High Resolution Stereo Camera Images Research Articles

Integrated Photogrammetric and Photoclinometric Processing of Multiple HRSC Images for Pixelwise 3-D Mapping on Mars

Images from the high-resolution stereo camera (HRSC) is an important data source for retrieving 3-D information of the Martian surface. Photogrammetry has been widely applied to HRSC images to generate digital elevation models (DEMs). However, in circumstances of insufficient textures or severe atmospheric influences on Mars, photogrammetry may fail to generate DEMs of favorable quality. Besides, photogrammetry is not able to recover pixelwise geometrical information. Meanwhile, photoclinometry is a promising method to retrieve pixelwise 3-D information from image intensities. Few works in the past have explored the appropriate use of photoclinometry for HRSC data. This article presents an innovative approach of integrating photogrammetry and photoclinometry for pixelwise 3-D mapping of the Martian surface using multiple HRSC images. First, an effective photogrammetric strategy is developed to process multiple HRSC images. For images influenced by haze or aerosol problems, an automatic object-based matching algorithm is formulated to compensate for obvious flaws on the disparity map. Second, multiview photoclinometry considering atmospheric effect is developed to refine the photogrammetric DEM to pixel resolution. Qualitative and quantitative validations are conducted using two representative sets of HRSC images and compared with the reference data. The results show that the generated DEMs have good geometric consistency with the reference data, but offer subtle topographic details conforming to the original images. The proposed method provides a promising solution to exploit the HRSC images for 3-D mapping of the Martian surface with better resolution and coverage, which is of significance for future Mars exploration missions and scientific research.

Generation of Large-Scale Orthophoto Mosaics Using MEX HRSC Images for the Candidate Landing Regions of China’s First Mars Mission

Planetary mapping products play a significant role in landing site selection, surface operations, and scientific investigations. This paper describes the techniques and processes used to create geometrically controlled image mosaics for the candidate landing regions of China’s first Mars exploration mission (i.e., Tianwen-1) using Mars Express (MEX) High-Resolution Stereo Camera (HRSC) images. In order to deal with the extremely complex situations due to large data volumes (hundreds of images), various imaging conditions (e.g., 5–80° incidence angles), and long time spans (>10 years), we developed corresponding methods and in-house software for the photogrammetric processing of MEX HRSC images. According to the characteristics of planetary images and multi-line pushbroom imaging, we optimized the algorithms of establishing control network, eliminating blunders, setting weights and processing abnormal images. The generated MEX HRSC image mosaics with a resolution of 12.5 m delivered a high relative accuracy (<1 pixel). Compared with the existing Mars global image mosaics, the generated image mosaics exhibit significantly better spatial resolution. The techniques and methods that we developed to solve the complicated photogrammetric processing problems can also be applied to produce global or large-scale Mars mapping products using existing and new returned orbital images.

Evaluating Stereo Digital Terrain Model Quality at Mars Rover Landing Sites with HRSC, CTX, and HiRISE Images

We have used high-resolution digital terrain models (DTMs) of two rover landing sites based on mosaicked images from the High-Resolution Imaging Science Experiment (HiRISE) camera as a reference to evaluate DTMs based on High-Resolution Stereo Camera (HRSC) and Context Camera (CTX) images. The Next-Generation Automatic Terrain Extraction (NGATE) matcher in the SOCET SET and GXP® commercial photogrammetric systems produces DTMs with good (small) horizontal resolution but large vertical error. Somewhat surprisingly, results for NGATE are terrain dependent, with poorer resolution and smaller errors on smoother surfaces. Multiple approaches to smoothing the NGATE DTMs give similar tradeoffs between resolution and error; a 5 × 5 lowpass filter is near optimal in terms of both combined resolution-error performance and local slope estimation. Smoothing with an area-based matcher, the standard processing for U.S. Geological Survey planetary DTMs, yields similar errors to the 5 × 5 filter at slightly worse resolution. DTMs from the HRSC team processing pipeline fall within this same trade space but are less sensitive to terrain roughness. DTMs produced with the Ames Stereo Pipeline also fall in this space at resolutions intermediate between NGATE and the team pipeline. Considered individually, resolution and error each varied by approximately a factor of 2. Matching errors were 0.2–0.5 pixels but most results fell in the 0.2–0.3 pixel range that has been stated as a rule of thumb in multiple prior studies. Horizontal resolutions of 10–20 image pixels were found, consistently greater than the 3–5 pixel spacing generally used for stereo DTM production. Resolution and precision were inversely correlated; their product varied by ≤20% (4–5 pixels squared). Refinement of the stereo DTM by photoclinometry can yield quantitative improvement in resolution (more than a factor of 2), provided that albedo variations over distances smaller than the stereo DTM resolution are not too severe. We offer specific guidance for both producers and users of planetary stereo DTMs, based on our results.

