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Mars 2020 Perseverance SHERLOC WATSON Camera Pre-delivery Characterization and Calibration Report
Abstract and Figures
This document is the 03 December 2019 pre-ship characterization and calibration report for the WATSON camera launched 30 July 2020 onboard the Perseverance rover, bound for Mars.
WATSON, a Wide Angle Topographic Sensor for Operations and eNgineering camera, is a subsystem of the SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) instrument mounted on the turret at the end of Perseverance’s robotic arm. The WATSON characterized in the 03 December 2019 report was the Flight Spare unit; by the time it was delivered to JPL-Caltech in October 2019, it had become the baseline flight instrument, intended for launch to Mars. A previous WATSON camera head became the Mars 2020 testbed article (testbed-WATSON).
“Pre-ship” refers to testing and activities performed before the WATSON camera head was delivered from Malin Space Science Systems (MSSS, San Diego, California, USA) to the California Institute of Technology’s Jet Propulsion Laboratory (Caltech JPL, Pasadena, California, USA), where WATSON was subsequently integrated with the SHERLOC Turret Assembly (STA). The STA was, in turn, integrated with the Perseverance rover at JPL.
The supplement file to accompany this report was published at Zenodo in July 2021:
Edgett, K.S., Caplinger, M.A., Ravine, M.A. (2021) Mars 2020 Perseverance SHERLOC WATSON camera pre-delivery characterization and calibration image data [data set], Zenodo. https://doi.org/10.5281/zenodo.5090820
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... Each WATSON or MAHLI camera is slightly different in terms of mechanical relations between motor count and lens focus, as well as performance at the minimum working distance and at infinity focus (the WATSON on Mars performs better than the MAHLI on Mars at both of these extreme ends of the focus range; Edgett et al., 2019). Thus, the relation between motor count and working distance must be determined empirically for each such camera. ...
... The relations between motor count, working distance, and pixel scale were determined for Perseverance's WATSON using data acquired in a clean room environment in October 2019 (Edgett et al., 2019). However, given typical pre-launch schedule and resource constraints, data collection over working distances in the 40 to 210 cm range was minimal (and this was acceptable, at the time, because most imaging will occur on Mars in the 2.5 to 40 cm range). ...
... Key preceding documents are the WATSON characterization and calibration report (Edgett et al., 2019) and the SHERLOC investigation description paper (Bhartia et al., 2021). Both of these provide a pre-launch assessment of the knowledge of FOD on the CCD and the relation between focus motor count, target range (working distance), and image pixel scale. ...
Refinement of the relations between motor count, working distance (range), and pixel scale for the SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) WATSON (Wide Angle Topographic Sensor for Operations and eNgineering) camera, located on the turret at the end of the Perseverance rover’s robotic arm, operating in Jezero crater, Mars. The refinements to estimate image range and scale from focus stepper motor count are based on data acquired on Mars as well as data acquired before launch. The report also considers the post-landing state of particulates on the CCD; these did not change despite pre-launch vibration testing and the launch, cruise, and entry-descent-and-landing vibration environments.
... The following sections provide an overview of the WATSON camera characterization and calibration results. Details can be found in Edgett et al. (2019) ...
... Both values met and exceeded a requirement of > 15% over the full WATSON focus range. Additional images regarding the flight model WATSON performance can be found in Edgett et al. 2019). ...
... We used images acquired at room temperature in a cleanroom laboratory setting on 03 October 2019 and found the PTC and linearity results to be: scale factor 15.84 e − per DN, read noise 18.7 e − , full well 24,507 e-. Addition images regarding the flight model WATSON performance can be found in Edgett et al. 2019). ...
