Exploring Geomorphic Processes and Martian Gale Crater Topography on Mars using CTX and HiRISE Express Image Dataset

Exploration of Martian surface and the crater deposition has recently attracted scientific community. We hypothesized the existence of momentous topographic features of different origin on the Martian surface. It was observed that Gale Crater has a thick sediment deposition mainly of fluvial and aeolian origin. This study has utilized spatially referenced topographic dataset Context Camera images acquired from Mars reconnaissance orbiter for exploring the geomorphic processes and topography of Gale Crater. A base map was prepared by mosaicking all images for preparing geomorphologic map of the crater. Surface map of the topography of the Crater was prepared using Mars Orbiter Laser Altimeter (MOLA) data. HiRISE images were used to examine the identified geomorphic features. Results revealed that the presence of both fluvial and aeolian processes and their respective associated landforms in the Crater. Depositional landforms such as alluvial fan, inverted channel and mound and erosional landform namely canyons were distinctly identified on the image. Yardangs produced by erosional and ripple and dunes formed by the depositional work of wind were also identified in the Crater. The fluvial channel, inverted channels and fan shaped deposits further signifies ongoing aqueous activity on the Gale Crater. Sinuous ridges are the common features present on the floor of Crater. Rock particles, sand and silt in the crater were found to have been transported and deposited by flowing water on its floor. Presence of different sedimentary structures and valley revealed ancient sedimentary deposition due to water action. Significant ejecta morphologies were also identified on Martian surface. Our study confirms the previous studies that presence of H2O sub surface volatiles. Concentrations of volatiles have produced double layer ejecta morphology. The concept and findings of this study will escalate knowledge about the surface features on Gale Crater. However, more coherent investigation is needed for modelling and understanding the processes and landforms of the crater. Context Camera (CTX) and HighResolution Imaging Science Experiment (HiRISE) images have proved useful for geomorphic and topographic mapping of the Mars planet. The dataset used in this study can be accessed on Mars Orbital Data Explorer (https://ode.rsl.wustl.edu/mars/indexproductsearch.aspx). Earth Syst. Sci. Data Discuss., https://doi.org/10.5194/essd-2019-4 O pe n A cc es s Earth System Science Data D icu ssio n s Manuscript under review for journal Earth Syst. Sci. Data Discussion started: 21 January 2019 c © Author(s) 2019. CC BY 4.0 License.

CTX images with 6 meters spatial resolution obtained from the MRO satellite were used for mapping the Martian geomorphological features (Fig. 2).Radiometric calibration of raw CTX image can be done with image manipulation using direct sets of calculations.The process of radiometric calibration not only enhanced the image quality for interpretation but also reduced the digital number (DN) values errors.

Decompanding
All CTX data within the instrument electronics are companded into 8-bit (0-255 DN) data files from their original 12-bit (0-4095 DN) format usinga square-root-like compression lookup table (LUT) by using the CCD gain and read noise during preflight camera testing developed by the CTX team.

Bias and Dark Current Subtraction and Even/Odd striping correction
During each CTX exposure both current signals i.e. bias and dark accumulate simultaneously.Although, small levels between the A and B channels of the CCD array can still differ slightly.In order to subtract this background signal level, a very simple process can be used.For this, the first step is to average DN values calculated separately in the odd (channel A) and even (channel B) masked-off reference pixels (pixels 1-38 and 5039-5056) and at second step, the calculated average values were subtracted from their corresponding odd and even unmasked pixels (pixels 39-5038).For additional cosmetic improvement of CTX images another small correction may be applied that attempts to explicitly remove any systematic detector gain effects that possibly exist between the channels A and B of the CTX detector.
Subtracted and flat fielded CTX row was scaled to radiance using the CTX response coefficient derived during pre-flight calibration using the equation: Where,  is the pixel value being evaluated in DN, exp is the exposure time in msec,  is the CTX response coefficient in (DN/msec)/(W/m 2 /µm/sr), and__ is the solar spectral radiance for CTX in (W/m 2 /µm/sr).

Calibration algorithm of HiRISE image
The radiometric correction process improves the interpretation and quality of images and reduces the errors in digital number

Fig. 3. SLE, MLE and DLE ejecta morphologies
The current study finds that symmetrical central pit has highest correlation between crater diameter and pit diameter (Fig. 4).
The single layer ejecta was found concentrated between equatorial latitude while double, multiple and radial layer were observed at middle latitudes.These varied topographic features are very much significant in idealizing the surface conditions on Martian topography.The percentage of ejecta was calculated for every 10 latitude on the Martial surface (Fig. 11).It means that if the diameter of crater is increases then the pit diameter also increases but it is not true in cases of complex craters.On the other hand, the relationship between crater diameter and pit diameter for the radial layer ejecta is strongest (r 2 =0.7947) than the single, double and multiple layer ejecta but the numbers of crater for the radial layer ejecta is less than other craters (Fig. 5).6

Fig. 1 .
Fig.1.Graphical abstract showing mapping and identification of geomorphological features