Mars 2020 Planetary Instrument for X-ray Lithochemistry (PIXL) Mars 2020 (Perseverance) Rover Mission Planetary Data System (PDS) Archive Bundle Overview ======== This bundle contains the following collections. data_raw_ancillary: Raw (EDR) ancillary data products. data_raw_spectroscopy: Raw (EDR) science data products. data_imaging: Image data products from the Micro-Context Camera (MCC). This collection only contains the logical identifiers (LID) for the images. The image products are archived as the Cartography and Imaging Node. data_processed: Calibrated and derived (RDR) data products. data_oxides_pmc: Compositional point-by-point results for each detector. document: Descriptions of the PIXL data products and the archive bundle organization. Data Products and PDS Labels ============================ Every PIXL data product is accompanied by a PDS label in a file with the same name as the data file, but with the extension ".xml", as PDS labels are written in XML (Extended Markup Language). The labels may be viewed in a text editor or web browser, preferably one that applies special formatting to XML files to make them more readable. The labels may also be read by software that can interpret XML. Data tables are comma-separated-value tables (.csv), which are text files that may be read using the PDS4 Viewer, or any text editor, or Microsoft Excel. Images from the MCC camera are archived primarily in the collection data_mcc_imgops in the m2020_imgops bundle. For cross-reference, the images are listed as secondary members of the collection data_imaging here in the m2020_pixl bundle. Documentation ============= The PIXL Bundle Software Interface Specification in the document collection describes the contents, format, and structure of the bundle. Users unfamiliar with PDS archives are advised to read this document first. The PIXL User's Guide in the document collection presents the information a data user is most likely to need in order to read and understand the data. The information is drawn from the following two documents, the PIXL EDR SIS and the PIXL RDR SIS, which have more detail. The PIXL EDR Software Interface Specification in the document collection describes the raw data products generated by the PIXL instrument, including how they are processed and labeled, the format of the data products and their labels, and applicable standards. The PIXL RDR Software Interface Specification in the document collection describes the data, metadata, and browse products derived from the PIXL raw data. Notes Regarding PMC Oxide and Localization Data =============================================== Quantification is performed using PIQUANT Version 3.2.8 and Configuration V7. For each of the datasets that were produced within this bundle, a fixed element list was used to fit and quantify all spectra. The elements and element-oxides interrogated for abundance are: Na2O, MgO, Al2O3, SiO2, P2O5, SO3, Cl, K2O, CaO, TiO2, Cr2O3, MnO, FeO-T, NiO, ZnO, Br. This list does not preclude the presence of other elements in PIXL-measured targets that might be detected if spectra processing were to be expanded to include additional elements. Elements, element oxides and their corresponding absolute uncertainties are reported in wt%. Each ucertainty is the quadrature sum of the peak statistical uncertainty (unc_N) with the calibration uncertainty (unc_C). unc_C was assessed at a 1-sigma level, as part of a pre-flight calibration exercise performed on the PIXL hardware. Details of this calibration and computation of the uncertainties are expanded upon in teh uncertainties section below. Spectra from this calibration will be provided to the PDS with a future release. Oxide compositional data are not normalized to 100 wt%. The uncertainty levels were derived from the root mean square error of deviations between PIQUANT-derived and certificate concentrations observed from measuring 30 homogeneous geological reference materials and pure element/compound substrates; spectra from this calibration will be provided to the PDS with a future release. Oxide compositional data are not normalized to 100 wt%. PMC represents a "PIXL Motor Count". This number is the unique identifier of a point in a scan where an action was taken by the PIXL instrument. PMCs are assigned