The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) is a robotic arm-mounted instrument on NASA’s Perseverance rover. SHERLOC has two primary boresights. The Spectroscopy boresight generates spatially resolved chemical maps using fluorescence and Raman spectroscopy coupled to microscopic images (10.1 μm/pixel). The second boresight is a Wide Angle Topographic Sensor for Operations and eNgineering (WATSON); a copy of the Mars Science Laboratory (MSL) Mars Hand Lens Imager (MAHLI) that obtains color images from microscopic scales (∼13 μm/pixel) to infinity. SHERLOC Spectroscopy focuses a 40 μs pulsed deep UV neon-copper laser (248.6 nm), to a ∼100 μm spot on a target at a working distance of ∼48 mm. Fluorescence emissions from organics, and Raman scattered photons from organics and minerals, are spectrally resolved with a single diffractive grating spectrograph with a spectral range of 250 to ∼370 nm. Because the fluorescence and Raman regions are naturally separated with deep UV excitation (<250 nm), the Raman region ∼ 800 – 4000 cm ⁻¹ (250 to 273 nm) and the fluorescence region (274 to ∼370 nm) are acquired simultaneously without time gating or additional mechanisms. SHERLOC science begins by using an Autofocus Context Imager (ACI) to obtain target focus and acquire 10.1 μm/pixel greyscale images. Chemical maps of organic and mineral signatures are acquired by the orchestration of an internal scanning mirror that moves the focused laser spot across discrete points on the target surface where spectra are captured on the spectrometer detector. ACI images and chemical maps (< 100 μm/mapping pixel) will enable the first Mars in situ view of the spatial distribution and interaction between organics, minerals, and chemicals important to the assessment of potential biogenicity (containing CHNOPS). Single robotic arm placement chemical maps can cover areas up to 7x7 mm in area and, with the < 10 min acquisition time per map, larger mosaics are possible with arm movements. This microscopic view of the organic geochemistry of a target at the Perseverance field site, when combined with the other instruments, such as Mastcam-Z, PIXL, and SuperCam, will enable unprecedented analysis of geological materials for both scientific research and determination of which samples to collect and cache for Mars sample return.
... WATSON, a reflight of MAHLI, was designed for the high-resolution optical investigation of geologic materials when using the robotic arm for proximity science activities (Bhartia et al., 2021;Edgett et al., 2012;Kah et al., 2018;Minitti et al., 2013;Yingst, Edgett, et al., 2016). This camera consists of a 1,200 × 1,600-pixel charge-coupled device (CCD) with a macro-lens capable of focusing from approximately 2 cm to infinity; color is produced by red-green-blue microfilters arranged on the CCD in a Bayer pattern (Bhartia et al., 2021;Edgett et al., 2012Edgett et al., , 2019. Typical high-spatial resolution imaging on Mars using WATSON involves placing the camera at working distances (i.e., the distance between the front lens and the image target) of approximately 2.5-40.0 ...
During its first year of operation, the Perseverance rover explored the cratered and fractured floor of Jezero crater on Mars. Here, we report the use of the Scanning Habitability Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) imaging system that includes two high‐resolution cameras, the Autofocus and Contextual Imager (ACI) and Wide Angle Topographic Sensor for Operations and eNgineering (WATSON). ACI is a fixed focus gray scale imager with a resolution of 10.1 μm/pixel whereas WATSON is a variable field of view, variable focus imager capable of resolution down to 14 μm/pixel. WATSON is a reflight of the MArs Hand Lens Imager (MAHLI) imager and has similar capabilities. During first‐time activities, WATSON was used to support both science and engineering operations related to sample and abrasion patch assessment and sample collection and caching. WATSON also documented the deployment of the Ingenuity helicopter. The Crater Floor Campaign identified two primary rock units, the Máaz formation and the Séítah formation, which have been interpreted as lava flows and an olivine cumulate, respectively. Interpretation of rock textures with WATSON and ACI images was limited to abraded surfaces because unmodified outcrop surfaces (herein termed “natural surfaces”) show high degrees of dust covering, wind abrasion, and coating by secondary mineral products. WATSON and ACI images support the hypothesis that the material of both the Máaz and Séítah formations consists of largely aqueously altered mafic materials with varying igneous origins.
SHERLOC is an arm-mounted fluorescence and Raman spectrometer that was recently selected to be part of the payload for the next proposed NASA rover mission to Mars, scheduled for launch in 2020. SHERLOC enables non-contact, spatially resolved, high sensitivity detection and characterization of organics and minerals on the Martian surface. The investigation goals are to assess past aqueous history, detect the presence and preservation potential of biosignatures, and support the selection of samples for caching and potential return to Earth. (c)2015 IEEE
MAHLI has conducted white light and UV LED-illuminated night imaging on four occasions, two focused on geologic targets and two focused on rover hardware.
The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.