A New South Polar Digital Terrain Model of Mars from the High-Resolution Stereo Camera (HRSC) onboard the ESA Mars Express

The first high-resolution Digital Terrain Model (DTM) of the entire South Pole of Mars has been produced. A modified version (Kim and Muller, 2009) of a NASA-VICAR-based pipeline developed by DLR (German Aerospace Centre) and JPL (Jet Propulsion Laboratory) has been employed with image matching based on the Gotcha (Gruen-Otto-Chau) algorithm (Shin and Muller, 2012) with a specialised setup for the polar region. DTM products have been produced with more than twice the resolution (50 m/pixel) of the gridded Mars Orbiter Laser Altimeter (MOLA) 512 pixels/degree (112 m/pixel) over the South Polar Residual Cap (SPRC) and the Mars South Polar region (82° - 90° S) in MOLA and areoid reference. The accuracy of the HRSC orbital DTMs are compared against a MOLA reference with good results. HRSC orthorectified strip images from 12.5 to 50 m have also been produced from the base DTMs and these have been processed into a 12.5 m mosaic. HRSC strip products are currently being assessed as base images for automatic co-registration of thousands of high-resolution images, making them geometrically consistent with the surface conditions imaged by HRSC. In some cases, Context Camera (CTX) DTMs have been automatically produced and co-registered to the HRSC image strips and these, in turn, are being employed for automated co-registration of higher-resolution images.

COMMUNITY TOOLS FOR CARTOGRAPHIC AND PHOTOGRAMMETRIC PROCESSING OF MARS EXPRESS HRSC IMAGES

COMMUNITY TOOLS FOR CARTOGRAPHIC AND PHOTOGRAMMETRIC PROCESSING OF MARS EXPRESS HRSC IMAGES

IDENTIFYING SURFACE CHANGES ON HRSC IMAGES OF THE MARS SOUTH POLAR RESIDUAL CAP (SPRC)

Abstract. The surface of Mars has been an object of interest for planetary research since the launch of Mariner 4 in 1964. Since then different cameras such as the Viking Visual Imaging Subsystem (VIS), Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), and Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) have been imaging its surface at ever higher resolution. The High Resolution Stereo Camera (HRSC) on board of the European Space Agency (ESA) Mars Express, has been imaging the Martian surface, since 25th December 2003 until the present-day. HRSC has covered 100 % of the surface of Mars, about 70 % of the surface with panchromatic images at 10-20 m/pixel, and about 98 % at better than 100 m/pixel (Neukum et. al., 2004), including the polar regions of Mars. The Mars polar regions have been studied intensively recently by analysing images taken by the Mars Express and MRO missions (Plaut et al., 2007). The South Polar Residual Cap (SPRC) does not change very much in volume overall but there are numerous examples of dynamic phenomena associated with seasonal changes in the atmosphere. In particular, we can examine the time variation of layers of solid carbon dioxide and water ice with dust deposition (Bibring, 2004), spider-like channels (Piqueux et al., 2003) and so-called Swiss Cheese Terrain (Titus et al., 2004). Because of seasonal changes each Martian year, due to the sublimation and deposition of water and CO2 ice on the Martian south polar region, clearly identifiable surface changes occur in otherwise permanently icy region. In this research, good quality HRSC images of the Mars South Polar region are processed based on previous identification as the optimal coverage of clear surfaces (Campbell et al., 2015). HRSC images of the Martian South Pole are categorized in terms of quality, time, and location to find overlapping areas, processed into high quality Digital Terrain Models (DTMs) and Orthorectified Images (ORIs) and projected into polar stereographic projection using DLR (Deutsches Zentrum für Luft- und Raumfahrt; German Aerospace Center)’s VICAR and GIS software with modifications developed by Kim &amp;amp; Muller (2009). Surface changes are identified in the Mars SPRC region and analysed based on their appearance in the HRSC images.