for each XRF scan point as well as other actions, such as the collection of images, or the execution of autonomous X, Y, Z position corrections. PIXL scans follow a boustrophedon scan pattern and the PMC index number is increased in integer units throughout the scan from the first point to the last point (Allwood et al., 2020). Certain conditions affect sodium quantification accuracy beyond the levels predicted from the elemental calibration. Large amounts of Cl, manifesting in the Cl escape peak, high prevalence of diffraction or surface roughness or atypically high levels of neighboring elemental peaks (Mg or Al) might all conspire to skew Na accuracy. PIQUANT is not always able to fit and detect Na2O at concentrations of 1.0 wt.% or less for any dwell duration. For per-PMC duration dwells typical of PIXL (i.e. 10 s), Na2O at levels at 3.0 wt.% abundance or less may still have relative uncertainties that exceed 100 %, if affected by any of the aforementioned factors. Ultimately, these effects have not been quantitatively assessed and interpretation of Na2O results at low concentration must be done with caution. Compositional tables with "rqa" correspond to geochemical results derived strictly from the data acquired by detector A. Likewise, "rqb" corresponds to results solely from detector B. Tables ending in "rqc" contain compositional data that were derived from the analysis of the combined (i.e., summed) spectrum from both detector A and B together. All concentrations in "rqa" and "rqb" were derived from spectra with a 10 second live time; "rqc" compositions were derived from spectra with a 20 second live time. Diffraction artifacts appear in PIXL spectra, primarily in the energy region ranging from 2 to 14 keV though intensity and spectral position are highly variable. Diffraction can be observed through the presence of a residual when overlaying A and B detector spectra. In compositional data tables, diffraction can cause deviation between compositional results obtained from each detector. Caution is therefore encouraged when interpreting these data and the use of rqa and rqb compositional similarities and differences should be in mind when considering results from an individual PMC. The compositional results presented do take into account the effects of pile-up and escape peaks, as well as diffraction peaks, however the latter especially remains an active area of improvement. The location of each PMC is given by the "rxl" .csv file in the data_processed collection. This file notes the pixel location (i,j) within the referenced .tif image. The specific image can be determined based on the noted PMC. For example, a column heading "PMC_0091_MCC_i" notes the pixel position in the i dimension within image centered on PMC 0091. The tif file ending in *0091###j##.tif is therefore the image referenced. References to (x,y,z) within E34 products (in the data_raw_ancillary collection) are in units of meters. Associated spectra are within the data_raw_spectroscopy collection and may be split among multiple sols, depending on acquisition time. Links to PIQUANT (PIXL fitting software) and PIXLISE (PIXL data visualization software) can be found here: PIXLISE Core https://github.com/pixlise/core PIXLISE UI https://github.com/pixlise/pixlise-ui PIXLISE Diffraction Detection https://github.com/pixlise/diffraction-peak-detection PIXLISE Data Formats https://github.com/pixlise/data-formats PIXLISE Organization https://github.com/pixlise PIQUANT Piquant https://github.com/pixlise/piquant Notes on Uncertainties ====================== The uncertainties quoted for each element are calculated by PIQUANT[1] PIXL's open source[2] quantitative XRF software. Each per-element uncertainty is the quadrature sum of two primary uncertainty components. the first component is the Poisson statistical uncertainty (+/-sqrt(N+2)) where N is the integrated number of counts under the elemental peak of interest. The addition of the value 2 prevents the uncertainty from going to zero for very small peaks. As N is entirely dependent on the number of counts integrated by the fitting code, this uncertainty component takes a unique value for every fit and is concentration dependent. I.e. as concentration decreases, the statistical uncertainty increases. The second