Several commercially available color standards exist, generated by a variety of manufacturers including LabSphere, Lucideon, and Avian Technologies. Previous work has characterized the photometric properties of LabSphere Spectralon targets. Here, we measure the visible and shortwave infrared (VSWIR; 0.4 to 2.5 μm) reflectance at multiple angles and determine the photometric properties of materials manufactured by Lucideon and Avian Technologies for potential use as calibration target materials for the Mars 2020 Mastcam-Z instrument. The Lucideon black, gray 33, green, and cyan samples are found to be significantly forward scattering. The yellow, red, and gray 70 samples are found to be weakly forward scattering. The Avian Technologies AluWhite98 sample was found to be weakly backward scattering. We characterize the absorptions observable and note the occurrence of wavelength-dependent photometric properties. The reflectance and photometric data collected and released here enable the use of these color standards for calibration of data from Mastcam-Z and other Mars-2020 rover instruments as well as provide key information for many other imaging and spectroscopy applications that require the calibration of data from multiple lighting or viewing geometries. © The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
Sedimentary rocks are composed of detrital grains derived from source rocks, which are altered by chemical weathering, sorted during transport, and cemented during diagenesis. Fluvio-lacustrine sedimentary rocks of the Bradbury group, observed on the floor of Gale crater by the Curiosity rover during its first 860 sols, show trends in bulk chemistry that are consistent with sorting of mineral grains during transport. The Bradbury group rocks are uniquely suited for sedimentary provenance analysis because they appear to have experienced negligible cation-loss (i.e., open-system chemical weathering) at the scale of the Alpha Particle X-ray Spectrometer bulk chemistry analyses based on low Chemical Index of Alteration values and successful modeling of >90% of the (volatile-free) targets as mixtures of primary igneous minerals. Significant compositional variability between targets is instead correlated to grain size and textural characteristics of the rocks; the coarsest-grained targets are enriched in Al_2O_3, SiO_2, and Na_2O, whereas the finer-grained targets are enriched in mafic components. This is consistent with geochemical and mineralogical modeling of the segregation of coarse-grained plagioclase from finer-grained mafic minerals (e.g., olivine and pyroxenes), which would be expected from hydrodynamic sorting of the detritus from mechanical breakdown of subalkaline plagioclase-phyric basalts. While the presence of a distinctive K_2O-rich stratigraphic interval shows that input from at least one distinctive alkali-feldspar-rich protolith contributed to basin fill, the dominant compositional trends in the Bradbury group are consistent with sorting of detrital minerals during transport from relatively homogeneous plagioclase-phyric basalts.
Imaging during and after the landing of the Mars Science Laboratory (MSL) rover in 2012 provides a means to examine two transitory phenomena for the first time: the settling of the plume of material raised by the powered terminal descent, and the possible dispersal of 140 kg of hydrazine into the atmosphere as fine-grained solid carbazic acid. The peri-landing images, acquired by the Mars Descent Imager (MARDI) and the rover hazard cameras (Hazcams), allow the first comparison of post-landing geological assessment of surface deflation with the plume itself. Examination of the Hazcam images acquired over a period of 4011 seconds shows that only a small fraction (350-1000 kg) of the total mass of fine-grained surface material displaced by the landing (4000 kg) remained in the atmosphere for this duration. Furthermore, a large component of this dust occurs as particles for which the characteristic optical radius is 20 – 60 μm, preventing them from being substantially mixed with the atmospheric column by eddy diffusion. Examination of the MARDI record over 225 seconds post-landing reveals a rapidly settling component that comprised approximately 1800-2400 kg and had a larger particle size with an optical radius of 360-470 μm. The possible release of hydrazine by the sky crane stage also may have created particles of carbazic acid that would, analogous to the dust, spread through eddy diffusivity and settle to the ground. Peri-landing Hazcam images of the plume created during sky crane destruction constrains the particle radius to be either less than 23 μm or greater than 400 μm. When combined with a Lagrangian model of the atmosphere, such particle sizes suggest that the carbazic acid was either deposited very near the sky crane crash site, or was widely dispersed as small particles which would have been quickly photodissociated to volatile ammonia and carbon dioxide. Surfaces visited by the MSL rover, Curiosity, would have received at most < 0.2 ppb of carbazic acid and levels of sky crane related organics would have fallen well below the detection threshold of the Sample Analysis at Mars (SAM) instruments within 4-6 sols, well before the rover acquired its first samples over 60 sols into the mission.