GLOBAL BUNDLE ADJUSTMENT WITH VARIABLE ORIENTATION POINT DISTANCE FOR PRECISE MARS EXPRESS ORBIT RECONSTRUCTION

Abstract. The photogrammetric bundle adjustment of line scanner image data requires a precise description of the time-dependent image orientation. For this task exterior orientation parameters of discrete points are used to model position and viewing direction of a camera trajectory via polynomials. This paper investigates the influence of the distance between these orientation points on the quality of trajectory modeling. A new method adapts the distance along the trajectory to the available image information. Compared to a constant distance as used previously, a better reconstruction of the exterior orientation is possible, especially when image quality changes within a strip. In our research we use image strips of the High Resolution Stereo Camera (HRSC), taken to map the Martian surface. Several experiments on the global image data set have been carried out to investigate how the bundle adjustment improves the image orientation, if the new method is employed. For evaluation the forward intersection errors of 3D points derived from HRSC images, as well as their remaining height differences to the MOLA DTM are used. In 13.5 % (515 of 3,828) of the image strips, taken during this ongoing mission over the last 12 years, high frequency image distortions were found. Bundle adjustment with a constant orientation point distance was able to reconstruct the orbit in 239 (46.4 %) cases. A variable orientation point distance increased this number to 507 (98.6 %).

GLOBAL BUNDLE ADJUSTMENT WITH VARIABLE ORIENTATION POINT DISTANCE FOR PRECISE MARS EXPRESS ORBIT RECONSTRUCTION

The photogrammetric bundle adjustment of line scanner image data requires a precise description of the time-dependent image orientation. For this task exterior orientation parameters of discrete points are used to model position and viewing direction of a camera trajectory via polynomials. This paper investigates the influence of the distance between these orientation points on the quality of trajectory modeling. A new method adapts the distance along the trajectory to the available image information. Compared to a constant distance as used previously, a better reconstruction of the exterior orientation is possible, especially when image quality changes within a strip. &amp;lt;br&amp;gt;&amp;lt;br&amp;gt; In our research we use image strips of the High Resolution Stereo Camera (HRSC), taken to map the Martian surface. Several experiments on the global image data set have been carried out to investigate how the bundle adjustment improves the image orientation, if the new method is employed. For evaluation the forward intersection errors of 3D points derived from HRSC images, as well as their remaining height differences to the MOLA DTM are used. &amp;lt;br&amp;gt;&amp;lt;br&amp;gt; In 13.5 % (515 of 3,828) of the image strips, taken during this ongoing mission over the last 12 years, high frequency image distortions were found. Bundle adjustment with a constant orientation point distance was able to reconstruct the orbit in 239 (46.4 %) cases. A variable orientation point distance increased this number to 507 (98.6 %).