uncertainty component is an empirically derived parameter that encompasses several systematic factors associated with performing an XRF measurement using PIXL or a PIXL-like instrument on a smooth but natural set of geological reference materials (GRMs). Systematic factors include 1) instrument uncertainties: variations in X-ray tube voltage and current, instrument standoff distance, target tilt uncertainty, 2) fitting code uncertainties: energy-channel calibration, peak fitting, database fundamental parameters discrepancies and, 3) materials uncertainties: GRM composition and mineral phase heterogeneities. To derive this second component across all elements over varying composition, a pre-flight elemental calibration of the PIXL flight hardware was performed in a simulated Martian environment. A set of 30 GRMs, pure element and pure compound target materials were measured for long duration dwells (2 hours per glass or powder GRM and 5 minutes per pure material)[3]. Elemental compositions determined by PIQUANT for all elements across all targets were compared against certificate or stoichiometric predicted compositions, calculated as percentage differences. All percentage differences were then assessed for deviation on a root mean square error of deviation (approx. 1-sigma level) basis. This was evaluated across various groupings of both elements and compositions within the full assessment range of (0.01 to 100 wt.%). This has led to production of the mesh outlined in the table below which plots the +/-relative uncertainties as a function of element composition. Table: The PIXL elemental quantification uncertainty mesh, applied by PIQUANT to all quantified datasets found in the NASA PDS. Numbers correspond to relative uncertainties in percent. Wt. % range | Z=11-27 | Z=28-42 | Z=43-56 | Z=57-71 | Z > 72 100 5 5 5 5 5 5 5 5 5 5 5 0.5 36 36 36 36 36 0.05 126 40 126 79 126 0 298 298 298 298 298 The PIQUANT software derives uncertainties from the mesh points by interpolating according to the elemental composition it computes for each element. This uncertainty is then applied to the quantified result for an element as the second, aforementioned component of the full uncertainty. Once combined with the peak statistical uncertainty in quadrature, the final uncertainty produced. An example of how this mesh is used is as follows. If 400 (or 0.04 wt.%) ppm of Cu were calculated by PIQUANT, the uncertainty would be interpolated from the Z = 28-42 column at a point between 0 and 0.05 wt.%, having uncertainties of 298 and 40%, respectively. This gives +/-92% relative uncertainty (evaluated at the 1-sigma level). Further details on this calibration will be discussed in a forthcoming publication[4]. Uncertainty-related references: [1] C.M. Heirwegh, W.T. Elam, L.P. O'Neil, K.P. Sinclair, A. Das, The Focused Beam X-ray Fluorescence Elemental Quantification Software Package PIQUANT, Spectrochim. Acta B, 196 (2022) 106520. doi:10.1016/j.sab.2022.106520. [2] W.T. Elam, C.M. Heirwegh, PIQUANT (Version 3.2.11) [Open source computer software] Zenodo. (2022). doi:10.5281/zenodo.6959225 [3] C. M. Heirwegh, Y. Liu, B. C. Clark, W. T. Elam, L. P. O'Neil, K. P. Sinclair, M. Tice, J. A. Hurowitz, A. C. Allwood, Calibrating the PIXL Instrument for Elemental Analysis of Mars, 52nd LPSC (2021) Abstract 1260. hou.usra.edu/meetings/lpsc2021/pdf/1260.pdf [4] C.M. Heirwegh, W.T. Elam, Y. Liu, C. Hummel, A. Das, A.C. Allwood, L.G. Armstrong, N. Bacop, K.P. Sinclair, L.P. O'Neil, J.A. Hurowitz, M.C. Foote, B.C. Clark III, G. Rossman, M. Anderson, Pre-flight calibration of PIXL for X-ray Fluorescence Elemental Quantification, draft manuscript in preparation for Space Science Reviews, open sourced, 2022. References ========== Allwood, A.C., Wade, L.A., Foote, M.C. et al. PIXL: Planetary Instrument for X-Ray Lithochemistry. Space Sci Rev 216, 134 (2020). doi:10.1007/s11214-020-00767-7 Heirwegh, C.M., Elam, W.T., O'Neil, N.P. et al. The focused beam X-ray fluorescence elemental quantification software package PIQUANT. Spec. Act. B, 196, 106520. doi:10.1016/j.sab.2022.106520 ============== This bundle was created and archived by the Geosciences Node of the Planetary Data System. Questions about this bundle may be directed to geosci@wunder.wustl.edu. Last updated 2022-09-18.