissivity data.
- Magellan SAR data. USGS Global mosaics.
- VIRTIS retrieved emissivity map at 1.02 μm.
- General description of the Magellan data sets.
- Access to Magellan data through the USGS Map a planet server.
- General view of the global SAR Venus Mosaic and the geology of the planet.
- Case study: Example of tessera terrain (Alpha Regio)
- Case study: Example of regional volcanic plains (Helen Planitia).
- Case study: Example of young volcanic highland (Imdr Regio).
- General description of the VIRTIS spectrometer and data sets.
- General view of the global VIRTIS coverage, radiance and emissivity maps.
- General simplified description of VIRTIS emissivity retrieval in the 1.02 μm spectral window
- General guide on the interpretation of VIRTIS emissivity data at 1.02 μm
- Comparison of VIRTIS emissivity with laboratory emissivity data
- Case study: Example of emissivity anomalies in young volcanic highland in Imdr Regio
- Case study: Example of emissivity anomalies corresponding to tessera terrain in Alpha Regio
- Participants will be able to identify the principal types of primary and secondary structures on Venus and the problems that we face to delineate contacts due to the nature of SAR data.
- Participants will recognize the principal types of terrains and volcanic structures present in the surface of Venus and the structures that characterize them.
- Participants will be able to identify and map areas of high and low emissivity anomalies using VIRTIS data in the 1.02 μm spectral window.
- Participants will be able to link the high and low-emissivity areas with the main geologic units and structures mapped in the first Venus hands-on practical activity (geologic mapping exercise with Ivan).
- Participants will be able to relate thermal emission variations from the Venus' surface to mineralogy.
- Simplified geologic and mineralogic mapping of the selected area and a geologic history of the study area.
- Area selected for the exercise: Transition between Themis Regio and Helen Planitia (Magellan SAR data and VIRTIS emissivity data in the 1.02 μm spectral window).
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A general view on the mapping area: Hands-on activity with the instructors to get familiarized with the study area (30 minutes aprox).
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Identification and mapping of the principal regional and local structural suites of the mapping area (manually using Mappy tool).
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Identification and mapping of primary structures (volcanic and impact related) of the mapping area (manually using Mappy tool).
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Scaling of VIRTIS emissivity value to infer the relative variation when assuming a reference emissivity.
- We want to scale the emissivity values adopting a global average emissivity of Venus plains of 0.58. This satisfies the constraint that the regions with the highest radiance measured on Venus have emissivity ≤ 1 (as used in previous studies as Smrekar et al., 2010; Basilevsky et al., 2012; Gilmore et al., 2015). This scales the emissivity of the area under investigation to a range of 0.5-0.7.
- To scale the VIRTIS emissivity data, use the Raster calculator tool and select the VIRTIS emissivity data@1 (which corresponds to the emissivity values extracted at the 1.02 µm spectral band) and proceed as shown in the screenshot below. The result will be a new generated raster with the scaled values of emissivity.
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Mapping of the principal areas showing high emissivity anomalies (manually using Mappy tool) using the raster generated in step 2.
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Mapping of the principal areas showing low emissivity anomalies (manually using Mappy tool) using the raster generated in step 2.
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Linking the high- and low-emissivity areas to the main geologic structures mapped in the previous hands-on (with Ivan)
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Relate the high- and low-emissivity to main mineralogical units.
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Automated mapping of high emissivity areas (using the Raster calculator tool)
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Using the Raster calculator tool as shown in step 2, it is possible to generate a new raster that automatically includes only the pixels with emissivity higher than the average value.
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Automated mapping of low emissivity areas (using the Raster calculator tool)
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Using the Raster calculator tool as shown in step 2, it is possible to generate a new raster that automatically includes only the pixels with emissivity lower than the average value.
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Comparison between results obtained with manual vs automated mapping.
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Compare how the areas mapped in the two new rasters automatically generated in step 7 and 8 match with the manually mapped areas with the Mappy tool in step 3 and 4.
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Identification and mapping of contacts between different units of the mapping area
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Establishment of a simplified sequence of events (geologic history) in the mapping area.
- Simplified geologic and mineralogic map of the study area.
- Identification of regional wrinkle ridges, local fractures suites and 3 types of volcanic structures.
- Identification of at least four units: basement materials, regional plains, recent volcanic flows and crater ejecta.
- Identification of low and high emissivity areas and link with main mineralogical units
TO BE CLARIFIED DURING THE SCHOOL
Relevant references are included below.
Basilevsky, A.T. et al., 2012. Geologic interpretation of the near-infrared images of the surface taken by the Venus Monitoring Camera, Venus Express. Icarus 217, 434--450.
Ford, J. P., Plaut. J. J., Weitz, C. M., Farr, T. G., Senske, D. A., Stofan, E. R., Michaels, G., Parker, T. J. (1993) Guide to Magellan Image Interpretation, Jet Propulsion Laboratory, California Institute of Technology, JPL Publication 93-24, - available online at https://ntrs.nasa.gov/api/citations/19940013181/downloads/19940013181.pdf
Hansen, V.L. (2000). Geologic mapping of tectonic planets. Earth and Planetary Earth Sciences. Volume 176, Issues 3--4, 30 March 2000, Pages 527-542.
Gilmore et al., (2015) VIRTIS emissivity of Alpha Regio, Venus, with implications for tessera composition. Icarus 254 (2015) 350--361.
López., I. and Hansen, V.L., 2008, Geologic map of the Helen Planitia quadrangle (V--52), Venus: U.S. Geological Survey Scientific Investigations Map 3026, 1:5,000,000 scale. (Available at https://pubs.usgs.gov/sim/3026/)
Smrekar, et al. (2010) Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science, 328, 605-608.
Stofan, E.R., Smrekar, S.E., Mueller, N. and Helbert, J. 2016. Themis Regio, Venus: Evidence for recent (?) volcanism from VIRTIS data. Icarus. 271, 375-386.
Stofan, E.R., and Brian, A.W., 2012, Geologic map of the Themis Regio quadrangle (V--53), Venus: U.S. Geological Survey Scientific Investigations Map 3165, 1:5,000,000 scale. (Available at https://pubs.usgs.gov/sim/3165/.)
Tanaka, K. L., Moore, H.J., Schaber, G. G., Chapman, M.G., Stofan, E. R., Campbell, D. B., Davis, P. A., et al. (1994) The Venus geologic mappers' handbook (2d edition). US Department of the Interior, US Geological Survey, Open-File Report 94-438 - available online at: https://pubs.usgs.gov/of/1994/0438/report.pdf
Tanaka, K. L., Anderson, R., Dohm, J. M., Hansen, V., Pappalardo, R., Watters, Thomas R., and Schultz, R. A. 2010. "Planetary Structural Mapping." in Planetary Tectonics, edited by Watters, Thomas R. and Schultz, R. A., 351--396. Oxford, UK: Cambridge University Press.