ANALYZING A BLOCK OF HRSC IMAGE STRIPS FOR A SIMULTANEOUS BUNDLE ADJUSTMENT

Abstract. 10 years ago the first European interplanetary mission Mars Express was launched and sent into orbit around Mars. One of the scientific instruments on board the orbiter is the High Resolution Stereo Camera (HRSC). This multi-line sensor with five panchromatic and four multispectral CCD lines was developed by the German Aerospace Center (DLR) for photogrammetric mapping purposes. It images the Martian surface with a resolution of up to 12 m per pixel, depending on the altitude. The along-track stereo capability of the camera delivers image strips with three-dimensional information, which cover nearly the whole planet. For a derivation of more accurate digital terrain models and orthoimages the orientation data of the camera is improved via bundle adjustment. To map larger regions overlapping image strips can be used to form photogrammetric blocks, thus allowing a simultaneous adjustment of the different strips. Compared to the adjustment of individual strips, an adjustment of the entire block reduces not only local, but also regional inconsistencies in the data. With the growing number of HRSC image strips in this ongoing mission, number, size and complexity of potential blocks increases. To cope with these data a method for a semi-automated analysis, selection and combination of suitable strips for the design of more accurate and reliable blocks has been developed. The method takes the inhomogeneity of the HRSC data into account by adapting the processing parameters, if necessary for each strip.

Phobos' shape and topography models

The global shape and the dynamic environment are fundamental properties of a body. Other properties such as volume, bulk density, and models for the dynamic environment can subsequently be computed based on such models. Stereo-photogrammetric methods were applied to derive a global digital terrain model (DTM) with 100m/pixel resolution using High Resolution Stereo Camera images of the Mars Express mission and Viking Orbiter images. In a subsequent least-squares fit, coefficients of the spherical harmonic function to degree and order 45 are computed. The dynamic models for Phobos were derived from a polyhedron representation of the DTM. The DTM, spherical harmonic function model, and dynamic models, have been refined and represent Phobos' dynamic and geometric topography with much more detail when compared to Shi et al. (2012) and Willner et al. (2010) models, respectively. The volume of Phobos has been re-determined to be in the order of 5741km3 with an uncertainty of only 0.6% of the total volume. This reduces the bulk density to 1.86±0.013g/cm3 in comparison to previous results. Assuming a homogeneous mass distribution a forced libration amplitude for Phobos of 1.14° is computed that is in better agreement with observations by Willner et al. (2010) than previous estimates.

PIXEL LEVEL DATA FUSION OF MARS EXPRESS HRSC LINEAR PUSHBROOM IMAGERY BASED ON THE RIGOROUS GEOMETRIC MODEL

Abstract. The High Resolution Stereo Camera (HRSC) on European spacecraft Mars Express is especially designed for topographic mapping of Mars. HRSC can acquire both panchromatic and multi-spectral images simultaneously. The resolution of panchromatic image is higher than that of multi-spectral image. Through image fusion, the high resolution multi-spectral image of Mars can be generated. In this paper, the HRSC raw image is geometrically rectified firstly based on rigorous geometric model. Then, the panchromatic image and multi-spectral image are fused based on IHS transformation. In order to improve the processing efficiency, a fast algorithm for back projection of ground points based on the geometric constraints of the central perspective planar of scan line is proposed. Experiments tested on HRSC images demonstrate our algorithm’s feasibility and efficiency.

Outflow channels with deltaic deposits in Ismenius Lacus, Mars

A connected series of outflow channels in the Ismenius Lacus quadrangle are identified for the first time and characterized using High Resolution Stereo Camera images of Mars Express, the Context camera images of Mars Reconnaissance Orbiter and the topography of the Mars Observer Laser Altimeter. These channels (named Okavango Valles), which stretch over >400km south to north and join the northern plains, were identified from braided channels, scour/groove marks, poorly sinuous valleys and depositional landforms. Discharge rates were estimated to 0.1–5×106m3s−1 from analysis of the topography of scour marks. Pathways of channels segments were extracted from topography showing a unique source at a breached crater rim, suggesting overflow from ponded depressions. A series of delta fans are observed inside depressions along the channel pathways. The presence of these deltas formed in former bodies of water is a compelling argument for formation of this outflow channel system by fluvial flows. The similarity of these flows with other outflow channels on Mars proves that volcanically-related outflows cannot explain all such features. In addition, this study also shows that catastrophic floods are able to create fan deltas in transient lakes. This example has to be taken into account in the interpretation of late stage fans associated with poorly branched valleys and single channels.