In 2011 NASA will launch the Mars Science Laboratory (MSL) as part of its Mars Exploration Program to learn more about the red planet's environment and geological history. To fulfill that goal, the MSL rover, built by NASA's Jet Propulsion Laboratory (JPL), is outfitted with the most extensive array of scientific instruments ever landed on the Martian surface. The Mars Hand Lens Imager (MAHLI), mounted on the end of the rover's robotic arm, is one of the primary science cameras for MSL. This camera affords many improvements over those used on previous Mars missions, particularly the ability to focus throughout a wide spatial range. A novel mechanism uses one motor to actuate an internal lens group, enabling focus capability, and manipulate a protective dust cover. This mechanism is designed to operate in the severe thermal environment of the MSL mission (-120deg C to +40deg C) and to survive for one Martian year with 3x margin (about 2000 Earth days) using non-standard materials and techniques in order to meet mass and optical requirements. Several issues involving lubrication and wear were encountered in developing this instrument; each solved through sound engineering and/or system level redesign. The qualification model passed full level life testing at temperatures throughout the operating range with negligible reduction in performance. Alliance Spacesystems, LLC supplied the flight model mechanism to Malin Space Science Systems (MSSS) where it was integrated with electronics and in turn delivered to JPL in October 2008.
It is anticipated that the Mars Science Laboratory rover, named Curiosity, will traverse 10–20 km on the surface of Mars during its primary mission. In preparation for this traverse, Earth-based tests were performed using Mars weight vehicles. These vehicles were driven over Mars analog bedrock, cohesive soil, and cohesionless sand at various slopes. Vehicle slip was characterized on each of these terrains versus slope for direct upslope driving. Results show that slopes up to 22 degrees are traversable on smooth bedrock and that slopes up to 28 degrees are traversable on some cohesive soils. In cohesionless sand, results show a sharp transition between moderate slip on 10 degree slopes and vehicle embedding at 17 degrees. For cohesionless sand, data are also presented showing the relationship between vehicle slip and wheel sinkage. Side by side testing of the Mars Exploration Rover test vehicle and the Mars Science Laboratory test vehicle show how increased wheel diameter leads to better slope climbing ability in sand for vehicles with nearly identical ground pressure. Lastly, preliminary data from Curiosity's initial driving on Mars are presented and compared to the Earth-based testing, showing good agreement for the driving done during the first 250 Martian days.
During Martian solar days 57–100, the Mars Science Laboratory Curiosity rover acquired and processed a solid (sediment) sample and analyzed its mineralogy and geochemistry with the Chemistry and Mineralogy and Sample Analysis at Mars instruments. An aeolian deposit—herein referred to as the Rocknest sand shadow—was inferred to represent a global average soil composition and selected for study to facilitate integration of analytical results with observations from earlier missions. During first-time activities, the Mars Hand Lens Imager (MAHLI) was used to support both science and engineering activities related to sample assessment, collection, and delivery. Here we report on MAHLI activities that directly supported sample analysis and provide MAHLI observations regarding the grain-scale characteristics of the Rocknest sand shadow. MAHLI imaging confirms that the Rocknest sand shadow is one of a family of bimodal aeolian accumulations on Mars—similar to the coarse-grained ripples interrogated by the Mars Exploration Rovers Spirit and Opportunity—in which a surface veneer of coarse-grained sediment stabilizes predominantly fine-grained sediment of the deposit interior. The similarity in grain size distribution of these geographically disparate deposits support the widespread occurrence of bimodal aeolian transport on Mars. We suggest that preservation of bimodal aeolian deposits may be characteristic of regions of active deflation, where winnowing of the fine-sediment fraction results in a relatively low sediment load and a preferential increase in the coarse-grained fraction of the sediment load. The compositional similarity of Martian aeolian deposits supports the potential for global redistribution of fine-grained components, combined with potential local contributions.
The Imager for Mars Pathfinder (IMP) obtained data on the midday sky
brightness in filters centered at 443.6, 481.0, 670.8, 896.1 and 965.3
nm. Useful data sets were returned on sols 27, 40, 56, 65, 68, 74, and
82. Data from sol 56 were fitted with multiple scattering radiative
transfer calculations, to extract the size distribution, optical
properties and shape of the aerosols suspended in the atmosphere. The
derived effective radius of the particles is about 1.71+0.29/-0.26μm
with an effective variance of νeff=0.25+0.05/-0.1. The
estimated values of the refractive index and shape parameters are close
to those derived from Viking and Phobos data. This in turn implies that
dust plays a significant and relatively constant role in the energy
budget of the Martian atmosphere over the last two decades. Estimates of
the optical depth agree well with those obtained independently from
direct IMP imaging of the Sun. The derived single scattering phase
function is more compatible with plate (clay) like particles rather than
equal dimensional particles. The presented analysis assumes a simple
single-component dust atmosphere. The data-model residuals exhibit,
albeit weak, wavelength dependence. This dependence can be interpreted
as an indication that during the time the analyzed images were taken,
the dust particle distribution was bimodal or that the Martian
atmosphere contained a second component, possibly submicron ice
particles, in the aerosol's population.