Data Set Overview :  The CheMin instrument captures diffracted and fluoresced X-rays on a CCD detector. Up to 2730 individual images can be stored in the instrument, but the downlink capability of the rover does not support the transmission of these raw frames in their entirety. Processing onboard the rover is used to reduce the downlink data volume while preserving the scientific content of the data.  Processing : CheMin EDR data products are considered CODMAC Level 2 or Edited Data (equivalent to NASA level 0) products. The EDR data files are generated from Level 1 or Raw Data, which are the telemetry packets within the project specific Standard Formatted Data Unit (SFDU) record.  The CheMin EDR data products will be generated by the MIPL (Multimission Image Processing Laboratory) at JPL under the Operations Product Generation System (OPGS). The EDR data products will be raw uncalibrated data reconstructed from telemetry data products in the format described by the CheMin EDR SIS. Meta-data collected when the rover prepared the science data for downlink will be provided in PDS label.  There will be multiple versions of a CheMin EDR. If telemetry data are missing during the initial downlink from the rover memory, partial data sets will be created and the missing data will be filled with zeroes. The data will be reprocessed after all data are received and the original version will be overwritten. There can be up to 2 EDRs created, one with a status of partial and the other with a complete status in the filename.  Data : The data types available from CheMin are described in the EDR SIS and are summarized as follows:  1. Diffraction - All: Multiple (e.g., 120) raw images are combined into a single array with the same dimensions as the original images where only pixel values within a specified window of DN values are counted. This window will typically be selected to represent diffracted Co-Kalpha X-rays. This will be the primary data product used for diffraction studies.  2. Diffraction - Single: Same as 'Diffraction - All' except pixel values within the specified window are counted only if they are surrounded entirely by pixels below a selected background threshold. This data set minimizes the contribution of diffracted Co-Kbeta X-rays and other extraneous events, but excludes many valid X-rays.  3. Diffraction - Split: Same as 'Diffraction-All' except pixels are counted only if two adjacent values sum to produce a value that is within the specified window. This data set attempts to recover split events (X-rays depositing charge over multiple pixels) and can be used when the count-rate is low.  4. Film: Multiple (e.g., 120) raw images are summed into a single array. This product will have a higher background noise level given that all fluoresced X-rays are added in, but it will be the best product to use for diffraction studies if the grain motion is poor and there is a large occurrence of pixels capturing multiple diffracted X-rays within a single image.  5. Energy - All: The individual pixel values from multiple (e.g., 120) raw images are combined into a single energy histogram representing counts versus instrumental digital number (DN) energy bins.  6. Energy - Single: Same as 'Energy-All' except pixel values are added to the histogram only if they are surrounded entirely by pixels below a selected background threshold. This will be the primary product used for selection of the diffraction window and for any chemical assessments of the data.  7. Energy - Split: Same as 'Energy-All' except the only values added to the histogram are from the sum of two adjacent pixels which are surrounded entirely by pixels below the background threshold. This data set can be used to add counts to 'Energy- single' when the overall count rate is low.  8. Raw frames: Unprocessed, single images are periodically retained for downlink to allow the science team to assess the performance of the onboard algorithms. One dark frame (no x-ray source) is collected before and after each analysis to track the health of the detector. CheMin can also be commanded to output 'thresholded' raw data where a selected range of raw frames are extracted from the instrument but all pixels with values below a specified threshold and all pixels with values above a second specified threshold are set to zero. Even though data in this format will compress well, some valuable information will be discarded and the downlink requirements will still be relatively large. Nonetheless, this data format could be used if issues are identified in the onboard processing.  9. Housekeeping: A full set of parameters, temperatures, voltages, and other health/status data is captured periodically for downlink.  10. CCD Frame: Individual CCD frames will be downlinked periodically to analyze CCD dark current, hot pixels, and overall CCD health. In the event that an off-nominal result is obtained such that K-alpha thresholds are incorrect or some other unforeseen circumstance renders the data reduction algorithms ineffectual, complete individual frames can be downlinked and processed using algorithms that can be written on the ground and uplinked to the rover.  Data File Names : Data file names in the CheMin EDR and RDR archive are named according to the following scheme:  .  where   : CM (CheMin)  : A_, B_, or __ (instrument configuration)  : 9-character spacecraft clock count  : 3-character product type  : 4-digit sol number  : 3-character site location  : 4-character drive position  : 7-character CheMin sequence identifier  : 1-character producer identifier  : 1-character version identifier  : IMG (image), DAT (binary table), CSV (ASCII delimited table)  See the CheMin EDR Data Product Software Interface Specification in the Document directory of the archive for details about the file naming scheme.

Confidence Level Overview : The data presented in the CheMin EDR is intended to be the least processed, most primitive data set released for CheMin. Data presented here are an accurate representation of CheMin data as received from the rover.  Review : The CheMin EDR products are reviewed internally by the CheMin team prior to release to the PDS. PDS also performs an external peer review of the CheMin EDR.  Data Coverage and Quality : This section will be updated with the first release of CheMin EDR data to the PDS.  Limitations : The major limitation of this data set is that this is level 0, minimally processed data. The data are received from the spacecraft telemetry and ingested into a database. If gaps exist in the telemetry, data are lost.  Data Compression : No data compression is used.