Modeling spacecraft oscillations in HRSC images of Mars Express

Abstract. Since January 2004 the High Resolution Stereo Camera (HRSC) is mapping planet Mars. The multi-line sensor on board the ESA Mission Mars Express images the Martian surface with a resolution of up to 12m per pixel in three dimensions and in color. As part of the Photogrammetric/Cartographic Working Group of the HRSC Science Team the Institute of Photogrammetry and GeoInformation (IPI) of the Leibniz Universit¨at Hannover is involved in photogrammetrically processing the HRSC image data. To derive high quality 3D surface models, color orthoimages or other products, the accuracy of the observed position and attitude information in many cases should be improved. This is carried out via a bundle adjustment. In a considerable number of orbits the results of the bundle adjustment are disturbed by high frequency oscillations. This paper describes the impact of the high frequency angular spacecraft movement to the processing results of the last seven years of image acquisition and how the quality of the HRSC data products is significantly improved by modeling these oscillations.

SYSTEMATIC BUNDLE ADJUSTMENT OF HRSC IMAGE DATA

Abstract. The European Mars Express mission was launched in June 2003 and sent into orbit around Mars. On board the orbiter is the German High Resolution Stereo Camera (HRSC). This multi-line sensor images the Martian surface with a resolution of up to 12m per pixel in three dimensions and provides RGB and infra-red color information. The usage of the stereoscopic image information for the improvement of the observed position and attitude information via bundle adjustment is important to derive high quality 3D surface models, color orthoimages and other data products. In many cases overlapping image strips of different orbits can be used to form photogrammetric blocks, thus allowing the simultaneous adjustment of the exterior orientation data. This reduces not only local, but also regional inconsistencies in the data. With the growing number of HRSC image strips in this ongoing mission, the size and complexity of potential blocks is increasing. Therefore, a workflow has been built up for the systematic improvement of the exterior orientation using single orbit strips and regional blocks. For a successful bundle adjustment of blocks using multiple image strips a sufficient number of tie points in the overlapping area is needed. The number of tie points depends mainly on the geometric and radiometric quality of the images. This is considered by detailed analysis of the tie point accuracy and distribution. The combination of methods for image pre-processing, tie point matching, bundle adjustment and evaluation of the results in an automated workflow allows for all HRSC images a global assessment of the quality and a systematic selection of data for larger blocks.

Multitemporal observations of identical active dust devils on Mars with the High Resolution Stereo Camera (HRSC) and Mars Orbiter Camera (MOC)

Active dust devils were observed in Syria Planum in Mars Observer Camera – Wide Angle (MOC-WA) and High Resolution Stereo Camera (HRSC) imagery acquired on the same day with a time delay of ∼26 min. The unique operating technique of the HRSC allowed the measurement of the traverse velocities and directions of motion. Large dust devils observed in the HRSC image could be retraced to their counterparts in the earlier acquired MOC-WA image. Minimum lifetimes of three large (avg. ∼700 m in diameter) dust devils are ∼26 min, as inferred from retracing. For one of these large dust devil (∼820 m in diameter) it was possible to calculate a minimum lifetime of ∼74 min based on the measured horizontal speed and the length of its associated dust devil track. The comparison of our minimum lifetimes with previous published results of minimum and average lifetimes of small (∼19 m in diameter, avg. min. lifetime of ∼2.83 min) and medium (∼185 m in diameter, avg. min. lifetime of ∼13 min) dust devils imply that larger dust devils on Mars are active for much longer periods of time than smaller ones, as it is the case for terrestrial dust devils. Knowledge of martian dust devil lifetimes is an important parameter for the calculation of dust lifting rates. Estimates of the contribution of large dust devils (>300–1000 m in diameter) indicate that they may contribute, at least regionally, to ∼50% of dust entrainment by dust devils into the atmosphere compared to the dust devils <300 m in diameter given that the size-frequency distribution follows a power-law. Although large dust devils occur relatively rarely and the sediment fluxes are probably lower compared to smaller dust devils, their contribution to the background dust opacity by dust devils on Mars could be at least regionally large due to their longer lifetimes and ability of dust lifting into high atmospheric layers.

