Rivers and lakes in Western Arabia Terra: The Fluvial catchment of the ExoMars 2022 rover landing site
This file contains the supplementary data to accompany ‘Rivers and lakes in Western Arabia Terra: The Fluvial catchment of the ExoMars 2022 rover landing site’
Peter Fawdon (firstname.lastname@example.org). The Open University, Walton Hall, Milton Keynes MK7 7EA United Kingdom,
All data is supplied in a equirectangular projection centered on Oxia Planum at 335.45deg east following Fawdon et al., (2021) A geographic framework for exploring the ExoMars rover landing site at Oxia Planum, Mars
Point data used to calculate Oxia Planum model watersheds
Polygons delimiting the extent of the Oxia Planum model watersheds
All channels observed in CTX data within the model watersheds.
‘Channel_ty’ field has 5 values: WFF, Wide Flat Floored. NUS - U-section. LRC, Low Relief channels. SLR, sinuous ridges. INT, channels within impact craters. INF, Inferred or possible channel pathways
All possible lakes identified in the within the model watersheds with the numbers of morphological indicators for each possible lake.
‘Type’ field has 4 values: 1, Large Crater lakes. 2, Rimless Crater lakes. 3. Irregular Dark depressions. 4, possible sediment fans.
Geomorphological features recorded are: Inlets, Outlets, Sediment fans, Interior channels, Smooth floor, Strandlines and Concentric albedo changes.
Possible maximum models volumes have been calculated for some lakes using the volume difference between unfilled and filled MOLA DEM within the boundary of the possible lake as defined by where the fill hillshade = 180.
Strahler stream order for the model flow accumulation pathways for the model watersheds areas.
Extract from the methord section of ‘Rivers and lakes in Western Arabia Terra: The Fluvial catchment of the ExoMars 2022 rover landing site’
Geomorphological observations of fluvial features were made using CTX, 6 meter/pixel data at a scale of 1:50,000, georeferenced to High Resolution Stereo Camera MC11 quadrangle mosaic basemap (HRSC; Gwinner et al., 2016; Neukum et al., 2004). THermal EMission Imaging System (THEMIS; Christensen et al., 2013) night and daytime IR global mosaics were used to inform identification of features observed in the CTX data, and Colour and Stereo Surface Imaging System (CaSSIS; Thomas et al., 2017) images were used where available for colour interpretation. Mars Orbital Laser Altimeter (MOLA; Zuber et al., 1992) data were used for topographic information. Using these data, a fluvial (valley/channel and sinuous ridges) and lacustrine features was identified. After the initial survey, a topographic flow accumulation model was used to identify areas to revise where the model suggested channels might be present, and these were then searched more closely for any subtle morphological evidence of fluvial landforms. This iterative, multi-data process enabled many more fluvial systems to be identified than using one dataset alone.
To determine the watershed area for Oxia Planum (Figure 1), the ArcMap 10.5 Spatial Analyst ‘ArcHydro’ toolset (Esri, 2016) was used to calculate a model of flow accumulation grids and a drainage network map using topographic data from the MOLA DEM (Smith et al., 2001). Areas in the DEM that created sinks or basins were filled prior to calculating flow direction and accumulation. It is important to note that these processing steps ‘fill in’ areas of low-lying terrain and impact craters, as well as unwanted error and noise in the DEM. These ‘filled in’ areas create model flow pathways stretched across basins that were retained to identify where ponding may have occurred and where the model flow is likely to deviate from the geomorphic observations.
The watershed and contributory areas were calculated using the flow accumulation model upslope of two pour points located in the Oxia Basin. The location of both pour points (see Figure 2) was based on the correspondence of preliminary model flow accumulation paths calculated for the whole MC-11 Quad and geomorphological features resolved in the MOLA DEM. The eastern pour point (the lowest point in the ‘fan’ watershed) was located where the channel of Coogoon Valles opens out into Oxia Basin at the highest elevation of the sediment fan remnants. The northern pour point (the lowest point in the basin watershed) was located at the lowest point of the Oxia Basin leading northwards to Chryse Planitia. The watershed is defined where the flow accumulation is 0 (i.e. there are no cells from which water would flow). The pour points, their watersheds, and the flow accumulation pathways were converted to Strahler stream order (Strahler, 1957).
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