Optical depth and its scale-height in Valles Marineris from HRSC stereo images

We measured the optical depth of the Martian atmosphere as a function of altitude above two opposing scree walls of the Valles Marineris, from stereo images that were taken with the High Resolution Stereo Camera (HRSC) of Mars Express on June 3, 2004, during orbit 471. The optical depths were measured from contrast differences between the stereo images with the so called “stereo method”. For 7 regions in the northern wall of the Valles, we estimated the optical depth and found values between 1.0 and 1.6. These regions span more than 6 km in altitude and the results show a clear relation with altitude. A fit on these results yielded a scale-height for the optical depth of 14.0 km + 1.3/−1.1 km. The expected local pressure–scale height is smaller: 11.5–12.0 km. The difference is most likely explained by small (around 1.5%) offset errors in the intensity calibration of HRSC images. We also selected 9 regions in the opposing southern wall and from these we measured values of optical depth in the range 1.3–1.5. Our result suggests the presence of clouds above this part of the Valles because the optical depth appears almost independent of the surface altitude. Possibly these are banner clouds, forming at the edge of the canyon, that contain dust that is blown over the canyon by winds from the high plains to the South.

Tyrrhena Patera: Geologic history derived from Mars Express High Resolution Stereo Camera

We used Mars Express High Resolution Stereo Camera images of the Tyrrhena Patera volcano to assign cratering model ages to material units defined in the VikingOrbiter‐based geologic mapping. Cratering model ages are generally consistent with their stratigraphy. We can identify three key intervals of major activity at Tyrrhena Patera: (1) formation of the volcanic edifice in the Noachian Period, ∼3.7–4.0 Ga, shortly following the Hellas impact (∼4 Ga) and coincident with the formation of Hadriaca Patera (∼3.9 Ga); (2) modification of the edifice and formation of the caldera rille and channels in the Hesperian Period, possibly extending into the Amazonian Period; and (3) a final stage of modification in the Late Amazonian Epoch, ∼0.8–1.4 Ga. Early‐ to mid‐Hesperian activity on Tyrrhena Patera is consistent with similar activity on Hadriaca Patera at ∼3.3–3.7 Ga. The most recent dateable event on Tyrrhena Patera is modification on the upper shield, caldera rille, and channel floors at ∼800 Ma. This coincidence of resurfacing in three units suggests a widespread process(es), which we speculate involved preferential (aeolian?) erosion of small craters on these flatter surfaces relative to the other units on the volcano. Alternatively, some combination of pyroclastic flow emplacement on the upper shield and fluvial activity in the caldera rille and channels, followed by differential aeolian erosion and deposition, could have produced the present surface. Regardless, major geologic resurfacing ended at Tyrrhena Patera nearly a billion years ago.

Topography of valley networks on Mars from Mars Express High Resolution Stereo Camera digital elevation models

Martian valley networks have been identified mainly in the Noachian heavily cratered uplands. The geometry of valley networks can be studied using Mars Orbiter Laser Altimeter (MOLA) altimetry, which is sufficient to map large valleys without a detailed 3‐D shape of valley networks. Imaging from the Mars Express High Resolution Stereo Camera (HRSC) is used to generate digital elevation models (DEMs) with resolution ≤50 m and vertical accuracy &lt;60 m. We studied valleys near Huygens crater and in the Aeolis region both in the Noachian bedrock and on the West Echus plateau in Hesperian bedrock. HRSC DEMs in these areas show that (1) drainage density is 3 times higher than is observed in MOLA data, (2) degree of ramification is 1 order more than with MOLA, (3) transverse valley profiles show a V shape more accurately and a minimum depth of ∼20 m, and (4) higher drainage density shows greater headward extension that is not correlated to greater valley depth. The deepest valleys (400 m) are found in the Huygens region, where the density in the DEM is 0.1 km−1, compared to shallow valleys (&lt;100 m) of the Echus region, where the density is higher (∼0.3 km−1). These regional differences are due to spatially variable preservation and bedrock lithology. Longitudinal profiles suggest variations in duration of activity: profile concavity is only developed in some Noachian terrains. Valleys visible in HRSC images correspond to topographic features in DEMs showing the same geometry as terrestrial valleys thought to be formed by overland flows and seepage.

Trends in effusive style at the Tharsis Montes, Mars, and implications for the development of the Tharsis province

We mapped lava flows on the Tharsis Montes (Arsia Mons, Pavonis Mons, and Ascraeus Mons) using High Resolution Stereo Camera images that centrally transect each shield from north to south, covering ∼20% of each shield's surface. These data were co‐registered to Mars Orbiter Laser Altimeter, Thermal Emission Imaging System, and Mars Orbiter Camera data, enabling lava flow structures and vents to be consistently differentiated across each volcano. Lava flow and vent abundances and relationships are used to provide new insight into the late Amazonian eruptive history of the Tharsis Montes. The volcanoes are divided into their main flanks, rift aprons, and small‐vent fields. Where present on the main flanks, channel‐fed flows always embay tube‐fed flows, indicating a change from long‐lived, stable tube‐forming eruption conditions to shorter‐lived, less stable channel‐forming eruption conditions. Superposition relationships suggest that main flank and rift apron development were likely separated by an eruptive hiatus. The rift aprons, as compared to the main flanks, show higher abundances of tube‐ and channel‐fed flows, and embayment of tube‐fed flows by channel‐fed flows is less consistent. Several trends from the Arsia Mons, to Ascraeus Mons, southwest rift aprons and small‐vent fields were identified, including increased tube abundance, median slope, and number of satellitic eruptive vents and a decrease in channel‐ to tube‐fed flow ratios, apron volumes, and maximum apron elevations. These trends suggest that the most recent volcanic activity at the Tharsis Montes might have originated from a single, shared magma source, possibly marking a change in magma production style from main flank construction.

Olympus Mons, Mars: Inferred changes in late Amazonian aged effusive activity from lava flow mapping of Mars Express High Resolution Stereo Camera data

Lava flow mapping was conducted on a north‐south transect of Olympus Mons using the European Space Agency's Mars Express High Resolution Stereo Camera (HRSC) image H0037. The HRSC image was coregistered to Mars Orbiter Laser Altimeter, Thermal Emission Imaging System, and Mars Orbiter Camera data, enabling lava flow structures to be differentiated and mapped consistently across the shield. Because different structures develop as a result of different effusive conditions, their abundance and distribution provide insight into the eruptive history of a shield volcano. Results show that lava channels are the dominant flow structure, whereas tabular sheets are most common beyond the basal scarp. A hummocky unit dominates the summit area and likely represents a combination of (1) volcanic lava flows, (2) pyroclastic deposits, (3) a dust mantle, and (4) frozen volatiles, all of which have been suggested to exist on Olympus Mons in the past. Lava fans are typically associated with lava tubes, indicating that they represent tube outbreaks as was previously suggested as one possible formation mechanism. No vents were identified, suggesting that major rift zones have not developed on the north or south flank. Younger channel‐fed flows typically embay older tube‐related flows, which they outnumber by a ratio of 5:1. Therefore Olympus Mons likely experienced a change in eruptive style from longer‐lived, stable, tube‐forming eruptions to shorter‐lived, less stable, channel‐forming eruptions in the late Amazonian. A similar trend exists for the Hawaiian volcanoes in which a decrease in the magma production rate drives a change to dominantly channel forming eruptions associated with increased shield age.